{"collection":"philosophy-ethics","full_text_available":true,"graph_url":"https://unchartedknowledge.5gfusion.net/v2/api/page/gutenberg_51897/graph","html_url":"https://unchartedknowledge.5gfusion.net/v2/page/gutenberg_51897","id":"gutenberg_51897","license":"Public Domain (US)","rights_basis":"gutenberg_metadata_copyright_false","source":"gutenberg","source_url":"https://www.gutenberg.org/ebooks/51897","summary":null,"tags":["Category: Philosophy & Ethics","Category: Science - Physics","Physics","Science"],"text":"THE\n\nPOETRY OF SCIENCE;\n\nOR,\n\nSTUDIES\n\nOF THE\n\nPHYSICAL PHENOMENA OF NATURE.\n\nBY\n\nROBERT HUNT,\n\nAUTHOR OF\n\n\u201cRESEARCHES ON LIGHT;\u201d \u201cELEMENTARY PHYSICS;\u201d\n\u201cPANTHEA, OR THE SPIRIT OF NATURE,\u201d ETC.\n\nPROFESSOR OF PHYSICS, METROPOLITAN SCHOOL OF SCIENCE, ETC., ETC.\n\nTHIRD EDITION, REVISED AND ENLARGED.\n\nLONDON:\n\nHENRY G. BOHN, YORK STREET, COVENT GARDEN.\n\nMDCCCLIV.\n\n\n  From Shakespeare to Plato--from the philosophic poet to the poetic\n      philosopher--the transition is easy, and the road is crowded with\n      illustrations of our present subject.\n\n       *       *       *       *       *\n\n  Hast thou ever raised thy mind to the consideration of EXISTENCE, in\n      and by itself, as the mere act of existing?\n\n  Hast thou ever said to thyself, thoughtfully, IT IS!--heedless, in\n      that moment, whether it were a man before thee, or a flower, or\n      a grain of sand,--without reference, in short, to this or that\n      particular mode or form of existence? If thou hast, indeed,\n      attained to this, thou wilt have felt the presence of a mystery,\n      which must have fixed thy spirit in awe and wonder.\n\n                                        _Coleridge._\n\n               LONDON:\n          WILSON and OGILVY,\n          57, Skinner Street.\n\n\n\n\nPREFACE.\n\n\nSince 1848, when the \u201cPoetry of Science\u201d was first submitted to the\npublic, two editions have been exhausted. This, were proofs required,\nwould of itself show that there is a large circle of readers to whom\nthe deductions of science have an unfailing interest. Beyond this,\nit conveys an assurance that every truth, however abstract it may\nappear, has a large popular value if studied in its relations to\nthose generalities which embrace great natural phenomena. With this\npersuasion the third edition of the \u201cPoetry of Science\u201d has been\nextended so as to include all the important discoveries which have\nbeen made in Natural Philosophy to the end of the year 1853. It is now\npresented to the world in a new and cheaper form, in the hope, that,\nwith the extension of its circulation, there may be awakened, in still\nlarger circles, a deep and healthful interest in the sciences of which\nthe volume treats.\n\n                                        R. H.\n\nEdinburgh, March 7, 1854.\n\n\n\n\nCONTENTS.\n\n                                                              Page\n\n\n  PREFACE.                                                     iii\n\n  CONTENTS.                                                      v\n\n  INTRODUCTION.                                                 ix\n\n\n  CHAPTER I.\n\n  GENERAL CONDITIONS OF MATTER.\n\n  Its varied Characters, and constant change of\n  external Form--The Grain of Dust, its Properties and\n  Powers--Combinations in inorganic Masses and in organized\n  Creations--Our knowledge of Matter--Theory of Ultimate\n  Atoms--The Physical Forces acting on the Composition\n  of Masses--The certainty of the exercise of subtile\n  principles, which are beyond the reach of experimental\n  Science                                                        1\n\n\n  CHAPTER II.\n\n  MOTION.\n\n  Are the Physical Forces modes of Motion?--Motion\n  defined--Philosophical Views of Motion, and the Principles\n  to which it has been referred--Motions of the Earth and\n  of the Solar System--Visible Proofs of the Earth\u2019s Motion\n  on its Axis--Influence of the proper Motions of the Earth\n  on the Conditions of Matter--Theory of the Conversion of\n  Motion into Heat, &c.--The Physical Forces regarded as\n  principles independent of Motion, although the Cause and\n  often apparently the Effects of it                             7\n\n\n  CHAPTER III.\n\n  GRAVITATION.\n\n  The Forms of Matter--Shape of the Earth--Probability\n  of the Mass forming this Planet having existed in a\n  Nebulous State--Zodiacal Lights--Comets--Volatilization\n  of Solid Matter by Artificial means--The principle\n  of Gravitation--Its Influence through Space and\n  within the smallest Limits--Gravitating powers of the\n  Planets--Density of the Earth--Certainty of Newton\u2019s Law\n  of the Inverse Square--Discovery of Neptune--State of a\n  Body relieved from Gravitation--Experiment explaining\n  Saturn\u2019s Ring, &c.--General inference                         21\n\n\n  CHAPTER IV.\n\n  MOLECULAR FORCES.\n\n  Conditions of Matter--Variety of organized\n  Forms--Inorganic Forms--All matter reducible to the\n  most simple conditions--Transmutation, a natural\n  operation--Chemical Elementary Principles--Divisibility\n  of Matter--Atom--Molecules--Particles--Molecular\n  Force includes several Agencies--Instanced\n  in the Action of Heat on Bodies--All Bodies\n  porous--Solution--Mixture--Combination--Centres\n  of Force--Different States of Matter (Allotropic\n  Conditions)--Theories of Franklin, \u00c6pinus, and\n  Coulomb--Electrical and Magnetic Agencies--Ancient\n  Notions--Cohesive Attraction, &c.                             35\n\n\n  CHAPTER V.\n\n  CRYSTALLOGENIC FORCES.\n\n  Crystallisation and Molecular Force\n  distinguished--Experimental Proof--Polarity of\n  Particles forming a Crystal--Difference between\n  Organic and Inorganic Forms--Decomposition of\n  Crystals in Nature--Substitution of Particles in\n  Crystals--Pseudomorphism--Crystalline Form not dependent\n  on Chemical Nature--Isomorphism--Dimorphism--Theories of\n  Crystallogenic Attraction--Influence of Electricity and\n  Magnetism--Phenomena during Crystallisation--Can a change\n  of Form take place in Primitive Atoms?--Illustrative\n  Example of Crystallisation                                    50\n\n\n  CHAPTER VI.\n\n  HEAT--SOLAR AND TERRESTRIAL.\n\n  Solar and Terrestrial Heat--Position of the Earth\n  in the Solar System--Heat and Light associated in\n  the Sunbeam--Transparency of Bodies to Heat--Heating\n  Powers of the Coloured Rays of the Spectrum--Undulatory\n  Theory--Conducting Property of the Earth\u2019s\n  Crust--Convection--Radiation--Action of the Atmosphere on\n  Heat Rays--Peculiar Heat Rays--Absorption and Radiation\n  of Heat by dissimilar Bodies--Changes in the Constitution\n  of Solar Beam--Differences between Transmitted and\n  Reflected Solar Heat--Phenomena of Dew--Action of\n  Solar Heat of the Ocean--Circulation of Heat by the\n  Atmosphere and the Ocean--Heat of the Earth--Mean\n  Temperature--Central Heat--Constant Radiation of Heat Rays\n  from all Bodies--Thermography--Action of Heat on Molecular\n  Arrangements--Sources of Terrestrial Heat--Latent Heat\n  of Bodies--Animal Heat--Eremacausis--Spheroidal State\n  Cold--Condensation--Freezing--Theories of Heat--Natural\n  Phenomena--and Philosophical Conclusion                       62\n\n\n  CHAPTER VII.\n\n  LIGHT.\n\n  Theories of the Nature of Light--Hypotheses\n  of Newton and Huygens--Sources of Light--The\n  Sun--Velocity of Light--Transparency--Dark\n  Lines of the Spectrum--Absorption of\n  Light--Colour--Prismatic Analysis--Rays of the\n  Spectrum--Rainbow--Diffraction--Interference--Goethe\u2019s\n  Theory--Polarisation--Magnetisation of Light--Vision--The\n  Eye--Analogy--Sound and Light--Influence of Light on\n  Animals and Vegetables--Phosphorescence arising from\n  several Causes--Artificial Light--Its Colour dependent on\n  Matter                                                       118\n\n\n  CHAPTER VIII.\n\n  ACTINISM--CHEMICAL RADIATIONS.\n\n  The Sun-ray and its Powers--Darkening of\n  Horn Silver--Niepce\u2019s Discovery--Prismatic\n  Spectrum--Refrangibility of Light, Heat, and\n  Actinism--Daguerre\u2019s Discovery--Photography--Chemical\n  Effects produced by Solar Radiations--Absorption of\n  Actinism--Phenomena of the Daguerreotype--Chemical\n  Change produced upon all Bodies--Power of Matter to\n  restore its Condition--Light protects from Chemical\n  Change--Photographs taken in Darkness--Chemical Effects\n  of Light on organized Forms--Chemical Effects of Solar\n  Heat--Influence of Actinism on Electricity--Radiations in\n  Darkness--Moser\u2019s Discoveries, &c.                           166\n\n\n  CHAPTER IX.\n\n  ELECTRICITY.\n\n  Discovery of Electrical Force--Diffused through all\n  Matter--What is Electricity?--Theories--Frictional\n  Electricity--Conducting Power of Bodies--Hypothesis\n  of two Fluids--Electrical Images--Galvanic\n  Electricity--Effects on Animals--Chemistry of Galvanic\n  Battery--Electricity of a Drop of Water--Electro-chemical\n  Action--Electrical Currents--Thermo-Electricity--Animal\n  Electricity--Gymnotus--Torpedo--Atmospheric\n  Electricity--Lightning Conductors--Earth\u2019s Magnetism due\n  to Electrical Currents--Influence on Vitality--Animal and\n  Vegetable Development--Terrestrial Currents--Electricity\n  of Mineral Veins--Electrotype--Influence of Heat, Light,\n  and Actinism on Electrical Phenomena                         193\n\n\n  CHAPTER X.\n\n  MAGNETISM.\n\n  Magnetic Iron--Knowledge of, by the Ancients--Artificial\n  Magnets--Electro-Magnets--Electro-Magnetism--Magneto-\n  Electricity--Theories of Magnetism--The Magnetic\n  Power of soft Iron and Steel--Influence of Heat\n  on Magnetism--Terrestrial Magnetism--Declination\n  of the Compass-needle--Variation of the\n  Earth\u2019s Magnetism--Magnetic Poles--Hansteen\u2019s\n  Speculations--Monthly and Diurnal Variation--Dip and\n  Intensity--Thermo-Magnetism--Aurora Borealis--Magnetic\n  Storms--Magnetic conditions of Matter--Diamagnetism, &c.     235\n\n\n  CHAPTER XI.\n\n  CHEMICAL FORCES.\n\n  Nature\u2019s Chemistry--Changes produced by Chemical\n  Combination--Atomic Constitution of Bodies--Laws\n  of Combination--Combining Equivalents--Elective\n  Affinity--Chemical Decomposition--Compound Character\n  of Chemical Phenomena--Catalysis or action of\n  Presence--Transformation of Organic Bodies--Organic\n  Chemistry--Constancy of Combining Proportions--The Law of\n  Volumes, the Law of Substitutions, Isomeric States, &c.      270\n\n\n  CHAPTER XII.\n\n  CHEMICAL PHENOMENA.\n\n  Water--Its Constituents--Oxygen--Hydrogen--Peroxide\n  of Hydrogen--Physical Property of\n  Water--Ice--Sea Water--Chlorine--Muriatic\n  Acid--Iodine--Bromine--Compounds of Hydrogen\n  with Carbon--Combustion--Flame--Safety\n  Lamp--Respiration--Animal Heat--The Atmosphere--Carbonic\n  Acid--Influence of Plants on the Air--Chemical Phenomena\n  of Vegetation--Compounds of Nitrogen--Mineral Kingdom, &c.\n  &c.                                                          295\n\n\n  CHAPTER XIII.\n\n  TIME.--GEOLOGICAL PHENOMENA.\n\n  Time, an element in Nature\u2019s Operations--Geological\n  Science--Its Facts and Inferences--Nebular Hypothesis\n  applied--Primary Formations--Plutonic and Metamorphic\n  Rocks--Transition Series--Pal\u00e6ozoic Rocks--Commencement\n  of Organic Arrangements--Existence of Phosphoric\n  Acid in Plutonic Rocks--Fossil Remains--Coal\n  Formation--Sandstones--Tertiary Formations--Eocene,\n  Miocene, and Pliocene Formations--Progressive changes\n  now apparent--General Conclusions--Physics applied in\n  explanation                                                  332\n\n\n  CHAPTER XIV.\n\n  PHENOMENA OF VEGETABLE LIFE.\n\n  Psychology of Flowers--Progress of Matter\n  towards Organization--Vital Force--Spontaneous\n  Generation--The Vegetable Cell--Simplest Development\n  of Organization--The Crystal and the Cell--Primitive\n  Germ--Progress of Vegetation--Influence of\n  Light--Morphology--Germination--Production of Woody\n  Fibre--Leaves--Chlorophylle--Decomposition of\n  Carbonic Acid--Influence of Light, Heat, and Actinism\n  on the Phenomena of Vegetable Life--Flowers and\n  Fruits--Etiolation--Changes in the Sun\u2019s Rays with the\n  Seasons--Distribution of Plants--Electrical and Combined\n  Physical Powers                                              357\n\n\n  CHAPTER XV.\n\n  PHENOMENA OF ANIMAL LIFE.\n\n  Distinction between the Kingdoms\n  of Nature--Progress of Animal\n  Life--Sponges--Polypes--Infusoria--Animalcula--Phosphorescent\n  Animals--Annelidans--Myriapoda--Animal\n  Metamorphoses--Fishes--Birds--Mammalia--Nervous\n  System--Animal Electricity--Chemical Influences--Influence\n  of Light on Animal Life--Animal Heat--Mechanical\n  Action--Nervous Excitement--Man and the Animal Races, &c.    383\n\n\n  CHAPTER XVI.\n\n  GENERAL CONCLUSIONS.\n\n  The Changes produced on Physical Phenomena by the Movement\n  of the Solar System considered--Exertion of the Physical\n  Forces through the Celestial Spaces--The Balance of\n  Powers--Varieties of Matter--Extension of Matter--Theory\n  of Nonentity--A Material Creation an indisputable\n  fact--Advantages of the Study of Science--Conclusion         403\n\n\n  INDEX.                                                       413\n\n  BOHN\u2019S BOOKS.\n\n  TRANSCRIBER\u2019S NOTE.\n\n\n\n\nINTRODUCTION.\n\n\nThe True is the Beautiful. Whenever this becomes evident to our senses,\nits influences are of a soul-elevating character. The beautiful,\nwhether it is perceived in the external forms of matter, associated in\nthe harmonies of light and colour, appreciated in the modulations of\nsweet sounds, or mingled with those influences which are, as the inner\nlife of creation, ever appealing to the soul through the vesture which\ncovers all things, is the natural theme of the poet, and the chosen\nstudy of the philosopher.\n\nBut, it will be asked, where is the relation between the stern labours\nof science and the ethereal system which constitutes poetry? The fumes\nof the laboratory, its alkalies and acids, the mechanical appliances of\nthe observatory, its specula and its lenses, do not appear fitted for\na place in the painted bowers of the Muses. But, from the labours of\nthe chemist in his cell,--from the multitudinous observations of the\nastronomer on his tower,--spring truths which the philosopher employs\nto interpret nature\u2019s mysteries, and which give to the soul of the poet\nthose realities to which he aspires in his high imaginings.\n\nScience solicits from the material world, by the persuasion of\ninductive search, a development of its elementary principles, and of\nthe laws which these obey. Philosophy strives to apply the discovered\nfacts to the great phenomena of being,--to deduce large generalities\nfrom the fragmentary discoveries of severe induction,--and thus to\nascend from matter and its properties up to those impulses which\nstir the whole, floating, as it were, on the confines of sense, and\nindicating, though dimly, those superior powers which, more nearly\nrelated to infinity, mysteriously manifest themselves in the phenomena\nof mind. Poetry seizes the facts of the one and the theories of the\nother; unites them by a pleasing thought, which appeals for truth to\nthe most unthinking soul, and leads the reflective intellect to higher\nand higher exercises; it connects common phenomena with exalted ideas;\nand, applying its holiest powers, it invests the human mind with the\nsovereign strength of the True.\n\nTruth is the soul of the poet\u2019s thought;--truth is the reward of the\nphilosopher\u2019s toil; and their works, bearing this stamp, live among\nmen through all time. Science at present rejoices in her ministry to\nthe requirements of advancing civilization, and is content to receive\nthe reward given to applications which increase the comforts of life,\nor add to its luxuries. Every improvement in the arts or manufactures,\nbeyond encreasing utilities for society, has a tendency to elevate the\nrace. Science is ever useful in the working days of our week, but it is\nnot to be neglected on our Sabbath,--when, resting from our labours,\nit becomes agreeable to contemplate the few truths permitted to our\nknowledge, and thus enter into communion as closely as is allowed to\nfinite beings, with those influences which involve and interpenetrate\nthe earth, giving to all things Life, Beauty, and Divinity.\n\nThe human mind naturally delights in the discovery of truth; and\neven when perverted by the constant operations of prevailing errors,\na glimpse of the Real comes upon it like the smile of daylight to\nthe sorrowing captive of some dark prison. The Psychean labours to\ntry man\u2019s soul, and exalt it, are the search for truth beneath the\nmysteries which surround creation,--to gather amaranths, shining with\nthe hues of heaven, from plains upon which hang, dark and heavy, the\nmists of earth. The poet may pay the debt of nature,--the philosopher\nmay return to the bosom of our common mother,--even their names fade\nin the passage of time, like planets blotted out of heaven but the\ntruths they have revealed to man burn on for ever with unextinguishable\nbrightness. Truth cannot die; it passes from mind to mind, imparting\nlight in its progress, and constantly renewing its own brightness\nduring its diffusion. The True is the Beautiful; and the truths\nrevealed to the mind render us capable of perceiving new beauties on\nthe earth. The gladness of truth is like the ringing voice of a joyous\nchild, and the most remote recesses echo with the cheerful sound. To be\nfor ever true is the Science of Poetry,--the revelation of truth is the\nPoetry of Science.\n\nMan, a creation endued with mighty faculties, but a mystery to himself,\nstands in the midst of a wonderful world, and an infinite variety of\nphenomena arise around him in strange form and magical disposition,\nlike the phantasma of a restless night.\n\nThe solid rock obeys a power which brings its congeries of atoms into\na thousand shapes, each one geometrically perfect. Its vegetable\ncovering, in obedience to some external excitation, developes itself\nin a curious diversity of forms, from the exquisitely graceful to the\nsingularly grotesque, and exhibits properties still more varied and\nopposed. The animal organism quickened by higher impulses,--powers\nworking within, and modifying the influence of the external\nforces,--presents, from the Monad to the Mammoth, and through every\nphase of being up to Man, a yet more wonderful series of combinations,\nand features still more strangely contrasted.\n\nLifting our searching gaze into the measureless space beyond our earth,\nwe find planet bound to planet, and system chained to system, all\nimpelled by a universal force to roll in regularity and order around a\ncommon centre. The pendulations of the remotest star are communicated\nthrough the unseen bond; and our rocking world obeys the mysterious\nimpulse throughout all those forces which regulate the inorganic\ncombinations of this earth, and unto which its organic creation is\nirresistibly compelled to bow.\n\nThe glorious sun by day, and the moon and stars in the silence and the\nmystery of night, are felt to influence all material nature, holding\nthe great Earth bound in a many-stranded cord which cannot be broken.\nThe tidal flow of the vast ocean, with its variety of animal and\nvegetable life, the atmosphere, bright with light, obscured by the\nstorm-cloud, spanned by the rainbow, or rent with the explosions of\nelectric fire,--attest to the might of these elementary bonds.\n\nThese are but a few of the great phenomena which play their part around\nthis globe of ours, exciting men to wonder, or shaking them with terror.\n\nThe mind of man, in its progress towards its higher destiny, is tasked\nwith the physical earth as a problem, which, within the limits of a\nlife, it must struggle to solve. The intellectual spirit is capable of\nembracing all finite things. Man is gifted with powers for studying\nthe entire circle of visible creation; and he is equal, under proper\ntraining, to the task of examining much of the secret machinery which\nstirs the whole.\n\nIn dim outshadowing, earth\u2019s first poets, from the loveliness of\nexternal nature, evoked beautiful spiritualizations. To them the shady\nforests teemed with a\u00ebrial beings,--the gushing springs rejoiced in\nfantastic sprites,--the leaping cataracts gleamed with translucent\nshades,--the cavernous hills were the abodes of genii,--and the\nearth-girdling ocean was guarded by mysterious forms. Such were the\ncreations of the far-searching mind in its early consciousness of the\nexistence of unseen powers. The philosopher picked out his way through\nthe dark and labyrinthine path, between effects and causes, and slowly\napproaching towards the light, he gathered semblances of the great\nReality, like a mirage, beautiful and truthful, although still but a\ncloud-reflection of the vast Unseen.\n\nIt is thus that the human mind advances from the Ideal to the Real,\nand that the poet becomes the philosopher, and the philosopher rises\ninto the poet; but at the same time as we progress from fable to\nfact, much of the soul-sentiment which made the romantic holy, and\ngave a noble tone to every aspiration, is too frequently merged in a\ncheerless philosophy which clings to the earth, and reduces the mind\nto a mechanical condition, delighting in the accumulation of facts,\nregardless of the great laws by which these are regulated, and the\nharmony of all Telluric combinations secured. In science we find the\nelements of the most exalted poetry; and in the mysterious workings\nof the physical forces we discover connections with the illimitable\nworld of thought,--in which mighty minds delight to try their\npowers,--as strangely complicated, and as marvellously ordered, as in\nthe psychological phenomena which have, almost exclusively, been the\nobjects of their studies.\n\nIn the aspect of visible nature, with its wonderful diversity of form\nand its charm of colour, we find the Beautiful; and in the operations\nof these principles, which are ever active in producing and maintaining\nthe existing conditions of matter, we discover the Sublime.\n\nThe form and colour of a flower may excite our admiration; but when\nwe come to examine all the phenomena which combine to produce that\npiece of symmetry and that lovely hue,--to learn the physiological\narrangement of its structural parts,--the chemical actions by which\nits woody fibre and its juices are produced,--and to investigate those\nlaws by which is regulated the power to throw back the white sunbeam\nfrom its surface in coloured rays,--our admiration passes to the higher\nfeeling of deep astonishment at the perfection of the processes, and\nof reverence for their great Designer. There are, indeed, \u201ctongues in\ntrees;\u201d but science alone can interpret their mysterious whispers, and\nin this consists its poetry.\n\nTo rest content with the bare enunciation of a truth, is to perform\nbut one half of a task. As each atom of matter is involved in an\natmosphere of properties and powers, which unites it to every mass of\nthe universe, so each truth, however common it may be, is surrounded\nby impulses which, being awakened, pass from soul to soul like musical\nundulations, and which will be repeated through the echoes of space,\nand prolonged for all eternity.\n\nThe poetry which springs from the contemplation of the agencies which\nare actively employed in producing the transformation of matter, and\nwhich is founded upon the truths developed by the aids of science,\nshould be in no respect inferior to that which has been inspired by the\nbeauty of the individual forms of matter, and the pleasing character of\ntheir combinations.\n\nThe imaginative view of man and his world--the creations of the\nromantic mind--have been, and ever will be, dwelt on with a\nsoul-absorbing passion. The mystery of our being, and the mystery\nof our ceasing to be, acting upon intelligences which are for ever\nstriving to comprehend the enigma of themselves, leads by a natural\nprocess to a love for the Ideal. The discovery of those truths which\nadvance the human mind towards that point of knowledge to which all\nits secret longings tend, should excite a higher feeling than any mere\ncreation of the fancy, how beautiful soever it may be. The phenomena\nof Reality are more startling than the phantoms of the Ideal. Truth\nis stranger than fiction. Surely many of the discoveries of science\nwhich relate to the combinations of matter, and exhibit results which\nwe could not by any previous efforts of reasoning dare to reckon on,\nresults which show the admirable balance of the forces of nature, and\nthe might of their uncontrolled power, exhibit to our senses subjects\nfor contemplation truly poetic in their character.\n\nWe tremble when the thunder-cloud bursts in fury above our heads. The\npoet seizes on the terrors of the storm to add to the interest of his\nverse. Fancy paints a storm-king, and the genius of romance clothes\nhis demons in lightnings, and they are heralded by thunders. These\nwild imaginings have been the delight of mankind; there is subject\nfor wonder in them: but is there anything less wonderful in the\nwell-authenticated fact, the dew-drop which glistens on the flower,\nthat the tear which trembles on the eye-lid, holds locked in its\ntransparent cells an amount of electric fire equal to that which is\ndischarged during a storm from a thunder-cloud?\n\nIn these studies of the effects which are continually presenting\nthemselves to the observing eye, and of the phenomena of causes, as far\nas they are revealed by Science in its search of the physical earth,\nit will be shown that beneath the beautiful vesture of the external\nworld there exists, like its quickening soul, a pervading power,\nassuming the most varied aspects, giving to the whole its life and\nloveliness, and linking every portion of this material mass in a common\nbond with some great universal principle beyond our knowledge. Whether\nby the improvement of the powers of the human mind, man will ever be\nenabled to embrace within his knowledge the laws which regulate these\nremote principles, we are not sufficiently advanced in intelligence\nto determine. But if admitted even to a clear perception of the\ntheoretical Power which we regard as regulating the known forces, we\nmust still see an unknown agency beyond us, which can only be referred\nto the Creator\u2019s will.\n\n\n\n\nTHE POETRY OF SCIENCE.\n\n\n\n\nCHAPTER I.\n\nGENERAL CONDITIONS OF MATTER.\n\n  Its varied Characters, and constant change of external Form--The\n    Grain of Dust, its Properties and Powers--Combinations in inorganic\n    Masses and in organized Creations--Our knowledge of Matter--Theory\n    of Ultimate Atoms--The Physical Forces acting on the Composition of\n    Masses--The certainty of the exercise of subtile principles, which\n    are beyond the reach of experimental Science.\n\n\nThe Physical Earth presents to us, in every form of organic and\ninorganic matter, an infinite variety of phenomena. If we select\nspecimens of rocks, either crystalline or stratified,--of metals in\nany of their various combinations with oxygen, sulphur, and other\nbodies,--of gems glistening with light and glowing with colour,--if\nwe examine the varied forms and hues of the vegetable world, or the\nmore mysterious animal creations, we must inevitably come to the\nconclusion, long since proclaimed, and admit that dust they are, and\nto dust must they return. Whatever permanency may be given to matter,\nit is certain that its form is ever in a state of change. The surface\nof the \u201cEternal Hills\u201d is worn away by the soft rains which fall to\nfertilize, and from their wrecks, borne by the waters to the ocean, new\ncontinents are forming. The mutations of the old earth may be read upon\nher rocks and mountains, and these records of former changes tell us\nthe infallible truth, that as the present passes into the future, so\nwill the form of Earth undergo an important alteration. The same forces\nwhich lifted the Andes and the Himalayas are still at work, and from\nthe particles of matter carried from the present lands by the rivers\ninto the sea, where they subside in stratified masses, there will, in\nthe great future, be raised new worlds, upon which the work of life\nwill go forward, and over which will be spread a vast Intelligence.\n\nIf we regard the conditions of the beautiful and varied organic\ncovering of the Earth, the certainty, the constancy, of change is ever\nbefore us. Vegetable life passes into the animal form, and both perish\nto feed the future plant. Man, moving to-day the monarch of a mighty\npeople, in a few years passes back to his primitive clod, and that\ncombination of elementary atoms, which is dignified with the circle of\nsovereignty and the robe of purple, after a period may be sought for in\nthe herbage of the fields, or in the humble flowers of the valley.\n\nWe have, then, this certain truth,--all things visible around us are\nbut aggregations of atoms. From particles of dust, which under the\nmicroscope could scarcely be distinguished one from the other, are all\nthe varied forms of nature created. This grain of dust, this particle\nof sand, has strange properties and powers. Science has discovered\nsome truths, but still more are hidden within this irregular molecule\nof matter which we now survey, than have yet been shadowed in the\ndreams of our philosophy. How strangely it obeys the impulses of\nheat--mysterious are the influences of light upon it--electricity\nwonderfully excites it--and still more curious is the manner in which\nit obeys the magic of chemical force. These are phenomena which we have\nseen; we know them, and we can reproduce them at our pleasure. We have\nadvanced a little way into the secrets of nature, and from the spot we\nhave gained, we look forward with a vision somewhat brightened by our\ntask; but we discover so much to be yet unknown, that we learn another\ntruth,--our vast ignorance of many things relating to this grain of\ndust.\n\nIt gathers around it other particles; they cling together, and each\nacting upon every other one, and all of them arranging themselves\naround the little centre according to some law, a beautiful crystal\nresults, the geometric perfection of its form being a source of\nadmiration.\n\nIt exerts some other powers, and atom cohering to atom, obeying the\ninfluences of many external radiant forces, undergoes inexplicable\nchanges, and the same dust which we find forming the diamond,\naggregates into the lordly tree,--blends to produce the graceful,\nscented, and richly painted flower,--and combines to yield the luxury\nof fruit.\n\nIt quickens with yet undiscovered energies; it moves with life: dust\nis stirred by the mysterious excitement of vital force; and blood and\nbone, nerve and muscle, are the results. Forces, which we cannot by\nthe utmost refinements of our philosophy detect, direct the whole,\nand from the same dust which formed the rock and grew in the tree, is\nproduced a living and a breathing thing, capable of receiving a Divine\nillumination, of bearing in its new state the gladness and the glory of\na Soul.\n\nThese considerations lead us to reflect on the amount of our knowledge.\nWe are led to ask ourselves, what do we know? We know that the world\nwith all its variety is composed of certain material atoms, which,\nalthough presented to us in a great variety of forms, do not in all\nprobability differ very essentially from each other.\n\nWe know that those atoms obey certain conditions which appear to be\ndependent upon the influences of motion, gravitation, heat, light,\nelectricity, and chemical force. These powers are only known to us\nby their effects; we only detect their action by their operations\nupon matter; and although we regard the several phenomena which we\nhave discovered, as the manifestations of different principles, it is\npossible they may be but modifications of some one universal power, of\nwhich these are but a few of its modes of action.\n\nIn examining, therefore, the truths which science has revealed to us,\nit is advantageous, for the purpose of fixing the mind to the subject,\nthat we assume certain conditions as true. These may be stated in a few\nsentences, and then, without wasting a thought upon those metaphysical\nsubtleties which have from time to time perplexed science, and served\nto impede the progress of truth, we shall proceed to examine our\nknowledge of the phenomena which constantly occur around us.\n\nEvery form, whether inorganic or organic, which we can discover within\nthe limits of human search, is composed of atoms, which are capable of\nassuming, under the influence of certain physical forces, conditions\nessential to the physical state of that body of which they constitute\na part.[1] The known forces, active in producing these conditions,\nare modes of motion; gravitation and aggregation, heat, light; and\nassociated with these, actinism or chemical radiation; electricity,\nunder all its conditions, whether static or dynamic; and chemical\naffinity, regarded as the result of a separate elementary principle.\n\nThese forces must be considered as powers capable of acting in perfect\nindependence of each other. They are possibly modifications of one\nprinciple; but this view being an hypothesis, which, as yet, is only\nsupported by loose analogies, cannot, without danger, be received in\nany explanation which attempts to deal only with the truths of science.\n\nWe cannot examine the varied phenomena of nature, without feeling that\nthere must be other and most active principles of a higher order than\nany detected by science, to which belong the important operations of\nvitality, whether manifested in the plant or the animal. In treating\nof these, although speculation cannot be entirely avoided, it will be\nemployed only so far as it gives any assistance in linking phenomena\ntogether.\n\nWe have to deal with the active agencies which give form and feature to\nnature--which regulate the harmony and beauty and vigour of life--and\nupon which depend those grand changes in the conditions of matter,\nwhich must convince us that death is but the commencement of a new\nstate of being.\n\n\nFOOTNOTES:\n\n[1] Sir Isaac Newton supposed matter to consist of hard, impenetrable,\nperfectly inelastic atoms.\n\nBoscovich regarded the constitution of matter differently. The ultimate\natom was with him a point surrounded by powers of infinite elasticity.\n(See _Dr. Robisons Mechanical Philosophy_, for a full explanation of\nthe theory of Boscovich.)\n\nThe view entertained by Dr. Faraday, which will be comprehended from\none or two short extracts from his valuable and suggestive paper,\nclaims attention:--\n\n\u201cIf the view of the constitution of matter already referred to be\nassumed to be correct--and I may be allowed to speak of the particles\nof matter, and the space between them (in water, or in the vapour\nof water, for instance), as two different things--the space must be\ntaken as the only continuous part, for the particles are considered\nas separated by space from each other. Space will permeate all masses\nof matter in every direction like a net, except that in the place of\nmeshes it will form cells, isolating each atom from its neighbours, and\nitself only being continuous.\u201d\n\nExamining the question of the conducting power of different bodies,\nand observing that as space is the only continuous part, so space,\naccording to the received view of matter, must be at one time a\nconductor, at others a non-conductor, it is remarked:\n\n\u201cIt would seem, therefore, that, in accepting the ordinary atomic\ntheory, space may be proved to be a non-conductor in non-conducting\nbodies, and a conductor in conducting bodies; but the reasoning ends\nin this--a subversion of that theory altogether; for, if space be\nan insulator, it cannot exist in conducting bodies; and if it be a\nconductor, it cannot exist in insulating bodies.\u201d--_A Speculation\ntouching Electric Conduction, and the Nature of Matter_: by Michael\nFaraday, D.C.L., F.R.S., &c.: Philosophical Magazine, vol. xxiv. Third\nSeries.\n\nSee also Wollaston, _On the Finite Extent of the Atmosphere_.--Phil.\nTrans. 1822. Young, _On the Essential Properties of Matter_.--Lectures\non Natural Philosophy. Mossotti, _On Molecular Action_.--Scientific\nMemoirs, vol. i. p. 448.\n\n\n\n\nCHAPTER II.\n\nMOTION.\n\n  Are the Physical Forces modes of Motion?--Motion\n    defined--Philosophical Views of Motion, and the Principles to\n    which it has been referred--Motions of the Earth and of the Solar\n    System--Visible Proofs of the Earth\u2019s Motion on its Axis--Influence\n    of the proper Motions of the Earth on the Conditions of\n    Matter--Theory of the Conversion of Motion into Heat, &c.--The\n    Physical Forces regarded as principles independent of Motion,\n    although the Cause and often apparently the Effects of it.\n\n\nMany of the most eminent thinkers of the present time are disposed to\nregard all the active principles of nature as \u201cmodes of motion,\u201d--to\nlook upon light, heat, electricity, and even vital force, as phenomena\nresulting from \u201cchange of place\u201d among the particles of matter; this\nchange, disturbance, or motion, being dependent upon some undefined\nmover.[2]\n\nThe habit of leaving purely inductive examination for the delusive\ncharms of hypothesis--of viewing the material world as a metaphysical\nbundle of essential properties, and nothing more--has led some eminent\nphilosophers to struggle with the task of proving that all the\nwonderful manifestations of the great physical powers of the universe\nare but modifications of motion, without the evidence of any antecedent\nforce.[3]\n\nThe views of metaphysicians regarding motion involve many subtle\nconsiderations which need not at present detain us. We can only\nconsider motion as a change of place in a given mass of matter. Now\nmatter cannot effect this of itself, no change of place being possible\nwithout a mover; and, consequently, motion cannot be a _property_ of\nmatter, in the strict sense in which that term should be accepted.[4]\n\nMotion depends upon certain external disturbing and directing forces\nacting upon all matter; and, consequently, as every mode of action\nis determined by some excitement external to the body moved, motion\ncannot, philosophically, be regarded otherwise than as a peculiar\naffection of matter under determinable conditions. \u201cWe find,\u201d says Sir\nIsaac Newton, \u201cbut little motion in the world, except what plainly\nflows from either the active principles of nature, or from the command\nof the willer.\u201d[5]\n\nPlato, Aristotle, and the Pythagoreans, supposed that throughout all\nnature an active principle was diffused, upon which depended all the\nproperties exhibited by matter. This is the same as the \u201cplastic\nnature\u201d of Cudworth,[6] the \u201cintellectual and artificial fire\u201d of\nBishop Berkeley;[7] and to these all modes of motion were referred.\nSir Isaac Newton also regards the material universe and its phenomena\nas dependent upon \u201c_active principles_\u201d--for instance, the cause of\ngravity--whereby the planets and comets preserve their motions in their\norbits, and all bodies acquire a degree of motion in falling; and the\ncause of fomentation--whereby the heart and blood of animals preserve\na perpetual warmth and motion--the inner parts of the earth are kept\nconstantly warmed--many bodies burn and shine--and the sun himself\nburns and shines, and with his light warms and cheers all things.\n\nThe earth turns on its axis at the rate of more than 1,000 miles an\nhour, and passes around the sun with the speed of upwards of 68,000\nmiles in the same time.[8] The earth and the other planets of our\nsystem move in ellipses around a common centre: therefore their motion\ncannot have been originally communicated merely by the impressed force\nof projection. Two forces, at least, must have operated, one making\nthe planets tend directly to the centre, and the other impelling them\nto fly off at a tangent to the curve described. Here we have a system\nof spheres, held by some power to a great central mass, around which\nthey revolve with a fearful velocity. Nor is this all; the Solar System\nitself, bound by the same mystic chain to an undiscovered centre, moves\ntowards a point in space at the rate of 33,550,000 geographical miles,\nwhilst our earth performs one revolution around the sun.[9]\n\nThe evidence of the motion of the Earth around its axis, as afforded\nby the swinging of a pendulum or the rotation of a sphere, is too\ninteresting to be omitted. In mechanical philosophy, we have two\nterms of the same general meaning--the conservation of the plane\nof vibration--and the conservation of the axis of rotation. For\nthe non-scientific reader, these terms require explanation, and in\nendeavouring to simplify this as much as possible, we must ask the\nindulgence of the Mechanical Philosopher. Let us fix in the centre\nof a small round table an upright rod, having an arm extending from\nits top, to which we can suspend a tolerably heavy weight attached\nto a string. This is our piece of apparatus: upon the table draw a\nchalk line, along which line we intend our pendulum to swing, and\ncontinuing this line upon the floor, or by a mark on the wall, our\narrangements are complete. Raise steadily the bob of our pendulum,\nand set it free, so that its plane of vibration is along the line\nwhich has been marked. As the pendulum is swinging firmly along this\nline, slowly and steadily turn the table round. It will then be seen\nthat the pendulum will still vibrate in the direction of the line we\nhave continued onward to the wall, but that the line on the table is\ngradually withdrawn from it. If we had no upright, we might turn the\ntable entirely round, without in the slightest degree altering the\nline along which the pendulum performs its oscillations. Now, if from\nsome elevated spot, say, from the centre of the dome of St. Paul\u2019s,\na long and heavy pendulum is suspended, and if on the floor we mark\nthe line along which we set the pendulum free to vibrate, it will be\nseen, as in the experiment with the table, that the marked line moves\naway from under the pendulum. It continues to vibrate in the plane it\nfirst described, although the line on the earth\u2019s surface continues\nto move forward by the diurnal rotation around the axis. Similar to\nthis is the law of the conservation of the axis of rotation. If a\ncommon humming-top, the spindle of which is its axis of rotation, is\nset spinning obliquely, it will be seen that the axis will continue\nto point along the line it took at the commencement of motion. By\nplacing a heavy sphere in a lathe, resting its projecting axial points\non some moveable bearings, and then getting the sphere into extremely\nrapid motion, one of the bearings may be removed without the mass\nfalling to the ground. The rapidity of motion changes so constantly and\nquickly the position of the particles which have a tendency to fall,\nthat we have motion balanced against the force of gravitation in a\nstriking manner; and we learn, from this experiment, the explanation\nof the planetary and stellar masses revolving on their axis at a speed\nsufficient to maintain them without support in space. A mass of matter,\na sphere or a disc, carefully balanced, is fixed in gymbals such as we\nemploy for fixing our compass needles, and it is set by some mechanical\ncontrivance in rapid rotation. The position of the axis of rotation\nremains unaltered, although the earth is moving; and thus, by this\ninstrument,--called the gyroscope,--we can determine, as with the\npendulum, the motion of the earth around its axis; and we learn why,\nduring its movement around the sun, its axis is undeviatingly pointed\ntowards one point in space, marked in our Heavens as the Polar Star.\n\nIn addition to these great rotations, the earth is subjected to other\nmotions, as the precession of the equinoxes and the nutation of its\naxis. Rocking regularly upon a point round which it rapidly revolves,\nwhilst it progresses onward in its orbit, like some huge top in\ntremulous gyration upon the deck of a vast a\u00ebrial ship gliding rapidly\nthrough space, is the earth performing its part in the great law of\nmotion.\n\nThe rapidity of these impulses, supposing the powers of the physical\nforces were for a moment suspended, would be sufficient to scatter the\nmass of our planet over space as a mere star-dust.\n\nLimiting, as much as possible, the view which opens upon the mind as we\ncontemplate the adjustments by which this great machine, our system, is\npreserved in all its order and beauty, let us forget the great movement\nof the whole through space, and endeavour to consider the effect of\nthose motions which are directly related to the earth, as a member of\none small group of worlds.\n\nWe cannot for a moment doubt, although we have not any experimental\nproof of the fact, that the proper motions of the earth materially\ninfluence the conditions of the matter of which it is formed. Every\npair of atoms is, like a balance, delicately suspended, under the\nconstant struggle which arises from the tendency to fly asunder,\ninduced by one order of forces--centrifugal force--and the efforts of\nothers, gravitation and cohesion, to chain them together. The spring is\nbrought to the highest state of tension--one tremor more, and it would\nbe destroyed.\n\nWe cannot, by any comparison with the labours of the most skilful human\nartisan, convey an idea of the exquisite perfection of planetary\nmechanics, even so far as they have been discovered by the labours of\nscience; and we must admit that our insight into the vast machinery has\nbeen very limited.\n\nAll we know is the fact that this planet moves in a certain order, and\nat a fixed rate, and that the speed is of itself sufficient to rend\nthe hardest rocks; yet the delicate down which rests so lightly upon\nthe flower is undisturbed. It is, therefore, evident that matter is\nendued with powers, by which mass is bound to mass, and atom to atom;\nthese powers are not the results of any of the motions which we have\nexamined, but, acting in antagonism to them, they sustain our globe in\nits present form.\n\nAre there other motions to which these powers can be referred? We\nknow of none. That absolute rest may not exist among the particles of\nmatter is probable. Electrical action, chemical power, crystalline\naggregation, the expansive force of heat, and many other known\nagencies, are in constant operation to prevent it. It must, however,\nbe remembered, that each and every atom constituting a mass may be\nso suspended between the balanced forces, that it may be regarded as\nrelatively at rest.\n\nTheory imagines Motion as producing Force--a body is moved, and its\nmere mechanical change of place is regarded as generating heat; and\nhence the refinements of modern science have advanced to the conclusion\nthat motion and heat are convertible. Admitting that the material atoms\nof which this world is formed are never in a state of quiescence, yet\nwe cannot suppose any gross ponderable particle as capable of moving\nitself; but once set in motion, it may become the secondary cause of\nmotion in other particles.[10] The difficulties of the case would\nappear to have been as follows:--Are heat, light, electricity, &c.,\nmaterial bodies? If they are material bodies--and heat, for example, is\nthe cause of motion--must not the calorific matter move itself--or if\nit be not self-moving, by what is it moved? If heat is material, and\nthe primary cause of motion, then matter must have an innate power of\nmoving; it can convert itself into active force, or be at once a cause\nand an effect, which can scarcely be regarded as a logical deduction.\n\nWe move a particle of matter, and heat is manifested; the force being\ncontinued, light, electricity, and chemical action result; all,\nas appears from a limited view of the phenomena, arising out of\nthe mechanical force applied to the particle first moved.[11] This\nmechanical force, it must be remembered, is external to the body moved,\nand is, in all probability, set up by the movement of a muscle, acted\nupon by nerves, under the influence of a will.\n\nThe series of phenomena we have supposed to arise admit of an\nexplanation free of the hypothesis of motion, and we avoid the\ndangerous ground of metaphysical speculation, and the subtleties of\nthat logic which rests upon the immateriality of all creation. This\nexplanation, it is freely admitted, is incomplete: we cannot distinctly\ncorrelate each feature of the phenomena, combine link to link, and thus\nform a perfect chain; but it is sufficiently clear to exhibit what we\ndo know, and leave the unknown free for unbiassed investigation.\n\nEach particle, each atom of that which conveys to our senses the only\nideas we have of natural objects--ponderable matter--is involved\nin, or interpenetrated by, those principles which we call heat and\nelectricity, with probably many others which are unknown to us; and\nalthough these principles or powers are, according to some law, bound\nin statical equilibrium to inert matter, they are freely developed\nby an external excitement, and the disturbance of any one of them,\nupsetting the equilibrium, leaves the other power equally free to be\nbrought under the cognizance of human sense by their effects.\n\nWhen we come to an examination of the influences exerted by these\npowers upon the physical earth, the position, that they must be\nregarded as the causes of motion rather than the effects of it, will\nbe further considered. At present it is only necessary to state\nthus generally the views we entertain of the conditions of matter\nin connection with the imponderable forces and mechanical powers.\nThe conversion, as it has been called, of motion into heat, in the\nexperiments of Count Rumford and Mr. Joule,[12] are only evidences that\na certain uniformity exists between the mechanical force applied, and\nthe amount of heat liberated. It does not appear that we have any proof\nof the conversion of motion into physical power.\n\nIt is necessary, to a satisfactory contemplation of the wonderful\nproperties of matter, and of the forces regulating the forms of\nthe entire creation, that we should be content with regarding the\nelementary bodies which chemistry instructs us form our globe, as\ntangible, ponderable atoms, having specific and distinguishing\nproperties. That we should, as far as it is possible for finite minds\nto do so, endeavour to conceive the powers or forces--gravitation,\nmolecular attraction, electricity, heat, light, and the principle which\ndetermines all chemical phenomena--as manifestations of agencies which\nhold a place between the most subtile form of matter and the hidden\nprinciples of vitality, which is still vastly inferior to the spiritual\nstate, which reveals itself dimly in psychological phenomena, and\narrives at its sublimity in the God of the universe.\n\n\nFOOTNOTES:\n\n[2] \u201cMotion, therefore, is a change of rectilinear distance between\ntwo points. Allowing the accuracy of this definition, it appears that\ntwo points are necessary to constitute motion; that in all cases, when\nwe are inquiring whether or no any body or point is in motion, we must\nrecur to some other point which we can compare with it; and that if a\nsingle atom existed alone in the universe, it could neither be said to\nbe in motion nor at rest.\n\n\u201cThe space which we call quiescent is in general the earth\u2019s surface;\nyet we well know, from astronomical considerations, that every point of\nthe earth\u2019s surface is perpetually in motion, and that in very various\ndirections: nor are any material objects accessible to our senses which\nwe can consider as absolutely motionless, or even as motionless with\nregard to each other; since the continual variation of temperature to\nwhich all bodies are liable, and the minute agitations arising from the\nmotion of other bodies with which they are connected, will always tend\nto produce some imperceptible changes in their distances.\u201d--_Lectures\non Natural Philosophy, &c._, by Thomas Young, M.D. Edited by the Rev.\nP. Kelland. 1845.\n\n[3] \u201cThe position which I seek to establish in this essay is, that\nthe various imponderable agencies, or the affections of matter which\nconstitute the main objects of experimental physics, viz., heat,\nlight, electricity, magnetism, chemical affinity, and motion, are all\ncorrelative, or have a reciprocal dependence;--that neither, taken\nabstractedly, can be said to be the essential or proximate cause of the\nothers; but that either may, as a force, produce, or be convertible\ninto, the other:--thus heat may mediately or immediately produce\nelectricity, electricity may produce heat, and so of the rest....\nAlthough strongly inclined to believe that the five other affections of\nmatter, which I have above named, are, and will ultimately be, resolved\ninto modes of motion, it would be going too far at present to assume\ntheir identity with it: I, therefore, use the term force, in reference\nto them, as meaning that active force inseparable from matter, which\ninduces its various changes.\u201d--_On the Correlation of Physical Forces_,\nby W. R. GROVE, Esq., M.A., F.R.S.\n\n[4] When discussing the hypothesis of Hobbes--_that no body can\npossibly be moved but by a body contiguous and moved_--Boyle asks:--\n\n\u201cI demand how there comes to be local motion in the world? For either\nall the portions of matter that compose the universe have motion\nbelonging to their natures, which the Epicureans affirmed for their\natoms, or some parts of matter have this motive power, and some have\nnot, or else none of them have it; but all of them are naturally\ndevoid of motion. If it be granted that motion does naturally belong\nto all parts of matter, the dispute is at an end, the concession quite\noverthrowing the hypothesis.\n\n\u201cIf Mr. Hobbes should reply that the motion is impressed upon any of\nthe parts of matter by God, he will say that which I most readily grant\nto be true, but will not serve his turn, if he would speak congruously\nwith his own hypothesis. For I demand whether this Supreme Being\nthat the assertion has recourse to, be a corporeal or an incorporeal\nsubstance? If it be the latter, and yet the efficient cause of motion\nin bodies, then it will not be universally true that whatever body is\nmoved is so by a body contiguous and moved. For, in our supposition,\nthe bodies that God moves, either immediately or by the intervention\nof any other immaterial being, are not moved by a body contiguous,\nbut by an incorporeal spirit.\u201d--_Some Considerations about the\nReconcileableness of Reason and Religion_: Boyle, vol. iii. p. 520.\n\n[5] Boyle has some ingenious speculations on this point:--\n\n\u201cThat there is local motion in many parts of matter is manifest to\nsense, but how matter came by this motion was of old, and is still,\nhotly disputed of: for the ancient Corpuscularian philosophers (whose\ndoctrine in most other points, though not in all, we are the most\ninclinable to), not acknowledging an author of the universe, were\nthereby reduced to make motion congenite to matter, and consequently\ncoeval with it. But since local motion, or an endeavour at it, is not\nincluded in the nature of matter, which is as much matter when it rests\nas when it moves; and since we see that the same portion of matter may\nfrom motion be reduced to rest, and after it hath continued at rest, so\nlong as other bodies do not put it out of that state, may by external\nagents be set a moving again; I, who am not wont to think a man the\nworse naturalist for not being an atheist, shall not scruple to say\nwith an eminent philosopher of old, whom I find to have proposed among\nthe Greeks that opinion (for the main) that the excellent Des Cartes\nhas revived amongst us, that the origin of motion in matter is from\nGod; and not only so, but that thinking it very unfit to be believed,\nthat matter barely put into motion, and then left to itself, should\ncasually constitute this beautiful and orderly world; I think also\nfurther, that the wise Author of things did, by establishing the laws\nof motion among bodies, and by guiding the first motions of the small\nparts of matter, bring them to convene after the manner requisite\nto compose the world; and especially did contrive those curious and\nelaborate engines, the bodies of living creatures, endowing most of\nthem with the power of propagating their species.\u201d--_Considerations and\nExperiments touching the Origin of Forms and Qualities_: Boyle\u2019s Works,\nvol. ii. p. 460. Edinburgh. 1744.\n\n[6] Cudworth\u2019s _Intellectual System_.\n\n[7] \u201cAccording to the Pythagoreans and Platonists, there is a life\ninfused throughout all things ... an intellectual and artificial\nfire--an inward principle, animal spirit, or natural life, producing\nor forming within, as art doth without--regulating, moderating, and\nreconciling the various motions, qualities, and parts of the mundane\nsystem. By virtue of this life, the great masses are held together in\ntheir ordinary courses, as well as the minutest particles governed in\ntheir natural motions, according to the several laws of attraction,\ngravity, electricity, magnetism, and the rest. It is this gives\ninstincts, teaches the spider her web, and the bee her honey;--this\nit is that directs the roots of plants to draw forth juice from the\nearth, and the leaves and the cortical vessels to separate and attract\nsuch particles of air and elementary fire as suit their respective\nnatures.\u201d--Bishop Berkeley, _Siris_, No. 277.\n\n[8] \u201cThe revolution of the earth is performed in a natural day,\nor, more strictly speaking, once in 23h. 56' 4\", and as its mean\ncircumference is 24,871 miles, it follows that any point in its\nequatorial surface has a rotatory motion of more than 1,000 miles per\nhour. This velocity must gradually diminish to nothing at either pole.\nWhilst the earth is thus revolving on its axis, it has a progressive\nmotion in its orbit. If we take the length of the earth\u2019s orbit at\n630,000,000, its motion through space must exceed 68,490 miles in the\nhour.\u201d--Enc. Brit. art. _Physical Geography_.\n\n[9] \u201cHere then we have the splendid result of the united studies of\nMM. Argelander, O. Struve, and Peters, grounded on observations made\nat the three observatories of Dorpat, Abo, Pulkova, and which is\nexpressed in the following thesis:--The motion of the solar system in\nspace is directed to a point of the celestial vault situated on the\nright line which joins the two stars \u03c0 and \u03bc _Herculis_, at a quarter\nof the apparent distance of these stars, reckoning from \u03c0 _Herculis_.\nThe velocity of this motion is such, that the sun, with all the bodies\nwhich depend upon it, advances annually in the above direction 1\u00b7623\ntimes the radius of the earth\u2019s orbit, or 33,550,000 geographical\nmiles. The possible error of this last number amounts to 1,733,000\ngeographical miles, or to a _seventh_ of the whole value. We may then\nwager 400,000 to 1 that the sun has a proper progressive motion, and\n1 to 1 that it is comprised between the limits of thirty-eight and\ntwenty-nine millions of geographical miles.\u201d--_Etudes d\u2019Astronomie\nStellaire: Sur la Voie Lact\u00e9e et sur les Distances des Etoiles Fixes_:\nM. F. W. G. Struve. [A report addressed to his Excellency M. Le Comte\nOuvaroff; Minister of Public Instruction and President of the Imperial\nAcademy of Sciences at St. Petersburg.]\n\n[10] \u201cThe first great agent which the analysis of natural phenomena\noffers to our consideration, more frequently and prominently than\nany other, is force. Its effects are either, 1st, to counteract the\nexertion of opposing force, and thereby to maintain _equilibrium_; or,\n2ndly, to produce _motion_ in matter,\n\n\u201cMatter, or that whatever it be of which all the objects in nature\nwhich manifest themselves directly to our senses consist, presents us\nwith two general qualities, which at first sight appear to stand in\ncontradiction to each other--activity and inertness. Its activity is\nproved by its power of spontaneously setting other matter in motion,\nand of itself obeying their mutual impulse, and moving under the\ninfluence of its own and other force; inertness, in refusing to move\nunless obliged to do so by a force impressed externally, or mutually\nexerted between itself and other matter, and by persisting in its state\nof motion or rest unless disturbed by some external cause. Yet, in\nreality, this contradiction is only apparent. Force being the cause,\nand motion the effect produced by it on matter, to say that matter is\ninert, or has _inertia_, as it is termed, is only to say that the cause\nis expended in producing its effect, and that the same cause cannot\n(without renewal) produce double or triple its own proper effect.\nIn this point of view, equilibrium may be conceived as a continual\nproduction of two opposite effects, each, undoing at every instant what\nthe other has done,\u201d?--See continuation of the argument in _Herschel\u2019s\nDiscourse on the Study of Natural Philosophy_, page 223.\n\nIn the Edinburgh New Philosophical Journal, vol. xlv., will be found a\npaper by Dr Robert Brown--\u201c_Of the sources of motions upon the Earth,\nand of the means by which they are sustained_,\u201d which will well repay\nan attentive perusal, as pointing to a class of investigation of the\nhighest order, and containing deductions of the most philosophic\ndescription.\n\n[11] Friction, it is well known, generates heat; by rapidly rubbing two\nsticks together, the Indian produces their ignition; heat and light\nbeing both manifested. Under every mechanical disturbance electrical\nchanges can be detected, and the action of heat in the combustion of\nthe wood is a chemical phenomenon.\n\n[12] Count Rumford\u2019s experiment consisted in placing a mass of metal\nin a box of water at a known temperature, and, by employing a boring\napparatus, ascertaining carefully the increase of heat after a given\nnumber of revolutions. He thus describes his most satisfactory\nexperiment:--\n\n\u201cEverything being ready, I proceeded to make the experiment I had\nprojected, in the following manner. The hollow cylinder having been\npreviously cleaned out, and the inside of its bore wiped with a clean\ntowel till it was quite dry, the square iron bar, with the blunt steel\nborer fixed to the end of it, was put into its place; the mouth of the\nbore of the cylinder being closed at the same time by means of the\ncircular piston through the centre of which the iron bar passed.\n\n\u201cThis being done, the box was put in its place; and the joinings of\nthe iron rod, and of the neck of the cylinder with the two ends of\nthe box, having been made water-tight, by means of collars of oiled\nleather, the box was filled with cold water (viz., at the temperature\nof 60\u00b0) and the machine was put in motion. The result of this beautiful\nexperiment was very striking, and the pleasure it afforded me amply\nrepaid me for all the trouble I had had, in contriving and arranging\nthe complicated machinery used in making it. The cylinder, revolving\nat the rate of about thirty-two times in a minute, had been in motion\nbut a short time, when I perceived, by putting my hand into the water\nand touching the outside of the cylinder, that heat was generated, and\nit was not long before the water which surrounded the cylinder began\nto be sensibly warm. At the end of one hour, I found, by plunging a\nthermometer into the water in the box (the quantity of which fluid\namounted to 18\u00b777 lbs. avoirdupois, or 2-1/4 wine gallons), that\nits temperature had been raised no less than 47\u00b0; being now 107\u00b0 of\nFahrenheit\u2019s scale. When thirty minutes more had elapsed, or one hour\nand thirty minutes after the machinery had been put in motion, the heat\nof the water in the box was 142\u00b0. At the end of two hours, reckoning\nfrom the beginning of the experiment, the temperature of the water\nwas found to be raised to 178\u00b0. At two hours twenty minutes it was at\n200\u00b0; and at two hours thirty minutes it _actually boiled_.\u201d--_Inquiry\nconcerning the Source of the Heat excited by Friction_: Philosophical\nTransactions, vol. lxxxviii. A.D. 1798.\n\n\u201cMr. Joule brought a communication on the same subject before the\nBritish Association at Cambridge, which was afterwards published in the\nPhilosophical Magazine, and from that journal the following notices are\nextracted:--\n\n\u201cThe apparatus exhibited before the Association consisted of a brass\npaddle-wheel, working horizontally in a can of water. Motion could\nbe communicated to this paddle by means of weights, pulleys, &c. The\npaddle moved with great resistance in the can of water, so that the\nweights (each of four pounds) descended at the slow rate of about one\nfoot per second. The height of the pulleys from the ground was twelve\nyards, and consequently when the weights had descended through that\ndistance they had to be wound up again in order to renew the motion of\nthe paddle. After this operation had been repeated sixteen times, the\nincrease of the temperature of the water was ascertained by means of a\nvery sensible and accurate thermometer.\n\n\u201cA series of nine experiments was performed in the above manner, and\nnine experiments were made in order to eliminate the cooling or heating\neffects of the atmosphere. After reducing the result to the capacity\nfor heat of a pound of water, it appeared that for each degree of heat\nevolved by the friction of water, a mechanical power equal to that\nwhich can raise a weight of 890 lbs. to the height of one foot, had\nbeen expended.\n\n\u201cAny of your readers who are so fortunate as to reside amid the\nromantic scenery of Wales or Scotland could, I doubt not, confirm my\nexperiments by trying the temperature of the water at the top and at\nthe bottom of a cascade. If my views be correct, a fall of 817 feet\nwill of course generate one degree of heat, and the temperature of the\nriver Niagara will be raised about one fifth of a degree by its fall of\n160 feet.\u201d--_Relation between Heat and Mechanical Power_: Philosoph.\nMag. vol. xxvii. 1845.\n\n\n\n\nCHAPTER III.\n\nGRAVITATION.\n\n  The Forms of Matter--Shape of the Earth--Probability of the Mass\n    forming this Planet having existed in a Nebulous State--Zodiacal\n    Lights--Comets--Volatilization of Solid Matter by Artificial\n    means--The principle of Gravitation--Its Influence through\n    Space and within the smallest Limits--Gravitating powers of the\n    Planets--Density of the Earth--Certainty of Newton\u2019s Law of the\n    Inverse Square--Discovery of Neptune--State of a Body relieved from\n    Gravitation--Experiment explaining Saturn\u2019s Ring, &c.--General\n    inference.\n\n\nLet us suppose the earth--consisting of three conditions of matter;\nthe solid, the fluid, and the a\u00ebriform--to be set free from that power\nby which it is retained in its present form of a spheroid flattened\nat the poles, but still subject to the influences of its diurnal and\nannual rotations. Agreeably to the law which regulates the conditions\nof all bodies moving at high velocities, the consequence of such a\nstate of things would be, that our planet would instantly spread itself\nover an enormous area. The waters and even the solid masses of this\nglobe would, in all probability, present themselves amidst the other\nphenomena of space in a highly attenuated state, revolving in an orbit\naround the sun, as a band of nebulous matter, which might sometimes\nbe rendered sensible to sight by still reflecting solar light, or by\ncondensation in the form of flights of shooting stars.[13]\n\nThis may be illustrated by experiment. If upon a rapidly revolving\ndisc we place a ball of dust, it will be almost immediately spread\nout, and its particles will arrange themselves in a series of regular\ncurves, varying with the velocity of the motion. In addition to the\ndisintegration which would arise from the tendency of the atoms to fly\nfrom the centre, the motion, in space, of the planetary mass would\nnaturally occasion a trailing out, and the only degree of uniformity\nwhich this orb could, under these imaginary conditions, possibly\npresent, would be derived from the combined effects of motions in\ndifferent directions.\n\nAmid the remoter stars, some remarkable cloud-like appearances are\ndiscovered. These nebul\u00e6, presenting to the eye of the observer\nonly a gleaming light, as from some phosphorescent vapour, were\nlong regarded as indications of such a condition as that which we\nhave just been considering. Astronomers saw, in those mysterious\nnebul\u00e6, a confirmation of their views, which regarded all the orbs\nof the firmament as having once been thin sheets of vapour, which\nhad gradually, from irregular bodies traversing space, been slowly\ncondensed about a centre, and brought within the limits of aggregating\nagencies, until, after the lapse of ages, they become sphered stars,\nmoving in harmony amid the bright host of heaven.[14] Geologists seized\non those views with eagerness, as confirming theoretical conclusions\ndeduced from an examination of the structure of the earth itself, and\nexplained by them the gradual accretion of atoms into crystalline rocks\nfrom a cooling mass.\n\nThe researches of modern astronomers, aided by the magnificent\ninstruments of Lord Rosse,[15] have, however, shown that many of the\nmost remarkable nebul\u00e6 are only clusters of stars; so remote from\nus, that the light from them appears blended into one diffused sheet\nor luminous film. There are, however, the Magellanic clouds, and\nother singular patches of light, exhibiting changes which can only\nbe explained on the theory of their slow condensation. There is no\nevidence to disprove the position that world-formation may still be\ngoing on; that a slow and gradual aggregation of particles, under the\ninfluence of laws with which we are acquainted, may be constantly in\nprogress, to end, eventually, in the formation of a sphere.\n\nMay we not regard the zodiacal light as the remains of a solar\nluminiferous atmosphere, which once embraced the entire system of which\nit is the centre?[16] Will not the strange changes which have been\n_seen to take place_ in cometary bodies, even whilst they were passing\nnear the earth,--as the division of Biela\u2019s comet and the ultimate\nformation of a second nucleus from the detached portion,--strongly\ntend to support the probability of the idea that attenuated matter\nhas, in the progress of time, been condensed into solid masses, and\nthat nebulous clouds must still exist in every state of tenuity in the\nregions of infinite space,[17] which, in the mysterious processes of\nworld-formation, will, eventually, become stars, and reflect across\nthe blue immensity of heaven, in brightness, that light which is the\nnecessary agent of organisation and all manifestations of beauty?\n\nThe inferences drawn from a careful study of the condition of our own\nglobe are in favour of the assumption of the existence of nebulous\nmatter. By the processes of art and manufacture, by the operation of\nthose powers on which organisation and life depend, solid matter is\nconstantly poured off in such a state that it cannot be detected, _as\nmatter_, by any of the human senses. Yet a thousand results, daily and\nhourly accumulating as truths around us, prove that the solid metals,\nthe gross earths, and the constituents of animal and vegetable life,\nall pass away invisible to us, and become \u201cthin air.\u201d We know that,\nfloating around us, these volatilized bodies exist in some material\nform, and numerous experiments in chemistry are calculated to convince\nus, that the most attenuated air is capable, with a slight change\nof circumstances, of being converted into the condition of solid\nmasses. Hydrogen gas, the lightest, the most ethereal of the chemical\nelements, dissolves iron and zinc, arsenic, sulphur, and carbon; and\nfrom the transparent combinations thus formed, we can with facility\nseparate those ponderous bodies. Such substances must exist in our\nown atmosphere; why not in the regions of space? Whether this planet\never floated a mass of nebulous matter, only known by its dim and\nfilmy light, or comet-like rushed through space with widely eccentric\norbit, are questions which can only receive the reply of speculative\nminds. Whether the earth and the other members of the Solar System were\never parts of a Central Sun,[18] and thrown from it by some mighty\nconvulsion, though now revolving with all the other masses around that\norb, chained in their circuits by some infinite power, is beyond the\nutmost refinements of science to discover. This hypothesis is, however,\nin its sublime conception, worthy of the master-mind that gave it birth.\n\nAll we know is, that our earth is an oblate sphere, which, by the\neffects of its rotation around an axis, is somewhat enlarged at the\nequator and flattened at the poles;--that it maintains its regular\ncourse around the sun, in virtue of the operation of two forces, one\nof which, acting constantly, would eventually draw it into the body\nof the sun itself; but that it is opposed by the other, centrifugal\nforce, and the varying momentum of the revolving mass;--that the same\nforce acting from the centre of the earth itself, and from the centre\nof every particle of its substance, resolves the whole into a globular\nform.\n\nThe principle of Gravitation[19] is that force which resides in every\nform of matter, by which particle is attracted by particle, and mass\nby mass, the less towards the greater. What this may be, we scarcely\ndare to speculate. In the vast area of its action, which opens before\nthe eye of the mind, we see a power spanning all space, and linking\ntogether every one of those myriads of worlds which spangle the robe\nof the Infinite, and we are compelled to pause. Is this principle of\ngravitation a property of matter, or is it a power higher than the\nmore tangible forces, is the question which presses on the mind. If\nwe regard it as a subtile principle pervading all space, we compel\nourselves to look beyond it for another power yet more refined; and we\ncannot halt until, ascending from the limitable to the illimitable, we\nresolve gravitation and its governing influences to the centre of all\npower--the will of the eternal Creator.\n\nScience has developed the grand truth, that it is by the exercise\nof this all-pervading influence that the earth is retained in its\norbit--that the pellucid globe of dew which glistens on the leaf is\nbound together--that the d\u00e9bris which float upon the lake accumulate\ninto one mass--that the sea exhibits the phenomena of the tides--and\nthe a\u00ebrial ocean its barometric changes. In all things this force is\nactive, and throughout nature it is ever present. Our knowledge of the\nlaws which it obeys, enables us to conclude that the sun and distant\nplanets are consolidated masses like this earth. We find that they have\ngravitating power, and by comparing this influence with that exerted\nby the earth, we are enabled to weigh the mass of one planet against\nanother. In the balance of the astronomer, it is as easy to poise the\nremote star, as it is for the engineer to calculate the weight of the\niron tunnel of the Menai Straits, or any other mechanical structure.\nThus throughout the universe the balance of gravitating force is\nunerringly sustained. If one of the most remote of those gems of light,\nwhich flicker at midnight in the dark distance of the starry vault,\nwas, by any power, removed from its place, the disturbance of these\ndelicately balanced mysteries would be felt through all the created\nsystems of worlds.\n\nFrom the peculiarity of the laws which this power called gravity obeys,\nit has been inferred that it acts from centres of force; it is proved\nthat its power diminishes in the inverse ratio of the square of the\ndistance, and that the gravitating power of every material body is in\nthe direct proportion of its mass. In astronomical calculations we have\nfirst to learn the mass of our earth. Experiment informs us that the\ndensity of our hardest rock is not above 2\u00b78; but from the enormous\npressure to which matter must be subjected, at great depths from the\nsurface, the weight of the superincumbent mass constantly increasing,\nit is quite certain that the earth\u2019s density must be far more than\nthis. Maskelyne determined the attraction of large masses by a plummet\nand line on the mountain Schehallion.[20] Cavendish, with exceedingly\ndelicate apparatus, observed the attraction of masses of known\nweight and size upon each other. Applying the powers of arithmetical\ncalculation, and the data obtained from the small experiments to the\nlarger phenomena, Maskelyne determined the earth\u2019s mean density to\nbe 4\u00b771, whilst Cavendish made it 5\u00b748, but the more recent refined\ninvestigations of Baily have determined it to be 5\u00b767.[21]\n\nFrom data thus obtained by severe inductive experiments and\nmathematical analyses, the astronomer, by observing the deviations of\na distant star, is enabled to determine the influence of those stellar\nbodies near which it passes, and, hence, to calculate the relative\nmagnitudes of each. The accuracy of the law is in this way put to the\nseverest test, and the precision of astronomical prediction is the\nstrongest proof of its universality and truth.\n\nRolling onward its lonely way, in the far immensity of our system,\nthe planet Uranus was discovered by the elder Herschel,--so great\nits distance that its diminished light could scarcely be detected\nby the most powerful telescopes; but since its discovery its path\nhas been carefully watched, and some irregularities noticed. Most\nof these disturbances were referable to known causes; but a little\nalteration in its rate of motion observed when the planet was in one\nportion of its vast orbit was unexplained. Convinced of the certainty\nof Newton\u2019s law, and having determined that the attraction of known\nmasses was insufficient to produce the disturbance observed, these\ndeviations were referred to the gravitating influence of a mass\nbeyond the known limits of our Solar System. By the investigations\nof Adams in England,[22] and Le Verrier in France,[23] the place of\nthe hypothetical mass was determined, and its size computed. As a\ngrand confirmation of the great law, and to the glory of those two\nfar-searching minds, who do honour to their respective countries and\ntheir age, the hypothesis became a fact, in the discovery of the planet\nNeptune in the place determined by rigorous calculation. Astronomy\naffords other examples of the sublime truth of the law of gravitation,\nthan which science can afford no more elevated poetry.\n\nSo completely is all nature locked in the bonds of this infinite power,\nthat it is no poetic exaggeration to declare, that the blow which rends\nany earthly mass is conveyed by successive impulses to every one of the\nmyriads of orbs, which are even too remote for the reach of telescopic\nvision.\n\nAn illustrative experiment must close our consideration of relative\noperations of rotation and gravitation. We well know that a body in\na fluid state would, if suspended above the earth, it being at the\nsame time free to take any form, naturally assume that of a flattened\nspheroid, from the action of the mass of the earth upon it: whereas the\nforce of cohesive attraction acting equally from all sides of a centre,\nwould, if uninfluenced, necessarily produce a perfect sphere. The best\nmethod of showing that this would be the case, is as follows:--\n\nAlcohol and water are to be mixed together until the fluid is of the\nsame specific gravity as olive oil. If, when this is effected, we\ndrop globules of the oil into the mixed fluid, it will be seen that\nthey take an orbicular form;--and, of course, in this experiment the\npower of the earth\u2019s gravitating influence is neutralized. The same\ndrops of oil under any other conditions would be flattened. Simple as\nthis illustration is, it tells much of the wondrous secret of those\nbeautifully balanced forces of cohesion and of gravitation; and from\nthe prosaic fact we rise to a great philosophical truth. Our experiment\nmay lead us yet farther in exemplification of known phenomena. If we\npass a steel wire through one of those floating spheres of oil, and\nmake it revolve rapidly and steadily, thus imitating the motion of a\nplanet on its axis, the oil spreads out, and we have the spheroidal\nform of our earth. Increase the rapidity of this rotation, and when a\ncertain rate is obtained the oil widens into a disc, a ring separates\nitself from a central globe, and at a distance from it still revolves\naround it.[24] Here we have a miniature representation of the ring\nof Saturn. This is a suggestive experiment, the repetition of which,\nby reflective minds, cannot fail to lead to important deductions. The\nphenomena of cohesion, of motion, and gravitation, are all involved;\nand we produce results resembling, in a striking manner, the conditions\nwhich prevail in the planetary spaces, under the influence of the same\npowers. If we take a glass globe, and having filled it with a fluid of\nthe proper density, drop into it large and small globules of oil, we\nmay produce an instructive representation of the stellar vault, with\nits beautiful spheres of light revolving in their respective orbits;\nand though crossing each other\u2019s paths, still moving in obedience to\nattracting and repelling forces--onward in perfect harmony.\n\nFrom the centre of our earth to the utmost extremity of the\nuniverse--from the infinitely small to the immensely vast--gravitation\nexerts its force. It is met on all sides by physical powers acting in\nantagonism to it, but, like a ruling spirit, it restrains them in their\nwildest moods.\n\n    The smallest dust which floats upon the wind\n    Bears this strong impress of the Eternal Mind.\n    In mystery round it, subtile forces roll;\n    And gravitation binds and guides the whole.\n    In every sand, before the tempest hurl\u2019d,\n    Lie locked the powers which regulate a world,\n    And from each atom human thought may rise\n    With might to pierce the mysteries of the skies,--\n    To try each force which rules the mighty plan,\n    Of moving planets, or of breathing man;\n    And from the secret wonders of each sod,\n    Evoke the truths, and learn the power of God.\n\n\nFOOTNOTES:\n\n[13] Three hypotheses may be used to account for this most curious\nphenomenon.\n\n1st. The body shines by its own light, and then explodes like a\nsky-rocket, breaking into minute fragments too small to be any longer\nvisible to the naked eye.\n\n2nd. Such a body, having shone by its own light, suddenly ceases to\nbe luminous. \u201cThe falling stars and other fiery meteors which are\nfrequently seen at a considerable height in the atmosphere, and which\nhave received different names according to the variety of their figure\nand size, arise from the fermentation of the effluvia of acid and\nalkaline bodies which float in the atmosphere. When the more subtile\nparts of the effluvia are burned away, the viscous and earthy parts\nbecome too heavy for the air to support, and by their gravity fall to\nthe earth.\u201d--Keith\u2019s _Use of the Globes_. According to Sir Humphry\nDavy, in the Philosophical Transactions for 1847, \u201cthe luminous\nappearances of shooting stars and meteors cannot be owing to any\ninflammation of elastic fluids, but must depend upon the ignition of\nsolid bodies.\u201d\n\n3. The body shines by the reflected light of the sun, and ceases to be\nvisible by its passing into the earth\u2019s shadow, or, in other words,\nis eclipsed. Upon the two former suppositions the fact of the star\u2019s\ndisappearance conveys to us no knowledge of its position, or of its\ndistance from the earth; and all that can be said is, that if it be\na satellite of the earth, the great rapidity of its motion involves\nthe necessity of its being at no great distance from the earth\u2019s\nsurface--much nearer than the moon; while the resistance it would\nencounter in traversing the air would be so great that it is probably\nwithout the limits of our atmosphere. _Sir J. W. Lubbock leans to the\nthird hypothesis._--Sir J. W. Lubbock, _On Shooting Stars_: Phil. Mag.\nNo. 213, p. 81.\n\nSir J. Lubbock also published a supplementary paper on the same\nsubject, in No. 214, p. 170.\n\nMr. J. P. Joule entertains an hypothesis with respect to Shooting\nStars similar to that advocated by Chladni to account for meteoric\nstones, and he reckons the ignition of these miniature planetary bodies\nby their violent collision with our atmosphere, to be a remarkable\nillustration of the doctrine of the equivalency of heat to mechanical\npower, or _vis viva_.\n\nIf we suppose a meteoric stone of the size of a six-inch cube to enter\nour atmosphere at the rate of eighteen miles per second of time, the\natmosphere being 1/100 of its density at the earth\u2019s surface, the\nresistance offered to the motion of the stone will in this case be at\nleast 51,600 lbs.; and if the stone traverse twenty miles with this\namount of resistance, sufficient heat will thereby be developed to give\n1\u00b0 Fahrenheit to 6,967,980 lbs. of water. Of course by far the largest\nportion of this heat will be given to the displaced air, every particle\nof which will sustain the shock, whilst only the surface of the stone\nwill be in violent collision with the atmosphere. Hence the stone may\nbe considered as placed in a blast of intensely heated air, the heat\nbeing communicated from the surface to the centre by conduction. Only\na small portion of the heat evolved will therefore be received by the\nstone; but if we estimate it at only 1/100 it will still be equal\nto 1\u00b0 Fahrenheit per 69,679 lbs. of water, a quantity quite equal\nto the melting and dissipation of any materials of which it may be\ncomposed.--Mr. J. P. Joule, _On Shooting Stars_: Phil. Mag. No. 216, p.\n348.\n\n[14] \u201cLaplace conjectures that in the original condition of the solar\nsystem, the sun revolved upon his axis, surrounded by an atmosphere\nwhich, in virtue of an excessive heat, extended far beyond the orbits\nof all the planets, the planets as yet having no existence. The heat\ngradually diminished, and as the solar atmosphere contracted by\ncooling, the rapidity of its rotation increased by the laws of rotatory\nmotion; and an exterior zone of vapour was detached from the rest,\nthe central attraction being no longer able to overcome the increased\ncentrifugal force. This zone of vapour might in some cases retain\nits form, as we see it in Saturn\u2019s ring; but more usually the ring\nof vapour would break into several masses, and these would generally\ncoalesce into one mass, which would revolve about the sun,\u201d--Whewell\u2019s\n_Bridgewater Treatise_.\n\nThe following passage is translated by the same author from Laplace:--\n\n\u201cThe anterior state (a state of cloudy brightness) was itself preceded\nby other states, in which the nebulous matter was more and more\ndiffuse, the nucleus being less and less luminous. We arrive in this\nmanner at a nebulosity so diffuse, that its existence could scarce be\nsuspected. Such is in fact the first state of the nebula which Herschel\ncarefully observed by means of his telescope.\u201d\n\nSir William Herschel has the following observations on these remarkable\nmasses:--\n\n\u201cThe nature of planetary nebul\u00e6, which has hitherto been involved in\nmuch darkness, may now be explained with some degree of satisfaction,\nsince the uniform and very considerable brightness of their apparent\ndisc accords remarkably well with a much condensed, luminous fluid;\nwhereas, to suppose them to consist of clustering stars will not so\ncompletely account for the milkiness or soft tint of their light, to\nproduce which it would be required that the condensation of the stars\nshould be carried to an almost inconceivable degree of accumulation.\n\n\u201cHow far the light that is perpetually emitted from millions of suns\nmay be concerned in this shining fluid, it might be presumptuous to\nattempt to determine; but notwithstanding the inconceivable subtilty\nof the particles of light, when the number of the emitting bodies\nis almost infinitely great, and the time of the continual emission\nindefinitely long, the quantity of emitted particles may well become\nadequate to the constitution of a shining fluid or luminous matter,\nprovided a cause can be found that may retain them from _flying off,\nor reunite them_.\u201d--_Observations on Nebulous Stars_: Philosophical\nTransactions, vol. lxxxi. A.D. 1791.\n\nIn addition, the following Memoirs on the same subject, by Sir\nWilliam Herschel, have been published in the Philosophical\nTransactions:--_Catalogue of 1000 Nebul\u00e6 and Clusters of Stars_, vol.\nlxxvi.; _Catalogue of another 1000, with remarks on the Heavens_, vol.\nlxxix.; _Catalogue of 500 more, with remarks as above_, vol. xcii.;\n_Of such as have a cometary appearance_, vol. ci.; _Of planetary\nnebul\u00e6_, ibid.; _Of stellar nebul\u00e6_, ibid.; _On the sidereal part of\nthe heavens, and its connection with the nebulous_, vol. civ.; _On the\nrelative distances of clusters of nebulous stars_, vol. cviii.\n\n[15] Lord Rosse\u2019s beautiful telescopes have been formed upon principles\nwhich appear to embrace the best possible conditions for obtaining\na reflecting surface which should reflect the greatest quantity of\nlight, and retain that property little diminished for a length of\ntime. The alloy used for this purpose consists of tin and copper in\natomic proportions, namely, one atom of tin to four atoms of copper,\nor by weight 58\u00b79 to 126\u00b74.--_On the Construction of large Reflecting\nTelescopes_: by Lord Rosse. Report of the Fourteenth Meeting of the\nBritish Association, 1844, p. 79.\n\n[16] The best description of the Zodiacal Light occurs in a letter\nfurnished by Sir John Herschel to the _Times_ newspaper in March,\n1843:--\u201cThe zodiacal light, as its name imports, invariably appears\nin the zodiac, or, to speak more precisely, in the plane of the sun\u2019s\nequator, which is 7\u00b0 inclined to the zodiac, and which plane, seen from\nthe sun, intersects the ecliptic in longitude 78\u00b0 and 258\u00b0, or so much\nin advance of the equinoctial points: in consequence it is seen to the\nbest advantage at, or a little after, the equinoxes; after sunset,\nat the spring, and before sunrise, at the autumnal equinox; not only\nbecause the direction of its apparent axis lies at those times more\nnearly perpendicular to the horizon, but also because at those epochs\nwe are approaching the situation when it is seen most completely in\nsection.\n\n\u201cAt the vernal equinox the appearance of the zodiacal light is that\nof a pretty broad pyramidal, or rather lenticular, body of light,\nwhich begins to be visible as soon as the twilight decays. It is very\nbright at its lower or broader part near the horizon, and, if there\nbe broken clouds about, often appears like the glow of a distant\nconflagration, or of the rising moon, only less red, giving rise, in\nshort, to amorphous masses of light such as have been noticed by one of\nyour correspondents as possibly appertaining to the comet. At higher\naltitudes, its light fades gradually, and is seldom traceable much\nbeyond the Pleiades, which it usually, however, attains and involves,\nand (what is most to my present purpose) its axis at the vernal equinox\nis always inclined (to the northward of the equator) at an angle of\nbetween 60\u00b0 and 70\u00b0 to the horizon, and it is most luminous at its\nbase, resting on the horizon, where also it is broadest, occupying,\nin fact, an angular breadth of somewhere about 10\u00b0 or 12\u00b0 in ordinary\nclear weather.\u201d\n\n[17] \u201cThe assumption that the extent of the starry firmament is\nliterally infinite has been made by one of the greatest of astronomers,\nthe late Dr. Olbers, the basis of a conclusion that the celestial\nspaces are, in some slight degree, deficient in _transparency_; so that\nall beyond a certain distance is, and must remain for ever, unseen; the\ngeometrical progression of the extinction of light far outrunning the\neffect of any conceivable increase in the power of our telescopes. Were\nit not so, it is argued, every part of the celestial concave ought to\nshine with the brightness of the solar disc, since no visual ray could\nbe so directed as not, in some point or other of its infinite length,\nto encounter such a disc.\u201d--_Edinburgh Review_, p. 185, for January,\n1848; _Etudes d\u2019Astronomie Stellaire_.\n\n[18] In the _Astronomische Nachrichten_ of July, 1846, appeared a\nMemoir by M. M\u00e4dler, _Die Centralsonne_. The conclusions arrived at by\nM\u00e4dler may be understood from the following quotation from a French\ntranslation, made by M. A. Gautier, in the _Archives des Sciences\nPhysiques et Naturelles_, for October, 1846:--\u201cQuoiqu\u2019il r\u00e9sulte\nde ce qui pr\u00e9c\u00e8de que la r\u00e9gion du ciel que j\u2019ai adopt\u00e9e satisfait\n\u00e0 toutes les conditions pos\u00e9es plus haut, il n\u2019en est pas moins\nconvenable de la soumettre \u00e0 toutes les \u00e9preuves possibles. Plusieurs\nessais de combinaisons diff\u00e9rentes m\u2019ont convaincu qu\u2019on ne pourrait\ntrouver aucun autre point dans le ciel qui p\u00fbt tenir lieu, m\u00eame d\u2019une\nmani\u00e8re approch\u00e9e, que celui que j\u2019ai adopt\u00e9. On pourrait maintenant\nm\u2019addresser l\u2019objection que, si la r\u00e9gion du ciel o\u00f9 se trouve le\ncentre de gravit\u00e9 de notre syst\u00e8me d\u2019\u00e9toiles fixes, est d\u00e9termin\u00e9e\npar ce qui pr\u00e9c\u00e8de entre certaines limites, il n\u2019en r\u00e9sulte pas la\nn\u00e9cessit\u00e9 de choisir Alcyone pour ce centre, attendu qu\u2019il pourrait\nbien tomber sur quelqu\u2019autre \u00e9toile situ\u00e9e dans le groupe ou dans son\nvoisinage. Mais outre que c\u2019est tout pr\u00e8s de l\u00e0 que se trouve le groupe\nle plus brillant et le plus riche en \u00e9toiles de tout le ciel, et qu\u2019il\nne s\u2019agit point ici d\u2019un point arbitraire situ\u00e9 dans le voisinage\npeu apparent et qui n\u2019ait rien qui le distingue, il ne se trouve nul\npart, m\u00eame dans la r\u00e9gion voisine, une aussi exacte concordance des\nmouvements propres qu\u2019ici, et ces mouvements correspondent mieux que\ntous les autres aux conditions \u00e9tablies plus haut. Or si l\u2019on doit\nconsid\u00e9rer ce groupe central, entre les \u00e9toiles \u00e9galement \u00e9loign\u00e9es, on\npeut pr\u00e9sumer que la plus brillante de beaucoup pr\u00e9sente la plus grande\nmasse. Outre cela Alcyone, consid\u00e9r\u00e9e optiquement, est au milieu du\ngroupe des Ple\u00efades; et son mouvement propre, d\u00e9termin\u00e9 par Bessel, est\nplus exactement en accord avec la moyenne de ceux des autres Ple\u00efades;\nainsi que des \u00e9toiles de cette r\u00e9gion jusqu\u2019\u00e0 10\u00b0 de distance. _Je puis\ndonc \u00e9tablir comme cons\u00e9quence de tout ce qui pr\u00e9c\u00e8de, que le groupe\ndes Ple\u00efades est le groupe central de l\u2019ensemble du syst\u00e8me des \u00e9toiles\nfixes, jusqu\u2019aux limites ext\u00e9rieures d\u00e9termin\u00e9es par la Voie Lact\u00e9e;\net que Alcyone est l\u2019\u00e9toile de ce groupe qui para\u00eet \u00eatre, le plus\nvraisemblablement, le vrai Soleil central._\u201d\n\n[19] See the article _On Gravitation_, Penny Cyclop\u00e6dia, from the pen\nof the Astronomer-Royal.\n\n[20] Delambre dates the commencement of modern astronomical observation\nin its most perfect form from Maskelyne, who was the first who gave\nwhat is now called a standard catalogue (A.D. 1790) of stars; that\nis, a number of stars observed with such frequency and accuracy, that\ntheir places serve as standard points of the heavens. His suggestion\nof the _Nautical Almanack_, and his superintendence of it to the end\nof his life, from its first publication in 1767, are mentioned in the\n_Almanack_ (vol. i. p. 364); his _Schehallion Experiment on Attraction_\nin vol. iii. p. 69; and the character of his _Greenwich Observations in\nGreenwich Observatory_ in vol. ii. p. 442.\n\n[21] _Experiments to determine the Density of the Earth._ By Henry\nCavendish, Esq., F.R.S. and F.A.S.--Philosophical Transactions, 1798.\n\n[22] Adams: _An Explanation of the observed irregularities in the\nmotion of Uranus, on the hypothesis of disturbance caused by a more\ndistant Planet_.--Appendix to Nautical Almanack for 1851.\n\n[23] Le Verrier: _Premier M\u00e9moire sur la th\u00e9orie d\u2019Uranus_, Comptes\nRendus, vol. xxi.; _Sur la plan\u00eate qui produit les anomalies observ\u00e9es\ndans le mouvement d\u2019Uranus_.--_Ib._ vol. xxiii.\n\n[24] The experiment alluded to is one of a series by M. Plateau, who\nthus describes his arrangement of the fluid:--\u201cWe begin by making a\nmixture of alcohol and distilled water, containing a certain excess\nof alcohol, so that when submitted to the trial of the test tube\nit lets the small sphere of oil fall to the bottom rather rapidly.\nWhen this point is obtained, the whole is thrown upon filters, care\nbeing taken to cover the funnels containing these last with plates\nof glass; this precaution is taken in order to prevent, as much as\npossible, the evaporation of the alcohol. The alcoholic liquor passes\nthe first through the filters, ordinarily carrying with it a certain\nnumber of very minute spherules of oil When the greater part has thus\npassed, the spherules become more numerous; what still remains in the\nfirst filters, namely, the oil and a residue of alcoholic liquor, is\nthen thrown into a single filter placed on a new flask. This last\nfiltration takes place much more slowly than the first, on account of\nthe viscosity of the oil; it is considerably accelerated by renewing\nthe filter once or twice during the operation. If the funnel has been\ncovered with sufficient care, the oil will collect into a single mass\nat the bottom of the flask under a layer of alcoholic liquor.\u201d--_On the\nPhenomena presented by a free Liquid Mass withdrawn from the action of\nGravity._ By Professor Plateau, of the University of Ghent. Translated\nfrom the _Memoirs of the Royal Academy of Brussels_, vol. xvi.; in the\n_Scientific Memoirs_, vol. iv. part 13.\n\n\n\n\nCHAPTER IV.\n\nMOLECULAR FORCES.\n\n  Conditions of Matter--Variety of organized\n    Forms--Inorganic Forms--All matter reducible to the\n    most simple conditions--Transmutation, a natural\n    operation--Chemical Elementary Principles--Divisibility of\n    Matter--Atoms--Molecules--Particles--Molecular Force includes\n    several Agencies--Instanced in the Action of Heat on Bodies--All\n    Bodies porous--Solution--Mixture--Combination--Centres of\n    Force--Different States of Matter (Allotropic Conditions)--Theories\n    of Franklin, \u00c6pinus, and Coulomb--Electrical and Magnetic\n    Agencies--Ancient Notions--Cohesive Attraction, &c.\n\n\nIn contemplating the works of nature, we cannot but regard, with\nfeelings of religious admiration, the infinite variety of forms under\nwhich matter is presented to our senses. On every hand the utmost\ndiversity is exhibited; through all things we trace the most perfect\norder; and over all is diffused the charm of beauty. It is the\nuneducated or depraved alone who find deformities in the creations by\nwhich we are surrounded.\n\nThe three conditions of matter are--the solid, the fluid, and the\na\u00ebriform; and these belong equally to the organic and the inorganic\nworld.\n\nIn organic nature we have an almost infinite variety of animal form,\npresenting developments widely different from each other, yet in every\ncase suited to the circumstances required by the position which the\ncreature, occupies in the scale of being. Through the entire series,\nfrom the Polype to the higher order of animals, even to man, we find a\nuniformity in the progress towards perfection, and a continuity in the\nseries, which betrays the great secret, that the mystery of life is\nthe same in all,--a pervading spiritual essence associated with matter,\nand modifying it by the master-mechanism of an Infinite mind.\n\nIn the vegetable clothing of the surface of the earth, which fits it\nfor the abode of man and animals--from the conferv\u00e6 of a stagnant pool,\nor the lichen of the wind-beaten rocks, to the lordly oak or towering\npalm--a singularly beautiful chain of being presents itself to the\ncontemplative mind, and we cannot but trace the gradual elevation in\nthe scale of organization.\n\nIn the inorganic world, where the great phenomena of life are wanting,\nwe have constantly exhibited the working of powers of a strangely\ncomplicated kind. The symmetrical arrangement of crystals--the\ndiversified characters of mineral formations--the systematic\naggregations of particles to form masses possessing properties of a\npeculiar and striking nature--all prove, that agencies, which science,\nwith all its refinements, has not yet detected, are unceasingly at\nwork. Heat, electricity, chemical power--whatever that may be--and\nthe forces of cohesion, are known to be involved in the production of\nthe forms we see; but contemplation soon leads to the conviction that\nthese powers are subordinate to others which we know not of. We know\nonly the things belonging to the surface of our planet, and these but\nsuperficially. The geologist traces rock-formations succeeding each\nother (from the primary strata holding no traces of organized forms,\nthrough the Paleozoic series, in which, step by step, the history of\nanimal life is recorded,) to the more recent formations, teeming with\nrelics, which, though allied to some animal types still existing, are\ngenerally such as have passed away. The naturalist searches the earth,\nthe waters, and the air, for their living things; and the diversity\nof form, the variety of condition, and the perfection of organization\nwhich he discovers as belonging to this our epoch--differing from,\nindeed bearing but a slight relation to, those which mark the earth\u2019s\nmutations--exhibit, in a most striking view, the endless variety of\ncharacters which matter can assume.\n\nWe are so accustomed to all these phenomena of matter, that it is with\nsome difficulty we can bend ourselves to the study of the more simple\nconditions in which it exists.\n\nThe solid crusts of this telluric sphere--the waters and the\natmosphere--the diversified fabrics of the vegetable kingdom--and the\nstill more complicated structures of men and animals--are, altogether,\nbut the aggregation of minute particles in accordance with certain\nfixed laws. By mechanical means all kinds of matter may be reduced to\npowder, the fine particles of which would not appear very different\nfrom each other, but each atom has been impressed with properties\npeculiar to itself, which man has no power to change.\n\nTo nature alone belongs the mysterious property of transmutation. The\nenthusiastic alchemist, by the agency of physical forces, dissipates a\nmetal in vapour; but it remains a metal, and the same metal still. By\nthe Hermetic art he breaks up the combination of masses; but he cannot\nalter the principles of any one of the elements which form the mass\nupon which his skill is tried.\n\nEvery atom is invested with properties peculiar to all of its class;\nand each one possesses powers, to which in mute obedience it is\ncompelled, by which these properties are modified, and the character of\nmatter varied. What are those properties? Do we know anything of those\npowers?\n\nThe earth, so far as we are acquainted with it, is composed of about\nsixty principles, which we call elementary. These are the most simple\nstates to which we can reduce matter, and from them all the forms of\ncreation yet examined by the chemist are produced. These elementary\nprinciples are, some of them, permanently gaseous under the ordinary\ntemperature, and others exist as solid masses; the difference between\nthe two conditions being regulated, as it appears, by the opposing\nforces of heat and cohesive attraction.\n\nMatter has been regarded by some as infinitely divisible; but the known\nconditions of chemical combinations lead to the conclusion that there\nare limits beyond which matter cannot be divided.[25] The theory of\natoms having determinate characters, and possessing symmetric forms,\ncertainly has the advantage of presenting to the human mind a starting\npoint--a sort of standing ground,--from which it can direct the survey\nof cosmical phenomena. The metaphysical hypothesis, which resolves all\nmatter into properties, and refers all things to ideas, leaves the\nmind in a state of uncertainty and bewilderment.\n\nAdapting the views of Dumas, with some modifications,[26] it will be\nfound more satisfactory to regard the _ultimate atoms_ of matter as\npoints beyond the reach of our examination; which, according to a law,\ndetermined by the influences of the so-called imponderable forces,\nunite to form _molecules_. Again, these molecules combine to form the\n_particles_ of the mass which we may regard as the limit of mechanical\ndivision. The particles of solid bodies are solid, those of fluids\nfluid, and those of gaseous bodies are themselves a\u00ebriform; but it does\nnot follow that the molecules of any body should be necessarily solid,\nfluid, or a\u00ebriform, from the circumstance of their having formed the\nparticles of a body in one of these states.\n\nAs this planet--a molecule in space--is formed of aggregated atoms, and\nenveloped by its own physical agencies--and as it is involved in the\ninfinitely extending influences of other planetary molecules, and thus\nforms part of a system--so the molecules of any mass are grouped into a\nsystem or particle, which possesses the great characteristic features\nof the whole.\n\nIn an a\u00ebriform body the particles are in a state of extreme tenuity,\nthe molecules being themselves, by the influence of some repulsive\nforce, just on the verge where cohesion exerts its decaying power. In\nfluid bodies the attenuation of the particles is less--the particles\nand also the molecules are nearer together,--whereas, in the solid\nbody, the forces of cohesion are most strongly exerted, and all the\nmolecular conditions brought more powerfully into action.\n\nUnder the term molecular force, we include several agencies,--not\nalike in the phenomena which they exhibit, but which are all-powerful\nin producing the general characteristics of bodies. These require a\nsomewhat close examination. All the particles of even a solid mass may\nbe brought under conditions on which they are free to move. By heat we\ncan increase the length and thickness of a bar of iron, or any other\nmetal, and at length produce the fluid state,--a melted metal flows as\nfreely as water in a stream. Fluids, and gases in like manner obey the\ndispersive influence of caloric. From these and other analogous results\nwe learn that all bodies have a greater or less degree of porosity.\nThe distance at which the particles of fluid bodies are maintained is\nstrikingly proved by the fact, that hydrated salts dissolved in water\noccupy no more space than that which is equal to the water contained\nin the crystalline body; while anhydrous salts dissolve without at\nall increasing the bulk of the fluid. All the solid matter of the salt\nmust, in these cases, it would appear, go to fill up the interstitial\nspaces which we suppose to exist in the liquid.[27]\n\nThe conditions which regulate the solubility of bodies, and the power\nof solution, regarded either as a mechanical or a chemical process, are\nvery obscure. We might be led to suppose, that those bodies possessing\nthe largest amount of unoccupied space were capable of holding the\ngreatest quantity of soluble matter dissolved. This, however, is far\nfrom being the case, the denser fluids generally having the greatest\nsolvent power.\n\nThe peculiar manner in which hydrogen gas appears to dissolve solid\nsubstances,--as iron, potassium, sodium, sulphur, phosphorus,\nselenium, and arsenic, may be explained by regarding the results as\na manifestation of the powers of chemical affinity over the forms of\nbodies. In like manner, the solution of salt in water, or the mixture\nof alcohol in that fluid, may be viewed as chemical phenomena, although\nusually considered as simple cases of solution or mixture: alterations\nof temperature and other physical changes taking place in either. If\ntwo masses of metal,--either tin and copper, for example,--are melted\nand combined, the united mass will not equal the bulk of the two\nmasses. If a pint measure of oil of vitriol and an equal quantity of\nwater are mixed together, the combined fluids will not fill a two pint\nmeasure.[28]\n\nIn these instances a large quantity of heat is rendered sensible, as\nif it had been squeezed out by the force with which the particles\ncombined, from interstices, which were filled with, what we may be\nallowed to call, an atmosphere of heat. Hence we conclude that, amongst\nthe influences determining the molecular constitution of a body, heat\nperforms an important part. All these facts go to prove that the atoms\nwhich form the compound body, whatever may be its character, are\ndisposed of as so many centres of force, which act by influences of a\npeculiar character upon each other. That these influences are dependent\nupon known physical forces is certain; but the laws by which the powers\nof the ultimate atom are altered remain still unknown.\n\nIn the great operations of nature, changes are produced which we cannot\nunderstand, and variations of condition do certainly occur, which may\nbe regarded as instances of transmutation.\n\nAmongst others, we may adduce the different states in which we\nknow carbon to exist. We have the diamond with its beautiful\nlight-refracting property, its hardness and high specific gravity,\ncapable of being converted into graphite and coke.[29] Charcoal,\ngraphite, and the diamond, are totally unlike each other, yet we know\nthey are each composed of the same atoms. Charcoal is a black irregular\nsubstance, light, and readily inflammable; graphite is crystallizable;\nbut the forms of its crystals cannot be referred to those of the\ndiamond, and it burns with difficulty. The diamond occurs in the most\nregular and beautifully transparent forms; and it can be burned only\nat the highest artificial temperatures. We are, however, convinced by\nexperiment that the brilliant and transparent gem is made up of the\nsame atoms as those which go to form the dull black mass of charcoal.\nFrom diamonds, as is above stated, coke has been formed by the heat\nof the voltaic battery, and recent experiments have proved that the\nvolatilized carbon constantly passing off from one of the poles of a\nsufficiently powerful battery, is deposited in a crystalline powder,\npossessing most of the properties, as it regards hardness, &c. of true\ndiamond dust. What is the mystery of this? We know not. The peculiar\nconditions have been the subjects of anxious study; but science has not\nyet let in a ray of light upon the mystery. That a different state--it\nhas been called an _allotropic_ condition--is often induced in the\nsame class of atoms is certain; and hence the variety of the resulting\ncompounds. To continue our illustrations with carbon--may not its\ncombinations, in uniform proportions with oxygen and hydrogen,[30] owe\ntheir differences to some allotropic change in the ultimate atoms of\nthis element.\n\nWe know that silicon--the metallic base of flint--is capable of\nassuming two or more different states; and that sulphur, selenium,\nphosphorus, and arsenic, are susceptible of these remarkable changes\nin which, without the slightest variation in the chemical character, a\ncomplete change in the physical condition is produced. Copper, iron,\ntin, and manganese, are known to exist in at least two states of\nphysical dissimilarity, and many of the rarer metals exhibit the same\npeculiarity.[31] Hence, may we not infer that some of those substances,\nwhich we now term elementary, are but altered conditions of the same\nelement? The resemblance between many of those bodies strengthens\nthe supposition. Iridium and platinum,--iron and nickel,--chlorine,\nbromine, iodine, and probably fluorine,--are good examples of these\nsimilarities, although these bodies are all distinguished by physical\nand chemical differences.\n\nThe light-refracting gem, which glistens on the neck of beauty, and is\nvalued for its transparency, differs only from the rude lump of coke in\nits molecular arrangement. Chemistry teaches us that we may, without\nproducing any disarrangement of the affinities, but by merely setting\nup molecular disturbance, effect decided changes, as is strikingly\nshown in the colour of iodide of mercury changing from red to yellow\nunder slight influences of heat, and back again to red by a gentle\nmechanical disturbance. By a slight change, merely molecular, iron may\nbe made to resemble platinum in its physical properties.[32] An iron\nwire plunged into nitric acid is attacked by the acid with violence;\nbut if one extremity of the wire is heated in the flame of a spirit\nlamp, such a change of state is produced throughout the entire length\nof the wire, that if it be now plunged into nitric acid no effect is\nproduced upon it. On studying this question, we find good reason for\nsupposing that bodies which, though physically different, resemble\neach other in some of their properties, iodine, bromine, &c., are the\nresults of different _allotropic_ conditions which have been impressed\nupon the ultimate atoms, similar to those observed in the substances\nnamed. This hypothesis appears to be more in accordance with the great\nprinciples which we must conceive guided the labours of an Infinite\nMind, than that which supposes a vast number of individual creations.\nIt will be seen in the sequel that light, heat, electricity, and\nchemical action, have the power of producing yet more striking changes\nin the forms of bodies. Is it not probable that, according to the\noperations of these agents, either combined or separate, acting over\ndifferent spaces of time, and under varying circumstances, in relation\nto the molecular forces, all those _allotropic_ states may be produced?\nHence bodies may be discovered, which,--from the imperfections of\nscience,--resisting our means of analysis, must, for a time, be\nregarded as new elements, whereas they are possibly only altered states\nof the same substance.\n\nThe experiments of Faraday and of Pl\u00fccker prove that all matter exists\nin certain polar conditions, having powers of mutual attraction\nand repulsion.[33] Are the molecular forces, so called, to be\nreferred to any of those powers which are involved in the general\nterm magnetic-polarity? Are they not probably the result of some\nultimate principle of which these properties are but the modified\nmanifestations? These questions will now be generally answered in\nfavour of magnetism; but in our ignorance we should pause; the next\ngeneration will without doubt find another solution for the problem.\n\nFranklin supposed the ultimate atoms of bodies to be surrounded by\na subtile fluid or ether, which they have the power of condensing\nupon their surfaces with great force--and we have experiments showing\nthat this is probable[34]--whilst he regarded the atoms of the ether\nitself as mutually repellent, thus establishing an equilibrium of\nforces. \u00c6pinus reduced the hypothesis of Franklin to a mathematical\ntheory; and Coulomb _proved_ that the force with which the repulsion\nof the ethereal atoms and the attraction of the material molecules\nare produced, is, like universal attraction,--to whatever power that\nmay be due,--regulated by the law of the inverse ratio of the square\nof the distance. These views are found, upon minute examination, to\nhold true to the phenomena with which inductive science has made us\nacquainted; and the striking manner in which, when submitted to the\nrigorous investigations of geometers, they agree with known conditions\nof electricity, appears certainly to favour the opinion that this power\nmay be materially connected with these molecular arrangements.\n\nMany of the phenomena which are connected with the magnetic influences\nalso bear in a remarkable manner upon this inquiry. But, without\nthe necessary proof of direct experimental evidence, it were as\nunphilosophical to refer the binding together of the molecules of\nmatter to the agency of electricity, as it would be to adopt the theory\nof the hooked atoms of Epicurus, or the astrological dream of the\nsympathies of matter.[35]\n\nScience, however, enables us to infer with safety that the mechanical\npowers which regulate the constitution of a cube of marble, or a\ngranite mountain, are of a similar order to those which determine the\nearth\u2019s relation to the other planets in the solar system, and that\nsolar system itself a unit, in the immensity of space, to the myriads\nof suns which spangle the stellar vault.\n\nIn fine, cohesion, or the attraction of aggregation, is a power\nemployed in binding particle to particle. To cohesion, we find we have\nheat opposed as a repellent force; and the mysterious operations of\nthose electrical phenomena, generally referred to as polar forces, are\nconstantly, it is certain, interfering with its powers. In addition,\nwe have seen that in nature there exists an agency which is capable\nof changing the constitution of the ultimate atoms, and of thus\ngiving variety to each resulting mass. What this power may be, our\nscience cannot tell; but our reason leads us, with firm conviction,\nto the belief that it is a principle which is, beyond all others in\nits subtile influences which equally universal with, appears to rise\nsuperior to gravitation; and which, like a spirituality, shadows forth\nto our dwarf conceptions the immensity of the divine power of the\nomniscient Creator.\n\nThe molecular forces involve a consideration of all the known physical\npowers, the study of which, in their operations on matter, will engage\nour attention. But it is pleasant to learn, as we advance step by step\nin our examination of the phenomena of creation, that we may study\nthe grand in what externally appears the simple, and learn, in the\nmysteries of a particle, the high truths which science has to tell of a\nplanet.\n\nIt may appear that the forces of gravitation and cohesion are regarded\nas identical. Many phenomena, which we are enabled to reach by the\nrefinements of inductive inquiry, certainly present to us a striking\nsimilarity in the laws which regulate the operations of these powers;\nbut it must be remembered that their identity is not established. So\nfar from this, we know the law of gravitating force. Newton determined\nwith surprising accuracy, that the action of this power diminishes with\nthe distance as the universe square, but cohesive force is exerted only\nat such distances that it is impossible to determine whether or not it\nis subjected to the same law. To quote the words of Young: \u201cThe whole\nof our inquiries respecting the intimate nature of forces of any kind\nmust be considered merely as speculative amusements, which are of no\nfurther utility than as they make our views more general, and assist\nour experimental investigations.\u201d[36]\n\n\nFOOTNOTES:\n\n[25] \u201cThe divisibility of matter is great beyond the power of\nimagination, but we have no reason for asserting that it is infinite;\nfor the demonstrations which have sometimes been adduced in favour\nof this opinion are obviously applicable to space only. The infinite\ndivisibility of space seems to be essential to the conception that we\nhave of its nature, and it may be strictly demonstrated that it is\nmathematically possible to draw an infinite number of circles between\nany given circle and its tangent, none of which shall touch either of\nthem except at the general point of contact; and that a ship following\nalways the same oblique course with respect to the meridian,--for\nexample, sailing north-eastwards,--would continue perpetually to\napproach the pole without ever completely reaching it. But when we\ninquire into the truth of the old maxim of the schools, that all\nmatter is infinitely divisible, we are by no means able to decide so\npositively. Newton observes that it is doubtful whether any human means\nmay be sufficient to separate the particles of matter beyond a certain\nlimit; and it is not impossible that there may be some constitution\nof atoms, or single corpuscles, on which their properties, as matter,\ndepend, and which would be destroyed if the units were further divided;\nbut it appears to be more probable that there are no such atoms, and\neven if there are, it is almost certain that matter is never thus\nannihilated in the common course of matter.\u201d--_The Essential Properties\nof Matter_: Young\u2019s _Natural Philosophy_; ed. by Rev. P. Kelland.\n\n[26] \u201cTwo very different hypotheses have been formed to explain the\nnature of matter, or the mode of its formation; the one known as\nthe _atomic_ theory, the other, the _dynamic_. The founder of the\nformer and earlier was Leucippus: he considered the basis of all\nbodies to be extremely fine particles, differing in form and nature,\nwhich he supposed to be dispersed through space, and to which his\nfollower Epicurus first gave the name of atoms. To these atoms he\nattributed a rectilinear motion, in consequence of which such as\nare homogeneous united, whilst the lighter were dispersed through\nspace. The author of the second hypothesis was the famous Kant. He\nimagined all matter existed, or was originated, by two antagonist and\nmutually counteracting principles, which he called attraction and\nrepulsion, all the predicates of which he referred to motion. Most\nmodern philosophers, and foremost amongst them Amp\u00e8re and Poisson, have\nadopted an hypothesis combining the features of both the preceding.\nThey regarded the atoms as data, deriving their origin from the Deity\nas the first cause, and consider their innate attractive and repulsive\nforce as a necessary condition to their combination in bodies. The\nmain features of this hypothesis are borrowed from Aristotle, inasmuch\nas he supposed the basis of all bodies to be the four elements known\nto the ancients, the particles of which, endued with certain powers,\nconstituted bodies. According to Amp\u00e8re, all bodies consist of equal\nparticles, and they again of molecules that, up to a certain distance,\nattract each other. Their distance from each other he supposed to be\nregulated by the intensity of the attractive and repulsive forces,\nthe latter of which preponderates.\u201d--Peschel\u2019s _Elements of Physics_;\ntranslated by E. West, 1845.\n\n[27] This was first proved by the researches of Dr. Dalton: the subject\nwill be again alluded to under the consideration of atomic volumes.\n\n[28] These peculiar phenomena may be studied advantageously in the\nworks of most of the eminent European chemists. In our own language the\nreader is referred to Dr. Thompson\u2019s _Outline of the Sciences of Heat\nand Electricity_, 2nd edition; Brande\u2019s _Manual of Chemistry_--Art.\n_Specific Heat_; Graham\u2019s _Elements of Chemistry_; and Daniell\u2019s\n_Introduction to the Study of Chemical Philosophy_.\n\n[29] The conversion of the diamond into graphite and coke was first\neffected by the agency of the galvanic arc of flame, by M. Jaquelini,\nand communicated to the Academy of Sciences in 1847, in a Memoir\nentitled, _De l\u2019action calorifique de la pile de Bunsen, du chalumeau \u00e0\ngaz oxyg\u00e8ne et hydrog\u00e8ne sur le carbon pur, artificiel et naturel_. See\n_Comptes Rendus_, 1847, vol. xxiv. p. 1050; also _Report of the British\nAssociation_, for 1847, (_Transactions of Sections_) p. 50.\n\n[30] \u201cIn the annual report on the progress of chemistry, presented\nto the Royal Academy of Stockholm, in March 1840, I have proposed to\ndesignate by the term _allotropic state_, that dissimilar condition\nwhich is observed in certain elements, and long known examples of which\nare found in the different forms of carbon, as graphite and diamond.\n\n\u201cAlthough these dissimilar conditions, which I have here called\nallotropic, have long since attracted attention in one or two elements,\nstill they have been regarded as exceptions to the general rule. It\nis at present my object to show that they are not so rare; that it\nis probably rather a general property of the elements to appear in\ndifferent allotropic conditions; and that although we have hitherto\nbeen unable to obtain several of the elements when uncombined in\ntheir allotropic states, still their compounds indicate the same with\ntolerable distinctness.\u201d--_Berzelius on the Allotropy of the Elementary\nBodies_, _&c._: Poggendorff\u2019s Annalen, 1844. Scientific Memoirs, vol.\niv. p. 240.\n\n[31] \u201cCopper, when reduced by hydrogen at a heat below that of\nredness, on exposure to air soon becomes converted throughout its\nmass into protoxide; and when it is triturated for some time with\nan equivalent quantity of sulphur, it combines with it according to\nB\u00f6ttcher\u2019s experiments, producing flame, and forming sulphuret of\ncopper. If, however, the copper be reduced by hydrogen at a red heat,\nstill considerably below the temperature at which it softens and\nbegins to melt, it remains for years unchanged by exposure to air,\nand cannot be made to combine with sulphur without the application of\nheat. Iron, cobalt, and nickel, when reduced by hydrogen below a red\nheat, inflame after they have cooled, if exposed to the air; and if\nthey are immediately placed in water to avoid their taking fire, they\ninflame when they are again removed, and have become nearly dry. If we\ncompare this behaviour with that of iron reduced by heat, and with iron\nin that state in which it forms the conductor of a galvanic current\nwithout becoming oxidized, it would appear that these peculiarities\ndepended upon something more than a difference of mechanical\ncondition.\u201d--_Berzelius on the Allotropy of Elementary Bodies._ See\n_On the Isomeric Conditions of the Peroxide of Tin_: by Prof. H.\nRose.--Chemical Gazette, Oct. 1848.\n\n[32] On this curious subject, and its history, see Bergman\u2019s _Dissert.\nde Phlog. quantitate in Metallis_, 1764. Kirwan, _On the Attractive\nPowers of Mineral Acids_: Philosophical Transactions. Kier\u2019s\n_Experiments and Observations on the Dissolution of Metals in Acids_:\nPhil. Trans. 1790.\n\nFrom these valuable papers it will be seen that the peculiar states\nof iron had already attracted attention, particularly those \u201cinactive\nconditions\u201d noticed in a \u201c_Note sur la Mani\u00e8re d\u2019agir de l\u2019Acide\nnitrique sur le Fer, par J. F. W. Herschel_,\u201d Aug. 1833; and previously\nindicated by M. H. Braconnot, _Sur quelques Propri\u00e9t\u00e9s de l\u2019Acide\nnitrique_, Annales de Chimie, vol. lii. p. 54. Reference should also be\nmade to the Memoirs of Sir John Herschel, _On the Action of the Rays\nof the Solar Spectrum on Vegetable Colours_, _&c._: Phil. Trans. vol.\ncxxxiii. p. 221; and _On the Separation of Iron from other Metals_:\nPhil. Trans. vol. cxi. p. 293; and several papers by Sch\u00f6nbein, in the\nPhilosophical Magazine, from 1837.\n\n[33] Faraday, in his memoir _On new Magnetic Actions, and on the\nMagnetic Conditions of all Matter_, says:--\u201cBy the exertion of this new\ncondition of force, the body moved may pass either along the magnetic\nlines or across them, and it may move along or across them in either\nor any direction, so that two portions of matter, simultaneously\nsubject to this power, may be made to approach each other as if they\nwere mutually attracted, or recede as if mutually repelled. All the\nphenomena resolve themselves into this, that a portion of such matter,\nwhen under magnetic action, tends to move from stronger to weaker\nplaces or points of force. When the substance is surrounded by lines\nof magnetic force of equal power on all sides, it does not tend to\nmove, and is then in marked contradistinction with a linear current of\nelectricity under the same circumstances.\u201d--Phil. Trans. for 1846, vol.\ncxxxvii.\n\n[34] _New Experiments and Observations on Electricity made at\nPhiladelphia, in America._--Addressed to Mr. Collinson, from 1747\nto 1754. By Benjamin Franklin. Of these Priestley remarks:--\u201cIt is\nnot easy to say whether we are most pleased with the simplicity and\nperspicuity with which the author proposes every hypothesis of his own,\nor the noble frankness with which he relates his mistakes, when they\nwere corrected by subsequent experiments.\u201d\n\n[35] \u201cThe atomic philosophy of Epicurus, in its mere physical\ncontemplation, allows of nothing but matter and space, which are\nequally infinite and unbounded, which have equally existed from all\neternity, and from different combinations of which every visible form\nis created. These elementary principles have no common property with\neach other; for whatever matter is, that space is the reverse of; and\nwhatever space is, matter is the contrary to. The actual solid part of\nall bodies, therefore, are matter, their actual pores space, and the\nparts which are not altogether solid, but an intermixture of solidity\nand pore, are space and matter combined.\n\n\u201cThe infinite groups of atoms, flying through all time and space in\ndifferent directions and under different laws, have interchangeably\ntried and exhibited every possible mode of rencounter: sometimes\nrepelled from each other by concussion, and sometimes adhering to each\nother from their own jagged or pointed construction, or from the casual\ninterstices which two or more connected atoms must produce, and which\nmay be just adapted to those of other figures,--as globular, oval, or\nsquare. Hence the origin of compound and visible bodies; hence the\norigin of large masses of matter; hence, eventually, the origin of the\nworld itself.\u201d--Dr. Good\u2019s _Book of Nature_.\n\n[36] Young\u2019s _Lectures on Natural Philosophy and the Mechanical Arts_.\nLecture 49, _On the Essential Properties of Matter_.\n\n\n\n\nCHAPTER V.\n\nCRYSTALLOGENIC FORCES.\n\n  Crystallisation and Molecular Force distinguished--Experimental\n    Proof--Polarity of Particles forming a Crystal--Difference\n    between Organic and Inorganic Forms--Decomposition\n    of Crystals in Nature--Substitution of Particles in\n    Crystals--Pseudomorphism--Crystalline Form not dependent\n    on Chemical Nature--Isomorphism--Dimorphism--Theories of\n    Crystallogenic Attraction--Influence of Electricity and\n    Magnetism--Phenomena during Crystallisation--Can a change of\n    Form take place in Primitive Atoms?--Illustrative Example of\n    Crystallisation.\n\n\n\u201cCrystallisation is a peculiar and most admirable work of nature\u2019s\ngeometry, worthy of being studied by all the power of genius, and the\nwhole energy of the mind, not on account of the delight which always\nattends the knowledge of wonders, but because of its vast importance\nin revealing to us the secrets of nature; for here she does, as it\nwere, betray herself, and, laying aside all disguise, permits us\nto behold, not merely the results of her operations, but the very\nprocesses themselves.\u201d--Such is the language of an Italian philosopher,\nGulielmini; and it is the striking peculiarity of beholding the process\nof the formation of the regular geometric figures of crystals, the\ngradual accretion of particle to particle, which induces us to separate\ncrystallization from mere molecular aggregation. Without doubt the\nformation of a crystal and the production of an amorphous block are\ndue to powers which bear a close resemblance in many points; but they\npresent remarkable differences in others.\n\nLet us take some simple case in illustration. In quiet water we\nhave very finely divided matter suspended, and matter in a state of\nsolution. The first is slowly precipitated, and in process of time\nconsolidates into a hard mass at the bottom, presenting no particular\ncharacter, unless it has been placed in some peculiar physical\nconditions; when, as in nature, we have a regular bedding which is\nintersected by lines of lamination or of cleavage, which we are, from\nexperiment, enabled to refer to the influence of current electricity.\nThe second--the matter in solution--is also slowly deposited; but it is\naccumulated upon nuclei which possess some peculiar disposing powers,\nand every particle is united by some particular face, and an angular\nfigure of the most perfect character results. Many pleasing experiments\nwould appear to show that electricity has much to do in the process\nof crystallization; but it is evident that it must be under some\npeculiarly modified conditions that this power is exerted, if, indeed,\nit has any direct action.\n\nThe same substances always crystallize in the same forms, unless the\nconditions of the crystallizing body are altered. It has been supposed\nthat each particle of a crystalline mass has certain points or poles\nwhich possess definite properties, and that cohesion takes place only\nalong lines which have some relation to the attracting or repelling\npowers of these poles. We shall have, eventually, to consider results\nwhich appear to prove that magnetism is universal in its influence, and\nthat this polarity of the particles of matter may be referred to it.\n\nBe the cause of crystallisation what it may, it presents to us in\nappearance a near approach in inorganic nature to some of the peculiar\nconditions of growth in the organised creation. In one, we have the\ngradual production of parts and the formation of members due to\npeculiar powers of assimilation, each individual preserving all its\ndistinguishing features; and in the other, we have a regular order of\ncohesion occurring under the influence of a power which draws like to\nlike, and arranges the whole into a form of beauty.\n\nThis appears to be the proper place for correcting an error too\nprevalent, relative to the formation of crystals, the development\nof cells, and the yet more fatal falsehood of referring the great\nphenomena of Life to any of the physical forces with which we are\nacquainted.\n\nTHE CRYSTAL _forms_, by the accretion of particle to particle, along\nlines determined by some yet unknown power. There is no change in the\ncharacter of any particle--like coheres to like; the first atom and the\nlast of the series being identical in character.\n\nTHE PLANT _grows_, not by the gathering together of similar particles\nof matter, but by the absorption of a compound particle--by that one\nwhich must be regarded as the primary nuclear atom or cell. After\nthis absorption--in virtue of a power which we call LIFE, excited\ninto action by LIGHT--the compound particle is decomposed, and one\nconstituent is retained to effect the formation of a new cell, whilst\nthe other is liberated as an invisible air. Here we have a change of\nchemical constitution effected; and this takes place through the whole\nperiod of vegetable growth, from the development of the plumule up to\nthe formation of the latest leaf upon the topmost branch of the most\nlordly tree.\n\nLife has been referred to electricity and to chemical power--as the\neffect of a known cause. Without doubt, during the operations of life\nthe whole of the physical powers are necessary to the production of\nall the phenomena of growth in the vegetable and the animal world. But\nthese powers are ever subsidiary to vital force, and are like attendant\nspirits chained to do an enchanter\u2019s bidding.\n\nLife is a force beyond the reach of human search, and he who fancies he\nhas a hold upon the principle which produced biological phenomena, has\ncommitted himself to as wild a pursuit as he who rashly endeavours to\ncatch a morass-meteor.\n\nSubtile as are the forces of light, heat, and electricity--that of\nlife, _vitality_, is infinitely more refined, and it must for ever\nelude the search of the philosopher.\n\nMan is permitted to test and try all things which are created, and\nto apply to useful ends the discoveries which he may make. But man\ncan never become a creator; and he who would attempt to give sense to\nan inert mass of matter, by electricity, heat, or light, will prove\nhimself as ignorant of nature\u2019s truth as is the senseless mass upon\nwhich he works.\n\n\u201cSo far shalt thou go, and no further,\u201d was said equally to the\ngreat tide-wave of human intellect, as to the mighty surge of the\nearth-girdling ocean.\n\nIt must not be forgotten that a striking difference exists between\nthe productions of the mineral and the other kingdoms of nature.\nAnimals and vegetables arrive at maturity by successive developments,\nand increase by the assimilation of substances, having the power of\nproducing the most important chemical changes upon such matter as comes\nwithin the range of their influence; but minerals are equally perfect\nin the earliest stages of their formation, and increase only, as\npreviously said, by the accretion of particles without their undergoing\nany change.\n\nThe animal and vegetable tribes cease to continue the functions of\nlife: death ensues, and a complete disorganisation takes place; but\nthis is not the case in the mineral world: the crystal being the result\nof a constantly acting force is not necessarily liable to decomposition.\n\nNevertheless, we sometimes find in nature that crystals, after arriving\nat what may be regarded as, in some sort, their maturity, are, owing\nto a change of the conditions under which they were formed, gradually\ndecomposed. In our mines we discover skeletons of crystals, and\nwithin the hollow shell thus formed, other crystals of a different\nconstitution and figure find nuclei, and the conditions required for\ntheir development. Again, to give a striking instance, the felspar\ncrystals of the granitic formations are liable to decomposition in a\nsomewhat peculiar manner. In decomposing, these crystals leave moulds\nof their own peculiar forms, and it not unfrequently happens, in the\nstanniferous districts of Cornwall, that oxide of tin gradually fills\nthese moulds, and we procure this metallic mineral in the form of the\nearthy one. Then we have the curious instances of bodies crystallising\nin a false form under change of circumstances. We find, for example,\nPseudomorphism, (or _false-form_), as this class of phenomena is named,\noccurring by the removal of the constituent atoms of one crystal, while\nanother set--which naturally assumes a different form--takes their\nplace, yet still preserving the original shape. It often happens that\ncopper pyrites will, in this manner, exhibit the angles of an ordinary\nvariety of crystallised carbonate of iron. These curious changes may\nbe familiarised by supposing a beautiful statue of gold, from which\nsome skilful mechanic removes particle by particle, and so skilfully\nsubstitutes a grain of brass for every one of gold removed, that the\nloss of the precious metal cannot be detected by any mere examination\nof its form.\n\nCrystalline form is not strictly dependent upon the chemical nature\nof the parts forming the crystal. The same number of atoms, arranged\nin the same way, produce the same form. Substances much unlike each\nother will assume the same crystalline arrangement. Magnesia, lime,\noxide of cadmium, the protoxides of iron, nickel, and cobalt, combined\nwith the same acid, present similarly formed bodies. These Isomorphic\n(_like-form_)[37] peculiarities are exceedingly common, and the\ndiscoverer of the phenomena, Mitscherlich, announced the above law.\nIt cannot, however, be regarded as a philosophical expression of the\nfact, and requires reconsideration--chemical elements of a dissimilar\ncharacter may have the same law of aggregation, and thus produce the\nsame form, without having any relation to the number of atoms.\n\nWe also find compounds which have two distinct systems of\ncrystallisation. This property, Dimorphism, is very strikingly shown\nin carbonate of lime, which occurs in rhombohedrons, in calc spar, and\nin rhombic prisms in arragonite. The molecular arrangements here are\nnot, however, of equal stability, and one form is evidently forced upon\nthe other, and is abandoned by it on the slightest disturbance. When a\nprism of arragonite is heated it breaks up into the rhombs of common\ncalc spar, at a temperature far below that at which the carbonate of\nlime is decomposed; but no alteration of temperature can convert calc\nspar into arragonite.\n\nCrystals are found in the most microscopic character, and of an\nexceedingly large size. A crystal of quartz at Milan is three feet and\na quarter long, and five feet and a half in circumference, and its\nweight is 870 pounds. Beryls have been found in New Hampshire measuring\nfour feet in length.[38]\n\nIn the dark recesses of the earth, where the influences which produce\norganisation and life cease to act, a creative spirit still pursues its\nnever-ending task of giving form to matter.\n\nThe science of crystallogeny,[39] embracing the theoretical and\npractical question of the causes producing these geometric forms,\nhas in various ways attempted to explain the laws according to which\nmolecules arrange themselves on molecules in perfect order, giving rise\nto a rigidly correct system of architecture. But it cannot be said that\nany theory yet propounded is sufficiently exact to embrace the whole\nof the known phenomena, and the questions,--What is crystallogenic\nattraction, and what is the physical nature of the ultimate particles\nof matter,--are still open for the inquiries of that genius which\ndelights in wrestling with the secrets of nature.\n\nThe great Epicurus speculated on the \u201cplastic nature\u201d of atoms, and\nattributed to this _nature_ the power they possess of arranging\nthemselves into symmetric forms. Modern philosophers satisfy themselves\nwith attraction, and, reasoning from analogy, imagine that each atom\nhas a polar system.\n\nElectricity, and light, and heat, exert remarkable powers, and\naccelerate or retard crystallisation according to the conditions under\nwhich these forces are brought to bear on the crystallising mass. We\nhave recently obtained evidence which appears to prove that some form\nof magnetism has an active influence in determining the natural forms\nof crystals, and we discover that magnetism exerts a peculiar influence\nin relation to the optic axes of crystals, which is not exerted in\nlines at right angles to these. Electricity appears to quicken the\nprocess of crystalline aggregation--to collect more readily together\nthose atoms which seek to combine--to bring them all within the limits\nof that influence by which their symmetrical forms are determined; and\nstrong evidence is now afforded, in support of the theory of magnetic\npolarity, by the refined investigations of Faraday and Pl\u00fccker, which\nprove that magnetism has a _directing_ influence upon crystalline\nbodies.[40]\n\nIt has been found that crystals of sulphate of iron, slowly forming\nfrom a solution which has been placed within the range of sufficiently\npowerful magnetic force, dispose themselves along certain magnetic\ncurves, such as are formed around a magnet by steel filings; whereas\nthe crystals of the Arbor Dian\u00e6, or silver tree, forming under the\nsame circumstances, take a position nearly at right angles to these\ncurves. Certain groups of crystals have been found in nature, which\nappear to show, by their positions, that terrestrial magnetism has been\nactive in producing the phenomena they exhibit; indeed, nearly all our\nmineral formations indicate the influences of this, or some similarly\nacting power.[41]\n\nDuring rapid crystallisation, some salts--as the sulphate of\nsoda, boracic acid, and arsenious acid crystallising in muriatic\nacid--exhibit decided indications of electrical excitement; light is\ngiven out in flashes. We have evidence that crystals exhibit a tendency\nto move towards the light, and that crystallisation takes place more\nreadily, and progresses with greater activity in the sunshine than in\nthe shade. Professor Pl\u00fccker has recently ascertained that certain\ncrystals--in particular the cyanite--\u201cpoint very well to the north,\nby the magnetic power of the earth only. It is a true compass needle;\nand, more than that, you may obtain its declination.\u201d We must remember\nthat this crystal, the cyanite, is a compound of silica and alumina\nonly. This is the amount of experimental evidence which science has\nafforded in explanation of the conditions under which nature pursues\nher wondrous work of crystal formation. We see just sufficient of\nthe operation to be convinced that the luminous star which shines in\nthe brightness of Heaven, and the cavern-secreted gem, are equally\nthe result of forces which are known to us in only a few of their\nmodifications.\n\nEvery substance, when placed under circumstances which allow of the\nfree movement of its molecules, has a tendency to crystallise. All the\nmetals may, by slowly cooling from the melting state, be exhibited\nwith a crystalline structure. Of the metallic and earthy minerals,\nnature furnishes us with an almost infinite variety of crystals, and,\nby a reduction of temperature, yet more simple bodies assume the\nmost symmetric forms. Water, in the conditions of ice and snow, is a\nfamiliar and beautiful example; and, by such extreme degrees of cold as\nare artificially produced, many of the gases exhibit a tendency to a\ncrystalline condition.\n\nMay not the solid elementary atoms be susceptible of change of form\nunder different influences? May not the different states under which\nthe same bodies are found--as, for example, silica, carbon, and\niron--be due entirely to a change in the form of the primitive atom?\n\nAdmitting the probability of this, we then easily see that the central\nmolecule, formed of an aggregation of such atoms, uniting by particular\nfaces, would present a determinate form; and that the resulting\ncrystal, a mass of such molecules, cohering according to a given law,\nat certain angles, would present such geometric figures as we find in\nnature, or produce in our laboratories, when we avail ourselves of\nprocesses which nature has taught us.\n\nIf we take a particle of marble, and place it in a large quantity\nof water acidulated with sulphuric acid, it dissolves, and a new\ncompound results. The marble disappears--the eye cannot detect it by\nform or colour: the acid also has been disguised--the taste discovers\nnothing sour in the fluid. We have, in combination with the water,\nthe lime and sulphuric acid; but that combination appears to the eye\nin no respect different from the water itself. It is colourless and\nperfectly transparent, although it holds a mass of solid matter which\npreviously would not allow of the permeation of a ray of light. Let\nus expose this fluid to such circumstances that the water will slowly\nevaporate, and we shall find forming in it, after a time, microscopic\nparticles of solid, light-refracting matter. These particles gradually\nincrease in size, and we may watch their growth until eventually we\nhave a symmetric figure, beautifully shaped, the primary form of\nwhich is a right rhomboidal prism. Thus in nature, by the action,\nin all probability, of vegetable matter on the sulphates held in\nsolution by the water of the great rivers and the ocean--aided by our\noxidizing atmosphere--sulphuric acid is produced to do its work upon\nthe limestone formations, and from this combination would result the\nwell-known gypsum, or plaster of Paris, which ordinarily exists as an\namorphous mass, but is often found in a crystalline form.[42]\n\nThis is a very perfect illustration of the wonderful process we have\nbeen considering, and in which, simple though it appears to be, we\nhave set to work a large proportion of the known physical elements\nof the universe. By studying aright the result which we have it in\nour power to obtain in a watch-glass, we may advance our knowledge of\ngigantic phenomena, which are now progressing at the bottom of the\nocean, or of the wondrous agencies which are in operation, producing\nlight-refracting gems within the secret recesses of the rocky crust of\nour globe.\n\nThe force of crystallisation is a subject worthy of much consideration.\nIf we examine our slate rocks, through which little veins filled with\nquartz crystals are spread, we shall see that the mechanical force\nexerted during the production of these crystals has been capable of\nrending those rocks in every direction. Those fissures formed by the\nfirst system of crystalline veins, in order of time, are filled in by\nanother set of crystalline bodies, which equally exert their mechanical\npower, and thus produce those curious intersections and dislocations\nwhich were long a puzzle to the geologist. The simplest power, slowly\nand constantly acting through a long period of time, may become\nsufficient, eventually, to rend the Andes from base to summit, or to\nlift a new continent above the waters of the ocean.\n\n\nFOOTNOTES:\n\n[37] \u201cGay Lussac first made the remark, that a crystal of potash alum,\ntransferred to a solution of ammonia alum, continued to increase\nwithout its form being modified, and might thus be covered with\nalternate layers of the two alums, preserving its regularity and proper\ncrystalline figure. M. Beudant afterwards observed that other bodies,\nsuch as the sulphates of iron and copper, might present themselves\nin crystals of the same form and angles, although the form was not a\nsimple one, like that of alum. But M. Mitscherlich first recognised\nthis correspondence in a sufficient number of cases to prove that it\nwas a general consequence of similarity of composition in different\nbodies.\u201d--Graham\u2019s _Elements of Chemistry_ (1842), p. 136.\n\nThe following remarks are from a paper by Dr. Hermann Kopp, _On the\nAtomic Volume and Crystalline Condition of Bodies, &c._, published in\nthe Philosophical Magazine for 1841:--\u201cThe doctrine of isomorphism\nshows us that there are many bodies which possess an analogous\nconstitution, and the same crystalline form. Our idea of the volume\n(or, in other words, of the crystalline form) of these bodies must\ntherefore be the same. From this it follows that their specific\nweight is connected with mass contained in the same volume. From\nthese considerations the following law may be deduced: _The specific\nweight of isomorphous bodies is proportional to their atomic weight,\nor isomorphous bodies possess the same atomic volume_.\u201d--page 255.\nA translation appears in the Cavendish Society, from Dr. Otto\u2019s\nChemistry, _On Isomorphism_, which may be advantageously consulted. See\nalso a paper by M. Rose, translated from the _Proceedings of the Royal\nBerlin Academy_ for the _Chemical Gazette_, Oct. 1848, entitled, _On\nthe Isomeric Conditions of the Peroxide of Tin_.\n\n[38] _A System of Mineralogy, comprising the most recent discoveries_,\nby James D. Dana, A.M., New York, 1844.\n\n[39] Crystallogeny, or the formation of crystals, is the term employed\nby Dana, in his admirable work quoted above: whose remarks on\n_Theoretical Crystallogeny_, p. 71, are well worthy of all attention.\n\n[40] _On the Magnetic Relations of the Positive and Negative Optic Axes\nof Crystals_, by Professor Pl\u00fccker, of Bonn.--Philosophical Magazine,\nNo. 231 (3rd Series), p. 450. _Experimental Researches on Electricity;\nOn the Crystalline Polarity of Bismuth and other bodies, and on its\nRelation to the Magnetic form of Force_: by Michael Faraday, Esq.,\nF.R.S.--Transactions of the Royal Society for 1848.\n\n[41] In the _Memoirs of the Geological Survey of the United Kingdom,\nand of the Museum of Economic Geology_, vol. i. 1846, will be found a\npaper, by the author of this volume, _On the Influences of Magnetism on\nCrystallisation, and other Conditions of Matter_, in which the subject\nis examined with much care. See also _Magn\u00e9tisme polaire d\u2019une montagne\nde Chlorite schisteuse et de Serpentine_: Annales de Chimie, vol. xxv.\np. 327; _Influence du Magn\u00e9tisme sur les actions chimiques_, by l\u2019Abb\u00e9\nRendus; and also a notice of the experiments of Ritter and Hansteen,\n\u201cAnalys\u00e9es par M. \u0152rsted;\u201d also _Effets du Magn\u00e9tisme terrestre sur\nla pr\u00e9cipitation de l\u2019Argent, observ\u00e9s par M. Muschman_: Annales de\nChimie, vol. xxxviii. p. 196-201.\n\n[42] The transparent varieties of sulphate of lime are distinguished\nby the name _Selenite_; and the fine massive varieties are called\n_Alabaster_. Gypsum forms very extensive beds in secondary countries,\nand is found in tertiary deposits; occasionally, in primitive rocks; it\nis also a product of volcanoes. The finest foreign specimens are found\nin the salt mines of Bex, in Switzerland; at Hall, in the Tyrol; in the\nsulphur-mines of Sicily; and in the gypsum formation near Ocana, in\nSpain. In England, the clay of Shotover Hill, near Oxford, yields the\nlargest crystals.--See Dana\u2019s _Mineralogy_, second edition, p. 241.\n\n\n\n\nCHAPTER VI.\n\nHEAT--SOLAR AND TERRESTRIAL.\n\n  Solar and Terrestrial Heat--Position of the Earth in the Solar\n    System--Heat and Light associated in the Sunbeam--Transparency\n    of Bodies to Heat--Heating Powers of the Coloured Rays of\n    the Spectrum--Undulatory Theory--Conducting Property of the\n    Earth\u2019s Crust--Convection--Radiation--Action of the Atmosphere\n    on Heat Rays--Peculiar Heat Rays--Absorption and Radiation\n    of Heat by dissimilar Bodies--Changes in the Constitution of\n    Solar Beam--Differences between Transmitted and Reflected\n    Solar Heat--Phenomena of Dew--Action of Solar Heat on the\n    Ocean--Circulation of Heat by the Atmosphere and the Ocean--Heat\n    of the Earth--Mean Temperature--Central Heat--Constant Radiation\n    of Heat Rays from all Bodies--Thermography--Action of Heat on\n    Molecular Arrangements--Sources of Terrestrial Heat--Latent\n    Heat of Bodies--Animal Heat--Eremacausis--Spheroidal State\n    Cold--Condensation--Freezing--Theories of Heat--Natural\n    Phenomena--and Philosophical Conclusion.\n\n\nWe receive heat from the sun, associated with light; and we have the\npower of developing this important principle by physical, mechanical,\nand chemical excitation, from every kind of matter. Our convictions\nare, that the calorific element, whether derived from a solar or a\nterrestrial source, presents no essential difference in its physical\ncharacters; but as there are some remarkable peculiarities in the\nphenomena, as they arise from either one or the other source, it will\nassist our comprehension of this great principle, if we consider it\nunder the two heads.\n\nUntutored man finds health and gladness in the warmth and light of the\nsun; he rears a rugged altar, and bows his soul in prayer, to the\nprinciple of fire, which in his ignorance he regards as the giver and\nthe supporter of life. The philosopher finds life and organization\ndependent upon the powers combined in the sunbeam; and, examining\nthe phenomena of this wonderful band of forces, he is compelled to\nacknowledge that the flame upon the altar--on the Persian hills,--was\nindeed a dim shadow of the infinite wisdom which abides behind the veil.\n\nThe present condition of our earth is directly dependent upon the\namount of heat we receive from the sun. It has frequently been said,\nthat if it were possible to move this planet so much nearer that orb\nthat the quantity of heat would be increased, the circumstances of\nlife would necessarily be so far changed, that all the present races\nof animals must perish; and that the same result would happen from\nany alteration which threw us yet further from our central luminary,\nwhen, owing to the extremity of cold and the wretchedness of gloom, all\nliving creatures would equally fail to support their organization.\n\nTo move the earth nearer to, or more distant from the sun, is an\nimpossibility; but it has been argued that those planets which are near\nto the sun must possess a temperature which would melt our solid rocks,\nand vaporize the ocean,--while Uranus and Neptune must, from their\ndistance from the source of heat, have so small an amount, that water\nmust become solid as the rock, and such an atmosphere as that of the\nearth exist as a dense liquid.\n\nIt will be shown that according to the physical condition of the\nmaterial substances, so are their powers regulated of absorbing and\nretaining the heat which falls as a radiant power upon their surfaces.\nHeat rays, in passing through the attenuated medium of planetary space,\nlose none of their power--this we know from the fact that even the less\ndense upper region of the earth\u2019s atmosphere takes from the solar rays\nbut an exceedingly small quantity of heat. Therefore, whether a solar\nheat ray traverses through one million, or one hundred million miles of\nspace, it still retains its power equally of imparting warmth to the\nsolid matter by which it is intercepted. There is no law of variation\nas the inverse square of the distance of those radiating powers.\nConsequently, there is no reason why the physical conditions, alike\nof the nearest and the most remote planetary bodies, should not be so\nadjusted that they all enjoy that life promoting temperature which\nbelongs to the earth.\n\nAll the objects around us are adapted to the circumstances of the\nearth\u2019s position in relation to the sun, to which we are bound by the\nprinciple of gravitation; opposed to that centrifugal force which tends\nconstantly to drive the moving planetary mass off from the centre of\npower. The balance maintains its perfect equilibrium, although we have\none power constantly drawing the earth towards the sun, and the other\nas constantly exerting itself to move it off into space at a tangent\nto the orbit in which the planet moves. In our examination it will be\nfound that one common system of harmony runs through all the cosmical\nphenomena, by which everything is produced that is so beautiful and\njoyous in this world.\n\nHeat, and the other elementary radiant principles, are often combined\nas the common cause of effects evident to our senses. The warmth of the\nsolar rays, and their luminous influence, are not, however, commonly\nassociated in the mind as the results of a single cause. It is only\nwhen we come to examine the physical phenomena connected with these\nradiations that we discover the complexity of the inquiry. Yet it is\nout of these very subtle researches that we draw the most refined\ntruths. The high inferences to which the analysis of the subtile\nagencies of creation leads us, render science, pursued in the spirit of\ntruth, a great system of religious instruction.\n\nAlthough we do not fear that heat and light can be confounded in the\nmind, so different are their phenomena,--we have heat rays, as from\ndark hot iron, which give no light, while in the full flood of the\nlunar rays the heat is scarcely appreciable by the most delicate\ninstruments;--yet it is important to show how far these two principles\nhave--been separated from each other. Transparent bodies have varied\npowers of calorific transparency, or transcalescence: some obstructing\nthe heat radiated from bodies of the highest temperatures almost\nentirely even in the thinnest layers; whilst others will allow the\nwarmth of the hand to pass through a thickness of several inches.\nLiquid chloride of sulphur, which is of a deep red colour, will allow\n63 out of 100 rays of heat to pass, and a solution of carmine in\nammonia, or glass stained with oxides of gold, or copper, rather a\ngreater number; yet these transparent media obstruct a large quantity\nof light. Colourless media obstructing scarcely any light, will, on\nthe contrary, prevent the passage of calorific rays. Out of every\nhundred rays, oil of turpentine will only transmit 31, sulphuric ether\n21, sulphuric acid 17, and distilled water only 11. Pure flint glass,\nhowever, is permeated by 67 per cent. of the thermic rays, and crown\nglass by 49 per cent. The body possessing the most perfect transparency\nto the rays of heat is diaphanous salt-rock, which transmits 92, while\nalum, equally translucent, admits the passage of only 12 per cent.[43]\n\nBlack mica, obsidian, and black glass, are nearly opaque to light, but\nthey allow 90 per cent. of radiant heat to pass through them; whereas\na pale green glass, coloured by oxide of copper,[44] covered with a\nlayer of water, or a very thin plate of alum, will, although perfectly\ntransparent to light, almost entirely obstruct the permeation of heat\nrays.\n\nWe thus arrive at the fact that heat and light may be separated from\neach other; and if we examine the solar beam by that analysis which the\nprism affords, we shall find that there is no correspondence between\nintense light and ardent heat. By careful observation, it has been\nproved, when we have a temperature of 62\u00b0 F. in the yellow ray, which\nray has the greatest illuminating power; that below the red ray, out of\nthe point of visible light, the temperature is found to be 79\u00b0, while\nat the other end of the spectrum, in the blue ray, it is 56\u00b0, and at\nthe end of the violet ray no thermic action can be detected.[45]\n\nFrom the circumstance, that as we, by artificial means, raise the\ntemperature of any body, and produce intense heat, so after a\ncertain point of thermic elevation has been obtained, we occasion a\nmanifestation of _light_.[46] It has been concluded, somewhat hastily,\nthat heat and light differ from each other only in the rapidity of the\nundulations of an hypothetical ether.\n\nIt must be admitted that the mathematical demonstrations of many of the\nphenomena of calorific and luminous power are sufficiently striking to\nconvince us that a wave-movement is common to both heat and light. The\nundulatory theory, however, requires the admission of so many premises\nof which we have no proof; its postulates are, indeed, in many cases\nso gratuitous, that notwithstanding the array of talent which stands\nforward in its support, we must not allow ourselves to be deceived by\nthe deductions of its advocates, or dazzled by the brilliancy of their\ndisplays of learning.\n\nRadiant heat appears to move in waves; but that calorific effects in\nmaterial bodies are established by any system of undulation, is a\ndeduction without a proof; and the thermic phenomena of matter are as\neasily explained by the hypothesis of a diffusive subtile fluid.\n\nWe have not, however, to prove the correctness of either of the\nopposing views; indeed, it is acknowledged that many phenomena require\nfor their explanation conditions which are not indicated by either\ntheory.\n\nThe earth receives its heat from the sun; a portion of it is\n_conducted_ from particle to particle into the interior of the rocky\ncrust. Another portion produces warmth in the atmosphere around us,\nby _convection_, or the circulation of particles; those warmed by\ncontact with the surface becoming lighter, and ascending to give place\nto the colder and heavier ones. A third portion is radiated off into\nspace, according to laws which have not been sufficiently investigated,\nbut which are dependent upon the colour, chemical composition, and\nmechanical structure of the surface.\n\nIt cannot but be instructive to contemplate the indications which we\nhave of the dependence of all that is beautiful on earth, on the heat\nand light radiations which we receive from the sun. Let us endeavour\nto realise some of the effects which arise from even the temporary\ndeprivation of solar heat.\n\nIt is winter, the vegetable world appears chilled to its centre. The\ntrees, except a few of the hardy evergreens, are bare of leaves, and\nstretching forth their branches into the cold air, they realise the\ncondition of vegetable skeletons. The lowly plants of the hedge-row,\nand the grasses of the field, show that their vital power is subdued\nto that minimum degree of action which is but a few slight removes\nfrom death. The life of the running stream is suspended, it is cased\nin the \u201cthick-ribbed ice,\u201d and the waters beneath no longer send forth\ntheir joyous music to the genial breeze. Even within the temperate\nlimits of our own land, the aspect of winter convinces the ordinary\nobserver, that the loss of heat has been followed by diminished\nactivity in the powers of life; and the philosopher discovers that the\nlessened energies of solar light, and the weaker action of the radiant\nheat, have aided in producing that repose which is a little more than\nsleep--a little less than death.\n\nIt is night, and winter: the earth is parting with its heat,--with\nthe absence of light, there is a still greater loss of vigour, a yet\nfurther diminution of the powers of life. Even the animal races,\nsustained by vital influences of a more exalted kind, sink under the\ntemporary deprivation of the solar rays to a monotonous, a melancholy\nrepose. All animals undergo different degrees of hybernation, and\neach in his winter retreat supports vitality by preying upon himself.\nThe world is hung in mourning black; there is no play of colours to\nharmonize the human spirit by sending their ethereal pulsations to the\nhuman eye, and it is only the consciousness that when the night is at\nthe darkest, the day is nearest, that even man\u2019s soul is sustained\nagainst the depressing influences of the absence of the sun.\n\nThe conditions which we must observe at our own doors cannot fail to\nconvey as a conviction to the least imaginative mind, that a slightly\nprolonged continuance of darkness, with its consequent increase of\ncoldness, would be fatal to the existence of the organic world.\n\nThe sun has entered Aries: it is spring. The length of the day and\nnight are equal, the powers of light and darkness are now exactly\nbalanced against each other, and light, like the Archangel, triumphs\nover the sombre spirit. The organic world awakes. Chemical action\ncommences in the seed, the vital spark is kindled in the embryo, and\nunder the impulsive force of some solar radiations the plant struggles\ninto light and life. The same invigorating force impels the circulation\nof the sap through the capillary tubes of the forest tree, until the\ntopmost branch trembles with the new flow of life. The buds burst forth\ninto leaf, and a fresh and lively covering spreads over those branches\nwhich, in their nakedness, could scarcely be distinguished from the\ndead.\n\nThe animal races are no less sensible of the new influence which is\ndiffused around. The birds float joyously upon the breeze, and give\nto heaven their trilling songs of praise. The beasts come forth from\nthe clefts of the rocks and the tangled shelters of the forests, and\ngambol in the full luxury of their renewed vigour. Man, even man, the\ninhabitant of cities, trained and tempered to an artificial state,\nawakes of a spring morning with a fuller consciousness of mind, and a\ndeeper and more pleased sense of his intelligence, than when the fogs\nand gloom of winter hung like the charmed robe upon the limbs of the\ngiant. Now, the dormant poetry of man seeks expression. As the morning\nsun is said to have awakened the musical undulations of the Memnonian\nstatue, so the sun of the vernal morning produces in the mind of the\nmost earthly, faint pulsations of that heaven-born music, which neither\nsin nor sorrow can entirely destroy. The psychologist, in studying the\npeculiar phenomena of the human mind, must associate himself with the\nnatural philosopher, and learn to appreciate the influence of physical\ncauses in determining effects which our elder philosophers and the\npoets of every age have attributed to spiritual agencies.\n\nSummer, with its increased heat and light, reigns over the land. The\nwork of life is now at its maximum, and every energy is quickened\nthroughout the organic creation. The laws of nature are arranged\non the principle of antagonistic forces, the constant struggle to\nmaintain them in equilibrium constituting the sensible phenomena of\nexistence. Heat and light, with chemical power and electricity, have\nbeen quickening the unknown principle of life, until it has become\nexhausted in the production of new parts--in the strange phenomenon of\ngrowth--the formation of organized matter from the inorganic stores of\ncreation.\n\nThe autumn, with its tempered sunlight, comes, but in the solar\nradiance we discover new powers, and under the influence of these the\nflower and the fruit have birth. The store of a new life is centered in\nthe seed, and though the leaf falls, and the flower fades, a new set\nof organisms are produced, by which the continuance of the species is\nsecured.\n\nLet any man examine himself as the seasons change, and he will soon be\nconvinced that every alternation of light and darkness, of heat and\nits absence, produces new sets of influences equally on the mind and\non the body, showing the entire dependence of the animal and vegetable\nkingdoms upon those causes which appear to flow from the centre of our\nplanetary system.\n\nThe phenomena which connect themselves with the changes of the seasons\ncannot fail to convince the most superficial thinker that there is an\nintimate connection between the sun and the earth which deserves our\nclose attention.\n\nIndeed, if we examine the most ancient of histories, we find one great\nfact at the base of all their philosophies. Moses connects darkness\nwith a void and formless earth, and light with the creation of harmony\nand life. Menis sings of a fearful world by \u201cmany formed darkness\nencircled,\u201d and links the idea of a \u201clife-breathing divinity\u201d with the\nawakening of light upon created things. The Egyptian Isis, the Grecian\nApollo, who,\n\n    The Lord of boundless light\n    Ascending calm o\u2019er the empyrean sails,\n    And with ten-thousand beams his awful beauty veils,\n\nthe fire-worshipper of the Persian hills and the sun-god of the\nPeruvian mountains, exhibit, through time and space, the full\nconsciousness of man to the influences of solar light and heat upon the\norganic creations of which he is himself the chief exemplar.\n\nThe investigations of modern philosophers have extended these\ninfluences to the inorganic masses which constitute the Planet\nEARTH:--and we now know that the physical forces, ever active in\ndetermining the chemical condition and the electrical relations of\nmatter, are directly influenced by the solar radiations.\n\nFew things within the range of our inquiry are more striking than\nthe phenomena of calorific radiation and absorption. They display so\nperfectly the most refined system of order, and exhibit so strikingly\nthe admirable adaptation of every formation to its particular\nconditions, and for its part in the great economy of being, that they\nclaim most strongly the study of all who would seek to discover a\npoetry in the inferences of science.\n\nOwing to the nature of our atmosphere, we are protected from the\ninfluence of the full flood of solar heat. The absorption of caloric by\nthe air has been calculated at about one-fifth of the whole in passing\nthrough a column of 6,000 feet. This estimate is, of course, made near\nthe earth\u2019s surface; but we are enabled, knowing the increasing rarity\nof the upper regions of our gaseous envelope in which the absorption\nis constantly diminishing, to prove, that about one-third of the solar\nheat is lost by vertical transmission through the whole extent of our\natmosphere.[47]\n\nExperience has proved that the conditions of the sun\u2019s rays are not\nalways the same; and there are few persons who have not observed that\na more than usual scorching influence prevails under some atmospheric\ncircumstances. This is also evidenced in the effects produced on the\nfoliage of trees, which, though often attributed to electricity, is\nevidently due to heat. An examination of the solar radiations, as\nexhibited in the prismatic spectrum, has proved the existence of a\nclass of heat rays, which manifest themselves by a very peculiar\ndeoxidizing power quite independent of their caloric properties,\nto which the name of _parathermic rays_ has been given.[48] We are\nprotected from the severe effects of these rays by the ordinary state\nof the medium through which the solar heat passes. Our atmosphere is a\nmixture of gases and aqueous vapour; and it has been found, as already\nstated, that even a thin film of water, however transparent, prevents\nthe passage of many calorific radiations, and the rays retarded are,\nfor the most part, of that class which have this peculiar scorching\npower. The air is, in this way, the great equaliser of the solar\nheat, rendering the earth agreeable to all animals, who, but for this\npeculiar absorbent medium, would have to endure, even in our temperate\nclime, the burning rays of a more than African sun.\n\nThe surface of the earth during the sunshine--and, though in a less\ndegree, even when the sun is obscured by clouds--is constantly\nreceiving heat; but the rate of its absorption varies. Benjamin\nFranklin showed, by a set of simple but most conclusive experiments,\nthat a piece of black cloth was warmed much sooner than cloth of a\nlighter colour;[49] and we know, from observations of a similar class,\nthat the bare brown soil receives heat more readily than the bright\ngreen grassy carpet of the earth. Consequently, during the winter\nseason, relatively to the quantity poured from its source, more heat\npenetrates the uncovered soil, than during the spring or summer.\n\nThere is a constant tendency to an equilibrium; and, during the night,\nthe surface is robbed of more heat, by the colder air, than by day; as,\nwhen the earth is not receiving heat, it is constantly radiating it\nback into space. Even in these processes of convection and radiation, a\nsimilar law prevails to that which is discovered in examining into the\nrate of calorific absorption.\n\nEvery tree spreading its green leaves to the sunshine, or exposing\nits brown branches to the air--every flower which lends its beauty to\nthe earth--possesses different absorbing and radiating powers. The\nchalice-like cup of the pure white lily floating on the lake--the\nvariegated tulip--the brilliant anemony--the delicate rose--and the\nintensely coloured peony or dahlia--have each powers peculiar to\nthemselves for drinking in the warming life-stream of the sun, and\nfor radiating it back again to the thirsting atmosphere. These are\nno conceits of a scientific dreamer; they are the truths of direct\ninduction; and, by experiments of a simple character, they may be put\nto a searching test.[50]\n\nA thermometric examination of the various coloured flowers, by\nenclosing a delicate thermometer amongst their leaves, will readily\nestablish the correctness of the one; and by a discovery of recent\ndate, connected with calorific radiation, which must be particularly\ndescribed presently, we can, with equal ease and certainty, test the\ntruth of the other;[51] the absorption and radiation of heat being\ndirectly regulated by the colours of the surfaces upon which the sun\nrays fall.\n\nIt follows, as a natural consequence of the position of the sun, as\nit regards any particular spot on the earth at a given time, that the\namount of heat is constantly varying during the year. This variation\nregulates the seasons.\n\nWhen it is remembered that the earth is, in the winter, nearly three\nmillions of miles nearer the sun than in the summer, some explanation\nis required to account for our suffering more cold when nearer the\nsource of heat, than when at the remotest distance.\n\nThe earth in her path around the sun describes an ellipse, the\nsun\u2019s place being one of its foci. In obedience to the law, already\ndescribed, of the conservation of the axis of rotation, the axis of\nthe earth constantly points towards the star in the constellation of\nthe Little Bear. Recollecting this, and also the two facts, that a\ndense solid body absorbs heat more readily than a fluid one, and that\nradiation from the surface is constantly going on when absorption is\nnot taking place, let us follow the earth in her orbit.\n\nIt is the time of the vernal equinox--we have equal day and\nnight--therefore the periods of absorption and radiation of heat are\nalike. But at this time of the year the southern hemisphere is opposite\nto the sun, consequently the degree of absorption by the wide-spread\noceans small.\n\nIt is the summer solstice--we have sixteen hours of daylight, when the\nabsorption of heat is going on--and but eight hours of night, during\nwhich heat is passing off. The northern hemisphere is now presented\nto the sun, and as here we have the largest portion of dry land, the\npowers of absorption are at their maximum.\n\nThe autumnal equinox has arrived, with its equal day and night, as in\nthe spring, but now the whole northern hemisphere is opposite the sun;\nhence, according to the laws already explained, we see the causes of\nthe increased heat of the autumnal season.\n\nThe winter solstice has come, with its long night and shortened day.\nThe time during which radiation is going on is nearly twice that in\nwhich absorption takes place, and the earth is in her worst position\nfor receiving heat, as that half which has the largest surface of water\nis towards the sun.\n\nThese are the causes which lead to the variations of the seasons, and\nthrough these we learn why we are colder when near the sun than when at\na considerably greater distance.\n\nAn analysis of the spectrum shows us that there are some changes\nregularly taking place in the state of the solar beam, which cannot\nbe referred to the mere alteration of position. It may be inferred,\nfrom facts by long-continued observations, that the three classes of\nphenomena--light, heat, and chemical power, distinguished by the term\nActinism--which we detect in the sun\u2019s rays, are constantly changing\ntheir relative proportions. In spring, the chemical agency prevails; in\nsummer, the luminous principle is the most powerful; and in the autumn,\nthe calorific forces are in a state of the greatest activity.[52] The\nimportance of these variations, to the great economy of vegetable life,\nwill be shown when we come to examine the phenomena connected with\norganisation.\n\nA remarkable change takes place in the character of heat in being\nreflected from material substances. In nature we often see this fact\ncuriously illustrated. Snow which lies near the trunks of trees or\nwooden poles melts much quicker than that which is at a distance from\nthem, the sun shining equally on both--the liquefaction commencing on\nthe side facing the sun, and gradually extending. We see, therefore,\nthat the direct rays of solar heat produce less effect upon the snow\nthan those which are radiated from coloured surfaces. By numerous\nexperiments, it has been shown that these secondary radiations are\nmore abundantly absorbed by snow or white bodies than the direct solar\nrays themselves. Here is one of the many very curious evidences, which\nscience lays open to us, of the intimate connection between the most\nethereal and the grosser forms of matter. Heat, by touching the earth,\nbecomes more earth-like. The subtile principle which, like the spirit\nof superstition, has the power of passing, unfelt, through the crystal\nmass, is robbed of its might by embracing the things of earth; and\nalthough it still retains the evidences of its refined origin, its\nmovements are shackled as by a clog of clay, and its wings are heavy\nwith the dust of this rolling ball. It has, however, acquired new\nproperties, which fit it for the requirements of creation, and by which\nits great tasks are facilitated. Matter and heat unite in a common\nbond, and, harmoniously pursuing the necessities of some universal law,\nthe result is the extension of beautiful forms in every kingdom of\nnature.\n\nAn easy experiment pleasingly illustrates this remarkable change. If a\nblackened card is placed upon snow or ice in the sunshine, the frozen\nmass underneath it will be gradually thawed, and the card sink into\nit, while that by which it is surrounded, although exposed to the full\npower of solar heat, is but little disturbed. If, however, we reflect\nthe sun\u2019s rays from a metal surface, an exactly contrary result takes\nplace; the uncovered parts are the first to melt, and the blackened\ncard stands high above the surrounding portion.\n\nThe evidences of science all indicate the sun as the source, not only\nof that heat which we receive directly through our atmosphere, but\neven of that which has been stored by our planet, and which we can,\nby several methods, develope. We have not to inquire if the earth was\never an intensely heated sphere;--this concerns not our question; as\nwe should, even were this admitted, still have to speculate on the\norigin--the primitive source of this caloric.\n\nBefore, however, we proceed to the examination of the phenomena of\nterrestrial heat, a few of the great results of the laws of radiation\nand convection claim our attention.\n\nNearly all the heat which the sun pours upon the ocean is employed in\nconverting its water into vapour at the very surface, or is radiated\nback from it, to perform the important office of producing those\ndisturbing influences in the atmosphere, which are essential to the\npreservation of the healthful condition of the great a\u00ebrial envelope in\nwhich we live.\n\nCurrents of air are generally due to the unequal degrees in which the\natmosphere is warmed. Heat, by expanding, increases the elasticity,\nand lessens the density, of a given mass. Consequently, the air heated\nby the high temperature of the tropics, ascends charged with aqueous\nvapours, whilst the colder air of the temperate and the frigid zones\nflows towards the equator to supply its place. These great currents of\nthe atmosphere are, independent of the minor disturbances produced by\nlocal causes, in constant flow, and by them a uniformity of temperature\nis produced, which could not in any other way be accomplished. By these\ncurrents, too, the equalisation of the constituents of the \u201cbreath\nof life\u201d is effected, and the purer oxygen of the \u201cland of the sunny\nsouth\u201d is diffused in healthful gales over the colder climes of the\nnorth. The waters, too, evaporated from the great central Atlantic\nOcean, or the far Pacific, are thus carried over the wide-spread\ncontinents, and poured in fertilising showers upon distant lands.\n\nHow magnificent are the operations of nature! The air is not much\nwarmed by the radiations of caloric passing from the sun to the earth;\nbut the surface soil is heated by its power of absorbing these rays.\nThe temperature of the air next the earth is raised, and we thus have\nthe circulation of those beneficial currents which are so remarkably\nregular in the Trade Winds. The air heated within the tropics would\nascend directly to the poles, were the earth at rest, but being in\nmotion, those great a\u00ebrial currents--the Trade Winds--are produced,\nand the periodical monsoons are due to the same cause. A similar\ncirculation, quite independent of the ordinary tidal movement,\ntakes place also in the earth-girdling ocean. The water, warmed, by\nconvection, from the hot surface of the tropical lands, sets across\nthe Atlantic from the Gulf of Mexico; and being under the influence of\nthe two forces--gravity and motion--it illustrates the parallelogram\nof forces, and flowing along the diagonal, reaches our own shores: the\ngenial influences of the gulf stream produce that tempered climate\nwhich distinguishes our insular home. Here we have two immense\ninfluences produced by one agency, rendering those parts of the earth\nhabitable and fertile, which but for these great results would sorrow\nin the cheerless aspect of an eternal winter.\n\nThe beautiful phenomenon of the formation of dew is also distinctly\nconnected with the peculiar properties which we have been studying.\nWhen from the bright blue vault of heaven, the sparkling constellations\nshower their mild light over the earth, the flowers of the garden\nand the leaves of the forest become moist with a fluid of the most\ntranslucid nature. Well might the ancients imagine that the dews were\nactually shed from the stars; and the alchemists and physicians of the\nmiddle ages conceive that this pure distillation of the night possessed\nsubtile and penetrating powers beyond most other things; and the\nladies of those olden times endeavour to preserve their charms in the\nperfection of their youthful beauty through the influences of washes\nprocured from so pure a source.[53]\n\nScience has removed the veil of mystery with which superstition had\ninvested the formation of dew; and, in showing to us that it is\na condensation of vapour upon bodies according to a fixed law of\nradiation, it has also developed so many remarkable facts connected\nwith the characters of material creations, that a much higher order of\npoetry is opened to the mind than that which, though beautiful, sprang\nmerely from the imagination.\n\nUpon the radiation of heat depends the formation of dew, and bodies\nmust become colder than the atmosphere before it will be deposited\nupon them. At whatever temperature the air may be, it is charged to\nsaturation with watery vapour, the quantity varying uniformly with\nthe temperature. Supposing the temperature of the air to be 70\u00b0 F.,\nand that a bottle of water at 60\u00b0 is placed in it, the air around\nthe bottle will be cooled, and will deposit on the glass exactly\nthat quantity of moisture which is due to the difference between the\ntemperature of the two bodies. Different substances, independent of\ncolour, have the property of parting with heat from their surfaces at\ndifferent rates. Rough and porous surfaces radiate heat more rapidly\nthan smooth ones, and are consequently reduced in temperature; and, if\nexposed, are covered with dew sooner than such as are smooth and dense.\nThe grass parterre glistens with dew, whilst the hard and stony walk is\nunmoistened.[54]\n\nColourless glass is very readily suffused with dampness, but polished\nmetals are not so, even when dews are heavily condensed on other\nbodies. To comprehend fully the phenomena of the formation of dew,\nwe must remember that the entire surface of the earth is constantly\nradiating heat into space; and that, as by night no absorption is\ntaking place, it naturally cools.[55] As the substances spread over\nthe earth become colder than the air, they acquire the power of\ncondensing the vapour with which the atmosphere is always charged. The\nbodies which cover this globe are very differently constituted; they\npossess dissimilar radiating powers, and consequently present, when\nexamined by delicate thermometers, varying degrees of temperature. By\nthe researches of Dr. Wells,[56] which may be adduced as an example of\nthe best class of inductive experiments, we learn that the following\ndifferences in sensible heat were observed at seven o\u2019clock in the\nevening:--\n\n    The air four feet above the grass      60-3/4\n    Wool on a raised board                 54-1/2\n    Swandown on ditto                      53\n    The surface of the raised board        57\n    Grass plat                             51\n\nDew is most abundantly deposited on clear, calm nights, during which\nthe radiation from the surface of the earth is uninterrupted. The\nincreased cold of such nights over those obscured by clouds is well\nknown. The clouds, it has been proved, act in the same way as the\nscreens used by gardeners to protect their young plants from the\nfrosts of the early spring, which obstruct the radiation, and, in all\nprobability, reflect a small quantity of heat back to the earth.\n\nIt is not improbable that the observed increase in grass crops, when\nthey have been strewn with branches of trees or any slight shades, may\nbe due to a similar cause.[57]\n\nThere are many remarkable results dependent entirely on the colours\nof bodies, which are not explicable upon the idea of difference in\nmechanical arrangement. We know that different colours are regulated\nby the powers which structures have of absorbing and reflecting light;\nconsequently a blue surface must have a different order of molecular\narrangement from a red one. But there are some physical peculiarities\nwhich also influence heat radiation, quite independently of this\n_surface_ condition. If we take pieces of red, black, green, and yellow\nglass, and expose them when the dew is condensing, we shall find that\nmoisture will show itself first on the yellow, then on the green glass,\nand last of all upon the black or red glasses. The same thing takes\nplace if we expose coloured fluids in white glass bottles or troughs,\nin which case the surfaces are all alike. If against a sheet of\nglass, upon which moisture has been slightly frozen, we place glasses\nsimilarly coloured to those already described, it will be found that\nthe earliest heat-rays will so warm the red and the black glasses, that\nthe ice will be melted opposite to them, long before any change will be\nseen upon the frozen film covered by the other colours.\n\nThe order in which heat permeates coloured media, it has already been\nshown, very nearly agrees with their powers of radiation.\n\nThese most curious results have engaged the attention of Melloni,\nto whose investigations we owe so much; and from the peculiar order\nof radiations, which present phenomena of an analogous character to\nthose of the coloured rays of light, obtained by him from dissimilarly\ncoloured bodies, he has been led to imagine the existence of a\n\u201cheat-colouration.\u201d That is, the heat-rays are supposed to possess\nproperties like luminous colour although invisible; and, consequently,\nthat a blue surface has a strong affinity for the blue heat-rays,\na red surface for the red ones, and so on through the scale. The\ningenuity of this hypothesis has procured it much attention; but now,\nwhen the Newtonian hypothesis of the refrangibility of light is nearly\noverturned, we must not, upon mere analogy, rush to the conclusion\nthat the rays of heat have different orders of refrangibility, which\nMelloni\u2019s hypothesis requires.[58]\n\nCan anything be more calculated to impress the mind with the\nconsciousness of the high perfection of natural phenomena, than the\nfact, that the colour of a body should powerfully influence the\ntransmission of a principle which is diffused through all nature,\nand also determine the rate with which it is to pass off from its\nsurface. Some recent experiments have brought us acquainted with other\nfacts connected with these heat-radiations, and the power of heat,\nas influenced by the calorific rays, to produce molecular changes in\nbodies, which bear most importantly on our subject.\n\nIf we throw upon a plate of polished metal a prismatic spectrum\n(deprived, as nearly as possible, of its chemical power, by being\npassed through a deep yellow solution--which possesses this property\nin a very remarkable manner, as will be explained when we come to the\nexamination of the chemical action of the sun\u2019s rays)--it will be\nfound, if we afterwards expose the plate to the action of vapour, very\nslowly raised from mercury, that the space occupied by the red rays,\nand those which lie without the spectrum below it, will condense the\nvapour thickly, while the portion corresponding with the other rays\nwill be left untouched. This affords us evidence of the power of solar\nheat to produce, very readily, a change in the molecular structure of\nsolid bodies. If we allow the sun\u2019s rays to permeate coloured glasses,\nand then fall upon a polished metallic surface, the result, on exposing\nthe plate to vapourisation, will be similar to that just described.\nUnder yellow and green glasses no vapour will be condensed; but on the\nspace on which the rays permeating a red glass, or even a blackened\none, fall, a very copious deposit of vapour will mark with distinctness\nthe spaces these glasses covered. More remarkable still, if these or\nany other coloured bodies are placed in a box, and a polished metal\nplate is suspended a few lines above them, the whole being kept _in\nperfect darkness_ for a few hours, precisely the same effect takes\nplace as when the arrangement is exposed to the full rays of the sun.\nHere we have evidence of the radiating heat of bodies, producing even\nin darkness the same phenomena as the transmitted heat-rays of the sun.\nWe must, however, return to the examination of some of these and other\nanalogous influences under the head of actino-chemistry.\n\nFrom these curious discoveries of inductive research we learn some high\ntruths. Associated with light--obeying many of the same laws--moving\nin a similar manner--we receive a power which is essential to the\nconstitution of our planet. This power is often manifested in such\nintimate combination with the luminous principle of the solar rays,\nthat it has been suspected to be but another form of the same agency.\nWhile, however, we are enabled to show the phenomena of one without\nproducing those which distinguish the other, we are constrained to\nregard heat as something dissimilar to light. It is true that we\nappear to be tending towards some point of proof on this problem; but\nwe are not in a position to declare them to be forms of one common\npower, or \u201cparticular solutions of one great physical equation.\u201d[59]\nIn many instances it would certainly appear that one of these forces\nwas directly necessary to the production of the other; but we have also\nnumerous examples in which they do not stand in any such correlation.\n\nWe learn, from the scientific facts which we have been discussing, a\nfew of the secrets of natural magic. In their relations to heat, every\nflower, which adds to the adornment of the wilds of nature or the\ncarefully-tended garden of the florist, possesses a power peculiar to\nitself;\n\n    \u201cNaiad-like lily of the vale,\u201d\n\nand,\n\n    \u201c---- The pied wind-flowers, and the tulip tall,\n    And narcissi, the fairest among them all,\u201d\n\nare, by their different colours, prevented from ever having the same\ntemperatures under the same sunshine.\n\nEvery plant bears within itself the measure of the heat which is\nnecessary for its well-being, and is endued with functions which mutely\ndetermine the relative amount of dew which shall wet its coloured\nleaves. Some of the terrestrial phenomena of this remarkable principle\nwill still further illustrate the title of this volume.\n\nTo commence with the most familiar illustrations, let us consider the\nconsequences of change of temperature. However slight the additional\nheat may be to which a body is subjected, it expands under its\ninfluence; consequently, every atom which goes to form the mass of\nthe earth moves under the excitation, and the first heat ray of the\nmorning which touches the earth\u2019s surface, sets up a vibration which\nis continued as a tremor to its very centre. The differences between\nthe temperature of day and night are considerable; therefore all bodies\nexpand under the influence of the higher, and contract under that of\nthe lower temperature. During the day, any cloud obscuring the sun\nproduces, in every solid, fluid, or a\u00ebriform body, within the range\nof solar influence, a check: the particles which had been expanding\nunder the force of heat suddenly contract. Thus there must of necessity\nbe, during the hours of sunshine, a tendency in all bodies to dilate,\nand during the hours of night they must be resuming their original\nconditions.\n\nNot only do dissimilar bodies radiate heat in different degrees, but\nthey conduct it also with constantly varying rates. Heat passes along\nsilver or copper with readiness, compared to its progress through\nplatinum. It is conducted by glass but slowly, and still more slowly\nby wood and charcoal. We receive some important intimations of the\nmolecular structure of matter, from those experiments which prove that\nheat is conducted more readily along some lines than others. In some\nplanes, wood and other substances are better conductors than in others.\nThe metallic oxides or earths are bad conductors of heat, by which\nprovision the caloric absorbed by the sun\u2019s rays is not carried away\nfrom the surface of this planet so rapidly as it would have been had\nit been of metal, but is retained in the superficial crust to produce\nthe due temperature for healthful germination and vegetable growth. The\nwool and hair of animals are still inferior conductors, and thus, under\nchanges of climate and of seasons, the beasts of the field are secured\nagainst those violent transitions from heat to cold which would be\nfatal to them. Hair is a better conductor than wool: hence, by nature\u2019s\nalchemy, hair changed into wool in the animals of some countries on the\napproach of winter, and feathers into down.\n\nIt is therefore evident that the rate at which solar heat is conducted\ninto the crust of the earth must alter with the condition of the\nsurface upon which it falls. The conducting power of all the rocks\nwhich have been examined is found to vary in some degree.[60]\n\nIt follows, as a natural consequence of the position of the sun to\nthe earth, that the parts near the equator become more heated than\nthose remote from it. As this heat is conducted into the interior of\nthe mass, it has a tendency to move to the colder portions of it, and\nthus the heat absorbed at the equator flows towards the poles, and\nfrom these parts is carried off by the atmosphere, or radiated into\nspace. Owing to this, there is a certain depth beneath the surface of\nour globe at which an equal temperature prevails, the depth increasing\nas we travel north or south from the equator, and conforming to the\ncontour of the earth\u2019s surface, the line sinking under the valleys and\nrising under the hills.[61]\n\nA question of great interest, in a scientific point of view, is the\ntemperature of the centre of the earth. We are, of course, without the\nmeans of solving this problem; but we advance a little way onwards\nin the inquiry by a careful examination of subterranean temperature\nat such depths as the enterprise of man enables us to reach. These\nresearches show us, that where the mean temperature of the climate\nis 50\u00b0, the temperature of the rock at 59 fathoms from the surface\nis 60\u00b0; at 132 fathoms it is 70\u00b0; at 239 fathoms it is 80\u00b0: being an\nincrease of 10\u00b0 at 59 fathoms deep, or 1\u00b0 in 35\u00b74 feet; of 10\u00b0 more at\n73 fathoms deeper, or 1\u00b0 in 43\u00b78 feet; and of 10\u00b0 more at 114 fathoms\nstill deeper, or 1\u00b0 in 64\u00b72 feet.[62]\n\nAlthough this would indicate an increase to a certain depth of about\none degree in every fifty feet, yet it would appear that the rate of\nincrease diminishes with the depth. It appears therefore probable, that\nthe heat of the earth, so far as man can examine it, is due to the\nabsorption of the solar rays by the surface. The evidences of intense\nigneous action at a great depth cannot be denied, but the doctrine of\na cooling mass, and of the existence of an incandescent mass, at the\nearth\u2019s centre, remains but one of those guesses which active minds\ndelight in. The mean annual temperature of this planet is subject to\nvariations, which are probably dependent upon some physical changes in\nthe sun himself, or in the atmospheric envelope by which that orb is\nsurrounded. The variations over the earth\u2019s surface are great. At the\nequator we may regard the temperature as uniformly existing at 80\u00b0,\nwhile at the poles it is below the freezing point of water; and as far\nas observations have been made, the subterranean temperatures bear a\nclose relation to the thermic condition of the climate of the surface.\nThe circulation of water through faults or fissures in the strata is,\nwithout doubt, one means of carrying heat downwards much quicker than\nit would be conducted by the rocks themselves. It is not, however,\nfound that the quantity of water increases with the depth. In the mines\nof Cornwall, unless where the ground is very loose, miners find that,\nafter about 150 fathoms (900 feet), the quantity of water rapidly\ndiminishes. That water must ascend from very much greater depths is\ncertain, from the high temperatures at which many springs flow out at\nthe surface. In the United Mines in Cornwall, water rises from one part\nof the lode at 90\u00b0; and one of the levels in these workings is so hot\nthat, notwithstanding a stream of cold water is purposely brought into\nit to reduce the temperature, the miners work nearly naked, and will\nbathe in water at 80\u00b0 to cool themselves. At the bottom of Tresavean\nMine, in the same county, about 320 fathoms from the surface, the\ntemperature is 100\u00b0.\n\nOne cause of the great heat of many of our deep mines, which appears\nto have been entirely lost sight of, is the chemical action going\non upon large masses of pyritic matter in their vicinity. The heat,\nwhich is so oppressive in the United Mines, is, without doubt, due to\nthe decomposition of immense quantities of the sulphurets of iron and\ncopper known to be in this condition at a short distance from these\nmineral works.\n\nThe heat which man is enabled to measure beneath the earth\u2019s surface,\nappears to be alone due to the conducting powers of the rocks\nthemselves; it has been observed that the line of equal temperature\nfollows, as nearly as possible, the elevations and depressions which\nprevail upon the surface, and the diminishing rate of increase beyond\nthis line, certainly is such as would arise, was all the heat so\nmeasured, the result of the passage of the heat by conduction through\nthe crust of rocks.\n\nWhether or not the subterranean bands of equal heat have any strict\nrelation, upon a large scale, to the isothermic lines which have been\ntraced around most portions of our globe, is a point which has not yet\nbeen so satisfactorily determined as to admit of any general deductions.\n\nThe Oriental story-teller makes the inner world a place of rare\nbeauty--a cavern temple, bestudded with self-luminous gems, in which\nreside the spiritual beings to whom the direction of the inorganic\nworld is confided.\n\nThe Philosopher, in the height of his knowledge, has had dreams as\nabsurd as this; and amid the romances of science, there are not to be\nfound any more strange visions than those which relate to the centre\nof our globe. At the same time it must be admitted, that many of the\npeculiar phenomena which modern geological researches have brought to\nlight, are best explained on the hypothesis of a cooling sphere, which\nnecessarily involves the existence of a very high temperature towards\nthe centre.\n\nWe have already noticed some remarkable differences between solar and\nterrestrial heat; but a class of observations by Delaroche[63] still\nrequires our attention. Solar heat passes freely through colourless\nglass, whereas the radiations from a bright fire or a mass of\nincandescent metal are entirely obstructed by this medium. If we place\na lamp or a ball of glowing hot metal before a metallic reflector, the\nfocus of accumulated heat is soon discovered; but if a glass mirror\nbe used, the light is reflected, but not the heat; whereas, with the\nsolar rays, but little difference is detected, whether vitreous or\nmetallic reflectors are employed. It is well known that glass lenses\nrefract both the light and heat of the sun, and they are commonly known\nas burning-glasses: the heat accumulated at their focal point being\nof the highest intensity. If, instead of the solar beam, we employ,\nin our experiments, an intense heat produced by artificial means,\nthe passage of it is obstructed, and the most delicate thermometers\nremain undisturbed in the focus of the lens. Glass exposed in front\nof a fire becomes warm, and by conduction the heat passes through it,\nand a secondary radiation takes place from the opposite side.[64] It\nhas been found that glass is transcalescent, or _diathermic_, to some\nrays of terrestrial heat, and _adiathemic_, or opaque for heat, to\nothers[65]--that the capability of permeating glass increases with the\ntemperature of the ignited body--and that rays which have passed one\nscreen traverse a second more readily. It would, however, appear that\nsomething more than a mere elevation of temperature is necessary to\ngive terrestrial heat-radiations the power of passing through glass\nscreens, or, in other words, to acquire the properties of solar heat.\n\nTo give an example. The heat of the oxy-hydrogen flame is most intense,\nyet glass obstructs it, although it may be assisted by a parabolic\nreflector. If this flame is made to play upon a ball of lime, by which\na most intense light is produced, the heat, which has not been actually\nincreased, acquires the power of being refracted by a glass lens, and\ncombustible bodies may be ignited in its focus.\n\nIt certainly appears from these results, that the undulatory hypothesis\nholds true, so far as the motion of the calorific power is concerned.\nAt a certain rate the vibrations are thrown back or stopped by the\nopposing body, while in a state of higher excitation, moving with\nincreased rapidity, they permeate the screen.[66] This does not,\nindeed, interfere with the refined theory of Pr\u00e9vost,[67] which\nsupposes a mutual and equal interchange of caloric between all bodies.\n\nThe most general effect of heat is the expansion of matter; solids,\nliquids, and airs, all expand under its influence. If a bar of metal\nis exposed to calorific action, it increases in size, owing to its\nparticles being separated farther from each other: by continuing this\ninfluence, after a certain time the cohesion of the mass is so reduced\nthat it melts, or becomes liquid, and, under the force of a still\nhigher temperature, this molten metal may be dissipated in vapour. It\nwould appear as if, under the agency of the heat applied to a body, its\natoms expanded, until at last, owing to the tenuity of the outer layer\nor envelope of each atom, they were enabled to move freely over each\nother, or to interpenetrate without difficulty. That heat does really\noccasion a considerable disturbance in the corpuscular arrangement\nof bodies, may be proved by a very interesting experiment. A bar of\nheated metal is placed to cool, with one end supported upon a wedge\nor a ring of a different metal the other resting on the ground. In\ncooling, a distinct musical sound is given out, owing to the vibratory\naction set up among the particles of matter moving as the temperature\ndeclines.[68]\n\nHeat is diffused through all bodies in nature, and, as we shall\npresently see, may be developed in many different ways. We may,\ntherefore, infer, that in converting a sphere of ice into water, and\nthat again into steam, we have done nothing more than interpenetrate\nthe mass with a larger quantity of heat, by which its atoms are more\nwidely separated, and that thus its molecules become free to move\nabout each other. Hence, from a solid state, the water becomes fluid;\nand then, if the expansive force is continued, an invisible vapour.\nIf these limits are passed by the powers of any greatly increased\nthermic action, the natural consequence, it must be seen, will be the\nseparation of the atoms from each other, to such an extent that the\nmolecule is destroyed, and chemical decomposition takes place.\n\nBy the agency of the electricity of the voltaic battery, we are enabled\nto produce the most intense heat with which we are acquainted, and by a\npeculiarly ingenious arrangement Mr. Grove has succeeded in resolving\nwater by the mere action of heat into its constituent elements--oxygen\nand hydrogen gases. That this decomposition is not due to the voltaic\ncurrent, but to the heat produced by it, was subsequently proved by\nemploying platina heated by the oxy-hydrogen flame.[69]\n\nThis interesting question has been examined with great care by Dr.\nRobinson of Armagh, who has shown that, as the temperature of water is\nincreased, the affinity of its elements is lessened, until at a certain\npoint it is eventually destroyed. This new and startling fact appears\nscarcely consistent with our knowledge that a body heated so as to\nbe luminous has the power of causing the combination of the elements\nof water with explosive violence.[70] But as this acute experimental\nphilosopher somewhat boldly but still most reasonably inquires: \u201cIs\nit not probable that, if not light, some other actinic power (like\nthat which accompanies light in the spectrum, and is revealed to us\nby its chemical effects in the processes of photography) is evolved\nby the heat, and, though invisible, determines, in conjunction with\nthe affinity, that atomic change which transforms the three volumes of\noxygen and hydrogen into two of steam?\u201d[71]\n\nThis speculation explains, in a very satisfactory manner, some\nresults which were obtained by Count Rumford, in 1798. In a series of\nexperiments instituted for the purpose of examining \u201cthose chemical\nproperties of light which have been attributed to it,\u201d he has shown\nthat many cases of chemical decomposition occur in perfect darkness,\nunder the influence of heat, which are precisely similar to those\nproduced by exposure to the sun\u2019s rays.[72]\n\nIt must, however, be remembered, that both solar light and heat are\nsometimes found in direct antagonism to actinic power, and that the\nmost decided chemical changes are produced by those rays in which\nneither heat nor light can be detected. The most remarkable phenomena\nof this class will be explained under the head of actinism.\n\nOne of the most curious relations which as yet have been discovered\nbetween light and heat is, that, the temperature at which all bodies\nbecome incandescent, excepting such as are phosphorescent, is uniform.\nThe point on the thermometer (Fahrenheit\u2019s scale) when the eye by\nperfect repose is enabled to detect the first luminous influence, may\nprobably be regarded as, or very near, 1000\u00b0. Daniel has fixed this\npoint at 980\u00b0, Wedgwood at 947\u00b0, and Draper at 977\u00b0.[73] Dr. Robinson\nand Dr. Draper, by independent observations, have both arrived at the\nconclusion, that the first gleam of light which appears from heated\nplatina is not red, but of a lavender gray, the same in character of\ncolour as that detected by Sir John Herschel among the most refrangible\nrays of the solar spectrum.[74]\n\nIt must be admitted, that the question of the identity, or otherwise,\nof light and radiant heat, is beset with difficulties. Many of their\nphenomena are very similar--many of their modes of action are alike:\nthey are often found as allied agencies; but they as frequently exhibit\nextreme diversity of action, and they may be separated from each other.\n\nWe have now examined the physical conditions and properties of this\nmost important element, and we must proceed to learn something of the\nmeans by which it may be developed, independently of its solar source.\n\nThis extraordinary principle exists in a latent state in all bodies,\nand may be pressed out of them. The blacksmith hammers a nail until it\nbecomes red hot, and from it he lights the match with which he kindles\nthe fire of his forge. The iron has by this process become more dense,\nand percussion will not again produce incandescence until the bar has\nbeen exposed in fire to a red heat. The only inference we can draw\nfrom this result is, that by hammering the particles have been driven\ncloser together, and the heat driven out; now further hammering will\nnot force the atoms nearer, and consequently no additional quantity of\nheat can be developed; the iron is made hot in a fire, it absorbs heat,\nthe particles are restored to their former state, and we can now again\nby hammering develope both heat and light. The Indian produces a spark\nby the attrition of two pieces of wood. By friction, two pieces of ice\nmay be made to melt each other; and could we, by mechanical pressure,\nforce water into a solid state, an immense quantity of heat would be\nset free. By the condensation of hydrogen and oxygen gases, pulverulent\nplatinum will become glowing red-hot, and, with certain precautions,\neven the compact metal, platinum, itself; the heat being derived from\nthe gases, the union of which it has effected. A body passing from the\nsolid to the fluid state absorbs heat from all surrounding substances,\nand hence a degree of cold is produced. The heat which is thus removed\nis not destroyed--it is held combined with the fluid; it exists in a\nlatent state. Fluids, in passing into a gaseous form, also rob all\nsurrounding bodies of an amount of heat necessary to maintain the\na\u00ebriform condition. From the air or from the fluid, this heat may,\nas we have shown above, be again extracted. Locked in a pint measure\nof air, there exists sufficient heat to raise several square inches\nof metal to glowing redness. By the compression of atmospheric air\nthis may be shown, and with a small condensing syringe a sufficient\nquantity of heat may be set free to fire the _Boletus igniarius_,\nwhich, impregnated with nitre, is known as _amadou_. We are acquainted\nwith various sources from which heat may be developed for artificial\npurposes: the flint-and-steel is an example of the production of heat\nby mechanical force, and the modern lucifer-match, of the combined\naction of friction and chemical affinity. These of themselves would\nadmit of a lengthened discourse; but it is necessary that we carefully\nexamine some of the less familiar phenomena of heat under the\ninfluences of changes of chemical condition.\n\nIf spirits of wine and water are mixed together, a considerable degree\nof heat is given out, and by mixing sulphuric acid and water, an\ninfinitely larger quantity. If sulphuric acid (oil of vitriol) and\nspirit of wine, or nitric acid (aquafortis) and spirits of turpentine,\nat common temperatures, be suddenly mixed, so much heat is set free\nas to ignite the spirit. In each of these instances there is a\ncondensation of the fluid. In nearly all cases of solution, cold is\nproduced by the absorption of the heat necessary to sustain the salt\nin a liquid form; but when potash dissolves in water, heat is given\nout, which is a fact we cannot yet explain. If potassium is placed on\nwater, it seizes the oxygen of the water and sets fire to the hydrogen\ngas liberated by the heat produced in the change of form. Antimony\nand many other metals thrown into chlorine gas ignite and burn with\nbrilliancy: the same phenomenon takes place in the vapours of iodine or\nbromine. Many chemical combinations, as the chloride of potassium and\nsulphur explode with a blow; whilst the slightest friction occasions\nthe detonation of the fulminating salts of silver, mercury, and\ngold. Compounds of nitrogen and chlorine, or iodine, are still more\ndelicately combined--the former exploding with fearful violence on\nthe contact of any oleaginous body, and the latter by the smallest\nelevation of temperature: both of them destroying the vessels in which\nthey may be contained.\n\nGun cotton presents some peculiar phenomena which may merit brief\nattention. This peculiar compound is prepared by the action of nitric\nacid on cotton fibre. The general appearance of the cotton is not\naltered, but a remarkable physical change has taken place. It is\nnow soluble in ether, and forms a gelatinous compound:--it explodes\nviolently at a temperature which is insufficient for the combustion\nof gunpowder. Indeed, from, as it would appear, slight electrical\ndisturbances taking place in the gun cotton itself, it not unfrequently\nexplodes spontaneously. These fearful disturbances of the forces\nwhich hold bodies in combination are explained with difficulty. May\nit not be, that an enormous quantity of the calorific and chemical\nprinciples is held in a state of extreme tension around the particles\nof the compound, and that the equilibrium being destroyed, the whole is\ndeveloped in destructive rapidity?\n\nThe fact of great heat being evolved during the conversion of a body\nfrom a solid to a gaseous state, as in the explosion of gunpowder or\ngun cotton, which is a striking exception to the law of latent heat, as\nit prevails in most cases, admits of no more satisfactory explanation.\n\nAs mechanical force produces calorific excitation, so we find that\nevery movement of sap in vegetables, and of the blood and fluids in\nthe animal economy, causes a sensible increase of heat. The chemical\nprocesses constantly going on in plants and animals are another source\nof heat, in addition to which nervous energy and muscular movement must\nbe regarded as producing the caloric which is essential to the health\nand life of the latter. Digestion has been considered as a process\nof combustion; and the action between the elements of food, and the\noxygen conveyed by the circulation of the blood to every part of the\nbody, regarded as the source of animal heat; and, without doubt, it\nis one great source, although it can scarcely be regarded as the only\none.[75]\n\nThe _vis vit\u00e6_, or vital power, influences the delicate and beautiful\nsystem of nerves; and as life (an essence of the rarest and most\nsubtile order, a diffusive influence) runs through them, from the brain\nto the extremities of the members of the body, it sets those tender\nthreads in rapid vibration, and heat is developed. By this action,\nthe circulation of the blood is effected; the muscle is maintained\nin an elastic condition, ready to perform the tasks of the will; and\nthrough these agencies is the warm and fluid blood fitted to receive\nits chemical restoratives in the lungs, and the stomach to support\nchanges for which it is designed--chemical also--by which more heat\nis liberated. Was digestion--_Eremacausis_, as the slow combustion\nproduced by combination with oxygen is called--the only source of\nanimal heat, why should the injury of one filmy nerve place a member of\nthe body for ever in the condition of stony coldness? Or why, chemical\naction being most actively continued after a violent death, by the\naction of the gastric juices upon the animal tissues, should not animal\nheat be maintained for a much longer period than it is found to be\nafter respiration has ceased?[76]\n\nIn studying the influences of caloric upon the conditions of matter,\nwe must regard the effects of extreme heat, and also of the greatest\ndegrees of cold which have been obtained.\n\nThere are a set of experiments by the Baron Cagniard de la Tour, which\nappear to have a very important bearing on some conditions that may\nbe supposed to prevail in nature, particularly if we adopt the view of\na constantly increasing temperature towards the centre of our earth.\nIf water, alcohol, or ether, is put into a strong glass tube of small\nbore, the ends hermetically sealed, and the whole exposed to a strong\nheat, the fluid disappears, being converted into a transparent gas;\nbut, upon cooling, it is again condensed, without loss, into its\noriginal fluid state.[77] In this experiment, fluid bodies have been\nconverted into elastic transparent gases with but small change of\nvolume, under the pressure of their own atmospheres. We can readily\nconceive a similar result occurring upon a far more extensive scale.\nIn volcanic districts, at great depths, and consequently under the\npressure of the superincumbent mass, the siliceous rocks, or even\nmetals, may, from the action of intense heat, be brought into a fluid,\nor even a gaseous condition, without any change of volume, since\nthe elastic force of heat is opposed by the rigid resistance of the\npressure of the surrounding rocks. Some beautiful experiments by Mr.\nHopkins, of Cambridge, have proved that the temperature necessary to\nmelt a body must be considerably elevated as the mechanical pressure to\nwhich it is subjected is increased.\n\nDirectly connected with the results of Cagniard de la Tour are a yet\nmore remarkable set of phenomena, which have been investigated by\nM. Boutigny,[78] and generally known as the \u201cspheroidal condition\u201d\nof bodies. If water is projected upon very hot metal it instantly\nassumes a spheroidal form--an internal motion of its particles may\nbe observed--it revolves with rapidity, and evaporates very slowly.\nIf a silver or platinum capsule, when brought to a bright red heat,\nis filled with cold water, the whole mass assumes the spheroidal\nstate, the temperature of the fluid remaining considerably below the\nboiling point, so long as the red heat is maintained. If we allow the\nvessel to cool below redness in the dark, the water then bursts into\nactive ebullition, and is dissipated into vapour with almost explosive\nviolence. An equal quantity of water being projected into two similar\nvessels, over the fire, one cold and the other red hot, it will be\nfound that the water in the cold vessel will boil and evaporate long\nbefore that in the one which is red hot.\n\nAnother form of this experiment is exceedingly instructive. If a mass\nof white hot metal is suddenly plunged into a vessel of cold water, the\nincandescence is not quenched, the metal shines with a bright white\nlight, and the water is seen to circulate around, but at some distance\nfrom the glowing mass, being actually repelled by calorific agency. At\nlength, when the metal cools, the water comes in contact with it, and\nboils with energy.\n\nA result similar to this was observed by Perkins, but its correctness\nmost unjustly doubted. Having made an iron shell containing water, and\ncarefully plugged up, white hot, it was found that the steam never\nexerted sufficient force to burst the vessel, as it was expected\nit would do. He caused a hole to be drilled into the bottom of the\nwhite-hot shell, and he was surprised to find that no water flowed\nthrough the orifice, until the iron was considerably cooled, when it\nissued forth with violence in the form of steam. Here we have the\n_Cagniard de la Tour state_ first induced, and the calorific repulsion\nof the spheroidal state supervenes. If water is poured upon an iron\nsieve, the wires of which are made red hot, it will not percolate;\nbut on cooling, it runs through rapidly. M. Boutigny, pursuing this\ncurious inquiry, has recently proved that the moisture upon the skin\nis sufficient to protect it from disorganization, if the arm is plunged\ninto baths of melted metal. The resistance of the surfaces is so great,\nthat little elevation of temperature is experienced.[79] Professor\nPl\u00fccker, of Bonn, has stated that by washing the arm with ether\npreviously to plunging it into melted metal, the sensation produced,\nwhile in the molten mass, is that of freezing coldness.\n\nWe have now seen that heat at different degrees of intensity appears\nto produce chemical composition--that it decomposes combined\nelements--that it alters the conditions of bodies, and actually\nmaintains so powerfully a repellent force, that fluids cannot touch the\nheated body. More than this, it exerts a most powerful antagonistic\ninfluence over all chemical relations. If, to give one example,\nthe volatile element iodine is put into a glowing hot capsule, it\nresolves itself immediately into a spheroid. Potash rapidly combines\nwith iodine; but if a piece of this alkali is thrown upon it in\nthe capsule, it also takes the spheroidal form, and both bodies\nrevolve independently of each other, their chemical affinities being\nentirely suspended;--but allow the capsule to cool, and they combine\nimmediately. Science teaches us that a temperature so exalted as not to\nburn organic bodies may be produced, and points to us this remarkable\nfact, that the destructive limits of heat are measured between certain\ndegrees--beyond which a fire, by reason of its intensity, ceases to\ndevelope heat. What is the radiant force into which this principle\nchanges?\n\nThe experiments of Cagniard de la Tour and of Boutigny (d\u2019Evreux),\nconnect themselves, in a striking manner, with those of Mr. Grove and\nDr. Robinson; and they teach us that but a very slight alteration in\nthe proportions of the calorific principle given to this planet would\ncompletely change the character of every material substance of which it\nis composed, unless there was an alteration in the physical condition\nof the elements themselves.\n\nSupposing the ordeal of fiery purification to take place upon this\nearth, these experiments appear to indicate the mighty changes which\nwould thence result. There would be no annihilation, but everything\nwould be transformed from the centre of the globe to the verge of its\natmosphere--old things would pass away, all things become new, and the\nbeautiful mythos of the ph\u0153nix be realized in the fresh creation.\n\nThe deductions to be drawn from the results obtained by abstracting\nheat from bodies are equally instructive. By taking advantage of the\ncooling produced by the rapid solution of salts of several kinds in\nwater, an intense degree of coldness may be produced.[80] Indeed, the\nabsorption of heat by liquefaction may be shown by the use of metallic\nbodies alone. If lead, tin, and bismuth, are melted together, and\nreduced to a coarse powder by being poured into water, and the alloy\nthen dissolved in a large quantity of quicksilver, the thermometer will\nsink nearly 50 degrees. An intense amount of cold will result from\nthe mixture of muriate of lime and snow, by which a temperature of\n50\u00b0 below the zero of Fahrenheit, or 82\u00b0 below the freezing point of\nwater, is produced. By such a freezing mixture as this, mercury will\nbe rendered solid. A degree of cold, however, far exceeding it, has\nlately been obtained by the use of solid carbonic acid and ether.[81]\nSolid carbonic acid is itself procured from the gas liquefied by\npressure; which liquid, when allowed to escape into the air, evaporates\nso rapidly that a large quantity of it is congealed by being robbed of\nits combined heat by the vaporizing portion. When this solid acid is\nunited with ether, a bath is formed in which the carbonic acid will\nremain solid for twenty or thirty minutes. By a mixture of this kind,\nplaced under the receiver of an air-pump, a good exhaustion being\nsustained, a degree of cold 166\u00b0 below zero is secured. By this intense\ncold, many of the bodies which have hitherto been known to us only in\nthe gaseous state have been condensed into liquids and solids. Olefiant\ngas, a compound of hydrogen and carbon, was brought into a liquid\nform. Hydriodic and hydrobromic acids could be condensed into either a\nliquid or a solid form. Phosphuretted hydrogen, a gas which inflames\nspontaneously when brought into contact with the air or with oxygen,\nbecame a transparent liquid at this great reduction of temperature.\nSulphurous acid may be condensed, by pressure and a reduction of\ntemperature, into a liquid which boils at 14\u00b0 Fahrenheit, but by the\ncarbonic acid bath it is converted into a solid body, transparent and\nwithout colour. Sulphuretted hydrogen gas solidifies at 122\u00b0 below\nzero, and forms a white substance resembling a mass of crystals of\nsea-salt.\n\nA combination of the two gases, chlorine and oxygen, becomes solid at\n-75\u00b0, and the protoxide of nitrogen at -150\u00b0. Cyanogen, a compound\nof carbon and nitrogen--the base of prussic acid--is solidified at\n30\u00b0 below the zero of our thermometric scale. The well-known pungent\ncompound, ammonia, so exceedingly volatile at common temperatures,\nis converted into a crystalline, translucent, white substance at the\ntemperature of -103\u00b0. The difficulties which necessarily attend the\nexposure of a body to extreme cold and great pressure at the same time,\nappear to be the only obstacle to the condensation of oxygen, hydrogen,\nand nitrogen gases. A sufficient amount of condensation was, however,\neffected by Dr. Faraday, to lead him to the conclusion, arrived at\nalso by other evidences, that hydrogen, the lightest of the ponderable\nbodies, partakes of the nature of a metal.[82]\n\nDuring the solidification of water by freezing, some remarkable facts\nmay be noticed.\n\nWater, in cooling, gradually condenses in volume until it arrives at\n40\u00b0 Fahr., which appears to be the point of greatest density. From this\ntemperature to that of 32\u00b0, the point at which it begins to solidify,\nits volume remains unchanged,[82] as crystallisation (freezing) begins,\nthe bulk increases, the mass becomes specifically lighter, and it swims\non the surface of the fluid. From 40\u00b0 to 32\u00b0 the particles of water\nmust be taking up that new position which is essential to the formation\nof the solid--ice; and while this is taking place, every substance held\nin solution by the water is rejected.\n\nIf we mix with water the deepest colouring matter--the strongest acid\nor the most acrid poison--they are each and all rejected during the\nprocess of freezing, and if the water has been kept in a state of\nagitation during the process--so that the liberated particles may not\nbe mechanically entangled--the ice will be transparent, colourless,\ntasteless, and inert--the substances rejected being gathered together\nin the centre of the frozen mass in a state of intense concentration.\nIn like manner, even the atmospheric air, which is always held in\nsolution, is rejected, and hence the reason why all the ice which\nforms upon still ponds is full of air-bubbles, while the ice which is\nproduced in agitated water is perfectly free from them. This in itself\nis a remarkable condition, the entire bearing of which is not clearly\nunderstood; but a still more singular fact has been discovered in\nintimate connection with the rejection of all matter from a freezing\nsolution. Water, which in this way is freed entirely of air, will not\nboil at 212\u00b0 F., the ordinary boiling point of water.\n\nIf a mass of ice formed in the manner described is placed in a vessel,\nand being just covered with a film of oil, to prevent the absorption of\nair, is melted over a lamp or fire, and the heat continued, it will,\nso far from being converted into steam at 212\u00b0, continue to increase\nin temperature up to 270\u00b0 or more, and then burst into ebullition with\nsuch explosive violence as to rend the vessel in which it is confined.\n\nFrom this experiment we learn that did water exist in any other\ncondition than that in which we find it--even with the apparently\nsimple difference of containing no air--it would not be safe to employ\nit in any culinary or manufacturing operation, since its use would be\nfollowed by explosions as dangerous as those of gunpowder.\n\nSuch researches as these prove to us the admirable adaptation of all\nthings to their especial ends--the beautiful adjustment of the balance\nof forces throughout creation.\n\nThe refinements of Grecian philosophy saw, without the aids of\ninductive science, that the outward vesture of nature covered a host\nof mysterious agencies to which its characteristics were directly\ndue. In their dream of the four elements, fire, the external and\nvisible form of heat, was regarded as the cause of vitality, and the\ndisposer of every organised and unorganised condition of matter. Their\nidealisations have assumed another form, but the researches of modern\nscience have only established their universality and truth.\n\nThe great agents at work in nature--the mighty spirits bound to\nnever-ending tasks, which they pursue with unremitting toil, are of so\nrefined a character, that they will probably remain for ever unknown\nto us. The arch-evocator, with the wand of induction, calls; but the\nonly answer to his evocation is the manifestation of power in startling\neffects. Science pursues her inquiries with zeal and care: she tries\nand tortures nature to compel her to reveal her secrets. Bounds are,\nhowever, set to the powers of mortal search: we may not yet have\nreached the limits within which we are free to exercise our mental\nstrength; but, those limits reached, we shall find an infinite region\nbeyond us, into which even conjecture wanders eyeless and aimless, as\nthe blind Cyclops groping in his melancholy cave.[83]\n\nAll we know of heat is, that striking effects are produced which we\nmeasure by sensation, and by instruments upon which we have observed\nthat given results will be produced under certain conditions: of\nanything approaching to the cause of these we are totally ignorant.\nThe wonder-working mover of some of the grandest phenomena in\nnature--giving health to the organic world, and form to the inorganic\nmass--producing genial gales and dire tornadoes--earthquake strugglings\nand volcanic eruptions--ministering to our comforts in the homely fire,\nand to advancement in civilisation in the mighty furnace, and the\ningenious engine which drains our mines, or traverses our country with\nbird-like speed,--will, in all probability, remain for ever unknown to\nman. The immortal Newton, many of whose guesses have a prophetic value,\nthus expresses himself:--\u201cHeat consists in a minute vibratory motion in\nthe particles of bodies, and this motion is communicated through an\napparent vacuum by the undulations of a very subtile elastic medium,\nwhich is also concerned in the phenomena of light.\u201d\n\nOur experimental labours and our mathematical investigations have\nconsiderably advanced our knowledge since the time of Newton; yet still\neach theory of heat strangely resembles the mystic lamp which the\nRosicrucian regarded as a type of eternal life--a dim and flickering\nsymbol, in the tongue-like flame of which imagination, like a child,\ncan conjure many shapes.\n\nModern theory regards heat as a manifestation of motion, and experiment\nproves that a body falling through a certain space generates a definite\nquantity of heat, while observation shows that the waters at the base\nof the Falls of Niagara possess a temperature 1\u00b0 higher than when they\nfirst glide over the edge of the precipice.\n\nThis increase of temperature is due to the mechanical force due to\nthe fall, and is no more an evidence of the conversion of motion into\nheat, than is the old experiment of rubbing a button until it becomes\nhot. At all events, the fact that a given amount of mechanical force\nalways produces an equivalent of heat is as applicable to the idea of\na \u201csubtile elastic medium\u201d which is diffused through all matter, as to\nthe, at present, favourite hypothesis.\n\nSo far has this view been strained, that the temperature of the planets\nhas been referred to their motions, and speculation has aided the\nmathematician in determining the cessation of planetary motion, by\nthe conversion of it into heat. It is true that other theorists have\nsupposed points in space upon which this heat might be concentrated and\nreflected back again to produce motion.\n\nThere may be much of the poetic element in such speculations, but it is\nof that order which belongs rather to the romantic than to the real.\n\nA speculation which has more of truth, and which is, indeed,\ndemonstrable, cannot fail to impress every mind with its beauty, and\nprobable correctness.\n\nIn the growth of a tree, its wood and all its products are the result\nof certain external forces effecting chemical changes. Carbonic acid\nis decomposed, the carbon is retained, and oxygen given off, and\nassimilations of a complex character are in constant progress to\nproduce the various compounds of oxygen, hydrogen, nitrogen, and carbon.\n\nEvery condition of organised forms is due to the external excitation\nof light and heat, and in the chemical changes which take place, an\nequivalent of these principles, or powers--it signifies but little\naccording to which view we may regard them--is absorbed, and retained\nas essential to the condition of the matter formed. Let us confine\nour attention to wood--although the position applies equally to every\norganic product. A cubic foot of wood is formed by the decomposition\nof a certain quantity of carbonic acid, by the vital function of the\nplant, excited by the solar rays, which are involved in the mass which\nnature by \u201cher wondrous alchemy\u201d has made. Eventually this cubic foot\nof wood is subjected to a process of chemical change--combustion; by\nthe application of a single spark,--and in the disintegration of the\nwood, its carbon combining with oxygen to form carbonic acid, its\nhydrogen to form water, which is returned to the air, a large amount of\nlight and heat is produced. This is exactly equivalent to the amount\nwhich was engaged in its formation. Indeed, the sunshine which fell\nupon the leaves of the forest tree, of which the log formed a part, has\nbeen hoarded up, and we again develope it in its original state of heat\nand light.\n\nThe vast coal beds of England were formed by the rapid growth and quick\ndecay of a peculiar class of plants under the influence of a tropical\nsun. They have been buried myriads of ages, under hundreds of feet of\nsandy rock. By the industry of the miner the coal is brought again\nto the surface, and we develope from it those powers by which it was\nformed.\n\nIn the fire which gives comfort to our homes--in the furnace which\ngenerates force for the purposes of manufacture, or to propel the\nrailway engine and its ponderous train--in the gas with which we\nillumine our streets and gladden during the long winter nights our\napartments, we are developing that heat and light which fell upon\nthe earth with all its quickening influences millions of ages before\nyet the Creator had called into existence the monarch Man, for whose\nnecessities these wondrous formations were designed.\n\n\nFOOTNOTES:\n\n[43] The following table of the rays penetrating coloured glass has\nbeen given by Melloni, in his memoir _On the Free Transmission of\nRadiant Heat through Different Bodies_:--\n\n    Deep violet               53\n    Yellowish red (flaked)    53\n    Purple red (flaked)       51\n    Vivid red                 47\n    Pale violet               45\n    Orange red                44\n    Clear blue                42\n    Deep yellow               40\n    Bright yellow             34\n    Golden yellow             33\n    Deep blue                 33\n    Apple green               26\n    Mineral green             23\n    Very deep blue            19\n\nTranslated in the Scientific Memoirs, vol. i. p. 30.\n\n[44] \u201cThe physical characters of this species of glass, which acts\nso differently from the other species of coloured glass in all the\nphenomena of calorific absorption, are, 1st, its intercepting almost\ntotally the rays which pass through alum; 2nd, its entirely absorbing\nthe red rays of the solar spectrum. I have already stated that their\ncolouration is produced almost entirely by the oxide of copper.\n\n\u201cThus, the colouring matters of the coloured glasses, while they\nso powerfully affect the relations of quantity which the different\nrays of ordinary light bear to each other, exercise no elective\naction on the concomitant calorific rays. This curious phenomenon is\nthe more remarkable as the colouring matters absorb almost always\na very considerable portion of the heat _naturally transmitted by\nthe glass_. The following are, in fact, the calorific transmissions\nof the seven coloured glasses referred to; the transmission of the\ncommon glass being represented by 100; red glass, 82\u00b75; orange, 72\u00b75;\nyellow, 55; bluish-green, 57\u00b75; blue, 52\u00b75; indigo, 30; violet, 85.\nThe quantity of heat absorbed through the action of the colouring\nsubstances is, therefore, 17\u00b75 in the red glass, 27\u00b75 in the orange,\n45 in the yellow, 42\u00b75 in the green, 47\u00b75 in the blue, 70 in the\nindigo, and 15 in the violet. Now, as these absorptions extinguish a\nproportional part of each of the rays which constitute the calorific\nstream transmitted by common glass, they may be compared, as we said\nbefore, with the absorbent action exercised on light by matters more\nor less deeply brown or dark, when they are immersed in water, or some\nother colourless liquid which dissolves, but does not affect them\nchemically.\u201d--_Annales de Chimie et de Physique_, tom. xl. p. 382.\n\nGuided by these principles, the author selected the glass employed in\nglazing the Royal Palm-House, at Kew Botanical Gardens, where it was\ndesired to obstruct the passage of those rays which have a particular\nscorching influence. Of this glass a description was given at the\nmeeting of the British Association at Oxford, which appears in the\nTransactions for that year. The result has been all that could be\ndesired--not a single instance of scorching having occurred during the\nthree years which have elapsed.\n\n[45] In the _Philosophical Transactions_, vol. xc., the following\npapers, by Sir William Herschel, may be consulted:--\n\n_Investigation of the powers of the prismatic colours to heat\nand illuminate objects; with remarks that prove the different\nrefrangibility of radiant heat. To which is added, an inquiry into the\nmethod of viewing the sun advantageously, with telescopes of large\napertures and high magnifying powers_, p. 255. _Experiments on the\nrefrangibility of the invisible rays of the sun_, p. 284. _Experiments\non the solar and on the terrestrial rays that occasion heat; with a\ncomparative view of the laws to which light and heat, or rather the\nrays which occasion them, are subject; in order to determine whether\nthey are the same or different_, pp. 293, 437.\n\nIn connection with this inquiry, Sir William Herschel remarks, that\nsince a _red glass_ stops no less than 692 out of 1,000 such rays as\nare of the refrangibility of red light, we have a direct and simple\nproof, in the case of the red glass, that the rays of light are\ntransmitted, while those of heat are stopped, and that thus they have\nnothing in common but a certain equal degree of refrangibility, which\nby the power of the glass must occasion them to be thrown together into\nthe place which is pointed out to us by the visibility of the rays of\nlight.\n\nOn the same subject, a Memoir, by Sir Henry Englefield, in the Journal\nof the Royal Institution for 1802, p. 202, may be consulted; and\n_Researches on Light_, by the Author.\n\n[46] Dr. Draper, _On the production of light by heat_, in the Phil.\nMag. for 1847.\n\nSir Isaac Newton fixed the temperature at which bodies become\nself-luminous at 635\u00b0; Sir Humphry Davy at 812\u00b0; Mr. Wedgewood at 947\u00b0;\nand Mr. Daniell at 980\u00b0; whilst Dr. Draper from his experiments gives\n977\u00b0; and Dr. Robinson 865\u00b0.\n\nIn a review of the above paper by Melloni, entitled _Researches on the\nRadiations of Incandescent Bodies, and on the Elementary Colours of the\nSolar Spectrum_, translated for Silliman\u2019s Journal for August, 1847, he\nremarks:--\n\n\u201cI say that they conduct, as do others heretofore known on light and\nradiant heat, to a perfect analogy between the general laws which\ngovern these two great agents of nature. I will add that I regard\nthe theory of their identity as the only one admissible by the rules\nof philosophy; and that I consider myself obliged to adopt it, until\nit shall have been proved to me that there is a necessity of having\nrecourse to two different principles, for the explanation of a series\nof phenomena which at present appear to belong to a solitary agent.\u201d\n\nReference should also be made to a paper by Dr. Robinson, _On the\neffects of Heat in lessening the Affinities of the Elements of Water_,\nin the Transactions of the Royal Irish Academy, 1848, where he says\nthat \u201cwhen a platinum wire is traversed by a current gradually\nincreased till it produces ignition, the first gleam that appears is\nnot red, but of a colour which, when I first saw it, I compared to\nthe \u2018lavender ray\u2019 discovered by Sir John Herschel beyond the violet,\nthough I was surprised at seeing the tint of that most refrangible ray\npreceding the ray which is least so. It is quite conspicuous at about\n865\u00b0; and as the mode in which it makes its appearance presents nothing\nabrupt or discontinuous, it seems likely that it is merely a transition\nfrom invisible rays excited at a lower temperature to ordinary\nlight.\u201d--p. 310.\n\n[47] In the _Bakerian Lecture_ for 1842, _On the transparency of the\nAtmosphere, and the law of extinction of the solar rays in passing\nthrough it_, by James D. Forbes, Esq., F.R.S., &c., will be found a\nmost complete investigation of this subject.\n\nThe experiments were, for the most part, made in Switzerland with Sir\nJohn Herschel\u2019s actinometer, and they prove satisfactorily,--\u201cThat\nthe absorption of the solar rays by the strata of air to which we\nhave immediate access, is considerable in amount for even moderate\nthicknesses.\u201d\n\n[48] After referring to several curious and instructive experiments, in\nwhich peculiar chemical changes are produced under the influence of the\nsolar rays by their HEAT, Sir John Herschel says:--\n\n\u201cThese rays are distinguished from those of Light by being invisible;\nthey are also distinguished from the pure calorific rays beyond the\nspectrum, by their possessing properties (_of a peculiar character,\nreferred to in former papers_) either exclusively of the calorific\nrays, or in a much higher degree. They may perhaps not improperly be\nregarded as bearing the same relation to the calorific spectrum which\nthe photographic rays do to the luminous ones. If the restriction\nto these rays of the term _thermic_, as distinct from _calorific_,\nbe not (as I think, in fact, it is not) a sufficient distinction, I\nwould propose the term _parathermic rays_ to designate them. These are\nthe rays which I conceive to be active in producing those singular\nmolecular affections which determine the precipitation of vapours in\nthe experiments of Messrs. Draper, Moser, and Hunt, and which will\nprobably lead to important discoveries as to the intimate nature of\nthose forces resident on the surfaces of bodies, to which M. Dutrochet\nhas given the name of epipolic forces.\u201d--_On certain improvements in\nPhotographic Processes, described in a former communication_ (Phil.\nTrans, vol. cxxxiii.); and _On the Parathermic Rays of the Solar\nSpectrum_, Phil. Trans, vol. cxxxiv.\n\nThe experiments of Mrs. Somerville, _On the Action of the Rays of the\nSpectrum on Vegetable Juices_ (Phil. Transactions, vol. cxxxvii.),\nappear to connect themselves with this particular class of rays in a\ncurious manner.\n\n[49] Experiments on the influence of heat on differently-coloured\nbodies were first made by Dr. Hooke; and it was not until long after\nthat Franklin made his ingenious experiments. Davy exposed to sunshine\nsix equal pieces of copper, painted white, yellow, red, green, blue,\nand black, in such a manner that one side only was illuminated. To\nthe dark side he attached a bit of cerate, ascertained by experiment\nto melt at 700. The cerate attached to the black became fluid first,\nthe blue next, then the green and red, and lastly the yellow and\nwhite.--Beddoes\u2019s _Contributions to Physical Knowledge_, and collected\nworks of Sir Humphry Davy, vol. ii. p. 27.\n\n[50] By reference to the Treatise on Heat, in the _Encyclop\u00e6dia\nMetropolitana_, numerous suggestive experiments will be found, all\nbearing on this subject. Peschel\u2019s _Elements of Physics_ may also be\nconsulted with advantage. The fact is, however, simply proved, as\nstated in the text, by placing the bulbs of delicate thermometers,\nso as to be completely involved in the petals of flowers exposed to\nsunshine, shading the upper portion of the stem of the instrument.\n\n[51] Moser, _On Vision, and on the Action of Light on Bodies_: and also\n_On Latent Light_: Scientific Memoirs, vol. iii. Draper, _On certain\nSpectral Appearances, and on the Discovery of Latent Light_: Phil.\nMag., Nov. 1842.\n\n[52] A particular examination of this curious question will be found in\nthe Author\u2019s report _On the Influence of the Solar Rays on the Growth\nof Plants_: Reports of the British Association for 1847.\n\n[53] Ammianus Marcellinus ascribes the longevity and robust health of\nmountaineers to their exposure to the dews of night. Dew was employed\nby the alchemists in their experiments on the solution of gold. The\nladies of old collected the \u201ccelestial wash,\u201d which they imagined had\nthe virtue of preserving their fine forms, by exposing heaps of wool\nto the influences of night radiation. It was supposed that the lean\nfeatures of the grasshopper arose from that insect feeding entirely on\ndew: \u201cDumque thymo pascentur apes, dum rore cicad\u00e6,\u201d Virgil, Eclog.\n\nSee some curious remarks by Boyle, _On the Power of Dew in Working on\nSolid Bodies_: Works of the Honourable R. Boyle, vol. v. p. 121. 1744.\n\n[54] See the _Researches on Heat_, by Professor James Forbes, in the\nTransactions of the Royal Society of Edinburgh; also Melloni\u2019s papers\non the same subject in the _Annales de Chimie_, several of which have\nbeen translated into the _Scientific Memoirs_, edited by Mr. Richard\nTaylor.\n\n[55] The phenomena of dew have constantly engaged the attention of\nman. Aristotle, in his book _De Mundo_, puts forth some just notions\non its nature. An opinion has almost always prevailed that dew falls.\nGersten appears to have been the first who opposed this motion. He was\nfollowed by Musschenbroek, and then by Du Fay. The researches of Leslie\nwere of a far more exact character. Dr. Wilson, in the Transactions of\nthe Royal Society of Edinburgh, 1st vol., published a _Memoir on Hoar\nFrost_ of much interest; but the questions involved remained unsettled\nuntil the researches of Dr. Wells, which were published in his _Essay\non Dew_.\n\n[56] By far the most complete set of experiments on the radiation\nof heat from the surface at night, which have been published since\nDr. Wells\u2019s memoir _On Dew_, are those of Mr. Glaisher, of the Royal\nObservatory at Greenwich. Instruments of the most perfect kind were\nemployed, and the observations made with sedulous care. The results\nwill be found in a memoir _On the Amount of the Radiation of Heat, at\nnight, from the Earth, and from various bodies placed on or near the\nSurface of the Earth_, by James Glaisher, Esq., Philosophical Trans.\nfor 1847, part 2.\n\n[57] Dr. Wells noticed the practical fact that very light shades\nprotected delicate plants from frost, by preventing radiation. Mr.\nGoldsworthy Gurney has made a series of interesting experiments, and\nhe imagines that by shading grasslands with boughs of trees, or any\nlight litter, a more abundant crop is produced. The subject has been\ndiscussed in the journals of the Royal Agricultural Society. May not\nthe apparent increase be due entirely to the succulent condition in\nwhich a plant always grows in the shade?\n\n[58] This paper of Melloni\u2019s will be found in the _Biblioth\u00e8que\nUniverselle de Gen\u00e8ve_, for 1843. The conclusions are highly ingenious,\nbut they rest entirely on the analogy supposed to be discovered\nbetween the relations of heat, like light, to the coloured rays of the\nspectrum. This, it must be remembered, is not the case, since even Sir\nWilliam Herschel showed that red light might exist with only a minimum\nof calorific power, notwithstanding the fact, that the maximum heat-ray\nof the spectrum coincides with the red rays.\n\n[59] Dr. Robinson, of Armagh, in his Memoir _On the Effects of Heat in\nlessening the Affinities of the Elements of Water_.--Transactions of\nthe Royal Irish Academy, vol. xxi. part 2.\n\n[60] On this subject consult Robert Were Fox, _On the Temperature of\nthe Mines of Cornwall_.--Cornwall Geological Transactions, vol. ii.; W.\nJ. Henwood, on the same subject, _Ib._ vol. v.; Reports of the British\nAssociation, 1840, p. 315; Edinburgh New Philosophical Journal, vol.\nxxiv. p. 140.\n\n[61] _On the causes of the temperature of Hot and Thermal Springs;\nand on the bearings of this subject as connected with the general\nquestion regarding the internal temperature of the Earth_: by Professor\nGustav Bischoff, of Bonn.--Edinburgh New Philosophical Journal, vol.\nxx. p. 376; vol. xxiii. p. 330. Some interesting information on\nthe temperature of the ground will be found in Erman\u2019s _Travels in\nSiberia_, translated by W. D. Cooley, vol. i. p. 339; vol. ii. p.\n366. _Sur la Profondeur \u00e0 laquelle se trouve la couche de Temp\u00e9rature\ninvariable entre les Tropiques_, by Boussingault: Annales de Chimie et\nde Physique, 1833, p. 225. Reference may also be made to Humboldt\u2019s\n_Cosmos_, Otto\u2019s translation; and to the excellent article on\n_Meteorology_, by George Harvey, in the Encyclop\u00e6dia Metropolitana.\nThese chthonisothermal lines, as they are called, have been traced by\nHumboldt and others over extensive districts.\n\n[62] These results are obtained from the valuable observations\nof Robert Were Fox, Esq., made with great care by that gentleman\nin several of the Cornish mines: _Report on some observations on\nSubterranean Temperature_.--British Association Reports, vol. ix. p.\n309; Philosophical Magazine, 1837, vol. ii. p. 520.\n\n[63] From his experiments, the following conclusions were arrived at by\nM. Delaroche:--\n\n1. Invisible radiant heat may, in some circumstances, pass directly\nthrough glass.\n\n2. The quantity of radiant heat which passes directly through glass\nis so much greater, relative to the whole heat emitted in the same\ndirection, as the temperature of the source of heat is more elevated.\n\n3. The calorific rays which have already passed through a screen of\nglass, experience, in passing through a second glass screen of a\nsimilar nature, a much smaller diminution of their intensity than they\ndid in passing through the first screen.\n\n4. The rays emitted by a hot body differ from each other in their\nfaculty to pass through glass.\n\n5. A thick glass, though as much or more permeable to light than a thin\nglass of worse quality, allows a much smaller quantity of radiant heat\nto pass. The difference is so much the less as the temperature of the\nradiating source is more elevated.\n\n6. The quantity of heat which a hot body yields in a given time, by\nradiation to a cold body situate at a distance, increases, _c\u00e6teris\nparibus_, in a greater ratio than the excess of temperature of the\nfirst body above the second.--Journal de Physique, vol. lxxv.\n\n[64] Sir David Brewster differs from the conclusions arrived at by\nDelaroche. He thus explains his views:--\u201cThe inability of radiant\nheat to pass through glass, may be considered as a consequence of its\nrefusing to yield to the refractive force; for we can scarcely conceive\na particle of radiant matter freely permeating a solid body, without\nsuffering some change in its velocity and direction. The ingenious\nexperiments of M. Pr\u00e9vost, of Geneva, and the more recent ones of\nM. Delaroche, have been considered as establishing the permeability\nof glass to radiant heat. M. Pr\u00e9vost employed moveable screens of\nglass, and renewed them continually, in order that the result which\nhe obtained might not be ascribed to the heating of the screen; but\nsuch is the rapidity with which heat is propagated through a thin\nplate of glass, that it is extremely difficult, if not impossible, to\nobserve the state of the thermometer before it has been affected by\nthe secondary radiation from the screen. The method employed by M.\nDelaroche, of observing the difference of effect, when a blackened\nglass screen and a transparent one were made successively to intercept\nthe radiant heat, is liable to an obvious error. The radiant heat would\nfind a quicker passage through the transparent screen; and, therefore,\nthe difference of effect was not due to the transmitted heat, but to\nthe heat radiated from the anterior surface. The truth contained in M.\nDelaroche\u2019s fifth proposition is almost a demonstration of the fallacy\nof all those that precede it. He found that \u2018a thick plate of glass,\nthough as much or more permeable to light than a thin glass of worse\nquality, allowed a much smaller quantity of radiant heat to pass.\u2019 If\nhe had employed very thick plates of the purest flint glass, or thick\nmasses of fluid that have the power of transmitting light copiously,\nhe would have found that not a single particle of heat was capable of\npassing directly through transparent media.\u201d--Sir D. Brewster, _On new\nproperties of heat as exhibited in its propagation along plates of\nglass_. Philosophical Transactions, vol. cvi. p. 107.\n\n[65] _Proposal of a New Nomenclature for the Science of Calorific\nRadiations_, by M. Melloni. Biblioth\u00e8que Universelle de Gen\u00e8ve, No.\n70. Scientific Memoirs, vol. iii. part 12. Many of the terms, as\n_Diathermasy_, or transparency for heat; _Adiathermasy_, opacity for\nheat; _Thermochroic_, coloured for heat, and others, are valuable\nsuggestions of forms of expression which are required in dealing with\nthese physical phenomena.\n\n[66] For a careful examination of the several theories of heat consult\nDr. Young\u2019s Course of Lectures on Natural Philosophy, &c., Lecture 52,\n_On the Measures and the Nature of Heat_; also Powell\u2019s very excellent\n_Reports on Radiant Heat_--Reports of the British Association, 1832,\n1840. The transcendental view which the immaterial theory leads to,\ncannot be better exemplified than by the following quotation from that\ninexplicable dream of a talented man, _Elements of Physiophilosophy_,\nby Lorenz Oken, M.D. (translated for the Ray Society, by Alfred Tulk):--\n\n\u201cHeat is not matter itself any more than light is; but it is only the\nact of motion in the primary matter. In heat, as well as in light,\nthere certainly resides a material substratum; yet, this substratum\ndoes not give out heat and light; but the _motion_ only of the\nsubstratum gives out heat, and the _tension_ only of the substratum\nlight. There is no body of heat; nitrogen is the body of heat, just\nas oxygen may be called the body of fire. Heat is real space; into it\nall forms have been resolved, as all materiality has been resolved\ninto gravity, and all activity, all polarity, into light. Heat is the\nuniversal form, consequently the want of form.\u201d\n\n[67] M\u00e9moires de la Soci\u00e9t\u00e9 Physique, &c., de Gen\u00e8ve, tom. ii. art. 2.\n\n[68] This curious phenomenon was first observed by Mr. Trevelyan, whose\n_Notice regarding some Experiments on the Vibration of Heated Metals_\nwill be found in the Transactions of the Royal Society of Edinburgh,\nvol. xii., 1837. In a Memoir in the same volume, entitled _Experimental\nResearches regarding certain vibrations which take place between\nmetallic masses having different temperatures_, Professor Forbes draws\nthe following conclusions:--\n\n1. \u201cThe vibrations never take place between substances of the same\nnature.\n\n2. \u201cBoth substances must be metallic. (This is now proved not to be\nnecessary.)\n\n3. \u201cThe vibrations take place with an intensity proportional (within\ncertain limits) to the difference of the conducting powers of the\nmetals for heat or electricity; the metal having the least conducting\npower being necessarily the coldest.\n\n4. \u201cThe time of contact of two points of the metals must be longer than\nthat of the intermediate portions.\n\n5. \u201cThe impulse is received by a distinct and separate process at each\ncontact of the bar and block, and in no case is the metallic connection\nof the bearing points in the bar, or those of the block, in any way\nessential.\n\n6. \u201cThe intensity of the vibration is (under certain exceptions)\nproportional to the difference of temperature of the\nmetals.\u201d--Transactions of the Royal Society of Edinburgh, vol. xii.\n\n[69] The Bakerian Lecture. _On certain Phenomena of Voltaic Ignition,\nand the Decomposition of Water into its Constituent Gases by Heat_: by\nW. R. Grove, Esq.--Philosophical Transactions, 1847. Part 1.\n\n[70] Davy\u2019s _Researches on Flame_. Works, vol. vi.--Philosophical\nTransactions for 1817.\n\n[71] _On the Effect of Heat in lessening the affinities of the Elements\nof Water_: by the Rev. Thomas Romney Robinson, D.D.--Transactions of\nthe Royal Irish Academy, vol. xxi. part 2.\n\n[72] _An Inquiry concerning the Chemical Properties that have been\nattributed to Light_: by Benjamin, Count of Rumford.--Philosophical\nTransactions, vol. lxxxviii. p. 449.--The results obtained by Count\nRumford were probably due to the non-luminous heat-rays--parathermic\nrays--which are known to be given off by boiling water.\n\n[73] For Dr. Drapers paper, see Philosophical Magazine for May, 1847,\nvol. xxx. 3rd series.\n\n[74] _On the Action of the Rays of the Solar Spectrum on Vegetable\nColours_: by Sir J. F. W. Herschel, Bart.\n\nThe proof of the continuation of the visible prismatic spectrum beyond\nthe extreme violet may be witnessed in the following manner:--\u201cPaper\nstained with tincture of turmeric is of a yellow colour; and, in\nconsequence, the spectrum thrown in it, if exposed in open daylight,\nis considerably affected in its apparent colours, the blue portion\nappearing violet, and the violet very pale and faint; but beyond the\nregion occupied by the violet rays, is distinctly to be seen a faint\nprolongation of the spectrum, terminated laterally, like the rest of\nit, by straight and sharp outlines, and which, in this case, affects\nthe eye with the sensation of a pale yellow colour.\u201d--Philosophical\nTransactions, p. 133.\n\n[75] The most complete exposition of the theory that animal heat is\nderived from chemical action only, will be found in _Animal Chemistry,\nor Chemistry in its applications to Physiology and Pathology_, by\nJustus Liebig: translated by Dr. Gregory. The conclusions arrived at\nby the author, notwithstanding his high--and deservedly high--position\nin chemical science, must, however, be received with great caution,\nmany of them being founded on most incorrect premises, and his\ngeneralizations being of the most hasty and imperfect character. At\npage 22 the following passage occurs:--\u201cIf we were to go naked, like\ncertain savage tribes, or if in hunting or fishing we were exposed\nto the same degree of cold as the Samoiedes, we should be able, with\nease, to consume ten pounds of flesh, and, perhaps, a dozen of tallow\ncandles into the bargain, daily, as warmly clad travellers have related\nwith astonishment of these people. We should then also be able to take\nthe same quantity of brandy or train-oil without bad effects, because\nthe carbon and hydrogen of these substances would only suffice to keep\nup the equilibrium between the external temperature and that of our\nbodies.\u201d\n\nA brief examination will exhibit the error of this. The analysis of\nBeef, by D. Lyon Playfair, is as follows:--\n\n    Carbon      51\u00b783\n    Hydrogen     7\u00b757\n    Nitrogen    15\u00b701\n    Oxygen      21\u00b737\n    Ashes        4\u00b723\n\nAnd the following has been given by Chevreul as the composition of\nmutton tallow:--\n\n    Carbon   96\n    Hydrogen 16\n    Nitrogen 16\n    Oxygen   48\n\nAbout three times the quantity of oxygen to the carbon eaten, is\nrequired to convert it into carbonic acid; hence, the Samoiede, eating\nmore highly carbonized matter, must inspire 288 oz. of oxygen daily,\nor nearly eight times as much as the \u201cordinary adult.\u201d By the lungs\nhe must take into the body 2,304 cubic feet of air besides what will\nbe absorbed by the skin. His respirations must be so much quickened,\nthat at the lowest possible calculation he must have 500 pulsations a\nminute. Under such conditions it is quite clear man could not exist.\nThere is no disputing the fact of the enormous appetites of these\npeople; but all the food is not removed from the system as carbonic\nacid gas.\n\n[76] An interesting paper by Dr. Davy, _On the Temperature of Man_,\nwill be found in the Philosophical Transactions, vol. cxxxvi. p.\n319.--Sir Humphry Davy, in his _Consolations in Travel, or the Last\nDays of a Philosopher_, in his fourth dialogue, _The Proteus_, has\nseveral ingenious speculations on this subject.\n\n[77] _Expos\u00e9 de quelques r\u00e9sultats obtenus par l\u2019action combin\u00e9e de la\nchaleur et de la compression sur certains liquides, tels que l\u2019eau,\nl\u2019alcool, l\u2019\u00e9ther sulfurique, et l\u2019essence de p\u00e9trole rectifi\u00e9e_: par\nM. le Baron Cagniard de la Tour.\n\nThe three following conclusions are arrived at:--\n\n1. Que l\u2019alcool \u00e0 36 degr\u00e9s, l\u2019essence de p\u00e9trole rectifi\u00e9e \u00e0 42\ndegr\u00e9s, et l\u2019\u00e9ther sulfurique soumis \u00e0 l\u2019action de la chaleur et de la\ncompression, sont susceptibles de se r\u00e9duire compl\u00e8tement en vapeur\nsous un volume un peu plus que double de celui de chaque liquide.\n\n2. Qu\u2019une augmentation de pression, occasionn\u00e9e par la pr\u00e9sence de\nl\u2019air dans plusieurs des experiences qui viennent d\u2019\u00eatre cit\u00e9es, n\u2019a\npoint apport\u00e9 d\u2019obstacle \u00e0 l\u2019\u00e9vaporation du liquide dans le m\u00eame\nespace; qu\u2019elle a seulement rendu sa dilatation plus calme et plus\nfacile \u00e0 suivre jusqu\u2019au moment o\u00f9 le liquide semble s\u2019\u00e9vanouir\ntout-\u00e0-coup.\n\n3. Que l\u2019eau, quoique susceptible sans doute d\u2019\u00eatre r\u00e9duite en vapeur\ntr\u00e8s-comprim\u00e9e, n\u2019a pu \u00eatre soumise \u00e0 des experiences compl\u00e8tes,\nfaute de moyens suffisans pour assurer l\u2019exacte fermeture de la\nmarmite de compression, non plus que dans les tubes de verre dont elle\nalt\u00e8re la transparence en s\u2019emparant de l\u2019alcali qui entre dans leur\ncomposition.--Annales de Chimie, vol. xxi.\n\n[78] _Sur les ph\u00e9nom\u00e8nes qui pr\u00e9sentent les corps projet\u00e9s sur des\nsurfaces chaudes_: par M. Boutigny (d\u2019Evreux).--Annales de Chimie et de\nPhysique, vol. xi. p. 16. _Cong\u00e9lation du mercure en trois secondes,\nen vertu de l\u2019\u00e9tat sph\u00e9ro\u00efdal dans un creuset incandescent_: by M.\nFaraday.--Ibid., vol. xix. p. 383.\n\n_Spheroidal Condition of Bodies_ (Extrait d\u2019une Note de M. Boutigny\nd\u2019Evreux).\n\n\u201cAu nombre des propri\u00e9t\u00e9s des corps \u00e0 l\u2019\u00e9tat sph\u00e9ro\u00efdal, il en est cinq\nqui me paraissent caract\u00e9ristiques et fondamentales, et c\u2019est sur ces\ncinq propri\u00e9t\u00e9s que je base la d\u00e9finition que je soumets aujourd\u2019hui au\njugement de l\u2019Acad\u00e9mie. Ces cinq propri\u00e9t\u00e9s sont:--\n\n\u201c1. La forme arrondie que prend la mati\u00e8re sur une surface chauff\u00e9e \u00e0\nune certaine temp\u00e9rature.\n\n\u201c2. Le fait de la distance permanente qui existe entre le corps \u00e0\nl\u2019\u00e9tat sph\u00e9ro\u00efdal et le corps sph\u00e9ro\u00efdalisant.\n\n\u201c3. La propri\u00e9t\u00e9 de r\u00e9fl\u00e9chir le calorique rayonnant.\n\n\u201c4. La suspension de l\u2019action chimique.\n\n\u201c5. La fixit\u00e9 de la temp\u00e9rature des corps \u00e0 l\u2019\u00e9tat sph\u00e9ro\u00efdal.\n\n\u201cCela pos\u00e9, voici la d\u00e9finition que je propose: un corps projet\u00e9 sur\nune surface chaude est \u00e0 l\u2019\u00e9tat sph\u00e9ro\u00efdal quand il rev\u00eat la forme\narrondie et qu\u2019il se maintient sur cette surface au del\u00e0 du rayon de sa\nsph\u00e8re d\u2019activit\u00e9 physique et chimique; alors il r\u00e9fl\u00e9chit le calorique\nrayonnant, et ses mol\u00e9cules sont, quant \u00e0 la chaleur, dans un \u00e9tat\nd\u2019\u00e9quilibre stable; c\u2019est-\u00e0-dire, \u00e0 une temp\u00e9rature invariable, ou qui\nne varie que dans des limites \u00e9troites.\u201d--Comptes Rendus, 6 Mars, 1848.\n\n[79] _Some Facts relative to the Spheroidal State of Bodies, Fire\nOrdeal, Incombustible Man, &c._: by P. H. Boutigny (d\u2019Evreux),\nPhilosophical Magazine, No. 233 (third, series), p. 80; Comptes Rendus,\nMay 14, 1849.\n\n[80] The theory of freezing mixtures is deduced from the doctrine of\nlatent caloric. These are mixtures of saline substances which, at the\ncommon temperature, by their mutual chemical action, pass rapidly into\nthe fluid form, or are capable of being rapidly dissolved in water,\nand, by this quick transition to fluidity, absorb caloric, and produce\ndegrees of cold more or less intense.--Rev. Francis Lunn, _On Heat_:\nEncyclop\u00e6dia Metropolitana.\n\n[81] _Propri\u00e9t\u00e9s de l\u2019Acide Carbonique liquide_, par M. Thilorier,\nAnnales de Chimie, vol. lx. p. 427. _Solidification de l\u2019Acide\nCarbonique_: Ibid. p. 432.\n\n[82] _On the Liquefaction and Solidification of Bodies generally\nexisting as Gases_, by Michael Faraday, D.C.L., F.R.S., &c.;\nPhilosophical Transactions, vol. cxxxvi, p. 155.\n\n[83] Burns, in one of his most natural and pathetic letters.\n\n\n\n\nCHAPTER VII.\n\nLIGHT.\n\n  Theories of the Nature of Light--Hypotheses of Newton\n    and Huygens--Sources of Light--The Sun--Velocity of\n    Light--Transparency--Dark Lines of the Spectrum--Absorption\n    of Light--Colour--Prismatic Analysis--Rays of the\n    Spectrum--Rainbow--Diffraction--Interference--Goethe\u2019s\n    Theory--Polarisation--Magnetisation of Light--Vision--The\n    Eye--Analogy--Sound and Light--Influence of Light on Animals and\n    Vegetables--Phosphorescence arising from several Causes--Artificial\n    Light--Its Colour dependent on Matter.\n\n\nLight, the first creation, presents to the enquiring mind a series\nof phenomena of the most exalted character. The glowing sunshine,\npainting the earth with all the brilliancy of colour, and giving to the\nlandscape the inimitable charm of every degree of illumination, from\nthe grey shadow to the golden glow;--the calm of evening, when, weary\nof the \u201cexcess of splendour,\u201d the eye can repose in tranquillity upon\nthe \u201ccloud-land\u201d of the west, and watch the golden and the ruddy hues\nfade slowly into the blue tincture of night;--and the pale refulgence\nof the moon, with the quiet sparkle of the sun-lit stars,--all tend\nto impress upon the soul, the great truth that, where there is light,\norganisation and life are found, and beyond its influence death and\nsilence hold supreme dominion.[84] Through all time we have evidences\nthat this has been the prevailing feeling of the human race, derived,\nof course, from their observation of the natural phenomena dependent\nupon luminous agency. In the myths of every country, impersonations of\nlight prevail, and to these are referred the mysteries of the perpetual\nrenewal of life on the surface of the earth.\n\nThis presentiment of a philosophic truth, in the instance of the poet\nsages of intellectual Greece, was advanced to the highest degree of\nrefinement; and the sublime exclamation of Plato: \u201cLight is truth, and\nGod is light,\u201d approaches nearly to a divine revelation.\n\nAs the medium of vision--as the cause of colour--as a power influencing\nin a most striking manner all the forms of organisation around us,\nlight presented to the inquiring minds of all ages a subject of the\nhighest interest.\n\nThe ancient philosophers, although they lost themselves in the\nmetaphysical subtleties of their schools, could not but discover in\nlight an element of the utmost importance in natural operations. The\nalchemists regarded the luminous principle as a most subtile fluid,\ncapable of interpenetrating and mingling with gross matter: gold\nbeing supposed to differ from the baser metals only in containing a\nlarger quantity of this ethereal essence.[85] Modern science, after\ninvestigating most attentively a greater number of the phenomena of\nlight, has endeavoured to assist the inquiry by the aid of hypotheses.\nNewton, in a theory, which exhibits the refined character of that\ngreat philosopher\u2019s mind, supposes luminous particles to dart from the\nsurfaces of bodies in all directions--that these infinitely minute\nparticles are influenced by the attracting and repelling forces of\nmatter, and thus turned back, or reflected, from their superficies in\nsome cases, and absorbed into their interstitial spaces in others.\n\nHuyghens, on the contrary, supposes light to be caused by the waves or\nvibrations of an infinitely elastic medium--ETHER--diffused through all\nspace, which waves are propagated in every direction from the luminous\nbody. In the first theory, a luminous particle is supposed actually to\ncome from the sun to the earth; in the other, the sun only occasions a\ndisturbance of the _ether_, which extends with great rapidity, in the\nsame manner as a wave spreads itself over the surface of a lake.\n\nNearly all the facts known in the time of Newton, and those discovered\nby him, were explained most satisfactorily by his hypothesis; but\nit was found they could be interpreted equally as the effects of\nundulation, with the exception of the production of colour by prismatic\nrefraction. Although the labours of many gifted minds have been given,\nwith the utmost devotion, to the support of the vibratory theory,\nthis simple fact has never yet received any satisfactory explanation;\nand there are numerous discoveries connected with the molecular and\nchemical disturbances produced by the sun\u2019s rays, which do not appear\nto be explained by the hypothesis of emission or of undulation.\n\nIn both theories a wave motion is admitted, and every fact renders\nit probable that this mode of progression applies not only to light,\nbut to the so-called _imponderable forces_ in general. Admitting,\ntherefore, the undulatory movement of luminous rays, we shall not stop\nto consider those points of the discussion which have been so ably\ndealt with by Young, Laplace, Fresnel, Biot, Fraunhofer, Herschel,\nBrewster, and others, but proceed at once to consider the sources of\nlight, and its more remarkable phenomena.[86]\n\nThe sun is the greatest permanently luminous body we are acquainted\nwith, and that orb is continually pouring off light from its surface\nin all directions at the rate, through the resisting medium of space\nand of our own atmosphere, of 192,000 miles in a second of time. It has\nbeen calculated, however, that light would move through a vacuum with\nthe speed of 192,500 miles in the same period. We, therefore, learn\nthat a ray of light requires eight minutes and thirteen seconds to\ncome from the sun to us. In travelling from the distant planet Uranus,\nnearly three hours are exhausted; and from the nearest of the fixed\nstars each ray of light requires more than six years to traverse the\nintervening space between it and the earth. Allow the mind to advance\nto the regions of nebul\u00e6, and it will be found that hundreds of years\nmust glide away during the passage of their radiations. Consequently,\nif one of those masses of matter, or even one of the remote fixed\nstars, was \u201cblotted out of heaven\u201d to-day, several generations of\nthe finite inhabitants of this world would fade out of time before\nthe obliteration could be known to man. Here the immensity of space\nassists us in our conception, limited though it be, of the for-ever of\neternity.[87]\n\nAll the planets of our system shine with reflected light, and the\nmoon, our satellite, also owes her silvery lustre to the sun\u2019s\nradiations. The fixed stars are, in all probability, suns shining from\nthe far distance of space, with their own self-emitted lights. By the\nphotometric researches of Dr. Wollaston, we learn, however, that it\nwould take 20,000 millions of such orbs as Sirius, the brightest of the\nfixed stars, to afford as much light as we derive from the sun. The\nsame observer has proved that the brightest effulgence of the full moon\nis yet 801,072 times less than the luminous power of our solar centre.\n\nThe cultivators of modern science are a bold race; not contented with\nendeavouring to understand the physical earth, they are endeavouring\nto comprehend the condition of the solar surface. The mind of man can\npenetrate far into nature, and, as it were, feel out the mysteries of\nuntraversed space. The astronomer learns of a peculiar condition of\nlight, which is termed polarisation, and he learns by this, too, that\nhe can determine if from a bright luminous disc the light is derived\nfrom a solid mass in a state of intense ignition, or from vapour in\nan incandescent condition. He adds a polarising apparatus to his\ntelescopes, and he determines that the light we derive from the sun\nis due to an envelope of vapour--burning, in all probability--only\nwith greater intensity, as the gas which we now employ. This\n_Photosphere_--as it has been called by the late French philosopher\nArago, is found to be subjected to violent disturbances, and the dark\nspots seen on the sun\u2019s disc are now known to be openings through this\nmysterious envelope of light, which enable us to look in upon the dark\nbody of the sun itself.\n\nLuminous phenomena may be produced by various means--chemical action\nis a source of light; and, under several circumstances in which the\nlaws of affinity are strongly exerted, a very intense luminous effect\nis produced. Under this head all the phenomena of combustion are\nincluded. In the electric spark we have the development of light;\nand the arc which is formed between charcoal points at the poles of\na powerful voltaic battery affords us the most intense artificial\nillumination with which we are acquainted. In addition to these, we\nhave the peculiar phenomena of phosphorescence arising from chemical,\ncalorific, electrical, actinic, and vital excitation, all of which must\nbe particularly examined.\n\nFrom whatever source we procure light, it is the same in character,\ndiffering only in intensity. In its action upon matter, we have the\nphenomena of transmission, of reflection, of refraction, of colour, of\npolarisation, and of vision, to engage our attention.\n\nA beam of white light falls upon a plate of colourless glass, and it\npasses freely through it, losing but little of its intensity; the\nlargest portion being lost by reflection from the first surface upon\nwhich the light impinges. If the glass is roughened by grinding, we\nlose more light by absorption and by reflection from the asperities of\nthe roughened surface; but if we cover that face with any oleaginous\nfluid, as, for instance, turpentine, its transparency is restored. We\nhave thus direct proof that transparency to light is due to molecular\ncondition. This may be most strikingly shown by an interesting\nexperiment of Sir David Brewster\u2019s:--\n\nIf a glass tube is filled with nitrous acid vapour, which is of a dull\nred colour, it admits freely the passage of the red and orange rays\nwith some of the others, and, if held upright in the sunshine, casts\na red shadow on the ground; by gently warming it with a spirit-lamp,\nwhilst in this position, it acquires a much deeper and blacker colour,\nand becomes almost impervious to any of the rays of light; but upon\ncooling it again recovers its transparency.\n\nIt has also been stated by the same exact experimentalist, that having\nbrought a purple glass to a red heat, its transparency was improved, so\nthat it transmitted green, yellow, and red rays, which it previously\nabsorbed; but the glass recovered its absorptive powers as it cooled.\nA piece of yellowish-green glass lost its transparency almost entirely\nby being heated. Native yellow orpiment becomes blood-red upon being\nwarmed, when nearly all but the red rays are absorbed; and pure\nphosphorus, which is of a pale yellow colour, and transmits freely all\nthe coloured rays upon being melted, becomes very dark, and transmits\nno light.\n\nChemistry affords numerous examples of a very slight change of\ncondition, producing absolute opacity in fluids which were previously\ndiaphanous.[88]\n\nCharcoal absorbs all the light which falls upon it, but in some\nof its states of combination, and in the diamond, which is pure\ncarbon, it is highly transparent. Gold and silver beaten into thin\nleaves are permeated by the green and blue rays, and the metals in\ncombination with acids are all of them more or less transparent. What\nbecomes of the light which falls upon and is absorbed by bodies,\nis a question which we cannot yet, notwithstanding the extensive\nobservations that have been made by some of the most gifted of men,\nanswer satisfactorily. In all probability, as already stated, it\nis permanently retained within their substances; and many of the\nexperiments of exciting light in bodies when in perfect darkness, by\nthe electric spark and other means, appear to support the idea of light\nbecoming latent or hidden.\n\nNo body is absolutely transparent; some light is lost in passing even\nthrough ethereal space, and still more in traversing our atmosphere.\n\nAmongst the most curious instances of absorption is that which is\nuniformly discovered in the solar spectrum, particularly when we\nexamine it with a telescope. We then find that the coloured rays are\ncrossed by a great number of dark bands or lines, giving no light;\nthese are generally called Fraunhofer\u2019s dark lines, as it was to the\nindefatigable exertions of that experimentalist, and by the aid of his\nbeautiful instruments, that most of them were discovered and measured,\nand enumerated, although they were previously noticed by Dr. Wollaston.\nIt is quite clear that those lines represent rays which have been\nabsorbed in their passage from the sun to the earth: although some\nof them have no doubt undergone absorption within the limits of the\nearth\u2019s atmosphere, we have every reason to believe, with Sir John\nHerschel, that the principal absorption takes place in the atmosphere\nof the sun.[89]\n\nIt has been proved by Dr. Miller, that the number of those dark\nlines is continually varying with the alteration of atmospheric\nconditions;[90] and the evidences which have been afforded, of peculiar\nstates of absorption by the gaseous envelope of the earth,--during the\nprosecution of investigations on the chemical agencies of the sun\u2019s\nrays,--are of a sufficiently convincing character.\n\nIt has been calculated by Bouguer, that if our atmosphere, in its\npurest state, could be extended rather more than 700 miles from the\nearth\u2019s surface instead of nearly 40, as it is at present, the sun\u2019s\nrays could not penetrate it, and this globe would roll on in darkness\nand silence, without a vestige of vegetable form or of animal life. In\nthe Hebrew version of the Mosaic History, the reading is, \u201cLet light\nappear:\u201d may not this really mean that the earth\u2019s atmosphere was so\ncleared of obstructing vapours, that the solar rays were enabled to\nreach the earth? The same calculation supposes that sea-water loses\nall its transparency at the depth of 730 feet; but a dim twilight must\nprevail much deeper in the ocean.\n\nThe researches of Professor Edward Forbes have proved, that at the\ndepth of 230 fathoms in the \u00c6gean sea, the few shelled animals that\nexist are colourless: no plants are found within that zone; and that\nindustrious naturalist fixes the zero of animal life of those waters at\nabout 300 fathoms.[91] Since these zones mark the rapidly diminishing\nlight, it is evident that where life ceases to be must be beyond the\nlimits to which life can penetrate.\n\nOur atmosphere, charged with aqueous vapour, serves to shield us from\nthe intense action of the solar powers. By it we are protected from\nthe destructive influences of the sun\u2019s light and heat; enjoy those\nmodified conditions which are most conducive to the healthful being of\norganic forms; to it we owe \u201cthe blue sky bending over all,\u201d and those\nbeauties of morning and evening twilight of which\n\n    ---- Sound and motion own the potent sway.\n    Responding to the charm with its own mystery.\n\nTo defective transparency, or rather to the different degrees of it, we\nmust attribute, in part, the colours of permeable media. Thus, a glass\nor fluid appears yellow to the eye, because it has the property of\nadmitting the permeation of a larger quantity of the yellow rays than\nof any others;--red, because the red rays pass it with the greatest\nfreedom; and so on for every other colour. In most cases the powers of\ntransmission and of reflection are similar; but it is not so in all; a\nvariety of fluor spar, which, while it transmits green light, reflects\nblue, and the precious opal, are striking instances to the contrary.\nSome glasses, which transmit yellow light have the singular power of\ndispersing blue rays from one surface; and a solution of quinine in\nwater acidulated with sulphuric acid, although perfectly transparent\nand colourless when held between the eye and the light, exhibits, if\nviewed in a particular direction, a lively cerulean tint. These effects\nbeing supposed to be due to the conditions of the surface, have been\ncalled _epipolic_ phenomena.[92]\n\nThe careful investigation of these phenomena has made us acquainted\nwith some very interesting facts, and indeed discovered to us a set\nof luminous rays which were previously unknown. The dispersion of\nblue light from the surface of some yellow glasses--such as have been\ncoloured by the oxide of silver--is of a different order from that\nwhich takes place with the solution of sulphate of quinine, or with\nthe fluor spar. The first depends upon a peculiar condition of the\nsurface, while the latter phenomena are due to a dispersion which\ntakes place _within_ the solid or fluid. In addition to the sulphate\nof quinine, and the fluor spar, we obtain the same results in a very\nmarked manner by a canary yellow glass, coloured with the oxide of\nuranium, and by a decoction of the inner bark of the horse-chesnut\ntree. Mr. Stokes, who has investigated this class of phenomena, and\nproposes to call it _Fluorescence_, from its being naturally seen in\nfluor-spar, has shown that the peculiar internal dispersion, and the\nconsequent alteration of the colour of the ray, is due to an alteration\nin its refrangibility. Whether this hypothesis prove to be the correct\none or not, it is certain that there exists a set of rays of far higher\nrefrangibility than those seen in the ordinary Newtonian spectrum. This\nmay be shown in the following manner: taking either of the solutions\nnamed, or a block of uranium glass, throw upon one face, by means of\na prism, a very pure spectrum. On looking _into_ the glass or fluid\nthere will be seen, commencing amidst the most refrangible rays, a\nnew set of spectral rays, struggling to make their way through the\nabsorbent medium. These are of a blue colour in the quinine or chesnut\nsolution, and green in the uranium glass, and are seen extending\nthemselves far beyond the most refrangible rays of the ordinary\nNewtonian spectrum. This is the space over which those rays which\nhave the power of producing chemical changes, such as are rendered\nfamiliar by the practice of Photography, are detected in their greatest\nactivity. It has, therefore, been supposed that these fluorescent rays\nare the chemical rays rendered luminous by the alteration of their\nrefrangibility. This view has received much support from the fact that\nthe extra spectral rays are crossed with numerous dark lines, and that\nin the chemical impressions these lines are marked by unchanged spaces\nwhich exactly coincide with them. There is, however, much doubt of the\ncorrectness of this, since, in the uranium glass of such a thickness\nthat these visible rays are quite absorbed, the chemical rays still\npass.\n\nHowever, the whole question requires, and is receiving, the most\nsearching investigation. The discovery of these phenomena, which are\nincluded under the term of Fluorescence, is of that interesting and\nimportant character, that it must be ranked as the most decided advance\nwhich has been made in physical optics since the days of Newton.\n\nIt is not improbable that those rays of such high refrangibility may,\nalthough they are under ordinary circumstances invisible to the human\neye, be adapted to produce the necessary degree of excitement upon\nwhich vision depends in the optic nerves of the night-roaming animals.\nThe bat, the owl, and the cat, may see in the gloom of night by the aid\nof rays which are invisible to, or inactive on the eyes of man, or of\nthose animals which require the light of day for perfect vision.\n\nIt is a general law of the radiant forces, that whenever they fall upon\nany surface, a portion is thrown back or reflected at the same time\nas other portions are absorbed or transmitted. Upon this peculiarity\nappear to depend the phenomena of natural colour in bodies.\n\nThe white light of the sun is well known to be composed of several\ncoloured rays. Or rather, according to the theory of undulations, when\nthe rate at which a ray vibrates is altered, a different sensation\nis produced upon the optic nerve. The analytical examination of\nthis question shows, that to produce a red colour the ray of light\nmust give 37,640 undulations in an inch, and 458,000000,000000 in\na second. Yellow light requires 44,000 undulations in an inch, and\n535,000000,000000 in a second; whilst the effect of blue results from\n51,110 undulations within an inch, and 622,000000,000000 of waves in\na second of time.[93] The determination of such points as these is\namong the highest refinements of science, and, when contrasted with the\nmost sublime efforts of the imagination, they must appear immeasurably\nsuperior.\n\nIf a body sends back white light unchanged, it appears white; if the\nsurface has the property of altering the vibration to that degree which\nis calculated to produce redness, the result is a red colour: the\nannihilation of the undulations produces blackness. By the other view,\nor the corpuscular hypothesis, the beam of white light is supposed to\nconsist of certain coloured rays, each of which has physical properties\npeculiar to itself, and thus is capable of producing different\nphysiological effects. These rays falling upon a transparent or an\nopaque body suffer more or less absorption, and being thus dissevered,\nwe have the effect of colour. A red body absorbs all the rays but the\nred; a blue surface, all but the blue; a yellow, all but the yellow;\nand a black surface absorbs the whole of the light which falls upon it.\n\nThat natural colours are the result of white light, and not innate\nproperties of the bodies themselves, is most conclusively shown by\nplacing coloured bodies in monochromatic light of another kind, when\nthey will appear either of the colour of that light, or, by absorbing\nit, become black; whereas, when placed in light of their own character,\nthe intensity of colour is greatly increasing.\n\nEvery surface has, therefore, a peculiar constitution, by which it\ngives rise to the diversified hues of nature. The rich and lively\ngreen, which so abundantly overspreads the surface of the earth, the\nvaried colours of the flowers, and the numberless tints of animals,\ntogether with all those of the productions of the mineral kingdom,\nand of the artificial combinations of chemical manufacture, result\nfrom powers by which the relations of matter to light are rendered\npermanent, until its physical conditions undergo some change.\n\nThere is a remarkable correspondence between the geographical position\nof a region and the colours of its plants and animals. Within the\ntropics, where\n\n    \u201cThe sun shines for ever unchangeably bright,\u201d\n\nthe darkest green prevails over the leaves of plants; the flowers\nand fruits are tinctured with colours of the deepest dye, whilst the\nplumage of the birds is of the most variegated description and of the\nrichest hues. In the people also of these climes there is manifested\na desire for the most striking colours, and their dresses have all\na distinguishing character, not of shape merely, but of chromatic\narrangement. In the temperate climates everything is of a more subdued\nvariety: the flowers are less bright of hue; the prevailing tint of the\nwinged tribes is a russet brown; and the dresses of the inhabitants of\nthese regions are of a sombre character. In the colder portions of the\nearth there is but little colour; the flowers are generally white or\nyellow, and the animals exhibit no other contrast than that which white\nand black afford. A chromatic scale might be formed, its maximum point\nbeing at the equator, and its minimum at the poles.[94]\n\nThe influence of light on the colours of organized creation is well\nshown in the sea. Near the shores we find sea-weeds of the most\nbeautiful hues, particularly on the rocks which are left dry by the\ntides; and the rich tints of the actini\u00e6, which inhabit shallow water,\nmust have been often observed. The fishes which swim near the surface\nare also distinguished by the variety of their colours, whereas those\nwhich live at greater depths are grey, brown, or black. It has been\nfound that after a certain depth, where the quantity of light is so\nreduced that a mere twilight prevails, the inhabitants of the ocean\nbecome nearly colourless. That the sun\u2019s ray alone gives to plants the\nproperty of reflecting colour is proved by the process of blanching, or\n_etiolation_, produced by artificially excluding the light.\n\nBy a triangular piece of glass--a prism,--we are enabled to resolve\nlight into its ultimate rays. The white pencil of light which falls\non the first surface of the prism is bent from its path, and coloured\nbands of different colours are obtained. These bands or rays observe a\ncurious constancy in their positions: the red ray is always the least\nbent out of the straight path: the yellow class comes next in the\norder of refrangibility; and the blue are the most diverted from the\nvertex of the prism. The largest amount of illuminating power exists\nin the yellow ray, and it diminishes towards either end.[95] It is not\nuninteresting to observe something like the same variety of colour\noccurring at each end of the prismatic spectrum. The strict order\nin which the pure and mixed coloured rays present themselves is as\nfollows:--\n\n1. The _extreme red_: a ray which can only be discovered when the eye\nis protected from the glare of the other rays by a cobalt blue glass,\nis of a crimson character--a mixture of the _red_ and the _blue_, red\npredominating.[96]\n\n2. The _red_: the first ray visible under ordinary circumstances.\n\n3. The _orange_: red passing into and combining with yellow.\n\n4. The _yellow_: the most intensely luminous of the rays.\n\n5. The _green_: the yellow passing into and blending with the blue.\n\n6. The _blue_: in which the light very rapidly diminishes.\n\n7. The _indigo_: the dark intensity of blue.\n\n8. The _violet_: the _blue_ mingled again with the _red_--blue being in\nexcess.\n\n9. The _lavender grey_: a neutral tint, produced by the combination of\nthe red, blue, and yellow rays, which is discovered most easily when\nthe spectrum is thrown upon a sheet of turmeric paper.\n\n10. The fluorescent rays: which are either a _pure silvery blue_ or a\ndelicate _green_.\n\nNewton regarded the spectrum as consisting of seven colours of\ndefinite and unvarying refrangibility. Brewster and others appear to\nhave detected a great diffusion of the colours over the spectrum,\nand regard white light as consisting only of three rays, which in the\nprismatic images overlap each other; and from these--red, yellow,\nand blue--all the others can be formed by combination in varying\nproportions. The truth will probably be found to be, that the ordinary\nprismatic spectrum is a compound of two spectra:--that is, as we have\nthe ordinary rainbow, and a supplementary bow, the colours of which are\ninverted, so the extraordinary may be somewhat masked by the intense\nlight of the ordinary spectrum; and yet by overlapping produce the\nvariations of colour in the rays. We have already examined the heating\npower found in these coloured bands, which, although shown to be in a\nremarkable manner in constant agreement with the colour of a particular\nray, is not directly connected with it; that is, not as the effect of a\ncause, or the contrary. The chemical action of the solar rays, to which\nfrom its important bearings we shall devote a separate chapter, has, in\nlike manner with heat, been confounded with the sun\u2019s luminous power;\nbut although associated with light and heat, and modified by their\npresence, it must be distinguished from them.\n\nWe find the maximum of heat at one end of the spectrum, and that of\nchemical excitation at the other--luminous power observing a mean point\nbetween them. Without doubt we have these powers acting reciprocally,\nmodifying all the phenomena of each other, and thus giving rise to the\ndifficulties which beset the inquirer on every side.\n\nWe have beautiful natural illustrations of luminous refraction in\nthe rainbow and in the halo: in both cases the rays of light being\nseparated by the refractive power of the falling rain drop, or the\nvesicles which form the moisture constituting a fog. In the simple toy\nof the child--the soap-bubble floating upon the air--the philosopher\nfinds subjects for his contemplation; and from the unrivalled play of\ncolours which he discovers in that attenuated film, he learns that the\nvarying thicknesses of surfaces influence, in a most remarkable manner,\nthe colours of the sunbeam. Films of oil floating upon water present\nsimilar appearances; and the colours developed in tempering steel\nare due entirely to the thickness of the oxidized surface produced\nby heat. There have lately been introduced some beautiful specimens\nof paper rendered richly iridescent by the following process:--A\nsolution of a gum resin in chloroform is floated upon water, where\nit forms a film giving all the colours of Newton\u2019s rings. A sheet of\npaper which has been previously sunk in the water is carefully lifted,\nand the film thus removed adheres with great firmness to the paper,\nand produces this rich and curious play of colour. The rich tints\nupon mother-of-pearl, in the feathers of many birds, the rings seen\nin the cracks of rock-crystal, or between the unequal faces of two\npieces of glass, and produced by many chemical and indeed mechanical\noperations--are all owing to the same cause;--the refraction of the\nluminous pencil by the condition of the film or surface. If we take\none of those steel ornaments which are formed by being covered with\nan immense number of fine lines, it will be evident that these stri\u00e6\npresent many different angles of reflection, and that, consequently,\nthe rays thrown back will, at some point or another, have a tendency\nto cross each other. The result of this is, that the quantity of\nlight is augmented at some points of intersection, and annihilated at\nothers.[97] Out of the investigation of the phenomena of diffraction,\nof the effects of thin and thick plates upon light, and the results of\ninterference, has arisen the discovery of one of the most remarkable\nconditions within the range of physical science.\n\n_Two bright lights may be made to produce darkness._--If two pencils\nof light radiate from two spots very close to each other in such a\nmanner that they cross each other at a given point, any object placed\nat that line of interference will be illuminated with the sum of the\ntwo luminous pencils. If we suppose those rays to move in waves, and\nthe elevation of the wave to represent the maximum of luminous effect,\nthen the two waves meeting, when they are both at the height of their\nundulation, will necessarily produce a spot of greater intensity. If\nnow we so arrange the points of radiation, that the systems of luminous\nwaves proceed irregularly, and that one arrives at the screen half an\nundulation before the other, the one in elevation falling into the\ndepression of the other, a mutual annihilation is the consequence. This\nfact, paradoxical as it may appear, was broadly stated by Grimaldi,\nin the description of his experiments on the inflection of light, and\nhas been observed by many others. The vibratory hypothesis, seizing\nupon the analogy presented by two systems of waves in water, explains\nthis plausibly, and many similar phenomena of what is called the\n_interference of light_; but still upon examination it does not appear\nthat the explanation is quite free from objection.[98]\n\nAnother theory, not altogether new to us, it being indicated in Mayer\u2019s\nhypothesis of three primary colours (1775), and to be found as a\nproblem in some of the Encyclop\u00e6dias of the last century, has been put\nforth, in a very original manner, by that master-mind of intellectual\nGermany, Goethe; and from the very comprehensive views which this\npoet-philosopher has taken of both animal and vegetable physiology\n(views which have been adopted by some of the first naturalists of\nEurope), we are bound to receive his theory of colours with every\nrespect and attention.\n\nGoethe regards colour as the \u201cthinning\u201d of light; for example, by\nobstructing a portion of white light, yellow is produced; by reducing\nit still farther, red is supposed to result; and by yet farther\nretarding the free passage of the beam, we procure a blue colour, which\nis the next remove from blackness, or the absence of light. There is\ntruth in this; it bears about it a simplicity which will satisfy many\nminds; by it many of the phenomena of colour may be explained: but it\nis insufficient for any interpretation of several of those laws to\nwhich the other theories do give us some insight.\n\nNewton may have allowed himself to be misled by the analogy presented\nbetween the seven rays of the spectrum and the notes in an octave.\nThe mystic number, seven, may have clung like a fibre of the web of\nsuperstition to the cloak of the great philosopher; but the attack made\nby Goethe upon the Newtonian philosophy betrays the melancholy fact of\nhis being diseased with the lamentable weakness of too many exalted\nminds--an overweening self-esteem.\n\nThe polarization of light, as it has been unfortunately\ncalled--unfortunately, as conveying an idea of determinate and\ndifferent points or poles, which only exists in hypothetical\nanalogy--presents to us a class of phenomena which promise to unclose\nthe mysterious doors of the molecular constitution of bodies.\n\nThis remarkable condition, as produced by the reflection of light from\nglass at a particular angle, was first observed by Malus, in 1808,[99]\nwhen amusing himself by looking at the beams of the setting sun,\nreflected from the windows of the Luxembourg Palace through a double\nrefracting prism. He observed that when the prism was in one position,\nthe windows with their golden rays were visible; but that turned\nround a quarter of a circle from that position, the reflected rays\ndisappeared although the windows were still seen.\n\nThe phenomenon of double refraction was noticed, in the first instance,\nby Erasmus Bartholin, in Iceland-spar, a crystal the primary form of\nwhich is a rhombohedron; who perceived that the two images produced by\nthis body were not in the same physical conditions.[100] It was also\nstudied by Huyghens and Sir Isaac Newton, and to our countryman we owe\nthe singular idea that a ray of light emerging from such a crystal\nhas _sides_. This breaking up of the beam of light into two,--which\nis shown by looking through a pin-hole on a card through a crystal of\nIceland spar, when two holes become visible, is due to the different\nstates of tension in which the different layers constituting the\ncrystal exist.\n\nIn thus separating the ray of light into two rays, the condition\ncalled polarisation has been produced, and by experiment we discover\nthat the single ray has properties different from those of the compound\nor ordinary ray.\n\nIt is somewhat difficult to explain what is meant by, and what are the\nconditions of, _polarised light_. In the first instance let us see by\nwhat methods this peculiar state may be brought about.\n\nIf we reflect a ray of light from the surface of any body, fluid or\nsolid, but not metallic, at an angle between 53\u00b0 and 68\u00b0 it undergoes\nwhat has been called _plane polarisation_. It may also be produced by\nthe refraction of light from several refracting surfaces acting upon\nthe pencil of light in succession; as by a bundle of plates of glass.\nEach surface polarises a portion of the pencil, and the number of\nplates necessary to polarise a whole beam depends upon the intensity of\nthe beam and the angle of incidence. Thus, the light of a wax candle\nis wholly polarised by forty-seven plates of glass at an angle of 40\u00b0\n41'; while at an angle of 79\u00b0 11' it is polarised by eight plates.\nAgain, plane polarisation may be produced by the double refraction of\ncrystals. Each of the two pencils is polarised, like light reflected\nfrom glass at an angle of 56\u00b0 45', but in opposite planes.\n\nNon-scientific readers will still ask,--What is this mysterious\ncondition of light which is produced by reflection and refraction at\npeculiar angles to the incident ray. It is one of the most difficult of\nproblems to express in popular language. The conditions are, however,\nthese:--\n\nAn ordinary ray of light will be reflected from a reflecting surface at\nwhatever angle that surface may be placed in relation to the incident\nbeam.\n\nA polarised ray of light is not reflected in all positions of the\nreflecting surface.\n\nAn ordinary ray of light is freely transmitted through a transparent\nmedium, as glass, in whatever position it may be placed relative to the\nsource of light.\n\nA polarised ray of light is not transmitted in all the positions of the\npermeable medium.\n\nSupposing a plate of glass is presented at the angle 56\u00b0 to a polarised\nray, and the plane of incidence or reflexion is at right angles to the\nplane of polarisation of the ray, _no light is reflected_. If we turn\nthe plate of glass round through 90\u00b0, when the plane of reflexion is\nparallel to that of polarisation _the light is reflected_. If we turn\nthe plate round another 90\u00b0, so that the plane of reflexion and of\npolarisation are parallel to each other, again _no light is reflected_;\nand if we turn it through another 90\u00b0 the reflection of the ray again\ntakes place.\n\nPrecisely the same result takes place when, instead of being reflected,\nthe polarised ray is transmitted.\n\nSome substances have peculiar polarizing powers: _the tourmaline_ is a\nfamiliar example. If a slice of tourmaline is taken, and we look at a\ncommon pencil of light through it, we see it in whatever position we\nmay place the transparent medium. If, however, we look at a pencil of\npolarised light, and turn the crystal round, it will be found that in\ntwo positions the light is stopped, and that in two other positions it\npasses freely through it to the eye.\n\nBy way of endeavouring to conceive something of what may be the\nconditions which determine this very mysterious state, let us suppose\neach ray of light to vibrate in two planes at right angles to each\nother: one wave being vertical and the other horizontal. We have many\nexamples of this compound motion. The mast of a ship, by the force with\nwhich she is urged through the water, describes a vertical wave, while\nby the roll of the billows across which she sails, a lateral undulation\nis produced at the same time. We may sometimes observe the same thing\nwhen a field of corn is agitated by a shifting wind on a gusty day.\n\nThe hypothesis therefore is, that every ray of ordinary light consists\nof two rays vibrating in different planes; and that these rays,\nseparated one from the other, have the physical conditions which we\ncall _polarized_.\n\nThe most transparent bodies may be regarded as being made up of atoms\narranged in certain planes. Suppose the plane of lamination of any\nsubstance to be vertical in position, it would appear that the ray\nwhich has a vertical motion passes it freely, whereas if we turn the\nbody round so that the planes of lamination are at right angles to the\nplane of vibration of the ray, it cannot pass.\n\nThat some action similar to that which it is here endeavoured to\nexpress in popular language does take place, is proved by the\ncorrectness of the results deduced by rigid mathematical analyses\nfounded on this hypothesis.\n\nThere are two other conditions of the polarization of light--called\n_circular_ and _elliptical_ polarization. The first is produced by\nlight when it is twice reflected from the second surface of bodies at\ntheir angle of maximum polarization, and the second by reflexions from\nthe surfaces of metals at angles varying from 70\u00b0 45' to 78\u00b0 30'. The\nmotion of the wave in the first is supposed to be circular, or to be\nthat which is represented by looking along the centre of a corkscrew\nas it is turned round. At every turn of the medium effecting _circular\npolarization_ the colour of the ray of light is changed after a uniform\norder. If turned in one direction, they change through red, orange,\nyellow, green, and violet; and if in the other direction, the colours\nappear in the contrary order.\n\nThe variety of striking effects produced by the polarization of light;\nthe unexpected results which have sprung from the investigation of the\nlaws by which it is regulated; and the singular beauty of many of its\nphenomena, have made it one of the most attractive subjects of modern\nscience.\n\nOrdinary light passes through transparent bodies without producing any\nvery striking effects in its passage; but this _extraordinary_ beam\nof light has the power of insinuating itself between the molecules\nof bodies, and by illuminating them, and giving them every variety\nof prismatic hue, of enabling the eye to detect something of the\nstructure of the mass. The chromatic phenomena of polarized light are\nso striking, that no description can convey an adequate idea of their\ncharacter.\n\nSpectra more beautiful and intense than the prismatic image,--systems\nof rings far excelling those of thin plates,--and forms of the most\nsymmetric order, are constantly presenting themselves, as the polarized\nray is passed through various transparent substances; the path of the\nray indicating whether the crystal has been formed round a single\nnucleus or axis, or whether it has been produced by aggregation\naround two axes. The coloured rings, and the dark or luminous crosses\nwhich distinguish the path of the polarized ray, are respectively\ndue to different states of tension amongst the particles, although\nthose differences are so slight, that no other means is of sufficient\ndelicacy to detect the variation.\n\nThe poetry which surrounds these, in every way, mysterious conditions\nof the solar beam, is such, that it is with difficulty that imagination\nis restrained by the stern features of truth. The uses of this peculiar\nproperty in great natural phenomena are not yet made known to us; but,\nsince we find on every side of us the natural conditions for thus\nseparating the beam of light, and effecting its polarization, there\nmust certainly be some most important end for which it is designed by\nHim who said, \u201cLet there be Light.\u201d\n\nIt must not be forgotten that we have at command the means of showing\nthat the chromatic phenomena of polarized light are due to atomic\narrangement. By altering the molecular arrangement of transparent\nbodies, either by heat or by mere mechanical pressure, the unequal\ntension or strain of the particles is at once indicated by means of\nthe polarized ray of light and its rings of colour. Differences in the\nchemical constitution of bodies, too slight to be discovered by any\nother mode of analysis, can be most readily and certainly detected by\nthis luminous investigator of the molecular forces.[101]\n\nAlthough we cannot enter into an examination of all the conditions\ninvolved in the polarization of, and the action of matter on, ordinary\nlight, it will be readily conceived, from what has been already stated,\nthat some most important properties are indicated, beyond those which\nscience has made known.\n\nAlmost every substance in nature, in some definite position, appears\nto have the power of producing this change upon the solar ray, as\nmay be satisfactorily shown by examining them with a polarizing\napparatus.[102] The sky at all times furnishes polarized light, which\nis most intense where it is blue and unclouded, and the point of\nmaximum polarization is varied according to the relative position of\nthe sun and the observer. A knowledge of this fact has led to the\nconstruction of a \u201cSolar Clock,\u201d[103] with which the hour can be\nreadily determined by examining the polarized condition of the sky.\nIt has been stated, that chemical change on the Daguerreotype plates\nand on photographic papers is more readily produced by the polarized\nthan by the ordinary sunbeam.[104] If this fact be established by\nfuture investigations, we advance a step towards the discovery so much\ndesiderated of the part it plays in natural operations.\n\nThe refined and accurate investigations of Dr. Faraday stand\nprominently forward amid those which will redeem the present age from\nthe charge of being superficial, and they will, through all time, be\nreferred to as illustrious examples of the influence of a love of truth\nfor truth\u2019s sake, in entire independence of the marketable value, which\nit has been unfortunately too much the fashion to regard. The searching\nexamination made by this \u201cinterpreter of nature\u201d into the phenomena\nof electricity in all its forms, has led him onward to trace what\nconnexion, if any, existed between this great natural agent and the\nluminous principle.\n\nBy employing that subtile analyzer, a polarized ray, Dr. Faraday\nhas been enabled to detect and exhibit effects of a most startling\ncharacter. He has proved magnetism to have the power of influencing a\nray of light in its passage through transparent bodies. A polarized ray\nis passed through a piece of glass or a crystal, or along the length\nof a tube filled with some transparent fluid, and the line of its path\ncarefully observed; if, when this is done, the solid or fluid body is\nbrought under powerful magnetic influence, such as we have at command\nby making a very energetic voltaic current circulate around a bar of\nsoft iron, it will be found that the polarized light is disturbed;\nthat, indeed, it does not permeate the medium along the same line.[105]\nThis effect is most strikingly shown in bodies of the greatest density,\nand diminished in fluids, the particles of which are easily moveable\nover each other, and has not hitherto been observed in any gaseous\nmedium. The question, therefore, arises,--does magnetism act directly\nupon the ray of light, or only indirectly, by producing a molecular\nchange in the body through which the ray is passing? This question,\nso important in its bearings upon the connexion between the great\nphysical powers, will, no doubt, before long receive a satisfactory\nreply. A medium is necessary to the production of the result, and, as\nthe density of the medium increases, the effect is enlarged: it would\ntherefore appear to be due to a disturbance by magnetic force of the\nparticles which constitute the medium employed.\n\nWithout any desire to generalize too hastily, we cannot but express\na feeling,--amounting to a certainty in our own mind,--that those\nmanifestations of luminous power, connected with the phenomena of\nterrestrial magnetism, which are so evident in all the circumstances\nattendant upon the exhibition of Aurora Borealis, and those luminous\nclouds which are often seen, independent of the Northern Lights, that\na very intimate, relation exists between the solar radiations and that\npower which so strangely gives polarity to this globe of ours.\n\nIn connexion with the mysterious subject of solar light, it is\nimportant that we should occupy a brief space in these pages with the\nphenomena of vision, which is so directly dependent upon luminous\nradiation.\n\nThe human eye has been rightly called the \u201cmasterpiece of divine\nmechanism;\u201d its structure is complicated, yet all the adjustments of\nits parts are as simple as they are perfect. The eye-ball consists of\nfour coats. The cornea is the transparent coat in front of the globe;\nit is the first optical surface, and this is attached to the sclerotic\nmembrane, filling up the circular aperture in the white of the eye;\nthe choroid coat is a very delicate membrane, lining the sclerotic,\nand covered with a perfectly black pigment on the inside; and close to\nthis lies the most delicately reticulated membrane, the retina, which\nis, indeed, an extension of the optic nerve. These coats enclose three\nhumours,--the aqueous, the vitreous, and the crystalline humours.\n\nThe eye, in its more superficial mechanical arrangements, presents\nexactly the same character as a camera obscura, the cornea and\ncrystalline lens receiving the images of objects refracting and\ninverting them; but how infinitely more beautiful are all the\narrangements of the organ of vision than the dark chamber of Baptista\nPorta![106] The humours of the eye are for the purpose of correcting\nthe aberrations of light, which are so evident in ordinary lenses,\nand for giving to the whole an achromatic character. Both spherical\nand chromatic aberration are corrected, the latter not entirely, and\nby the agency of the cornea and the crystalline lens perfect images\nare depicted on the retina, in a similar way to those very charming\npictures which present themselves in the table of the camera obscura.\n\nThe seat of vision has been generally supposed to be the retina;\nbut Mariotte has shown that the base of the optic nerve, which is\nimmediately connected with the retina, is incapable of conveying an\nimpression to the brain. The choroid coat, which lies immediately\nbehind the retina, is regarded by Mariotte and Bernoulli as the more\nprobable seat of vision. The retina, being transparent, offers no\nobstruction to the passage of the light onward to the black surface of\nthe choroid coat, from which the vibrations are, in all probability,\ncommunicated to the retina and conveyed to the brain. Howbeit, upon one\nor the other of these delicate coats a distinct image is impressed\nby light, and the communication made with the brain possibly by a\nvibratory action. We may trace up the phenomena of vision to this\npoint; we may conceive undulations of light, differing in velocity and\nlength of wave, occasioning corresponding tremors in the neuralgic\nsystem of the eye; but how these vibrations are to communicate\ncorrect impressions of length, breadth, and thickness, no one has yet\nundertaken to explain.\n\nIt has, however, been justly said by Herschel:--\n\n\u201cIt is the boast of science to have been able to trace so far the\nrefined contrivances of this most admirable organ, not its shame to\nfind something still concealed from scrutiny; for, however anatomists\nmay differ on points of structure, or physiologists dispute on modes\nof action, there is that in what we _do_ understand of the formation\nof the eye, so similar, and yet so infinitely superior to a product\nof human ingenuity; such thought, such care, such refinement, such\nadvantage taken of the properties of natural agents used as mere\ninstruments for accomplishing a given end, as force upon us a\nconviction of deliberate choice and premeditated design, more strongly,\nperhaps, than any single contrivance to be found whether in art or\nnature, and renders its study an object of the greatest interest.\u201d[107]\n\nHas the reader ever asked himself why it is, having two eyes, and\nconsequently two pictures produced upon the tablets of vision, that we\nsee only one object? According to the law of visible direction, all the\nrays passing through the crystalline lenses converge to one point upon\nthe retina,--and as the two images are coincident and nearly identical,\nthey can only produce the sensation of one upon the brain.\n\nWhen we look at any round object, as the ornamented moderator lamp\nbefore us, first with one eye, and then with the other, we discover\nthat, with the right eye, we see most of the right-hand side of the\nlamp, and with the left eye more of the left-hand side. These two\nimages are combined, and we see an object which we know to be round.\n\nThis is illustrated in a most interesting manner by the little optical\ninstrument, _the Stereoscope_. It consists either of two mirrors placed\neach at an angle of 45\u00b0, or of two semi-lenses turned with their curved\nsides towards each other. To view its phenomena, two pictures are\nobtained by the camera obscura on photographic paper of any object in\ntwo positions, corresponding with the conditions of viewing it with the\ntwo eyes. By the mirrors or the lenses these dissimilar pictures are\ncombined within the eye, and the vision of an actually solid object is\nproduced from the pictures represented on a plane surface. Hence the\nname of the instrument; which signifies, _Solid I see_.\n\nAnalogy is often of great value in indicating the direction in which to\nseek for a truth; but analogical evidence, unless where the resemblance\nis very striking, should be received with caution. Mankind are so ready\nto leap to conclusions without the labour necessary for a faithful\nelucidation of the truth, that too often a few points of resemblance\nare seized upon, and an inference is drawn which is calculated to\nmislead.\n\nThere is an idea that the phenomena of sound bear a relation to those\nof light,--that there exists a resemblance between the chromatic\nand the diatonic scales. Sound, we know, is conveyed by the beating\nof material particles--the air--upon the auditory membrane of the\near, which have been set in motion by some distant disturbance of\nthe medium through which it passes. Light has been supposed to act\non the optic nerve in the same manner. If we imagine colour to be\nthe result of vibrations of different velocities and lengths, we can\nunderstand that under some of these tremors, first established on the\nnerves, and through them conveyed to the brain, sensations of pain\nor pleasure may result, in the same way as sharp or subdued sounds\nare disagreeable or otherwise. Intensely coloured bodies do make an\nimpression upon perfectly blind men; and those who, being born blind,\nknow no condition of light or colour, will point out a difference\nbetween strongly illuminated red and yellow media. When the eyes are\nclosed we are sensible to luminous influence, and even to differences\nof colour. We must consequently infer that light produces some peculiar\naction upon the system of nerves in general; this may or may not\nbe independent of the chemical agency of the solar radiations; but\ncertainly the excitement is not owing to any calorific influence. The\nsystem of nerves in the eye is more delicately organized, and of course\npeculiarly adapted to all the necessities of vision.\n\nThus far some analogy does appear to exist between light and sound;\nbut the phenomena of the one are so much more refined than those of\nthe other--the impressions being all of them of a far more complicated\ncharacter, that we must not be led too far by the analogical evidence\nin referring light, like sound, to mere material motion.\n\nIt was a beautiful idea that real impressions of external objects\nare made upon the seat of vision, and that they are viewed, as in a\npicture, by something behind the screen,--that these pictures become\ndormant, but are capable of being revived by the operations of the mind\nin peculiar conditions; but we can only regard it as a philosophical\nspeculation of a poetic character, the truth or falsehood of which we\nare never likely to be enabled to establish.[108]\n\nThat which sees will never itself be visible. The secret principle\nof sensation,--the mystery of the life that is in us,--will never be\nunfolded to finite minds.\n\nNumerous experiments have been made from time to time on the influence\nof light upon animal life. It has been proved that the excitement of\nthe solar rays is too great for the healthful growth of young animals;\nbut, at the same time, it appears probable that the development of\nthe functional organs of animals requires, in some way, the influence\nof the solar rays. This might, indeed, have been inferred from the\ndiscovery that animal life ceases in situations from which light is\nabsolutely excluded. The instance of the Proteus of the Illyrian lakes\nmay appear against this conclusion. This remarkable creature is found\nin the deep and dark recesses of the calcareous rocks of Adelsburg, at\nSittich; and it is stated, also in Sicily, and in the Mammoth caves\nof Kentucky. Sir Humphry Davy describes the Proteus anguinus as \u201can\nanimal to whom the presence of light is not essential, and who can\nlive indifferently in air and in water, on the surface of the rock,\nor in the depths of the mud.\u201d The geological character of rocks,\nhowever, renders it extremely probable that these animals may have\ndescended with the water, percolating through fissures from very near\nthe surface of the ground. All the facts with which science has made us\nacquainted--and both natural and physical science has been labouring\nwith most untiring industry in the pursuit of truth--go to prove\nthat light is absolutely necessary to organization. It is possible\nthe influence of the solar radiations may extend beyond the powers\nof the human senses to detect luminous or thermic action, and that\nconsequently a development of animal and vegetable forms may occur\nwhere the human eye can detect no light; and under such conditions\nthe Proteus may be produced in its cavernous abodes, and also those\ncreatures which live buried deep in mud. Some further consideration of\nthe probable agency of light will occupy us, when we come to examine\nthe phenomena of vital forces.\n\nLight is essentially necessary to vegetable life; and to it science\nrefers the powers which the plant possesses of separating carbon from\nthe air breathed by the leaves, and secreting it within its tissues for\nthe purpose of adding to its woody structure. As, however, we have, in\nthe growing plant, the action of several physical powers exerted to\ndifferent ends at the same time, the remarkable facts which connect\nthemselves with vegetable chemistry and physiology are deferred for a\nseparate examination.\n\nThe power of the solar rays to produce in bodies that peculiar gleaming\nlight which we call phosphorescence, and the curious conditions under\nwhich this phenomenon is sometimes apparent, independent of the sun\u2019s\ndirect influence, present a very remarkable chapter in the science of\nluminous powers.\n\nThe phosphorescence of animals is amongst the most surprising of\nnature\u2019s phenomena, and it is not the less so from our almost entire\nignorance of the cause of it. Many very poetical fancies have been\napplied in description of these luminous creations; and imagination\nhas found reason why they should be gifted with these extraordinary\npowers. The glow-worm lights her lamp to lure her lover to her bower,\nand the luminous animalcules of the ocean are employed in lighting up\nthe fathomless depths where the sun\u2019s rays cannot penetrate, to aid its\nmonsters in their search for prey. \u201cThe lamp of love--the pharos--the\ntelegraph of the night,--which scintillates and marks, in the silence\nof darkness, the spot appointed for the lover\u2019s rendezvous,\u201d[109] is\nbut a pretty fiction; for the glow-worm shines in its infant state,\nin that of the larva, and when in its aurelian condition. Of the\ndark depths of the ocean it may be safely affirmed that no organized\ncreation lives or moves in its grave-like silence to require this\nfairy aid. Fiction has frequently borrowed her creations from science.\nIn these cases science appears to have made free with the rights of\nfiction.\n\nThe glow-worms (_lampyris noctiluca_), it is well known, have the\npower of emitting from their bodies a beautiful pale bluish-white\nlight, shining during the hours of night in the hedge-row, like crystal\nspheres. It appears, from the observations of naturalists, that these\ninsects never exhibit their light without some motion of the body or\nlegs;--from this it would seem that the phosphorescence was dependent\nupon nervous action, regulated at pleasure by the insect; for they\ncertainly have the power of obscuring it entirely. If the glow-worm is\ncrushed, and the hands or face are rubbed with it, luminous streaks,\nsimilar to those produced by phosphorus, appear. They shine with\ngreatly increased brilliancy in oxygen gas and in nitrous oxide. From\nthese facts may we not infer that the process by which this luminosity\nis produced, whatever it may be, has a strong resemblance to that of\nrespiration?\n\nThere are several varieties of flies, and three species of beetles of\nthe genus _Elater_, which have the power of emitting luminous rays.\nThe great lantern-fly of South America is one of the most brilliant, a\nsingle insect giving sufficient light to enable a person to read. In\nSurinam a very numerous class of these insects are found, which often\nilluminate the air in a remarkable manner. In some of the bogs of\nIreland a worm exists which gives out a bright green light; and there\nare many other kinds of creatures which, under certain circumstances,\nbecome luminous in the dark. This is always dependent upon vitality;\nfor all these animals, when deprived of life, cease to shine.\n\nAt the same time we have many very curious instances of phosphorescence\nin dead animal and vegetable matter; the lobster among the Crustacea,\nand the whiting among fishes, are striking examples; decayed wood\nalso emits much light under certain conditions of the atmosphere.\nThis development of light does not appear to be at all dependent upon\nputrefaction; indeed, as this process progresses, the luminosity\ndiminishes. We cannot but imagine that this light is owing, in the\nfirst place, to direct absorption by, and fixation within, the\ncorpuscular structure of those bodies, and that it is developed by the\ndecomposition of the particles under the influence of our oxygenous\natmosphere.\n\nThe pale light emitted by phosphorus in the dark is well known; and\nthis is evidently only a species of slow combustion, a combination of\nthe phosphorus with the oxygen of the air. Where there is no oxygen,\nphosphorus will not shine; its combustion in chlorine or iodine vapour\nis a phenomenon of a totally different character from that which we are\nnow considering. This phosphorescence of animal and vegetable matter\nhas been regarded as something different from the slow combustion of\nphosphorus; but, upon examination, all the chemical conditions are\nfound to be the same, and it is certainly due to a similar chemical\nchange.\n\nThe luminous matter of the dead whiting or the mackerel may be\nseparated by a solution of common salt or of sulphate of magnesia; by\nconcentrating these solutions the light disappears; but it is again\nemitted when the fluid is diluted. The entire subject is, however,\ninvolved in the mystery of ignorance, although it is a matter quite\nwithin the scope of any industrious observer. The self-emitted light\nof the carbuncle of the romancer is realized in these remarkable\nphenomena.\n\nThe phosphorescence of some plants and flowers is not, perhaps, of\nthe same order as that which belongs to either of the conditions we\nhave been considering. It appears to be due rather to an absorption of\nlight and its subsequent liberation. If a nasturtium is plucked during\nsunshine, and carried into a dark room, the eye, after it has reposed\nfor a short time, will discover the flower by a light emitted from its\nleaves.\n\nThe following remarkable example, and an explanation of it by the poet\nGoethe, is instructive:--\n\n\u201cOn the 19th of June, 1799, late in the evening, when the twilight was\ndeepening into a clear night, as I was walking up and down the garden\nwith a friend, we very distinctly observed a flame-like appearance\nnear the oriental poppy, the flowers of which are remarkable for their\npowerful red colour. We approached the place, and looked attentively\nat the flowers, but could perceive nothing further, till at last, by\npassing and repassing repeatedly, while we looked side-ways on them, we\nsucceeded in renewing the appearance as often as we pleased. It proved\nto be a physiological phenomenon, and the apparent corruscation was\nnothing but the spectrum of the flower in the complementary blue-green\ncolour. The twilight accounts for the eye being in a perfect state\nof repose, and thus very susceptible, and the colour of the poppy is\nsufficiently powerful in the summer twilight of the longest days to act\nwith full effect, and produce a complementary image.\u201d[110]\n\nThe leaves of the _\u0153nothera macrocarpa_ are said to exhibit phosphoric\nlight when the air is highly charged with electricity. The agarics\nof the olive-grounds of Montpelier have been observed to be luminous\nat night; but they are said to exhibit no light, even in darkness,\n_during the day_. The subterranean passages of the coal mines near\nDresden are illuminated by the phosphorescent light of the _rhizomorpha\nphosphoreus_, a peculiar fungus. On the leaves of the Pindoba palm, a\nspecies of agaric grows which is exceedingly luminous at night; and\nmany varieties of the lichens, creeping along the roofs of caverns,\nlend to them an air of enchantment by the soft and clear light which\nthey diffuse. In a small cave near Penryn, a luminous moss is abundant;\nand it is also found in the mines of Hesse. According to Heinzmann, the\n_rhizomorpha subterranea_ and _aidul\u00e6_ are also phosphorescent.\n\nIt is but lately that a plant which abounds in the jungles in the\nMadura district of the East Indies was sent to this country, which,\nalthough dead, was remarkably phosphorescent; and, when in the\nliving state, the light which it emitted was extraordinarily vivid,\nilluminating the ground for some distance. Those remarkable effects\nmay be due, in some cases, to the separation of phosphuretted hydrogen\nfrom decomposing matter, and, in others, to some peculiar electric\nmanifestation.\n\nThe phosphorescence of the sea, or that condition called by fishermen\n_brimy_, when the surface, being struck by an oar, or the paddle-wheels\nof a steamer, gives out large quantities of light, has been attributed\nto the presence of myriads of minute insects which have the power\nof emitting light when irritated. The night-shining nereis (_Nereis\nnoctiluca_) emits a light of great brilliancy, as do several kinds of\nthe mollusca. The nereides attach themselves to the scales of fishes,\nand thus frequently render them exceedingly luminous. Some of the\ncrustace\u00e6 possess the same remarkable property;--twelve different\nspecies of _cancer_ were taken up by the naturalists of the Zaire\nin the Gulf of Guinea.[111] The _cancer fulgens_, discovered by Sir\nJoseph Banks, is enabled to illuminate its whole body, and emits\nvivid flashes of light. Many of the medus\u00e6 also exhibit powerful\nphosphorescence.[112] These noctilucous creatures are, many of them,\nexceedingly minute, several thousands being found in a tea-cup of sea\nwater. They float near the surface in countless myriads, and when\ndisturbed they give out brilliant scintillations, often leaving a train\nof light behind them.[113] By microscopic examination no other fact has\nbeen elicited than that these minute beings contain a fluid which, when\nsqueezed out, leaves a line of light upon the surface of water. The\nappearance of these creatures is almost invariably on the eve of some\nchange of weather, which would lead us to suppose that their luminous\nphenomena must be connected with electrical excitation; and of this,\nthe investigations of Mr. C. Peach, of Fowey, communicated to the\nBritish Association at Birmingham, furnish the most satisfactory proofs\nwe have as yet obtained.\n\nBenvenuto Cellini gave a curious account of a carbuncle which shone\nwith great brilliancy in the dark.[114] The same thing has been stated\nof the diamond; but it appears to be necessary to procure these\nemissions of light, that the minerals should be first warmed near a\nfire. From this it may be inferred that the luminous appearance is\nof a similar character to that of fluor spar, and of numerous other\nearthy minerals, which, when exposed to heat, phosphoresce with great\nbrilliancy. Phosphorescent glow can also be excited in similar bodies\nby electricity, as was first pointed out by Father Beccaria, and\nconfirmed by Mr. Pearsall.[115] These effects, it must be remembered,\nare distinct from the electric spark manifested upon breaking white\nsugar in the dark, or scratching sulphuret of zinc.\n\nIn the instances adduced there is not necessarily any exposure to the\nsunshine required. It is probable that two, if not three, distinct\nphenomena are concerned in the cases above quoted, and that all of them\nare distinct from animal phosphorescence, or the luminous appearance\nof vegetables. They, however, certainly prove, either that light is\ncapable of becoming latent, or that it is only a condition of matter,\nin which it may be made manifest by any disturbance of the molecular\nforces. We have, in answer to this, very distinct evidence that\nsome bodies do derive this property from the solar rays. Canton\u2019s\nphosphorus, which is a sulphuret of calcium, will, having been exposed\nto the sun, continue luminous for some time after it is carried into\nthe dark; as will also the Bolognian stone,--a sulphuret of barium.\nThis result appears to be due to a particular class of the solar rays;\nfor it has been found, if these sulphurets, spread smoothly on paper,\nare exposed to the influence of the solar spectrum for some little\ntime, and then examined in the dark, that luminous spaces appear,\nexactly corresponding with the most refrangible rays, or those which\nexcite chemical change; and one very remarkable fact must not be\nforgotten--the dark rays of the spectrum beyond the violet produce a\nlively phosphorescence, which is _extinguished_ by the action of the\nrays of least refrangibility, or the heat rays--whilst artificial heat,\nsuch as a warm iron, produces a very considerable elevation of the\nphosphorescent effect.[116] It is not improbable, that the fluorescent\nrays of Mr. Stokes may be materially concerned in producing the\nphenomena of phosphorescence: experiments are, however, required to\nprove this.\n\nIn these allied phenomena we have effects which are evidently dependent\nupon several dissimilar causes. The phosphorescence of the living\nanimal is due, without doubt, to nervous excitation: that of the living\nvegetable to solar luminous influence; and in the case of the mosses of\ncaverns, &c. to the chemical agency of the sun\u2019s rays, which appears to\nbe capable of conduction. In the dead organic matter we have a purely\nchemical action developing the light, and in the inorganic bodies we\nhave peculiar molecular constitution, by which an absorption of light\nappears to take place.\n\nThe subject is one of the greatest difficulty; the torch of science\nis too dim to enable us to see the causes at work in producing these\nmarvellous effects. The investigation leads, to a certain extent, to\nthe elucidation of many of the secrets of luminous action; and the\ndetermination of the question, whether light is an emanation from the\nsun, or only a subtile principle diffused through all matter, which is\nexcited by solar influence, is intimately connected with the inquiry.\n\nIt has been stated that matter is necessary to the development of\nlight; that no luminous effect would be produced if it were not for\nthe presence of matter. Of this we not only have no proof, but such\nevidence as we have is against the position. There is no loss of light\nin the most perfect vacuum we can produce by any artificial means,\nwhich should be the case if matter was concerned in the phenomena of\nlight, as a cause.\n\nColour is certainly a property regulated by material bodies; or\nrather, the presence of matter is necessary to the production of\ncolour. Chlorine gas is a pale yellow, and nitrous vapour a yellowish\nred. These and one or two other vapours, which are near the point of\ncondensation into fluids, are the only coloured gaseous or vaporiform\nbodies. The sky is blue, because the material particles of the\natmosphere reflect back the blue rays. But we have more practical\nillustrations than this. The flame of hydrogen burning with oxygen\ngives scarcely any light; allow it to impinge on lime, a portion of\nwhich is carried off by the heat of the flame, and the most intense\nartificial light with which we are acquainted is produced. Hydrogen gas\nalone gives a flame in which nearly all but the blue rays are wanting:\nplace a brush of steel or asbestos in it, and many of the other rays\nare at once produced. An argand lamp, and more particularly the lamp\nin which camphine--a purified turpentine,--is burnt, gives a flame\nwhich emits most of the rays found in sunlight. Spirit of wine mixed\nwith water, warmed and ignited, gives only yellow rays; add nitrate\nof strontian and they become red; but nitrate of barytes being mixed\nwith the fluid, they are changed to green and yellow; salts of copper\nafford fine blue rays, and common salt intense yellow ones. Many of\nthese coloured rays and others can be produced in great power by the\nuse of various solid bodies introduced into flame. This has not been\nsufficiently pointed out by authors; but it is clear from experiments\nthat light requires the presence of matter to enable it to diffuse its\ncoloured glories. How is it that the oxygen and hydrogen flame gives so\nlittle light, and with a solid body present, pours forth such a flood\nof brilliancy?\n\nThe production of artificial light by electrical and chemical agencies\nwill necessarily find some consideration under their respective\nheads. There are numerous phenomena which connect themselves with\nluminous power, or appear to do so, which, in the present state of\nour knowledge, cannot come immediately under our attention. We are\ncompelled to reserve our limited space for those branches of science\nwhich we are enabled to connect with the great natural operations\nconstantly going on around us. Many of these more abstruse results\nwill, however, receive some incidental notice when we come to examine\nthe operation of the combined physical forces on matter.\n\nWe see in light a principle which, if it has not its source in the\nsun, is certainly dependent upon that luminary for its manifestations\nand powers. From that \u201cfountain of light\u201d we find this principle\ntravelling to us at a speed which almost approaches the quickness of\nthought itself; yet by the refinements of science we have been enabled\nto measure its velocity with the utmost accuracy. The immortal poet of\nour own land and language, in his creations of Ariel, that \u201ctricksy\nspirit,\u201d who could creep like music upon the waters, and of the\nfantastic Puck, who could girdle the earth in thirty minutes, appears\nto have approached to the highest point to which mere imagination could\ncarry the human mind as to the powers of things ethereal. Science has,\nsince then, shown to man that this \u201cspirit, fine spirit,\u201d was a laggard\nin his tasks, and a gross piece of matter, when compared with the\nsubtile essences which man, like a nobler Prospero, has now subdued to\ndo him service.\n\nLight is necessary to life; the world was a dead chaos before its\ncreation, and mute disorder would again be the consequence of its\nannihilation. Every charm which spreads itself over this rolling globe\nis directly dependent upon luminous power. Colours, and probably,\nforms, are the result of light; certainly the consequence of solar\nradiations. We know much of the mysterious influences of this great\nagent, but we know nothing of the principle itself. The solar beam has\nbeen tortured through prismatic glasses and natural crystals; every\nchemical agent has been tried upon it, every electrical force in the\nmost excited state brought to bear upon its operations, with a view\nto the discovery of the most refined of earthly agencies; but it has\npassed through every trial without revealing its secrets, and even the\neffects which it produces in its path are unexplained problems, still\nto tax the intellect of man.\n\nEvery animal and every plant alike proclaim that life and health are\ndue to light; and even the crystallizing forms of inorganic matter, by\nbending towards it, confess its all-prevailing sway. From the sun to\neach planet revolving around that orb, and to the remotest stars which\ngleam through the vast immensity of heaven, we discover this power\nstill in its brightness, giving beauty and order to these unnumbered\ncreations; no less completely than to this small island of the universe\nwhich we call our Earth. Through every form of matter we can mark\nits power, and from all, we can, under certain conditions, evoke it\nin lustre and activity. Over all and through all light spreads its\nethereal force, and manifests, in all its operations, powers which\nmight well exalt the mind of Plato to the idea of an omniscient and\nomnipresent God. Science, with her Ithuriel wand, has, however, shown\nthat light is itself the effect of a yet more exalted cause, which we\ncannot reach.\n\nIndeed, the attentive study of the fine abstractions of science lifts\nthe mind from the grossness of matter, step by step, to the refinements\nof immateriality, and there appear, shadowed out beyond the physical\nforces which man can test and try, other powers still ascending, until\nthey reach the Source of every good and every perfect gift.\n\n\nFOOTNOTES:\n\n[84] \u201cThese--oxygen, hydrogen, nitrogen, and carbon--are the four\nbodies, in fact, which, becoming animated at the fire of the sun,\nthe true torch of Prometheus, approve themselves upon the earth\nthe eternal agents of organisation, of sensation, of motion and of\nthought.\u201d--Dumas, _Le\u00e7ons de Philosophie Chimique_, p. 100. Paris, 1837.\n\n[85] It will be found in examining any of the works of the\nalchemists,--particularly those of Geber, _De inveniendi arte Auri et\nArgenti_, and his _De Alchemi\u00e2_; Roger Bacon\u2019s _Opus Majus, or Alchymia\nMajor_; Helvetius\u2019 _Brief of the Golden Calf_; or Basil Valentine\u2019s\n_Currus Triumphalis_,--that in the processes of transmutation the solar\nlight was supposed to be marvellously effective. In Boyle\u2019s _Sceptical\nChemist_ the same idea will be found pervading it.\n\nAmid all their errors, the alchemists were assiduous workmen, and to\nthem we are indebted for numerous facts. Of them, and of their age, as\ncontrasted with our own, Gibbon remarks:--\u201cCongenial to the avarice\nof the human heart, it was studied in China, as in Europe, with equal\neagerness and equal success. The darkness of the middle ages ensured\na favourable reception to every tale of wonder; and the revival of\nlearning gave new vigour to hope, and suggested more specious arts\nof deception. Philosophy, with the aid of experience, has at length\nbanished the study of alchemy; and the present age, however desirous of\nriches, is content to seek them by the humbler means of commerce and\nindustry.\u201d--_Decline and Fall_, vol. ii. p. 137.\n\n[86] On the two theories the following maybe consulted:--Young,\n_Supplement to Encyclop\u00e6dia Britannica_, article _Chromatics_;\nFresnel, _Suppl\u00e9ment \u00e0 la Traduction Fran\u00e7aise de la 5i\u00e8me \u00e9dition du\nTrait\u00e9 de Chimie de Thomson_, par Riffault, Paris, 1822; Herschel\u2019s\nArticle, _Light_, in the Encyclop\u00e6dia Metropolitana, and the French\nTranslation of it by Quetelet and Verhulst; Airy\u2019s _Tract on the\nUndulatory Theory_, in his Tracts, 2nd edition, Cambridge, 1831; Powel,\n_The Undulatory Theory applied to Dispersion_, &c. p. 184; Lloyd\u2019s\n_Lectures_, Dublin, 1836-41; Cauchy, _Sur le Mouvement des Corps\n\u00e9lastiques_, M\u00e9moires de l\u2019Institut, 1827, vol. ix. p. 114; _Th\u00e9orie de\nla Lumi\u00e8re_, Ibid. vol. x. p. 293; M\u2019Cullagh, _On Double Refraction_,\nIbid., vol. xvi.; _Geometrical Propositions applied to the Wave Theory\nof Light_, Ibid., vol. xvii.; Sir David Brewster\u2019s papers in the\nTransactions of the Royal Society of Edinburgh, and the Philosophical\nMagazine.\n\n[87] _Results of Astronomical Observations made during the years\n1834-38, at the Cape of Good Hope, &c._ By Sir John Herschel, Bart.,\nK.H., D.C.L., F.R.S.--\u201cIn the contemplation of the infinite, in number\nand in magnitude, the mind ever fails us. We stand appalled before this\nmighty spectre of boundless space, and faltering reason sinks under the\nload of its bursting conceptions. But, placed as we are on the great\nlocomotive of our system, destined surely to complete at least one\nround of its ethereal course, and learning that we can make no apparent\nadvance on our sidereal journey, we pant with new ardour for that\ndistant bourne which we constantly approach without the possibility\nof reaching it. In feeling this disappointment, and patiently bearing\nit, let us endeavour to realise the great truth from which it flows.\nIt cannot occupy our mind without exalting and improving it.\u201d--_Sir D.\nBrewster_: North British Review.\n\n[88] For examples of this, consult Graham\u2019s _Elements of Chemistry_;\nBrande\u2019s _Manual of Chemistry_; or, indeed, any work treating of the\nscience. The formation of ink, by mixing two colourless solutions,\none of gallic acid and another of sulphate of iron, may be taken as a\nfamiliar instance.\n\n[89] Sir John Herschel, in his paper _On the Chemical Action of the\nRays of the Solar Spectrum on Preparations of Silver_, remarks that,\n\u201cit may seem too hazardous to look for the cause of this very singular\nphenomenon in a real difference between the chemical agencies of those\nrays which issue from the central portion of the sun\u2019s disc, and those\nwhich, emanating from its borders, have undergone the absorptive\naction of a much greater depth of its atmosphere; and yet I confess\nmyself somewhat at a loss what other cause to assign for it. It must\nsuffice, however, to have thrown out the hint; remarking only, that\nI have other, and, I am disposed to think, decisive evidence (which\nwill find its place elsewhere) of the existence of an absorptive solar\natmosphere, extending beyond the luminous one. The breadth of the\nborder, I should observe, is small, not exceeding 0\u00b75 or 1/7 part of\nthe sun\u2019s radius, and this, from the circumstances of the experiment,\nmust necessarily err in excess.\u201d--Philosophical Transactions, 1840.\n\n[90] _Experiments and Observations on some Cases of Lines in the\nPrismatic Spectrum, produced by the passage of Light through Coloured\nVapours and Gases, and from certain Coloured Flames._ By W. A.\nMiller, M.D., F.R.S., Professor of Chemistry in King\u2019s College,\nLondon.--Philosophical Magazine, vol. xxvii.\n\n[91] _Report on the Mollusca and Radiata of the \u00c6gean Sea, and on their\ndistribution, considered as bearing on Geology._ By Edward Forbes,\nF.R.S., &c.--Reports of the British Association, vol. xii. Professor\nForbes remarks:--\u201cA comparison of the testacea, and other animals of\nthe lowest zones, with those of the higher, exhibits a very great\ndistinction in the hues of the species, those of the depths being, for\nthe most part, white or colourless, while those of the higher regions,\nin a great number of instances, exhibit brilliant combinations of\ncolour. The results of an enquiry into this subject are as follows:--\n\n\u201cThe majority of shells of the lowest zone are white or transparent; if\ntinted rose is the hue, a very few exhibit markings of another colour.\nIn the seventh region, white species are also very abundant, though\nby no means forming a proportion so great as the eighth. Brownish\nred, the prevalent hue of the brachiopoda, also gives a character\nof colour to the fauna of this zone; the crustacea found in it are\nred. In the sixth zone the colours become brighter, reds and yellows\nprevailing,--generally, however, uniformly colouring the shell. In\nthe fifth region many species are banded or clouded with various\ncombinations of colours, and the number of white species has greatly\ndiminished. In the fourth, purple hues are frequent, and contrasts of\ncolour common. In the second and third, green and blue tints are met\nwith, sometimes very vivid; but the gayest combinations of colour are\nseen in the littoral zone, as well as the most brilliant whites.\n\n\u201cThe animals of Testacea, and the Radiata of the higher zones, are\nmuch more brilliantly coloured than those of the lower, where they are\nusually white, whatever the hue of the shell may be. Thus the genus\n_Trochus_ is an example of a group of forms mostly presenting the\nmost brilliant hues both of shell and animal; but whilst the animals\nof such species as inhabit the littoral zone are gaily chequered with\nmany vivid hues, those of the greater depth, though their shells are\nalmost as brightly covered as the coverings of their allies nearer the\nsurface, have their animals, for the most part, of a uniform yellow or\nreddish hue, or else entirely white. The chief cause of this increase\nof intensity of colour as we ascend is, doubtless, the increased amount\nof light above a certain depth.\u201d--p. 172.\n\n[92] \u1f09\u03bc\u1f41\u03c1\u03c6\u03c9\u03c4\u03b1. _On the Epipolic Dispersion of Light_, being a paper\nentitled, _On a case of Superficial Colour presented, by a homogeneous\nliquid internally colourless_. By Sir J. F. W. Herschel, Bart, K.H.,\nF.R.S., &c.--_An epipolized beam of light_ (meaning thereby a beam\nwhich has once been transmitted through a quiniferous solution, and\nundergone its dispersing action) _is incapable of further undergoing\nepipolic dispersion_. In proof of this the following experiment may be\nadduced,--\n\nA glass jar being filled with a quiniferous solution, a piece of plate\nglass was immersed in it vertically, so as to be entirely covered, and\nto present one face directly to the incident light. In this situation,\nwhen viewed by an eye almost perpendicularly over it, so as to graze\neither surface very obliquely, neither the anterior nor posterior face\nshowed the slightest trace of epipolic colour. Now, the light, at its\negress from the immersed glass, entered the liquid under precisely the\nsame circumstances as that which, when traversing the anterior surface\nof the glass jar, underwent epipolic dispersion on first entering\nthe liquid. It had, therefore, lost a property which it originally\npossessed, and could not, therefore, be considered _qualitatively_ the\nsame light.--Philosophical Transactions, vol. cxxxvi.\n\n[93] In connection with this view, the Newtonian theory should be\nconsulted, for which see--_A Letter of_ Mr. Isaac Newton, _Professor\nof the Mathematicks in the University of Cambridge; containing his new\nTheory about Light and Colors: sent by the Author to the Publisher,\nfrom Cambridge, Feb. 6, 1671-72, in order to be communicated to the\nRoyal Society._\n\n[94] In that admirable work, _The Physical Atlas_ of Dr. Berghaus, of\nwhich a very complete edition by Alexander Keith Johnstone is published\nin this country, the following order of the distribution of plants is\ngiven:--\n\n    1. The region of palms and bananas    Equatorial zone.\n    2. Tree ferns and figs                Tropical zone.\n    3. Myrtles and laurels                Sub-tropical zone.\n    4. Evergreen trees                    Warm temperate zone.\n    5. European trees                     Cold temperate zone.\n    6. Pines                              Sub-arctic zone.\n    7. Rhododendrons                      Arctic zone.\n    8. Alpine plants                      Polar zone.\n\nConsult Humboldt, _Essai sur la G\u00e9ographie des Plantes_, Paris,\n1807; _De Distributione Geographic\u00e2 Plantarum_, Paris, 1817. Schouw,\n_Grundz\u00fcge der Pflanzengeographie_. Also his _Earth, Plants, and Man_;\ntranslated by Henfrey, in _Bohn\u2019s Scientific Library_. Lamouroux,\n_G\u00e9ographie Physique_. _The Plant, a Biography_: by Schleiden;\ntranslated by Henfrey. _Physical Geography_: by Mrs. Somerville.\n\n[95] Fraunhofer\u2019s measure of illuminating power is as follows:--\n\n    At the 22nd degree of the red       0\u00b7032\n       \"   34th degree of the red       0\u00b7094\n       \"   22nd degree of the orange    0\u00b7640\n       \"   10th degree of the yellow    1\u00b7000\n       \"   42nd degree of the yellow    0\u00b7480\n       \"   2nd degree of the blue       0\u00b7170\n       \"   16th degree of the indigo    0\u00b7031\n       \"   43rd degree of the violet    0\u00b70056\n\n[96] Herschel, _On the Action of Crystallized Bodies on Homogeneous\nLight, and on the causes of the deviation from Newtons scale in\nthe tints which many of them develope on exposure to a polarized\nray_.--Phil. Trans., vol. cx., p. 88.\n\n[97] _On the Nature of Light and Colours_: Lecture 39, in Young\u2019s\n_Lectures on Natural Philosophy_, Kelland\u2019s Edition, p. 373, and the\nauthorities there quoted.\n\n[98] Brewster\u2019s _Optics_: Lardner\u2019s Cabinet Cyclop\u00e6dia. Herschel, _On\nLight_: Encyclop\u00e6dia Metropolitana.\n\n[99] Malus, _Sur une Propri\u00e9t\u00e9 de la Lumi\u00e8re R\u00e9fl\u00e9chie_: M\u00e9moires\nd\u2019Arcueil. Numerous memoirs by Sir David Brewster, in the Philosophical\nTransactions.\n\n[100] Bartholin, _On Iceland Crystals_: Copenhagen, 1669. _An\nAccompt of sundry Experiments made and communicated by that Learn\u2019d\nMathematician_ Dr. Erasmus Bartholin, _upon a Chrystal like Body sent\nto him out of Island_: in connection with which Dr. Matthias Paissenius\nwrites:--The observations of the excellent Bartholin upon the Island\nChrystal are, indeed, considerable, as well as painful. We have here,\nalso, made some tryals of it upon a piece he presented me with, which\nconfirm his observations. Mean time he found it somewhat scissile and\nreducible by a knife into thin laminas or plates, which, when single,\nshew\u2019d the object single, but laid upon one another shew\u2019d it double;\nthe two images appearing the more distant from one another, the\ngreater the number was of those thin plates laid on one another. With\nsubmission to better judgements I think it to be a kind of Selenites.\nSome of our curious men here were of opinion that the Rhomboid figure\nproper to this stone was the cause of the appearances doubled thereby.\nBut having tryed whether in other transparent bodies of the like figure\nthe like would happen, we found no such thing in them, which made us\nsuspect some peculiarity in the very Body of the stone.--Phil. Trans.\nfor 1670, vol. v.\n\n[101] _On the Application of the Laws of Circular Polarization to the\nResearches of Chemistry_: by M. Biot.--Nouvelles Annales du Mus\u00e9um\nd\u2019Histoire Naturelle, vol. iii., and Scientific Memoirs, vol. i.\np. 600. _On Circular Polarization_: by Dr. Leeson.--Memoirs of the\nChemical Society.\n\n[102] In Sir David Brewster\u2019s Treatise _On Optics_, chap, xviii., _On\nPolarization_, the best arrangements for a polarizing apparatus will be\nfound described.\n\n[103] This beautiful application was recently made by Professor\nWheatstone, the particulars of which will be found in his interesting\ncommunication.--_On a means of determining the apparent Solar Time\nby the diurnal changes of the Plane of Polarization at the Northern\nPole of the Sky_: Report of the Eighteenth Meeting of the British\nAssociation.\n\n[104] _On the Polarization of the Chemical Rays of Light_: by John\nSutherland, M.D., in which the author refers to the following\nexperiment of M. J. E. B\u00e9rard--\u201cI received the chemical rays directed\ninto the plane of the meridian on an unsilvered glass, under an\nincidence of 35\u00b0 61'. The rays reflected by the first glass were\nreceived upon a second, under the same incidence. I found that when\nthis was turned towards the south, the muriate of silver exposed to\nthe invisible rays which it reflected was darkened in less than half\nan hour; whereas, when it was turned towards the west, the muriate\nof silver exposed in the place where the rays ought to have been\nreflected, was not darkened, although it was left exposed for two\nhours. It is consequently to be presumed that the chemical rays can\nundergo double refraction in traversing certain diaphanous bodies; and\nlastly, we may say that they enjoy the same physical properties as\nlight in general.\u201d--Philosophical Magazine, vol. xx.\n\nDr. Leeson has stated that Daguerreotype pictures can be taken more\nreadily under the influence of polarized light, than by ordinary\nradiation.\n\n[105] _On the Magnetization of Light, and the Illumination of Magnetic\nLines of Force_: by Michael Faraday, D.C.L., F.R.S.--Philosophical\nTransactions, vol. cxxxvii.--The following remarks are to the point\nof doubt referred to in the text.--\u201cThe magnetic forces do not act\non the ray of light directly and without the intervention of matter,\nbut through the mediation of the substance in which they and the ray\nhave a simultaneous existence; the substances and the forces giving to\nand receiving from each other the power of acting on the light. This\nis shown by the non-action of a vacuum, of air or gases, and it is\nalso further shown by the special degree in which different matters\npossess the property. That magnetic force acts upon the ray of light\nalways with the same character of manner, and in the same direction,\nindependent of the different varieties of substance, or their states\nof solid or liquid, or their specific rotative force, shows that\nthe magnetic force and the light have a direct relation; but that\nsubstances are necessary, and that these act in different degrees,\nshows that the magnetism and the light act on each other through the\nintervention of the matter. Recognising or perceiving _matter_ only by\nits powers, and knowing nothing of any imaginary nucleus abstract from\nthe idea of these powers, the phenomena described must strengthen my\ninclination to trust in the views I have advanced in reference to its\nnature.\u201d--Phil. Mag. vol. xxiv.\n\n[106] The invention of the camera obscura certainly belongs to\nGiambattista Porta, and is described in his _Magi\u00e6 Naturalis, sive de\nMiraculis Rerum Naturalium, Libri Viginti_; Antwerp, 1561. An English\ntranslation made in 1658 exists, but I have not seen it.\n\nHooke, in one of the earliest volumes of the Philosophical\nTransactions, describes as new many of the phenomena mentioned by\nPorta, and particularly the images of the dark chamber.\n\n[107] Herschel, _On Light_,--Encyclop\u00e6dia Metropolitana.\n\n[108] \u201cI would here observe that a consideration of many such\nphenomena (the obliteration and revival of photographic drawings) has\nled me to regard it as not impossible that the retina itself may be\n_photographically_ impressed by strong light, and that some at least\nof the phenomena of visual spectra and secondary colours may arise\nfrom the sensorial perception of actual changes in progress in the\nphysical state of that organ itself subsequent to the cessation of the\ndirect stimulant.\u201d--_On the action of the Rays of the Solar Spectrum on\nVegetable Colours, &c._: by Sir J. F. W. Herschel, Bart.\n\n[109] Dumeril.\n\n[110] _Theory of Colours_: by Goethe; translated by Eastlake.\n\n[111] See Tuckey\u2019s Narrative of the Expedition of the Zaire.\n\n[112] The most complete examination of this subject will be found in\ntwo Memoirs:--\n\n1. _Experiments and observations on the light which is spontaneously\nemitted with some degree, of permanency from various bodies._--Phil.\nTrans., vol. xc.\n\n2. _A continuation of the above, with some experiments and observations\non solar light, when imbibed by Canton\u2019s phosphorus_: by Nathaniel\nHulm, M.D.--Phil. Trans., vol. xci.; and in the _Monograph of the\nBritish Naked-eyed Medus\u00e6_, by Professor Edward Forbes (published\nfor the Ray Society). See Wilson\u2019s note to the account of _Pennalata\nphosphorea_ in Johnston\u2019s Zoophytes, 2nd edition.\n\n[113] _A General Outline of the Animal Kingdom_: by Thomas Rymer Jones,\nF.L.S.--Acaleph\u00e6, p. 64. _Lettre \u00e0 M. Dumas sur la Phosphorescence des\nVers luisants_: par M. Ch. Matteucci.--Annales de Chimie, vol. ix. p.\n71, 1843.\n\n[114] _Memoirs of Benvenuto Cellini--Bohn\u2019s Standard Library._ See also\nhis Treatise on his Art as a Sculptor and Engraver. Florence, 1568. 4to.\n\n[115] _Phosphorescence of the Diamond_: by M. Reiss (Revue Scientifique\net Industrielle, vol. xxiii. p. 185).--\u201cThe diamond, phosphorescent\nby insulation, lost rapidly its phosphorescence when submitted to the\naction of the red rays of the solar spectrum. On the contrary, the\nblue rays are those which render the diamond the most luminous in\nthe dark. It is probable that the phosphorescence produced by heat\nis equally diminished by the action of the red rays of the solar\nspectrum.\u201d Giovanni Battista Beccaria published his experiments in\n1769. See Priestley\u2019s _History of Electricity_; and _On the Effects\nof Electricity upon Minerals which are Phosphorescent by Heat_; and\n_Further Experiments on the communication of Phosphorescence and Colour\nto bodies of Electricity_; by Thomas J. Pearsall.--Journal of the\nRoyal Institution of Great Britain, Oct. 1830, Feb. 1831.--These two\nmemoirs contain the most complete set of experiments on this subject\nwhich have yet been made; see _Placidus Heinrich_, _Phosphorescenz\nder K\u00f6rper_, vol. iv.; Gmelin\u2019s _Handbuch der Chemie_, part 1.;--_On\nthe Phosphorescence of Minerals_, Brewster: Edinburgh Philosophical\nJournal, vol. i. p. 137.;--_The A\u00ebrial Noctiluca, or some New\nPhenomena, and a process of a factitious self shining substance_:\nBoyle\u2019s Works, vol. iv.\n\n[116] _Des Effets produits sur les corps par les Rayons Solaires_: par\nM. Edmond Becquerel.--Annales de Chimie, vol. ix. p. 257. 1843.\n\nM. Becquerel has applied the term _phosphorog\u00e9nique_ to those rays\nproducing phosphorescence.\n\n\n\n\nCHAPTER VIII.\n\nACTINISM--CHEMICAL RADIATIONS.\n\n  The Sun-ray and its Powers--Darkening of Horn Silver--Niepce\u2019s\n    Discovery--Prismatic Spectrum--Refrangibility of Light, Heat, and\n    Actinism--Daguerre\u2019s Discovery--Photography--Chemical Effects\n    produced by Solar Radiations--Absorption of Actinism--Phenomena of\n    the Daguerreotype--Chemical Change produced upon all Bodies--Power\n    of Matter to restore its Condition--Light protects from Chemical\n    Change--Photographs taken in Darkness--Chemical Effects of Light\n    on organized Forms--Chemical Effects of Solar Heat--Influence\n    of Actinism on Electricity--Radiations in Darkness--Moser\u2019s\n    Discoveries, &c.\n\n\nHeat and light are derived from the sun, and we have attempted to show,\nnot only that the phenomena of these two principles are different, but\nthat they can scarcely, in the present condition of our knowledge, be\nregarded as modified manifestations of _one_ superior power. Associated\nwith these two remarkable elements, others may exist in the solar rays.\nElectrical phenomena are certainly developed by both heat and light,\nand peculiar electric changes are produced by exposure to sunshine.\nElectricity may be merely _excited_ by the solar rays, or it may\n_flow_ like light from the sun. Chemical action may be only due to the\ndisturbance of some diffused principle; or it may be directly owing to\nsome agency which is radiated at once from the sun.\n\nA sun ray is a magical thing: we connect it in our fancy with the\nmost ethereal of possible creations. Yet in its action on matter it\nproduces colour; it separates the particles of solid masses farther\nfrom each other, and it breaks up some of the strongest forces of\nchemical affinity. To modern science is entirely due the knowledge\nwe have gained of the marvellous powers of the sunbeam; and it has\nrendered us familiar with phenomena, to which the incantation scenes\nof the Cornelius Agrippas of the dark ages were but ill-contrived\ndelusions, and their magic mirrors poor instruments. The silver tablets\nof the photographic artist receiving fixed impressions of the objects\nrepresented in the dark chamber by a lens, are far superior as examples\nof natural magic.\n\nIn the dark ages, or rather as the earliest gleams of the bright\nmorning of inductive research were dispelling the mists of that\nphantom-peopled period, it was observed, for the first time, that the\nsun\u2019s rays turned a white compound black. Man must have witnessed, long\nbefore, that change which is constantly taking place in all vegetable\ncolours: some darkening by exposure to sunlight, while others were\nbleached by its influence. Yet those phenomena excited no attention,\nand the world knew nothing of the mighty changes which were constantly\ntaking place around them. The alchemists--sublime pictures of credulous\nhumanity--toiling in the smoke of their secret laboratories, waiting\nand watching for every change which could be produced by fire, or by\ntheir \u201croyal waters,\u201d caught the first faint ray of an opening truth;\nand their wild fancy, that light could change silver into gold, if they\nbut succeeded in getting its subtile beams to interpenetrate the metal,\nwas the clue afforded to the empirical philosopher to guide him through\na more than Cretan labyrinth.[117]\n\nThe first fact recorded upon this, point was, that horn silver\nblackened when exposed to the light. Without doubt many anxious\nthoughts were given by these alchemists to that fact. Here was, as it\nappeared, a mixing up of light and matter, and behold the striking\nchange! It was a step towards the realization of their dreams. Alas!\npoor visionaries! in pursuing an ideality they lost the reality which\nwas within their grasp.\n\nTruths come slowly upon man, and long it is before these angel visits\nare acknowledged by humanity. The world clings to its errors, and\navoids the truth, lest its light should betray their miserable follies.\n\nAt length a man of genius announced that \u201c_No substance can be\nexposed to the sun\u2019s rays without undergoing a chemical change_;\u201d\nbut his words fell idly upon the ear. His friends looked upon his\nlight-produced pictures as singular; they preserved them in their\ncabinets of curiosities; but the truths which he enunciated were soon\nforgotten. Howbeit his words were recorded, and it is due to the\nsolitary experimentalist of Ch\u00e2lons on the Sa\u00f4ne, to couple the name\nof Niepce with the discovery of a fact which is scarcely second to\nthe development of the great law of universal gravitation.[118] But\nan examination awaits us, which, for its novelty, has more charms\nthan most branches of science, and which, for the extensive views it\nopens to the inquirer, has an interest in nowise inferior to any other\nphysical investigation.\n\nThe prismatic spectrum affords us the means of examining the conditions\nof the solar rays with great facility. In bending the ray of white\nlight out of its path, by means of a triangular piece of glass, we\ndivide it in a remarkable manner. We learn that heat is less refracted\nby the glass than the other powers; we find the maximum point of the\ncalorific rays but slightly thrown out of the right line, which the\nsolar pencil would have taken, had it not been interrupted by the\nprism; and the thermic action is found to diminish with much regularity\non either side of this line. We discover that the luminous power is\nsubject to greater refraction, and that its maximum lies considerably\nabove that of heat; and that, in like manner, on each side the light\ndiminishes, producing orange, red, and crimson colours below the\nmaximum point, and green, blue, and violet above it. Again, we find\nthat the radiations which produce chemical change are more refrangible\nthan either of the others, and the maximum of this power is found\nat the point where light rapidly diminishes, and where scarcely any\nheat can be detected: it extends in full activity, above its maximum,\nto a considerable distance, where no trace of light under ordinary\nconditions exists, and below that point, until light, appearing to\nact as an interfering agent, quenches its peculiar properties. These\nare strong evidences that _light_ and _actinism_--as this principle\nhas been named--are not identical: and we may separate them most\neasily and effectually from each other. Certain glasses, stained dark\nblue, with oxide of cobalt, admit scarcely any light; but they offer\nno interruption to the passage of actinism or the chemical rays; on\nthe contrary, a pure yellow glass, or a yellow fluid, which does not\nsensibly reduce the intensity of any one colour of the chromatic band\nof luminous rays, completely cuts off this chemical principle, whatever\nit may be. In addition to these, there are other results which we shall\nhave to describe, which prove that, although associated in the solar\nbeam, light and actinism are in constant antagonism.\n\nWhen Daguerre first published his great discovery, the European public\nregarded his metal tablets with feelings of wonder: we have grown\naccustomed to the beautiful phenomena of this art, and we have become\nacquainted with a number of no less beautiful processes on paper,\nall of which, if studied aright, must convince the most superficial\nthinker, that a world of wonder lies a little beyond our knowledge,\nbut within the reach of industrious and patient research. Photography\nis the name by which the art of sun-painting will be for ever known.\nWe regard this as unfortunate, conveying as it does a false idea,--the\npictures not being _light-drawn_. Could we adopt the name given\nby Niepce to the process, the difficulty would be avoided, since\nHeliography involves no hypothesis, and strictly tells the undeniable\ntruth, that our pictures are _sun-drawn_. That pictures can be produced\nby the rays from artificial sources, presents no objection to this;\nthese rays were still originally derived from the sun.\n\nBy whatever name we determine to convey our ideas of these phenomena,\nit is certain that they involve a series of effects which are of the\nhighest interest to every lover of nature, and of the utmost importance\nto the artist and the amateur. By easy manipulation we are now enabled\nto give permanence to the charming pictures which are produced by means\nof that pleasing invention of Baptista Porta, the _Camera Obscura_. Any\nimage, which being refracted by the lens of this instrument falls upon\nthe table in its dark chamber, may be secured with its most delicate\ngradations of shadows, upon either a metallic or a paper tablet.\n\nBut let us proceed to the examination of a few of the more striking\nphenomena of these chemical changes. To commence with some of the more\nsimple but no less important results.\n\nChlorine and hydrogen will not unite in darkness, nor will chlorine and\ncarbonic oxide; but, if either of those gaseous mixtures is exposed to\nsunshine, they combine rapidly, and often with explosion. A solution of\nthe sulphate of iron in ordinary water may be preserved for a long time\nin the dark without undergoing any change; expose it to the sunshine,\nand a precipitation of oxide of iron is very rapidly produced. The\nmineral chameleon, the _manganesiate of potash_ in solution, is\nalmost instantly decomposed in daylight; but it is a long time before\nit undergoes any change in darkness. The same thing occurs with a\ncombination of platinum and lime: indeed, it appears that precipitation\nis at all times, and under all circumstances, accelerated by the solar\nrays. As these precipitations are in exact agreement with the quantity\nof actinic radiation to which the solutions have been exposed, we may\nactually weigh off the relative quantities, representing in grains the\nequivalent numbers to the amount of actinism which has influenced the\nchemical compound.[119]\n\nWe have evidence which appears to prove that this chemical agent may\nbe absorbed by simple bodies, and that by this absorption an actual\nchange of condition, is produced, in many respects analogous to those\nallotropic changes which we have previously considered. Chlorine, in\nits ordinary state, does not combine with hydrogen in the dark. If we\nemploy the yellow medium of chlorine gas, for the purpose of analyzing\nthe sun\u2019s rays previously to their falling upon some chemical compound\nwhich is sensitive to actinic power, we shall find that the chlorine\nobstructs all this actinism, and, however unstable the compound,\nit remains unchanged. But the chlorine gas which has interrupted\nthis wonderful agent, appears to have absorbed it, and it is so far\naltered in its constitution that _it will unite with hydrogen in the\ndark_.[120] In like manner, if, of two portions of the same solution\nof sulphate of iron, one is kept in the dark and the other exposed\nto the sunshine, it will be found that the solution which has been\nexposed will precipitate gold and silver from their combinations much\nmore speedily than that which has been preserved in darkness--the\ntemperature and every other condition being the same.\n\nThe phenomena of the Daguerreotype involve many strange conditions.\nA plate of silver, on which a slight chemical action has been\nestablished by the use of iodine, is exposed to the lenticular image\nin the camera obscura. If allowed to remain under the influence of\nthese radiations for a sufficient length of time, a faithful picture\nof the illuminated objects is delineated on the plate, as shown by\nthe visible decomposition and darkening of the iodized surface. The\nplate is not, however, in practice allowed to assume this condition;\nafter an exposure of a few seconds the radiant influence is cut off,\nand the eye cannot detect any evidence of change upon the yellow\nplate. It is now exposed to the vapour of mercury, and that metal in\na state of exceedingly fine division is condensed upon the plate;\nbut the condensation is not uniformly spread upon its face. The\ndeposit of mercurial vapour is in exact proportion to the amount of\nchemical action produced. Is the change, by which this peculiar power\nof condensation is effected, a chemical, calorific, electrical, or\nmerely a molecular one? The evidences, at present, are not sufficient\nto determine the question. It has lately been suggested, that the\nmercury acts chemically only, and effects the full decomposition of\nthe iodide of silver; and that the picture is due to this, and not to\nthe deposition actually of the mercury vapour. In all probability we\nhave the involved action of several forces. We have some experiments\nwhich show, clearly enough, that mercury is deposited in proportions\nwhich correspond with the intensity of solar action. A chemically\nprepared surface is not necessary to exhibit this result. A polished\nplate of metal, of glass, of marble, or a piece of painted wood, being\npartially exposed, will, when breathed upon, or presented to the action\nof mercurial vapour, show that a disturbance has been produced upon\nthe portions which were illuminated, whereas no change can be detected\nupon the parts which were kept in the dark. It was thought, until\nlately, that a few chemical compounds, such as the iodide of silver,\nthe material employed in the Daguerreotype and Calotype,--chloride of\nsilver, the ordinary photographic agent,--a few salts of gold, and one\nor two of lead and iron, were the only materials upon which these very\nremarkable changes were produced. We now know that it is impossible\nto expose any body, simple or compound, to the sun\u2019s rays, without\nits being influenced by this chemical and molecular disturbing power.\nTo take our examples from inorganic nature, the granite rock which\npresents its uplifted head in firmness to the driving storm, the stones\nwhich genius has framed into forms of architectural beauty, or the\nmetal which is intended to commemorate the great acts of man, and which\nin the human form proclaims the hero\u2019s deeds and the artist\u2019s talent,\nare all alike destructively acted upon during the hours of sunshine,\nand, but for provisions of nature no less wonderful, would soon perish\nunder the delicate touch of the most subtile of the agencies of the\nuniverse.\n\nNiepce was the first to show that all bodies which underwent this\nchange during daylight possessed the power of restoring themselves\nto their original conditions during the hours of night, when this\nexcitement was no longer influencing them. Resins, the Daguerreotype\nplate, the unprepared metal tablet, and numerous photographic\npreparations, prove this in a remarkable manner.[121]\n\nThe picture which we receive to-day, unless we adopt some method of\nsecuring its permanency, fades away before the morrow, and we try to\nrestore it in vain. With some of our chemical preparations this is\nvery remarkably shown, but by none in so striking a manner as by paper\nprepared with the iodide of platinum, which, being impressed with an\nimage by heliographic power, which is represented by dark brown tints,\nrestores itself in the dark, in a few minutes, to its former state of\na yellow colour, and recovers its sensibility to sunshine.[122] The\ninference we alone can draw from all the evidences which the study\nof actino-chemistry affords, is, that the hours of darkness are as\nnecessary to the inorganic creation as we know night and sleep to be\nto the organic kingdom. But we must not forget that there does exist\nin the solar rays a balance of forces which materially modifies the\namount of disturbing influence exerted by them on matter. Not only do\nwe find that the chemical action is not extended over the whole length\nof the prismatic spectrum, but we discover that over spaces, which\ncorrespond with the maximum points of light and heat, a protective\naction is exerted. That is, that highly sensitive photographic agents,\nwhich blacken rapidly under exposure to diffused daylight, are entirely\nprotected from change in full sunshine, if at the same time as a strong\nlight is thrown upon them by reflection, the yellow and extra red rays\nare brought to bear upon their surface. Not only so, but by employing\nmedia which will cut off all the chemical rays of the spectrum,\nadmitting freely at the same time the luminous and calorific rays, we\nfind that a protected band, the length of the spectrum, remains white,\nwhilst every other portion has blackened.[123]\n\nAmong the many curious instances of natural magic, none are more\nremarkable than an experiment not long since proposed, by which\nDaguerreotype pictures may be taken in absolute darkness to the human\neye. This is effected in the following manner:--A large prismatic\nspectrum is thrown upon a lens fitted into one side of a dark chamber;\nand as we know that the actinic power resides in great activity beyond\nthe violet ray, where there is no light, the only rays which we allow\nto pass the lens into the chamber are those which are extra-spectral\nand non-luminous. These are directed upon, any white object, and from\nthat object radiated upon a highly sensitive plate in a camera obscura.\nThus a copy of the subject will be obtained by the agency of radiations\nwhich produce no sensible effect upon the optic nerve. This experiment\nis the converse of those which show us that we may illuminate any\nobject with the strongest sunlight which has passed through yellow\nglass, the yellow solution of sulphuret of calcium, or of the\nbichromate of potash--these being non-transparent to the chemical\nrays--and yet fail to secure any Daguerreotype copy of it, even upon\nthe most exquisitely sensitive plate. Indeed, the image of the sun\nitself, when setting through an atmosphere which reduces its light to\na red or rich yellow colour, not only produces no chemical change,\nbut protects an iodized plate from it; and whilst every other part\nof the tablet gives a picture of surrounding objects in the ordinary\ncharacter, the bright sun itself is represented by a spot upon which\nno change has taken place.[124] In tropical climes, where a brilliant\nsun is giving the utmost degree of illumination to all surrounding\nobjects, all photographic preparations are acted upon relatively more\nslowly than in the climate of England, where the light is less intense.\nAs a remarkable instance of this fact, a circumstance may be mentioned,\nwhich is curiously illustrative of the power of light to interfere with\nactinism:--\n\nA gentleman, well acquainted with the Daguerreotype process, obtained\nin the city of Mexico all the necessary apparatus and chemicals,\nexpecting, under the bright light and cloudless skies of that climate,\nto produce pictures of superior excellence. Failure upon failure was\nthe result; and although every care was used, and every precaution\nadopted, it was not until the rainy season set in that he could secure\na good Daguerreotype of any of the buildings of that southern city.\n\nThe first attempts, which were made at the instigation of M. Arago,\nby order of the French Government, to copy the Egyptian tombs and\ntemples, and the remains of the Aztecs in Central America, were\nfailures. Although the photographers employed succeeded to admiration\nin Paris, in producing pictures in a few minutes, they found often that\nan exposure of an hour was insufficient under the bright and glowing\nillumination of a southern sky.\n\nExperiments with the spectrum have been made in different latitudes,\nand it is found, that, as we proceed towards the equator, a band which\nis always left unchanged, corresponding exactly with the rays of\ngreatest illuminating power, regularly enlarges in size, thus proving\nthe increase of light over actinism--and the interfering power of the\nformer.\n\nBy increasing the sensibility of the photographic preparation, this\ndifficulty is overcome, and particularly when any organic compound\nenters into the preparation. So that we are now enabled to copy nature\nin all her varying moods, whether we employ our photographic tablets in\ntemperate Europe, or in tropical Africa.\n\nThe degree of sensibility which has been attained is remarkable. Mr.\nFox Talbot, by uniting a process devised by Dr. Woods, of Parsonstown,\nand another which was first introduced by the author of this volume,\nand combining them with an ether, obtains a most unstable compound,\nwhich he thus employs. A glass plate is covered with albumen united\nwith the above solution, and then with nitrate of silver: this forms\nthe sensitive surface. The plate being placed in the dark, in a camera,\nit is so adjusted that the image of a printed bill fixed upon a wheel\nmay fall upon it when uncovered, and the wheel illuminated. The wheel\nis made to revolve with the utmost rapidity, in a perfectly dark\nroom, and the sensitive plate uncovered. Then the whirling bill is\nilluminated for an inappreciably short space of time by the discharge\nof a Leyden jar. Notwithstanding the rapid rate at which the pointed\npaper is moving, and the instantaneous nature of the illumination--a\nminiature flash of lightning--the bill is found to be copied with\nunfailing fidelity upon the photographic plate. It unfortunately\nhappens, that the preparation by which this extraordinary degree of\nsensibility is obtained, is very uncertain in its action--and hence it\nis not generally useful; but here we have the evidence to show that\nat a speed as rapid as that of a rifle-ball an impression may be made\nupon a photographic plate. There are, however, some new processes which\npromise eventually to rival the above for sensibility, and to be by no\nmeans of difficult manipulation. Of this character is the collodion\nprocess. The gun cotton dissolved in ether possesses some very great\naccelerating properties, and in combination with the silver salts, and\none of the vegetable acids, it forms a sensitive surface upon which\npictures may be obtained in less than a second of time.\n\nColour, natural colour too, has been very decidedly secured. The sun\nhas been solicited to display his palette, and the answer has been a\npicture in which colour for colour in all their fidelity have been\nimpressed. The plate upon which this result has been obtained is of a\ndark brown colour, and the chromatic variety is, as it were, eaten out\nby the solar rays. These colours have not yet been permanently fixed\nupon the plate employed, but from the temporary degree of fixedness\nwhich has been obtained, we may fairly hope that in a short time colour\nmay be rendered as permanent on the productions of the photographer\nas on those of the painter. It is a curious and striking fact, that\nin the preparation of these plates, salts are used which give colours\nto flame; and according to the colour which is produced by them when\nburning, so, on the photographic plate, is that colour impressed\nwith greater intensity than the others. To what is this leading us?\nMysteries surround our advances on the domain of truth. We dare not\nspeculate upon them: the time of their full development will arrive.\n\nBy the aid of this beautiful art, we are enabled to preserve the\nlineaments of those who have benefited their race by their intellect,\nor their heroism. We can hand down to future ages portraits of our own\nWellington, and the illustrious Arago, unerring in their truthfulness.\nHow great would be the joy of all, could we now obtain a daguerreotype\nportrait of a Greek poet, or of a Roman philosopher, of a Sophocles,\nor of a Seneca! How much discussion would be prevented did we possess\na calotype portrait of the Bard of Avon, or of the Philosopher of\nGrantham!\n\nBy the agency of those very rays which give life and brilliancy to the\nlaughing eye and the roseate cheek, we can at once correctly trace the\noutline of the features we admire, with all those shadowy details which\ngive a reality to the \u201cpresentment.\u201d The objects of our love may be for\never present with us in these self-painted pictures. The vicious, whom\nwe would avoid, may be made known to us by this unerring painter. The\nprocess which nature employs is perfect; the imperfections are those of\nman, and these being few, he may soon learn to remedy.\n\nTo the traveller, how valuable are the processes of photography! He\nsecures representations of those remains of temples which were in their\nglory when Moses wrote. He copies by one operation a tomb at Karnac,\ncovered with myriads of hieroglyphics, or an inscribed stone in Arabia,\nwhich it would occupy him days to trace. These he can carry to his home\nand read at his leisure. The relics of hoar antiquity speaking to the\npresent of the past, and recording the histories of races which have\nfleeted away like shadows, are thus preserved to tell their wondrous\ntales.\n\nThe admirer of nature may copy her arrangements with the utmost\nfidelity. Every modulation of the landscape, each projecting rock or\nbeetling tor--the sinuous river in its rapid flow--the meandering\nstream, \u201cgliding like happiness away;\u201d and the spreading plains\nover which are scattered the homes of honest industry and domestic\npeace, intermingled with the towers of those humble temples in which\nsimple-hearted piety delights to \u201cbow the head and bend their knee;\u201d\nthese, all of these, may, by the sunbeam which illuminates the whole,\nbe faithfully pencilled upon our chemical preparations.\n\nOur art enables us to do more even than this; we have but to present\nour sensitive tablet to the moon, and she, by her own light, prints her\nmountains and her valleys, and indicates with all truth the physical\nconditions of her surface.\n\nAny reference to the _chemical agency_ of LIGHT--_the luminous rays_ as\ndistinguished from the _chemical and calorific rays_--has been avoided\nuntil we came to the consideration of this particular question of\nchemical change.\n\nUpon organic compounds, as, for instance, upon the colouring matter\nof leaves and flowers, _light_ does exert a chemical power: and it\nis found that vegetable colours are bleached, not by rays of their\nown colour, but by those which are _complementary_ to them. A red dye\nfades under the influence of a green ray, and a yellow under that of a\nviolet one, much more speedily than when exposed to rays of any other\ncolour; and this, it must be remembered, is due to the coloured ray\nitself, and not to any _actinic_ power masked, as it were, behind the\ncolour, as is generally believed.[125] It was long a question whether\nthe decomposition of carbonic acid by plants was due to the luminous or\nthe chemical rays. It is now clearly established that the luminous rays\nare the most active in producing this effect; which they do indirectly,\nby exciting the vital powers of the organized structures. Therefore we\nwould refer this phenomenon of gaseous decomposition to a vital power\nquickened by luminous excitement.[126]\n\nWe have already noticed some chemical phenomena due to heat,\nparticularly those experiments of Count Rumford\u2019s, which appeared to\nhim to prove that the chemical agency of the sun\u2019s rays was due to its\ncalorific power. Certain chemical phenomena, we know, may be produced\nby thermic action; but the only variety of thermo-chemical action which\nconnects itself immediately with the solar radiations, belongs to a\nclass of rays to which the name of _Parathermic_ has been given, and to\nwhich the scorching, as it is called, of plants, the browning of the\nautumnal leaves, and the ripening of fruits, appear to be due.[127]\nWhen we come to the consideration of those physical phenomena which\nbelong to the growth of plants, all these peculiarities of solar action\nmust be attended to in detail.\n\nThe manner in which we find the actinic power influencing electrical\naction, also shows us that the equilibrium of forces is continued\nthrough all the great principles of nature. If a galvanic arrangement\nis made, by which small quantities of metals may be slowly precipitated\nat one of the poles in the dark, and a similar arrangement be exposed\nto sunshine, it will be found that no metal is deposited: the sun\u2019s\nrays have interfered with the decomposing power of the electrical\ncurrent. At the same time we learn, that by throwing a beam of light\nupon a plate of copper which forms one of a galvanic pair, whilst\nit is under the influence of an acidulated solution, an additional\nexcitation takes place, and the galvanometer will indicate the passage\nof an increased current of electricity. These two dissimilar actions\nappear enigmatical; but they may, there is no doubt, receive some\nsolution from the influence of different rays on the contrary poles\nof the battery. One thing is quite evident,--electricity suffers a\ndisturbance of one order, by light; and an excitement of another by its\nassociated principles in the sunbeam. If a yellow glass is interposed\nbetween the galvanic arrangement and the sun, the electro-chemical\nprecipitation goes on in the same manner as it would in perfect\ndarkness, and no extra excitement is produced upon the plates of the\nbattery. From this it would appear that actinism and not light is to be\nregarded as the disturbing power.[128] It has already been shown that\nyellow media possess the power of stopping back the chemical agent.\n\nWe have already, detailed many of the peculiarities of the different\nvarieties of Phosphori, which would seem to be the result of light.\nPhosphorescence is probably excited by those rays which produce\nno direct effect upon the eye. If we spread sulphuret of calcium\nupon paper, and expose it to the action of the solar spectrum, it\nis found to glow (in the dark) only over those spaces occupied by\nthe violet rays and the ordinarily dark rays beyond them; proving\nthat the excitation necessary to the development of the phenomena\nof phosphorescence is due to a class of rays distinct from the true\nlight-giving principle, and more nearly allied to that principle or\npower which sets up chemical decomposition. Whether the fluorescent\nrays, before mentioned, which are found so abundantly over the space\nwhich produces the greatest phosphorescent effect, are active in\nproducing the phenomena, is as yet an unsolved problem.\n\nVision and colour, calorific action, chemical change, molecular\ndisturbance, electrical phenomena, and phosphorescent excitation, all,\neach one with a strange duality, are connected with the sunbeam.\n\nWe find, when we receive solar spectra upon iodized plates, or on\nseveral kinds of photographic paper, that a line, over which no action\ntakes place, is preserved at the top and bottom of the impressed image,\nand in many cases along the sides also. The only way in which this can\nbe accounted for, as the spectrum represents the sun in a distorted\nform, is by supposing that rays come from the edges of the sun of a\ndifferent character from those which proceed from the centre of that\norb.[129]\n\nLight from the centre of the solar disc is under different conditions\nfrom that which comes from the edge of the sun: this is due to the\nvarying angle, which is presented to us by a circular body: calorific\naction seems to be more strongly manifested when the envelope of\nlight, extending like an atmosphere to the sun, is thrown into great\nagitation, and waves, and great hollows--solar spots--are produced.\nThere is some indication of the existence of a third condition on the\nsun\u2019s surface, to which probably belongs the mighty chemical power\nwhich we call actinism. Electricity may be, as some have speculated,\nthe exciting agent; a constant and violent Aurora Borealis may exist on\nthe sun, and under the excitation of this force the others named may be\nquickened into full activity.\n\nThat actinism is one of the great powers of creation we have abundant\nproof. Nearly all the phenomena of chemical change which have been\nreferred to light, are now proved to be dependent upon actinic power;\nand beyond the influence which has been ascertained to be exerted by\nit upon all inorganic bodies, we shall have occasion to show still\nfurther the dependence of the vegetable and animal worlds upon its\nagency. The influence of the solar beams on vegetation is proved by\ncommon experience; the closer examination of its action on vegetable\nlife is reserved for the chapter devoted to its phenomena. Of its\ninfluence on animals nothing is very correctly known; but some early\nexperiments prove that they, like other organised bodies, are subject\nto all the radiant forces, as indeed, independent of experiment, every\nobservation must teach. Certain it is, that organisation can take place\nonly where the sun\u2019s rays can penetrate: where there is unchanging\ndarkness, there we find all the silence of death. Prometheus stole\nfire from heaven, and gave the sacred gift to man, as the most useful\nto him of all things in his necessities: by the aid of it he could\ntemper the severities of climate, render his food more digestible and\nagreeable, and illuminate the hours of darkness. So says the beautiful\nfiction of the Grecian mind,--which appears as the poetic dream or\nprophetic glance of a gifted race, who felt the mysterious truth\nthey were yet unable to describe. Pheaton and Apollo are only other\nforeshadowings of the creative energies which dwell in the glorious\ncentre of our universe. The poetry of the Hellenic people ascended\nabove the littlenesses of merely human action, and sought to interpret\nthe great truths of creation. Reflective, they could not but see that\nsome mysterious powers were at work around them; imaginative, they gave\nto fine idealisations the government of those inexplicable phenomena.\nModern science has shown what vastly important offices the solar rays\nexecute, and that the principles discovered in a sunbeam are indeed the\nexciters of organic life, and the disposers of inorganic form.\n\nIt must not be forgotten that we have already alluded to a speculation\nwhich supposes this actinic influence to be diffused through all\nnature, to be indeed the element to which chemical force in all its\nforms is to be referred, and that it is merely excited by the solar\nrays. This hypothesis receives some support from the very peculiar\nmanner in which chemical action once set up is carried on, independent\nof all extraneous excitement, after the first disturbance has been\nproduced. If any of the salts of gold are exposed in connection with\norganic matter, as on paper, to sunshine for a moment, an action is\nbegun, which goes on unceasingly in the dark, until the gold is reduced\nto its most simple state.[130] The same thing occurs with chromate of\nsilver, some of the salts of mercury, argentine preparations combined\nwith protosulphate of iron or gallic acid, and some other chemical\ncombinations. These progressive influences point to some law not yet\ndiscovered, which seems to link this radiant actinism with the chemical\nagent existing in all matter.\n\nThis problem also connects itself with another class of facts which,\nalthough due, in all probability, to a great extent, to calorific\nradiations, and hence known under the general term of Thermography,\nappear to involve both chemical and electrical excitation. From the\ninvestigations of Moser and of others, we learn the very extraordinary\nfact, that even inanimate masses act and react upon each other by\nthe influence of some dark radiations, and seem to exchange some of\nthe peculiarities which they possess. This appears generally in the\ncurious experiments which have been referred to, as confined merely\nto form or structure. Thus an engraved plate will give to a polished\nsurface of metal or glass placed near it, after a very little time,\na neat distinct image of itself; that is, produce such a structural\ndisturbance as will occasion the plate to receive vapour differently\nover those spaces opposite to the parts in cameo or in intaglio, from\nwhat it does over the opposite. If a piece of wood is used instead of a\nmetal, there will, by similar treatment, be produced a true picture of\nthe wood, even to the representation of its fibres.[131]\n\nIt is also probable that chemical decomposition is produced by the\nmere juxtaposition of different bodies. Iodide of gold or silver,\nperfectly pure, has been placed upon a plate of glass, and a plate of\ncopper covered with mercury suspended over it: a gradual decomposition\nof those salts is said to have been observed, iodide of mercury to\nbe formed, and the gold or silver salts reduced to a finely divided\nmetallic state.[132]\n\nA body whose powers of radiating heat are low, being brought near\nanother whose radiating powers are more extensive, will, in the course\nof a short time, undergo such an amount of molecular disturbance as\nwill effect a complete change in the arrangement of its surface, and\nan impression of the body having the highest radiating powers will be\nmade upon the other. This impression is dormant, but may be developed\nunder the influence of vapour, or of oxidation.[133] A body, such\nas charcoal, of low conducting power, being placed near another,\nsuch as copper, which is a good conductor, will, in a very short\ntime, produce, in like manner, an impression of itself upon the metal\nplate. Thus any two bodies, whose conducting or radiating powers are\ndissimilar, being brought near each other, will occasion a molecular\ndisturbance, or impress the one with the image of the other. However\nsmall the difference may be, an effect is perceived, and that of the\nmost extraordinary kind, giving rise to the production of actual images\nupon each surface exposed. It is thus that a print on paper may be\ncopied on metal, by merely suspending it near a well-polished plate of\nsilver or copper for a few days. The white and black lines radiate very\ndifferently; consequently an effect is produced on the bright metal in\nthe parts corresponding to the black lines, dissimilar to that which\ntakes place opposite to the white portions of the paper; and, on the\napplication of vapour, a true image of the one is found impressed upon\nthe other.[134]\n\nBodies which are in different electrical states act upon each other in\nan analogous manner. Thus arsenic, which is highly electro-negative,\nwill, when placed near a piece of electro-positive copper, readily\nimpart to its surface an impression of itself, and so in like manner\nwill other bodies if in unlike conditions. Every substance physically\ndifferent (it signifies not whether as it regards colour, chemical\ncomposition, mechanical structure, calorific condition, or electrical\nstate,) has a power of radiation by which a sensible change can be\nproduced in a body differently constituted.\n\nFable has told us that the magicians of the East possessed mirrors in\nwhich they could at will produce images of the absent. Science now\nshows us that representations quite sufficient to deceive the credulous\ncan be produced on the surface of polished metals without difficulty.\nA highly polished plate of steel may be impressed with images of any\nkind, which would remain invisible, the polished surface not being in\nthe least degree affected, as it regards its reflecting powers; but\nby breathing over it, the dormant images would develope themselves,\nand fade away again as the condensed moisture evaporated from the\nsurface.[135]\n\nThese, which are but a few selected from a series of results of an\nequally striking character, serve to convince us that nature is\nunceasingly at work, that every atom is possessed of properties by\nwhich it influences every other atom in the universe, and that a most\nimportant class of natural phenomena appear to connect themselves\ndirectly with the radiant forces.\n\nThe alchemists observed that a change took place in chloride of silver\nexposed to sunshine. Wedgwood first took advantage of that discovery to\ncopy pictures. Niepce pursued a physical investigation of the curious\nchange, and found that all bodies were influenced by this principle\nradiated from the sun. Daguerre produced effects from the solar pencil\nwhich no artist could approach to; and Talbot and others extended the\napplication. Herschel took up the inquiry; and he, with his usual\npower of inductive search and of philosophical deduction, presented\nthe world with a class of discoveries which showed how vast a field of\ninvestigation was opening for the younger races of mankind,--a field\nin which a true spirit may reap the highest reward in the discovery of\nnew facts, and to which we must look for a further development of those\ngreat powers with which we have already some slight acquaintance, and\nfor the discovery of higher influences which are not yet dreamed of in\nour philosophy.\n\n    If music, with its mysteries of sound,\n      Gives to the human heart a heavenward feeling;\n    The beauty and the grandeur which are found\n    Spread like a vesture this fair earth around,\n      Creation\u2019s wond\u2019rous harmonies revealing,\n      And to the soul in truth\u2019s strong tongue appealing,\n    With all the magic of those secret powers,\n      Which, mingling with the lovely band of light,\n    The sun in constant undulation showers\n    To mould the crystals, and to shape the flowers,\n      Or give to matter the immortal might\n    Of an embracing soul--should, from this sod,\n    Exalt our aspirations all to God.\n\n\nFOOTNOTES:\n\n[117] See _Researches on Light_, by the Author.--Reference to any of\nthe works of the alchemists will prove the prevalence of the idea\nexpressed in the text. We find that gold was considered to be always\nunder the influence of light and solar heat.--\u201cIt is said of gold that\nit waxeth cold towards daylight, insomuch that they who wear rings of\nit may perceive when the day is ready to dawn.\u201d--_Speculum Mundi, or a\nGlass representing the face of the World_. Cambridge, 1643.\n\n[118] Daguerre\u2019s Report to the Academy of Sciences: _La Daguerr\u00e9otype\nHistorique, et description des proc\u00e9d\u00e9s du Daguerr\u00e9otype et du Diorama_\n(Paris, 1839); particularly the description of _Heliography_, by M.\nNiepce. See also the letters by Niepce, published for the first time in\n_Researches on Light_.\n\n[119] \u201cIf a solution of peroxalate of iron be kept in a dark place,\nor if it be exposed to 212\u00b0 of Fahr. for several hours, it does not\nundergo any sensible change in its physical properties, nor does it\nexhibit any phenomenon which may be considered as the result of any\nelementary action.\n\n\u201cIf, however, it be exposed to the influence of solar light in a glass\nvessel provided with a tube, the concentrated solution of oxalate\nof iron soon presents a very interesting phenomenon: in a short\ntime the solution receiving the solar rays, developes an infinite\nnumber of bubbles of gas, which rise in the liquor with increasing\nrapidity, and give the solution the appearance of a syrup undergoing\nstrong fermentation. This ebullition always becomes stronger, and\nalmost tumultuous, when an unpolished glass tube is immersed in it\nwith a small piece of wood; the liquid itself is afterwards thrown\ninto ascending and descending currents, becomes gradually yellowish,\nturbid, and eventually precipitates protoxalate of iron, in the form\nof small brilliant crystals of a lemon-yellow colour, gas continuing\nto evolve.\u201d _Chemical action of light, and formation of Humboldtine\nby it_; Phil. Mag., 1832, second series.--\u201cWhen a solution of\nplatinum in nitro-muriatic acid, in which the excess of acid has been\nneutralized by the addition of lime, and which has been well cleared\nby filtration, is mixed with lime-water in the dark, no precipitation\nto any considerable extent takes place for a long while,--indeed, none\nwhatever, though after very long standing a slight flocky sediment\nis formed, after which the action is arrested entirely. But if the\nmixture, either freshly made or when cleared by subsidence of this\nsediment, is exposed to sunshine, it instantly becomes milky, and a\ncopious formation of a white precipitate (or a pale yellow one, if the\nplatinic solution be in excess) takes place, which subsides quickly\nand is easily collected. The same takes place more slowly in cloudy\ndaylight.\u201d--_On the action of light in determining the precipitation of\nMuriate of Platinum by Lime water_; being an extract from a letter from\nSir John F. W. Herschel, K.H., F.R.S., &c., to Dr. Daubeny.--Phil. Mag.\n1832.\n\n[120] _On a change produced by Exposure to the Beams of the Sun, in\nthe properties of an elementary substance_, by Professor Draper;\n_On the changes which bodies undergo in the dark_, by Robert Hunt:\nReport of the Thirteenth Meeting of the British Association, vol.\nxii,--_Description of the Tithonometer, an instrument for measuring\nthe chemical force of the Indigo-tithonic rays_: by J. W. Draper,\nM.D.--Philosophical Magazine, Dec. 1843, vol. xxiii.\n\n[121] For several illustrations of this remarkable phenomenon, see _On\nthe Action of the Rays of the Solar Spectrum on Vegetable Colours,\nand on some new Photographic Processes_; by Sir John F. W. Herschel,\nBart., K.H., F.R.S.--Phil. Trans. June, 1842, vol. cxxxiii.; _On\ncertain improvements on Photographic Processes described in a former\ncommunication, and on the Parathermic Rays of the Solar Spectrum_;\nby Sir John F. W. Herschel, Bart., K.H., F.R.S., &c., in a letter\naddressed to S. Hunter Christie.--Phil. Trans. 1843, vol. cxxxiv.\n\n[122] Sir J. F. W. Herschel; see also _Researches on Light_, by the\nAuthor.\n\n[123] Attention has been directed to the protecting action of certain\nrays of the spectrum by Sir John Herschel and others. See the\nEighteenth Report of the British Association for an experiment by\nthe Author, in which it was proved that all the LIGHT rays protected\nphotographic papers from chemical change, and, therefore, convincingly\nshow that light and actinism were not similar powers.\n\n[124] \u201cHaving noticed, one densely foggy day, that the disc of the sun\nwas of a deep red colour, I directed my apparatus towards it. After\nten seconds of exposure, I put the prepared plate in the mercury box,\nand I obtained a round image perfectly black;--the sun had produced no\nphotogenic effect. In another experiment, I left the plate operating\nfor twenty minutes; the sun had passed over a certain space of the\nplate, and there resulted an image seven or eight times the sun\u2019s\ndiameter in length; it was black throughout, so that it was evident,\nwherever the red disc of the sun had passed, not only was there a\nwant of photogenic action, but the red rays had destroyed the effect\nproduced previous to the sun\u2019s passage. I repeated these experiments\nduring several days successively, operating with a sun of different\ntints of red and yellow. These different tints produced nearly the same\neffect; wherever the sun had passed, there existed a black band.\u201d--Mr.\nClaudet, _On different properties of Solar Radiation, modified by\ncoloured glass media, &c._: Phil. Trans. 1847. Part 2.\n\n[125] \u201cIt may also be observed that the rays effective in destroying\na given tint are, in a great many cases, those whose union produces a\ncolour complementary to the tint destroyed, or at least one belonging\nto that class of colours to which such complementary tint may be\nreferred. For example, yellows tending towards orange are destroyed\nwith more energy by the blue rays; blue by the red, orange, and yellow\nrays; purples and pinks by yellow and green rays.\u201d--Sir J. F. W.\nHerschel, _On the action of the rays of the Solar Spectrum on Vegetable\nColours_: Phil. Trans., vol. cxxxiii. 1842.\n\n[126] The following memoirs and works are necessary to a complete\nhistory of the inquiry:--_Experiments and observations relating\nto various branches of natural philosophy, with a continuation of\nthe observation on air_: by Dr. Priestley. London, 1779. _M\u00e9moires\nPhysico-chimiques, &c._: by J. Senebier. _Exp\u00e9riences sur les\nv\u00e9g\u00e9taux_, by De la Ville: Paris, 1782; and Phil. Trans. 1782.\n_Observations sur les exp\u00e9riences de M. Ingenhousz_: by De la Ville;\nRoz. obs. 23, 290. _Exp\u00e9riences propres \u00e0 d\u00e9velopper les effets de la\nlumi\u00e8re sur certaines plantes_: by Tessier; M\u00e9m. de l\u2019Ac. des Sc. de\nParis, 1783, p. 132; Licht. Mag. iv. 4, 146. _Sur la vertu de l\u2019eau\nimpregn\u00e9e d\u2019air fixe pour en obtenir, par le moyen des plantes et de\nla lumi\u00e8re du soleil, de l\u2019air d\u00e9phlogistiqu\u00e9_: by Ingenhousz; Roz.\nobs. 24, 337. _Exp\u00e9riences sur l\u2019action de la lumi\u00e8re solaire dans la\nv\u00e9g\u00e9tation_: by Senebier; Gen\u00e8ve et Paris, 1788, p. 61. _Extrait des\nexp\u00e9riences de M. Senebier sur l\u2019action de la lumi\u00e8re solaire dans la\nv\u00e9g\u00e9tation_: by Hasenfratz; Ann. Chim. iii. 2nd. ser. 266. _Exp\u00e9riences\nrelatives \u00e0 l\u2019influence de la lumi\u00e8re sur quelques v\u00e9g\u00e9taux_: by De\nCandolle; Jour. de Ph. lii. 124: Voigt\u2019s Mag. ii. 483; Gilb. Ann.\nxiii. 372; M\u00e9m. des Sav. Etr. i. 329. _Recherches chimiques sur la\nv\u00e9g\u00e9tation_: by Saussure; Ann. Chim. l. 225; Jour. de Ph. lvii. p.\n393; Gilb. Ann. xviii 208. _Recherches sur la respiration des plantes\nexpos\u00e9es \u00e0 la lumi\u00e8re du soleil_; by Ruhland; Ann. Ch. Ph. iii. 411;\nJour. de Ph. 1816. _On the action of light upon plants, and of plants\nupon the atmosphere_: by Dr. Daubeny; Phil. Trans. cxxvii January,\n1836. _On the action of yellow light in producing the green colour, and\nof indigo light on the movements of plants_: by P. Gardner; Phil. Mag.\nxxiv.; Bibl. Univ. xlix. p. 376, and lii. p. 381. _On the influence of\nlight on plants_: by R. Hunt; Phil. Mag. xxiv. p. 96; Bibl. Univ. xlix.\np. 383; Athen. 1844. _Note on the decomposition of carbonic acid by\nthe leaves of plants, under the influence of yellow light_: by Draper;\nPhil. Mag. xxv. p. 169. _On the action of the yellow rays of light on\nvegetation_: by Harkness; Phil. Mag. xxv. p. 339. _Influence des rayons\nsolaires sur la v\u00e9g\u00e9tation_: by Zantedeschi; Inst. No. 541, p. 157.\n\n[127] Sir John Herschel\u2019s Memoirs already referred to; and _Reports on\nthe influence of the Solar Rays on the growth of Plants_, by Robert\nHunt: Report of the British Association for the Advancement of Science,\nfor 1847.\n\n[128] _Memoir on the Constitution of the Solar Spectrum_, presented at\nthe meeting of the Academy of Sciences, 1842, by M. Edmond Becquerel;\n_Des effets produits sur les corps par les rayons solaires_, par M.\nEdmond Becquerel, aide au Mus\u00e9um d\u2019Histoire Naturelle: M\u00e9moire pr\u00e9sent\u00e9\n\u00e0 l\u2019Acad\u00e9mie des Sciences, le 23 Octobre, 1843.--\u201cDans le courant de\nce m\u00e9moire, j\u2019ai employ\u00e9 les noms de rayons lumineux, chimiques, et\nphosphorog\u00e9niques, pour d\u00e9signer, dans chaque cas, la portion des\nrayons solaires qui agit pour produire, en particulier, les effets\nlumineux, chimiques, et phosphorog\u00e9niques; mais cela est sans pr\u00e9judice\nde l\u2019opinion que je viens d\u2019\u00e9mettre touchant l\u2019existence d\u2019un seul et\nm\u00eame rayonnement.\u201d\n\n\u201cMy reply is this,\u201d says M. Arago, in his paper entitled\n_Considerations relative to the action of Light_: \u201cIt is by no means\nproved that the photogenic modifications of sensitive substances\nresult from the action of the solar light itself. The modifications\nare, perhaps, engendered by invisible radiations mixed with light\nproperly so called, proceeding with it, and being similarly refracted.\nIn this case, the experiment would prove not only that the spectrum\nformed by these invisible rays is not continuous, that there are\nsolutions of continuity as in the visible spectrum, but also that in\nthe two superposed spectra these solutions correspond exactly. This\nwould be one of the most curious, one of the most strange results of\nphysics.\u201d--Taylor\u2019s Scientific Memoirs.\n\n[129] The chemical evidence of this will be found in Sir John\nHerschel\u2019s Memoir _On the Solar Spectrum_, and particularly as\nexemplified in the changes produced on the tartrate of silver. Similar\ninfluences are described as observed on a Daguerreotype plate, in\na paper entitled _Experiments and Observations on Light which has\npermeated coloured media, and on the Chemical Action of the Solar\nSpectrum_; by Robert Hunt.--Philosophical Magazine, vol. xxvi. 1840.\n\n[130] This peculiar continuance of an effect has frequently been\nobserved in many of the photographic processes. In a note to a memoir\n_On certain improvements in Photographic processes_, Sir John Herschel\nthus refers to this property:--\u201cThe excitement is produced on such\npaper by the ordinary moisture of the atmosphere, and goes on slowly\nworking its effect in the dark, apparently without other limit than is\nafforded by the supply of ingredients present. In the case of silver it\nultimately produces a perfect _silvering_ of all the sunned portions.\nVery singular and beautiful photographs, having much resemblance to\nDaguerreotype pictures, are thus produced; the negative character\nchanging by keeping, and by quite insensible gradations to positive,\nand the shades exhibiting a most singular _chatoyant_ change of colour\nfrom ruddy-brown to black, when held more or less obliquely. No doubt,\nalso, gold pictures with the metallic lustre might be obtained by the\nsame process, though I have not tried the experiment.\u201d\n\n[131] The details of this curious subject may be studied in the\nfollowing memoir and communications:--_On vision and the action of\nlight on all bodies_: by Professor Ludwig Moser, of K\u00f6nigsberg; from\nPoggendorff\u2019s Annalen, vol. lvi. p. 177, No. 6, 1845. _Some remarks\non Invisible Light_: by Professor Ludwig Moser, of K\u00f6nigsberg; from\nPoggendorff\u2019s Annalen, vol. lvi. p. 569, No. 8. _On the power which\nlight possesses of becoming latent_: by Professor Ludwig Moser, of\nK\u00f6nigsberg; from Poggendorff\u2019s Annalen, vol. lvii. No. 9, p. 1. 1842.\n_On certain spectral appearances, and on the discovery of latent\nlight_: by J. W. Draper, M.D., Professor of Chemistry in the University\nof New York; Phil. Mag. p. 348, Nov. 1842. _On a new imponderable\nsubstance, and on a class of chemical rays analogous to the rays of\ndark heat_: by Professor Draper; Phil. Mag., Dec. 1842. _On the action\nof the rays of the solar spectrum on the Daguerreotype plate_; by Sir\nJ. F. W. Herschel, Bart.; Phil. Mag., Feb. 1843. See remarks in this\npaper on the use which Moser has made of coloured glasses: also a\ncommunication by Professor Draper, _On the rapid Detithonizing power of\ncertain gases and vapours, and on an instantaneous means of producing\nspectral appearances_: Phil. Mag., March 1843; and _On the causes which\nconcur in the production of the images of Moser_: Comptes Rendus, Nov.\n1842. See _Scientific Memoirs_, vol. iii.\n\n[132] This fact was first observed by myself, and described in the\npaper already referred to, Philosophical Magazine, vol. xxii. p. 270.\nIt does not, however, appear to have attracted the attention of any\nother observer.\n\n[133] _On Thermography, or the Art of copying Engravings or any printed\ncharacters from paper or plates of metal, and on the recent discovery\nof Moser, relative to the formation of images in the dark_, by Robert\nHunt: Reports of the Royal Cornwall Polytechnic Society for 1842, and\nPhilosophical Magazine, vol. xxi. p. 462.--_On the Spectral Images of\nM. Moser_, by Robert Hunt: Philosophical Magazine, vol. xxiii. p. 415.\n\n[134] _Catalytic force, or attraction of surface concerned in the\ndiffusive power of gases: an occult energy or power in saturated saline\nsolutions_; Prater.--Mechanic\u2019s Magazine, vol. xlv. p. 106. _Ueber\nelektrische Abbildungen_; by G. Karsten.--Poggendorff\u2019s Annalen, vol.\nlvii. p. 402.--Melloni and Brewster may be consulted for much that is\nmost remarkable connected with radiation from coloured surfaces.\n\n[135] Cornelius Agrippa is said to have possessed such a mirror.\nThe Chinese make mirrors which, when placed in a particular light,\nshow upon their polished faces the pattern on the back of the metal,\nalthough it is invisible in every other position. This is effected by\ngiving different degrees of hardness to the various parts of the metal.\nIn _Natural Magic_, by Sir David Brewster, several curious experiments\nbelonging to this class are named.\n\n\n\n\nCHAPTER IX.\n\nELECTRICITY.\n\n  Discovery of Electrical Force--Diffused through all Matter--What\n    is Electricity?--Theories--Frictional Electricity--Conducting\n    Power of Bodies--Hypothesis of two Fluids--Electrical\n    Images--Galvanic Electricity--Effects on Animals--Chemistry of\n    Galvanic Battery--Electricity of a Drop of Water--Electro-chemical\n    Action--Electrical Currents--Thermo-Electricity--Animal\n    Electricity--Gymnotus--Torpedo--Atmospheric Electricity--Lightning\n    Conductors--Earth\u2019s Magnetism due to Electrical Currents--Influence\n    on Vitality--Animal and Vegetable Development--Terrestrial\n    Currents--Electricity of Mineral Veins--Electrotype--Influence of\n    Heat, Light, and Actinism on Electrical Phenomena.\n\n\nIf a piece of amber, _electrum_, is briskly rubbed, it acquires the\nproperty of attracting light bodies. This curious power excited the\nattention of Thales of Miletus; and from the investigations of this\nGrecian philosopher we must date our knowledge of one of the most\nimportant of the natural forces--Electricity.\n\nIf an inquiring mind had not been led to ask why does this curious\nnatural production attract a feather, the present age, in all\nprobability, would not have been in possession of the means by which it\nis enabled to transmit intelligence with a rapidity which equals the\npoet\u2019s dream of the \u201cswift-winged messengers of thought.\u201d To this age\nof application a striking lesson does this amber teach. Modern utility\nwould have regarded Thales as a madman. Holding a piece of yellow\nresin in his hand, rubbing it, and then picking up bits of down, or\ncatching floating feathers, the old Greek would have appeared a very\nimbecile, and the _cui bono_ generation would have laughed at his silly\nlabours. But when he announced to his school that this amber held a\nsoul or essence, which was awakened by friction, and went forth from\nthe body in which it previously lay dormant, and brought back the small\nparticles floating around it, he gave to the world the first hint of\na great truth which has advanced our knowledge of physical phenomena\nin a marvellous manner, and ministered to the refinements and to the\nnecessities of civilisation. Each phenomenon which presents itself to\nus, however simple it may appear to be, is an outward expression of\nsome internal truth, the interpretation of which is only to be arrived\nat by assiduous study, but which, once discovered, directs the way to\nnew knowledge, and gives to man a great increase of power. There is no\ntruth so abstract that it will not find its useful application, and\nevery example of the ministration of Physical Science to the purposes\nof humanity is an evidence of the value of abstract study, and a reply\nto the utilitarian in his own language.\n\nElectricity appears to be diffused through all nature; and it is,\nbeyond all doubt, one of the most important of the physical forces, in\nthe great phenomena of creation. In the thunder-cloud, swelling with\ndestruction, it resides, ready to launch its darts and shake the earth\nwith its explosions: in the a\u00ebrial undulations, silent and unseen, it\npasses, giving the necessary excitement to the organisms around which\nit floats. The rain-drop--the earth-girdling ocean--and the ringing\nwaters of the hill-born river, hold locked this mighty force. The\nsolid rocks--the tenacious clays which rest upon them--the superficial\nsoils--and the incoherent sands, give us evidence of the presence of\nthis agency; and in the organic world, whether animal or vegetable, the\nexcitement of electrical force is always to be detected.\n\nIn the solar radiations we have perhaps the prime mover of this\npower. In our atmosphere, when calm and cloudless, a great ocean of\nlight, or when sombre with the mighty aspect of the dire tornado, we\ncan constantly detect the struggle between the elements of matter to\nmaintain an equilibrium of electrical force.\n\nDiffused throughout matter, electricity is ever active; but it must\nbe remembered that although it is evidently a necessary agent in all\nthe operations of nature, that it is not the agent to which everything\nunknown is to be referred. Doubtless the influence of this force is\nmore extensive than we have yet discovered; but that is an indolent\nphilosophy which refers, without examination, every mysterious\nphenomenon to the influence of electricity.\n\nThe question, what is electricity? has ever perplexed, and still\ncontinues to agitate, the world of science. While one set of\nexperimentalists have endeavoured to explain the phenomena they have\nwitnessed, upon the theory that electricity is a peculiar subtile\nfluid pervading matter, and possessing singular powers of attraction\nand repulsion, another party find themselves compelled to regard\nthe phenomena as giving evidence of the action of two fluids which\nare always in opposite states; while again, electricity has been\nconsidered by others as, like the attraction of gravitation, a mere\nproperty of matter.[136] Certain it is, that in the manifestations\nof electrical phenomena we have, as it appears, the evidence of two\nconditions of force; but of the states of _positive_ or _negative_, of\n_vitreous_ or _resinous_ electricity, we have a familiar explanation\nin the assumption of some current flowing into or out of the material\nbody,--of some principle which is ever active in maintaining its\nequilibrium, which, consequently, must act in two directions, and\nalways exhibit that duality which is a striking characteristic of this\nsubtile agent. It is a curious, and it should be an instructive fact,\nthat each of the three theories of electricity is capable of proof,\nand has, indeed, been most ably supported by the rigorous analysis\nof mathematics. When we remember that some of the most enlightened\ninvestigators of this and the past age have severally maintained,\nin the most able manner, these dissimilar views, we should hesitate\nbefore we pronounce an opinion upon the cause or causes of the very\ncomplicated phenomena of electrical force.\n\nAlthough we discover, in all the processes of nature, the\nmanifestations of this principle or force in its characteristic\nconditions, it will be necessary, before we regard the great phenomena,\nto examine the known sources from which we can most readily evoke the\nmighty power of electricity. If we rub a piece of glass or resin, we\nreadily render this agent active; these substances appear, by this\nexcitement, to become surrounded by an attractive or a repellent\natmosphere. Let us rub a strip of writing paper with Indian rubber,\nor a strip of Gutta Percha with the fingers, in the dark, and we have\nthe manifestation of several curious phenomena. We have a peculiar\nattracting power; we have a luminous discharge in the shape of a spark;\nand we have very sensible evidence of muscular disturbance produced by\napplying the knuckle to the surface of the material. In each case we\nhave the development of the same power.\n\nEvery substance in nature is an electric, and, if so disposed that its\nelectricity may not fly off as it is developed, we may, by friction,\nmanifest its presence, and, indeed, measure its quantity or its force.\nAll bodies are not, however, equally good electrics; shell-lac, amber,\nresins, sulphur, and glass, exhibiting more powerfully the phenomena\nof frictional or mechanical electricity, than the metals, charcoal,\nor plumbago. Solid bodies allow this peculiar principle to pass along\nthem also in very different degrees. Thus electricity travels readily\nthrough copper and most other metals, platinum being the worst metallic\nconductor. It also passes through living animals and vegetables, smoke,\nvapour, rarified air, and moist earth; but it is obstructed by resins\nand glass, paper when dry, oils, and dry metallic oxides, and in a very\npowerful manner by Gutta Percha.[137]\n\nIf, therefore, we place an electric upon any of those non-conducting\nbodies, the air around being well dried, we are enabled to gather\na large quantity of the force for the production of any particular\neffect. Taking advantage of this fact, arrangements are made for the\naccumulation and liberation at pleasure of any amount of electricity.\n\nA Leyden phial,--so called from its inventor, Musschenbroek, having\nresided at Leyden,--is merely a glass bottle lined within and without,\nto within a few inches of the top, with a metal coating. If a wire or\nchain, carrying an electric current, is allowed to dip to the bottom\nof the bottle, the inner coat of the jar becomes charged, or gathers\nan excess, whilst the outer one is in its natural condition--one is\nsaid to be in a _positive_, and the other in a _negative_ state. If\nthe two coatings are now connected by a good conductor, as a piece of\ncopper wire, passing from one to the other, the outside to the inside,\na discharge, arising from the establishment of the equilibrium of the\ntwo coatings, takes place; and, if the connection is made through the\nmedium of our bodies, we are sensible of a severe disturbance of the\nnervous system.\n\nThe cause of the conducting and non-conducting powers of bodies we know\nnot; they bear some relation to their conducting powers for caloric;\nbut they are not in exact obedience to the same laws. When we consider\nthat resin, a comparatively soft body, in which, consequently,\ncohesive attraction is not very strong, is an imperfect conductor,\nand that copper, in which cohesion is much more powerful, is a good\nconductor, we may be disposed to consider that it is regulated by the\ncloser approximation of the particles of matter. But in platinum the\ncorpuscular arrangement must be much more dense than it is in copper,\nand yet it is, compared with it, a very bad conductor.[138]\n\nWe have now learnt that we may, by friction, excite the electricity\nin a vitreous substance; but it must not be forgotten that we cannot\nincrease the quantity which is, under ordinary conditions, natural to\nthe electric; to do so, we must in some way establish a channel of\ncommunication with the earth, from which, through the medium we excite,\nwe draw our supply. We have the means of confining this mighty force\nwithin certain limits of quantity and of time. If we place bodies which\nare susceptible of electrical excitation in a sensible degree upon\ninsulating ones, we may retain for a considerable time the evidences of\nthe excitement, in the same way as with the Leyden jar; but there is a\nconstant effort to maintain a balance of conditions, and the body in\nwhich we have accumulated any extraordinary quantity by conduction soon\nreturns to its natural state.\n\nA very simple means may be adopted of showing what is thought to be\none of the many evidences in favour of two electricities. If the\nwire carrying the current flowing from the machine, is passed over\npaper covered with nitrate of silver, it produces no change upon it;\nbut if the wire which conveys the current to the instrument, when\nit is excited, is passed over the same paper, the silver salt is\ndecomposed.[139] We may, however, explain this result in a satisfactory\nmanner, upon the hypothesis that the decomposition is produced by the\nabstraction of electricity, rather than by any physical difference in\nthe fluid itself. By frictional electricity we may produce curious\nmolecular disturbances, and give rise to molecular re-arrangements,\nwhich have been called \u201celectrical images,\u201d in glass, in stone, and in\nthe apparently less tractable metals: these images are rendered visible\nby the manner in which, according to their electrical states, some\nlines receive any particular powder, or vapour, which is repelled from\nother spaces. Many of the great natural phenomena, such as Lightning\nand Thunder, the Aurora Borealis, and Meteors, may be imitated in a\ncuriously exact manner by the electrical machine and a few familiar\narrangements.[140]\n\nVoltaic electricity, as the active force produced by chemical change\nis commonly called, in honour of the illustrious Volta, is now to\nbe considered. It differs from frictional electricity in this:--the\nelectricity developed by friction of the glass plate or cylinder of\nthe electrical machine is a discharge with a sort of explosion. It\nis electricity suddenly liberated from the highest state of tension,\nwhereas that which is generated by chemical action in the voltaic\nbattery is a steady flowing current. We may compare one to the ignition\nof a mass of gunpowder at once, and the other to the slow burning of\nthe same quantity spread out into a very prolonged train.\n\nThere are numerous ways in which we may excite the phenomena of\nVoltaism, but in all of them the decomposition of one of the elements\nemployed appears to be necessary. This is the case in the arrangements\nof batteries in which two dissimilar metals, zinc and copper, silver\nand platinum, or the like, is immersed in fluids; the zinc or the\nsilver are gradually converted into soluble salts, which are dissolved,\nwhilst the copper or platinum is protected from any action. The most\nsimple manner of illustrating the development of this electricity is by\nplacing a piece of silver on the tongue, and a piece of zinc or lead\nunderneath it. No effect will be observed so long as the two metals\nare kept asunder, but when their edges are brought together, a slight\ntremulous sensation will pass through the tongue, a saline taste be\ndistinguished by the palate, and if in the dark, light will be observed\nby the eye.\n\nThis, the germ of the most remarkable of the sciences, was noticed by\nSulzar, fifty years before Galvani observed the convulsions in the\nlimbs of frogs, when excited by the action of dissimilar metals; but\nthe former paid little attention to the phenomenon, and the discovery\nled to no results.\n\nWhen Galvani\u2019s observant mind was directed to the remarkable fact that\nthe mere contact of two dissimilar metals with the moist surface of\nliving muscles produced convulsions, there was an awakening in the soul\nof that philosopher to a great fundamental truth, which was nurtured\nby him, tried and tested, and preserved to work its marvels for future\nages.\n\nAlthough the world of science looks back to Volta as the man who gave\nthe first true interpretation of this discovery, yet the ordinary world\nwill never disconnect this important branch of physical science from\nthe name of Galvani, and chemical electricity in all its forms will for\never be known under the familiar name of Galvanism. And it must not be\nforgotten, that the phenomena of the manifestation of electricity, in\nconnection with the conditions of vitality, are entirely due to Galvani.\n\nLet us examine the phenomena of Galvanism in its most simple phases:--\n\nIf we place a live flounder upon a plate of zinc, put a shilling on its\nback, and then touch both metals with the ends of a metallic wire, the\nfish will exhibit painful convulsions. The zinc becomes oxidized by\nthe separation of oxygen from the fluid on the surface with which it is\nin contact, whilst hydrogen gas is liberated at that surface touched\nby the other metal. Here we have, in the first place, a chemical\nchange effected, then a peculiar muscular disturbance. Each successive\ncombination or decomposition, like a pulsation, is transmitted along\nthe circuit from one extremity to the other. How the impulse which is\nderived from the zinc is transmitted through the body of the animal, or\nthe tongue, to the silver or copper is the next consideration.\n\nWe can only understand this upon the supposition that a series of\nimpulses are communicated in the most rapid manner along the connecting\nline; the idea of a current, although the term is commonly employed,\ntends to convey an imperfect impression to the mind. It would seem\nrather that a disturbance throughout the entire circuit is at once set\nup by a series of vibrations or impulses communicated from particle to\nparticle, and along the strange net-work of nerves. One set of chemical\nelements have a tendency to develope themselves at that point where\nvibration is first communicated to the mass from a better conductor\nthan it is, and another set at the point where it passes from the\nbody to a better conductor than itself. The cause of this is to be\nsought for in the laws which regulate molecular constitution--by which\nchemical affinity is disturbed,--and a new attractive force exerted,\nin obedience to which the vital energy is itself agitated. We must\nnot, however, forget that it is probable after all, although not yet\nsusceptible of proof, that the electricity does nothing more than\ndisturb or quicken the unknown principles upon which chemical and vital\nphenomena depend; being, indeed, a secondary agent.[141]\n\nNotwithstanding our long acquaintance with the phenomena of galvanism,\nthere are but few who entertain a correct idea of the enormous amount\nof electricity which is necessary to the existing conditions of matter.\nTo Faraday we are indebted for the first clear set of deductions from a\nseries of inductive researches, which are of the most complete order.\nHe has proved, by a series of exceedingly conclusive experiments, that\nif the electrical power which holds a grain of water in combination,\nor which causes a grain of oxygen and hydrogen to unite in the right\nproportions to form water, could be collected and thrown into the\ncondition of a voltaic current, it would be exactly the quantity\nrequired to produce the decomposition of that grain of water, or the\nliberation of its elements, hydrogen and oxygen.[142]\n\nBy direct experiment it has been proved that one equivalent of zinc in\na voltaic arrangement evolves such a quantity of electricity in the\nform of a current, as, passing through water, will decompose exactly\none equivalent of that fluid. The law has been thus expressed:--The\nelectricity which decomposes, and that which is evolved by the\ndecomposition of a certain quantity of matter, are alike. The\nequivalent weights of bodies are those quantities of them which contain\nequal quantities of electricity; electricity determining the equivalent\nnumber, because it determines the combining force.[143]\n\nThe same elegant and correct experimentalist has shown that zinc and\nplatinum wires, one-eighteenth of an inch in diameter, and about half\nan inch long, dipped into water in which is mixed sulphuric acid so\nweak that it is not sensibly sour to the tongue, will evolve more\nelectricity in one-twentieth of a minute than is given by thirty turns\nof a large and powerful plate electrical machine in full action, a\nquantity which, if passed through the head of a cat, is sufficient to\nkill it as by a flash of lightning. Pursuing this interesting inquiry\nyet further, it is found that a single grain of water contains as\nmuch electricity as could be accumulated in 800,000 Leyden jars, each\nrequiring thirty turns of the large machine of the Royal Institution to\ncharge it,--a quantity equal to that which is developed from a charged\nthunder-cloud. \u201cYet we have it under perfect command,--can evolve,\ndirect, and employ it at pleasure; and when it has performed its full\nwork of electrolisation, it has only separated the elements of a single\ngrain of water.\u201d\n\nIt has been argued by many that the realities of science will not admit\nof anything like a poetic view without degrading its high office; that\npoetry, being the imaginative side of nature, has nothing in common\nwith the facts of experimental research, or with the philosophy which\ngeneralises the discoveries of severe induction. If our science was\nperfect, and laid bare to our senses all the secrets of the inner\nworld; if our philosophy was infallible, and always connected one\nfact with another through a long series up to the undoubted cause of\nall--then poetry, in the sense we now use the term, would have little\nbusiness with the truth; it would, indeed, be lost or embodied, like\nthe stars of heaven, in the brightness of a meridian sun. But to take\nour present fact as an example, how important a foundation does it\noffer upon which to build a series of thoughts, capable of lifting\nthe human mind above the materialities by which it is surrounded,--of\nexalting each common nature by the refinement of its fresh ideas to a\npoint higher in the scale of intelligence,--of quickening every impulse\nof the soul,--and of giving to mankind the most holy longings.\n\nWhat does science tell us of the drop of water? Two gases, the one\nexciting life and quickening combustion, the other a highly inflammable\nair, are, by the influence of a combination of powers, brought into\na liquid globe. We can, from this crystal sphere, evoke heat, light,\nelectricity, and actinism in enormous quantities; and beyond these\nwe can see powers or forces, for which, in the poverty of our ideas\nand our words, we have not names; and we learn that each one of these\nprinciples is engaged in maintaining the conditions of the drop of\nwater which refreshes organic nature, and gives gladness to man\u2019s\ndwelling-place.\n\nHas poetry a nobler theme than this? Agencies are seen like winged\nspirits of infinite power, each one working in its own peculiar way,\nand all to a common end,--to produce, under the guidance of omnipotent\nrule, the waters of the rivers and the seas. As the great ocean mirrors\nthe bright heaven which overspreads it, and reflects back the sunlight\nand the sheen of the midnight stars in grandeur and loveliness; so\nevery drop of water, viewed with the knowledge which science has given\nto us, sends back to the mind reflections of yet distant truths which,\nrightly followed, will lead us upwards and onwards in the tract of\nhigher intelligences,--\n\n    \u201cTo the abodes where the eternals are.\u201d\n\nIn the discoveries connected with electricity, we have results of\na more tangible character than are as yet connected with the other\nphysical forces; and it does appear that this science has advanced\nour knowledge of nature and of the mysteries of creation far more\nextensively than any other department of purely experimental inquiry.\n\nThe phenomena of electro-chemical action are so strange that we must\nreturn for a moment to the consideration of the decomposition of\nwater, and the appearance of hydrogen at one pole, and of oxygen at\nthe other. It appears that some confusion of our ideas has arisen\nfrom the views which have been received of the atomic constitution of\nbodies. We have been accustomed to regard water,--to take that body as\nan example of all,--as a compound of two gases, hydrogen and oxygen;\nan equivalent, or one atom of the first, united to an equivalent or\none atom of the last, forming one atom of water. This atom of water we\nregard as infinitely small; consequently a drop of water is made up of\nmany hundreds of these combined atoms, and a pint of water of not less\nthan 10,000 drops. Now, if this pint of water is connected with the\nwires of a galvanic battery, although their extremities may be some\ninches apart, for every atom of oxygen liberated at one pole, an atom\nof hydrogen is set free at the other. It has been thought that an atom\nhas undergone decomposition at one point, its oxygen being torn from\nit, and then there has arisen the difficulty of sending the atom of\nhydrogen through all the combined atoms of water across to the other\npole. A series of decompositions and recompositions have been supposed\nto take place, and the communication of effects from particle to\nparticle.\n\nAn attracting power for one class of bodies has been found in one pole,\nwhich is repellent to another class; and the reverse order has been\ndetected at the opposite pole of a galvanic arrangement.[144] That\nis, the wire which carries the current from an excited zinc plate has\na relation to all bodies, which is directly opposite to that which\nis exhibited by the wire conveying the current from, or completing\nthe circuit with, the copper plate. The one, for instance, collects\nand carries acids and the like, the other the metallic bases. At the\nextremity of one galvanic wire, placed into a drop of water, oxygen is\nalways liberated; and at the end of the other, necessary to complete\nthe circuit with the battery, hydrogen is set free.\n\nIt appears necessary, to a clear understanding of what takes place in\nthis experiment, that we should regard each mass, howsoever large, as\nthe representative of a single atom. Nor is this difficult, as the\nfollowing illustration will show.\n\nLet us take one particle of common salt (_chloride_ of _sodium_)\nweighing less than a grain, and put it into a hundred thousand grains\nof distilled water. In a few minutes the salt has diffused itself\nthrough the whole of the fluid, and in every drop we can detect\nchlorine and soda. We cannot believe that this grain of salt has split\nitself up into a hundred thousand parts; we conceive rather that the\nphenomenon of solution is one of diffusion. One infinitely elastic body\nhas interpenetrated with another.\n\nInstead of an experiment with a pint of water, let us take our stand\non Dover heights, and, with a gigantic battery at our command, place\none wire into the ocean on our own shores, and convey the other through\nthe air across the channel, and let its extremity dip into the sea\noff Calais pier--the experiment is a practicable one--we have now an\nelectrical circuit of which the British channel forms a part, and the\nresult will be exactly the same as that which we may observe in a\nwatch-glass with a drop of water.\n\nWe cannot suppose that the instantaneous and simultaneous effect\nwhich takes place in the water at Calais and at Dover, is due to\nanything like what we have studied under the name of convection, when\nconsidering Heat.\n\nA thousand balls are placed in a line touching each other; the first\nball receives a blow, and the last ball flies off with a force exactly\nequal to the power applied to the first; none of the intermediate balls\nbeing moved.\n\nWe cannot conceive that the particle _A_ excites the particle _B_ next\nit, and so on through the series between the two shores; but regarding\nthe channel as one large drop, charged with the electric principle as\nwe know it to be, it is excited by undulation or tremor throughout\nits width, and we have an equivalent of oxygen thrown off on one side\nof the line, and an exact equivalent of hydrogen at the other, the\nelectro-chemical influence being exerted only where the current or\nmotion is transferred from one medium to another.[145] The imperfect\ncharacter of this view is freely admitted; no other, consistent with\nknown facts, presents itself by which the effect can be explained. The\nfact stands as a truth; the hypothesis by which it is attempted to\nbe interpreted is open to doubt, and it is opposed to some favourite\ntheories.\n\nBefore we pass to the consideration of the other sources of\nelectricity, it is important we should understand that no chemical\nor physical change, however slight it may be, can occur without the\ndevelopment of electrical power. If we dissolve a salt in water, if\nwe mix two fluids together, if we condense a gas, or convert a fluid\ninto vapour, electricity is disturbed, and may be made manifest to our\nsenses.[146]\n\nIt has been shown that this power may be excited by friction\n(machine electricity) and by chemical action (voltaic electricity,\ngalvanism); it now remains to speak of the electricity developed by\nheat (thermo-electricity), the electricity exhibited under nervous\nexcitement by the gymnotus and torpedo (animal electricity); magnetism\nand its phenomena being reserved for a separate consideration.\n\nIf a bar of metal is warmed at one end and kept cool at the other,\nan electrical current circulates through the bar, and may be carried\noff by connection with any good conductor, and shown to exhibit the\nproperties of ordinary electricity. The metals best suited for showing\nthe effects of thermo-electricity appear to be bismuth and antimony. By\nbinding two bars of these metals together at one end, and connecting\nthe other ends with a galvanometer, it will be discovered that an\nelectric current passes off through the instrument by the slightest\nvariation of temperature. Merely clasping the two metals, where bound\ntogether, with the finger and thumb, is sufficient to exhibit the\nphenomenon. By a series of such arrangements,--which form what have\nbeen called thermo-electric multipliers,--we obtain the most delicate\nmeasurers of heat with which philosophers are acquainted, by the aid of\nwhich Melloni has been enabled to pursue his beautiful researches on\nradiant caloric.\n\nThat this electricity is identical with the other forms has been proved\nby employing the current thus excited for the purpose of producing\nchemical decomposition, magnetism, and electric light.[147]\n\nThe phenomenon of thermo-electricity--the discovery of Seebeck, is\nanother proof of the very close connection of the physical forces. We\nwitness their being resolved as it were into each other, electricity\nproducing heat, and heat again electricity; and it is from these\ncurious results that the arguments in favour of their intimate\nrelations and actual identity have been drawn. It will, however, be\nfound to be the best philosophy to regard these forces as dissimilar,\nuntil we are enabled to prove them to be only modified forms of one\nprinciple or power. At the same time it must not be forgotten that\nin natural operations we invariably find the combined action of\nseveral forces producing a single phenomenon. The important fact to be\nparticularly regarded is, that we have evidence that every substance\nwhich is unequally heated becomes the source of this very remarkable\nform of electricity.[148]\n\nThere exist a few fishes gifted with the very extraordinary power of\nproducing electrical phenomena by an effort of muscular or nervous\nenergy.\n\nThe _Gymnotus electricus_, or electrical eel, and the _Raia torpedo_,\na species of ray, are the most remarkable. This power is, it would\nappear, given to these curious creatures for purposes of defence, and\nalso for enabling them to secure their prey. The _Gymnotus_ of the\nSouth America rivers, will, it is said, when in full vigour, send forth\na discharge of electricity sufficiently powerful to knock down a man,\nor to stun a horse; while it can destroy fishes, through a considerable\nspace, by exerting its strange artillery.[149]\n\nFaraday\u2019s description of a _Gymnotus_, paralyzing and seizing its\nprey, is too graphic and important to be omitted.\n\n\u201cThe _Gymnotus_ can stun and kill fish which are in very various\npositions to its own body; but on one day, when I saw it eat, its\naction seemed to me to be peculiar. A live fish, about five inches in\nlength, caught not half a minute before, was dropped into the tub.\nThe _Gymnotus_ instantly turned round in such a manner as to form a\ncoil, inclosing the fish, the latter representing a diameter across\nit; a shock passed, and there, in an instant, was the fish struck\nmotionless, as if by lightning, in the midst of the waters, its side\nfloating to the light. The _Gymnotus_ made a turn or two to look for\nits prey, which, having found, he bolted, and then went about searching\nfor more. A second smaller fish was given him, which being hurt in the\nconveyance, showed but little signs of life, and this he swallowed at\nonce, apparently without shocking it. The coiling of the _Gymnotus_\nround its prey had, in this case, every appearance of being intentional\non its part, to increase the force of the shock, and the action is\nevidently well suited for that purpose, being in full accordance\nwith the well-known laws of the discharge of currents in masses of\nconducting matter; and though the fish may not always put this artifice\nin practice, it is very probable he is aware of its advantages, and may\nresort to it in cases of need.\u201d[150]\n\nAnimal electricity has been proved to be of the same character as that\nderived from other sources. The shock and the spark are like those\nof the machine; and the current from the animal, circulating around\nsoft iron, like galvanic electricity, has the property of rendering it\nmagnetic.\n\nIt is important that we should now review these conditions of\nelectrical force in connexion with the great physical phenomena of\nnature.\n\nIt is sufficiently evident, from the results which have been examined,\nthat all matter, whatever may be its form or condition, is for ever\nunder the operation of the physical forces, in a state of disturbance.\nFrom the centre to the surface all is in an active condition: a state\nof mutation prevails with every created thing; and science clearly\nshows that influences are constantly in action which prevent the\npossibility of absolute repose.\n\nUnder the excitement of the several agencies of the solar beams, motion\nis given to all bodies by the circulation of heat, and a full flow of\nelectricity is sent around the earth to perform its wondrous works.\nThe solar influences, which regulate, and possibly determine, every\nphysical force with which we are acquainted, are active in effecting\nan actual change of state in matter. The sunbeam of the morning falls\non the solid earth, and its influence is felt to the very centre.\nThe mountain-top catches the first ray of light, and its base, still\nwrapt in mists and darkness, is disturbed by the irradiating power.\nThe crystalline gems, hidden in the darkness of the solid rock, are\ndependent, for that form which makes them valued by the proud and gay,\non the influence of those radiations which they are one day to refract\nin beauty. The metals locked in the chasms of the rifted rocks are, for\nall their physical peculiarities, as dependent on solar influence as is\nthe flower which lifts its head to the morning sun, or the bird which\nsings \u201cat heaven\u2019s high gate.\u201d\n\nLet us, then, examine how far electricity, as distinguished from the\nother powers, acts in producing any of these effects.\n\nWe find electricity in the atmosphere, which the electrical kite of Dr.\nFranklin proved to be identical with that principle produced by the\nfriction of glass. In the grandeur and terror of a thunderstorm, many\nsee nothing but manifestations of Almighty wrath. When the volleys of\nthe bursting cloud are piercing the disturbed air, and the thunders\nof the discharge are pealing their dreadful notes above our heads,\nthe chemical combinations of the noxious exhalations arising from the\nputrefying animal and vegetable masses of this earth are effected,\nelements fitted for the purposes of health and vegetation are formed,\nand brought to the ground in the heavy rains which usually follow these\nstorms. Science has taught man this--has shown him that the \u201cpartial\nevil\u201d arising from the \u201cwinged bolt\u201d is a \u201cuniversal good;\u201d and, more\nthan this, it has armed him with the means of protecting his life and\nproperty from the influence of lightnings. So that, like Ajax, he can\ndefy the storm. By metallic rods, carried up a chimney, a tower, or a\nmast, we may form a channel through which the whole of the electricity\nof the most terrific thunder-cloud may be carried harmlessly into\nthe earth or the sea; and it is pleasing to observe that at length\nprejudice has been overcome, and \u201cconductors\u201d are generally attached\nto high buildings, and to most of the ships of our navy.[151] It was\ndiscovered that the devastating hailstorms of the south of France\nand Switzerland, so destructive to the vineyards and crops, were\naccompanied by evidences of great electrical excitation, and it was\nproposed to discharge the electricity from the air by means of pointed\nmetallic rods. These have been adopted, and, it is said, with real\nadvantage--each rod protecting an area of one hundred yards. Thus it\nis that science ministers to our service; and how much more pleasing\nis it to contemplate the lightning, with the philosopher, as an agent\ndestroying the elements of pestilence, and restoring the healthfulness\nof the air we breathe, than with the romancer, to see in it only the\ndreaded aspect of a demon of destruction.\n\nThe laws which regulate the spread of a pestilence are unknown. The\ndifficulties of the investigation are great, but they are by no means\ninsurmountable. A plague passes from the east to the west across\nthe world--it spreads mourning over the gayest cities, and sorrow\nsitteth in the streets. The black death rises in the Orient: it goes\non in unchecked strength, and only finishes its course when it has\nmade the circuit of the civilized world. The cholera spreads its\nebon wings--mankind trembles--watches its progress, and looks upon\nthe path which is marked by the myriads of the dead, who have fallen\nbefore the dire fiend. The diseases pass away--the dead are buried,\nand all is forgotten. The rush and the riot of life are pursued: and\nuntil man is threatened with another advent, he cares not to trouble\nhimself. Accompanying the last visitation, there appear certain\npeculiar meteorological conditions, which point a line of inquiry. It\nmay or may not be the path which leads to the truth, but certainly\nits indications are worthy of careful examination. It may be asked,\ncan weak man stop a pestilence; can a mortal\u2019s puny hand retard the\nafflictions of the Almighty? The question asked--it must be answered in\nreverence, yet without fear. No human power can produce a change in the\nphysical conditions of the earth, or of the air; and if our diseases\nare connected with those changes, as beyond all doubt a number of them\nare, they lie above man\u2019s control. But when there are indications that\ncauses secondary to these are producing some dire effect, and when\nwe know that these secondary causes may be modified, it is sufficient\nevidence to prove that man is permitted to control thus far the\nafflictions which are sent to try his powers.\n\nWe find a disease winging its way from lane to alley and closed court,\nsweeping with destructive violence its way through damp cellars and\ncrowded attics; it is rife with mischief along the banks of reeking\nditches, and on the borders of filthy streams. Certain it is,\ntherefore, that some ultimate connexion exists between the conditions\nof dirt and this speedy death. Can science tell of these? has it yet\nsearched out the connecting link? Let the question be answered by a few\nfacts.\n\nWhen the cholera first made its appearance, and subsequently, it has\nbeen observed that the electrical intensity of the atmosphere was\nunusually low.\n\nThe disease has departed, and it is then found that the electricity of\nthe air has been restored to its ordinary condition.\n\nThis appears to show some connexion; but how do these conditions link\nthis physical force with the ditch-seeking disease?\n\nFrom all stagnant places, from all the sinks of overcrowded humanity,\nfrom fermenting vegetable and from putrefying animal matter, there\nare constantly arising poisonous exhalations to do their work of\ndestruction.\n\nWhere death and decay is a law, this must of necessity constantly\noccur; but the poisonous reek may be diffused, or it may be\nconcentrated, and Nature has provided for this, and ordered the means\nfor rendering the poison harmless.\n\nBy the agency of electricity,--probably, too, by the influence of\nlight,--the oxygen in the air undergoes a peculiar change, by which\nit is rendered far more energetic than it is in its ordinary state.\nThis is the condition to which the name of _ozone_ has been applied.\nNow, this ozone, or this peculiar oxygen, always exists in the air we\nbreathe; but its quantity is subject to great and rapid variations. It\nis found that when electrical intensity is high the quantity of this\nprinciple is great; when the electrical intensity is low, as in the\ncholera years, the proportion of ozone is relatively low.\n\nThis remarkable chemical agent possesses the power of instantly\ncombining with organic matter,--of removing with singular rapidity all\nnoxious odours; and it would appear to be the most active of all known\ndisinfectants.\n\nMay we not infer from the facts stated that the pestilence we dread is\nthe result of organic poison, which from a deficiency of ozone,--its\nnatural antidote,--exerts its baneful influences on humanity. This\ndeficiency is due to alterations in the electrical character of the\nair, possibly dependent upon phenomena taking place in the sun itself,\nor it may be still more directly influenced by variations in the\ncharacter of solar light, which we have not yet detected, by which the\nconditions of the electric power are determined.\n\nThis may be a line along which it is fair to push enquiry. But such\nan enquiry must be made in all the purity of the highest inductive\nphilosophy, and speculation must be held firmly in the controlling\nchains of experiment and observation. In the truths, however, which are\nknown to us, there is so much harmony and consistence that even the\nmelancholy theme links itself--a tragedy--with the Poetry of Science.\n\nIt has been thought, and much satisfactory evidence has been brought\nforward to support the idea, that the earth\u2019s magnetism is due to\ncurrents of electricity circulating around the globe; as a great\nnatural current from east to west--that, indeed, it has an unvarying\nreference to the motion of the earth in relation to the sun.[152]\n\nThese terrestrial currents, as they have without doubt a very important\nbearing on the structural conditions of the rock-formations and the\ndistribution of minerals, require an attentive consideration; but we\nmust, in the first place, examine, as far as we know, the influences\nexerted, or supposed to be exerted, by electricity, in its varied forms.\n\nThe phenomena of vitality have, by many, been considered as immediately\ndependent upon its influence; and a rather extensive series of\nexperiments has been made in support of this hypothesis. The researches\nof Philip on the action of the organs of digestion, when separated\nfrom their connection with the brain, but united with a galvanic\nbattery, have been proved by Dr. Reid to be delusive;[153] since, as\nthe organ is not removed from the influence of the living principle,\nit is quite evident that the electricity here is only secondary to\nsome more important power. Matteucci has endeavoured to show that\nnervous action is intimately connected with electric excitation, and\nthat electricity may be made a measurer of nervous irritability.[154]\nThere can be no doubt that a peculiar susceptibility to excitement\nexists in some systems, and this is very strikingly shown in the\ndisturbances produced by electric action; but in the experiments which\nhave been brought forward we have only the evidence that a certain\nnumber of muscular contractions are exhibited in one animal by a\ncurrent of electricity, giving a measured effect by the voltameter,\nwhich are different from those produced upon another by a current of\nthe same power. An attempt has recently been made by Mr. A. Smee to\nreduce the electrical phenomena connected with vitality to a more\nexact system than had hitherto been done. We cannot, however, regard\nthe attempt as successful. The author has trusted almost entirely\nto analogical reasoning, which is in science always dangerous.[155]\nIn the development of electricity during the operation of the vital\nforce, we see only the phenomena produced by the action of any two\ndissimilar chemical compounds upon each other. It has been thought\nthat the structure of the brain presents an analogy to that of the\ngalvanic battery, and the nerves represent the conducting wires.\nAlthough, however, some of the conditions appear similar, there are\nmany which have no representatives in either the mechanical structure\nor the physical properties of the brain, so far as we know it. That\nthe brain is the centre, the source, and termination of sensation is\nvery clearly proved by physiological investigations. That the nerves\nare the media by which all sensation is conveyed to the brain, and\nalso the instruments by which the will exerts its power over the\nmuscles, is equally well established. But to say that we have any\nevidence to support the idea that electricity has aught to do directly\nwith these great physiological phenomena, would be a bold assertion,\nbetraying a want of due caution on the part of the investigator. That\nelectric effects are developed during the operations of vitality is\nmost certain. Such must be the case, from the chemical changes taking\nplace during respiration and digestion, and the mechanical movements\nby which, even during external repose, the necessary functions of the\nbody are carried on. Whether electricity is the cause of these, or an\neffect arising from them, we need not stop to examine, as this is,\nin the present state of our knowledge, a mere speculation. We have\nno evidence that electricity is an exciting power, but rather that\nit is one of those forces which tend to establish the equilibrium of\nmatter. When disturbed--when its equilibrium is overset--it does, in\nits efforts to regain its stability, produce most remarkable effects.\nAn electrical machine must be rubbed to exhibit any force. In all\ngalvanic arrangements, even the most simple, dissimilar bodies are\nbrought together, and the latent electricity of both is disturbed;\nand, even in the magnet, it is only when this takes place that its\nelectrical powers are developed. In the _Gymnotus_, electricity appears\nto be dependent upon the power of the will of the animal; but even in\nthis extraordinary fish, it is only under peculiar conditions that the\nelectrical excitement takes place, and \u201cwhat they inflict, they feel\u201d\nduring the restoration of that equilibrium which is necessary to their\nhealthy state. In every case, therefore, we see that some power far\nsuperior to this is the ultimate cause; indeed, light and heat, and\nprobably actinism, appear to stand superior to this principle; and on\nthese, in some combined mode of action, in all probability, sensible\nelectricity is dependent. Beyond even these elements, largely as they\nare engaged in the organic and inorganic changes of this world, there\nare occult powers which may never be understood by finite beings.\nWe advance step by step from the most solid to the most ethereal of\nmaterial creations, and we examine a series of extraordinary effects\nproduced by powers which we know not whether to regard as material or\nimmaterial, so subtile are they. On these, it appears, we may exhaust\nour inductive investigations--we may discover the laws by which these\nprinciples act upon the grosser elements, and develope phenomena of\na very remarkable kind which have been unobserved or misunderstood.\nWhether light, heat, and electricity are modifications of one power,\nor different powers very closely united in action, is a problem we may\npossibly solve; but to know what they are, appears to be beyond the\nhopes of science; and it were idle to dream of elucidating the causes\nhidden beyond these forces, and by which they are regulated in all\ntheir actions on dead or living matter.\n\nM. Du Bois Raymond, from a series of researches remarkable alike for\ntheir difficulty and the delicacy with which they have been pursued,\ndraws the following, amongst many others, as his conclusions as to the\nconnection of electricity and vital phenomena.\n\nThe muscles and nerves, including the brain and the spinal chord, are\nendowed during life with an electromotive power, which acts according\nto a definite law.\n\nThe electromotive power _lasts after death_, or in dissected nerves and\nmuscles after separation from the body of the animal, as long as the\nexcitability of the nervous and muscular fibre; whether these fibres\nare permitted to die gradually from the cessation of the conditions\nnecessary to the support of life, or whether they are suddenly deprived\nof their vital properties by heat or chemical action.\n\nLet us not suppose for a moment that these conclusions indicate in the\nremotest degree that electricity is life,--that vital power is due to\nelectricity.\n\nDuring life, with every motion, and, indeed, with every emotion,\nwhether we move a muscle or exert the mind, there is a change of state.\nThe result of this is chemical phenomena,--heat and electricity; but\nthese are not life. We excite them equally by giving motion to a dead\nmass.\n\nNotwithstanding the assertions of those who have zealously followed\nthe path of Mesmer, and examined, or they have thought so, the\npsychological effects dependent upon some strange physiological\nconditions, there is not an experiment on record,--there is not an\nobservation worthy of credit, which shows that electricity has any\nconnection with their results. All around their subject is uncertainty:\ndoubt involves every experiment, and deception clouds a large number.\nSome few grains of truth, and these are sufficiently strange, are mixed\nup in an enormous mass of error.\n\nAll the phenomena of life,--of the _vis vit\u00e6_ or vitality, are beyond\nhuman search. All the physical forces, or elements, we may examine by\nthe test of experiment: but the principle on which sensation depends,\nthe principle even upon which vegetable _life_ depends, cannot be\ntested. Life is infinitely superior to every physical force; it holds\nthem all in control, but is not itself controlled by them; it keeps\nits state sacred from human search,--the invisible hidden behind the\nveil of mortality.\n\nDuring changes in the electrical conditions of the earth and\natmosphere, vegetables give indications of being in a peculiar manner\ninfluenced by this power. It is proved by experiments that the leaves\nof plants are among the best conductors of electricity, and it has\nhence been inferred that it must necessarily be advantageous to\nvegetation. That vegetable growth is, equally with animal growth,\nsubject to electricity, as one of its quickening powers, must be\nadmitted; but all experiments which have been fairly tried with the\nview of stimulating the growth of plants by its agency, have given\nresults of a negative character.[156] That a galvanic arrangement may\nproduce chemical changes in the soil, which may be advantageous to the\nplant, is probable; but that a plant can be brought to maturity sooner,\nor be made to develope itself more completely, under the direct action\nof electrical excitation, appears to be one of those dreams of science\nwhich will have a place amongst the marvels of alchemy and the fictions\nof astrology. An attentive examination of all the conditions necessary\nfor the satisfactory development of the plant, will render it evident,\nthat although the ordinary electrical state of the earth and atmosphere\nmust influence the processes of germination and vegetable growth,\nyet that any additional excitement must be destructive to them. The\nwonders wrought by electrical power are marvellous; a magic influence\nis exerted by it, and naturally the inquiring mind is led at first to\nbelieve that electricity is the all-powerful principle of creation; but\na little reflection will serve to convince us that it is a subordinate\nagent, although a powerful one.\n\nIn proceeding with our examination of the phenomena which present\nthemselves in connection with the terrestrial currents, we purposely\nseparate magnetism from those more distinct electro-chemical agencies\nwhich play so important a part in the great cosmical operations.\n\nElectricity, we have already stated, flows through or involves all\nbodies; but, like heat, it appears to undergo a very remarkable change\nin becoming associated with some forms of matter. We have the phenomena\nof magnetism when an electric current circulates through a metallic\nwire, and it would appear that all other bodies acquire a peculiar\npolar condition under the influence of this principle, which will be\nexplained in the next chapter.\n\nThe rocks, taken as masses, will not conduct an electric current when\ndry: granite, porphyry, slate, and limestone, obstructing its passage\neven through the smallest spaces. But all the metallic formations admit\nof its circulating with great freedom. This fact it must, however,\nbe remembered does not in any way interfere with the hypothesis of\nthe existence of electricity in all bodies, in what we must regard as\nits latent state, from which, under prescribed conditions, it may be\nreadily liberated. Neither does it affect the question of circulation,\nin relation to the great diffusion of electricity which we suppose to\nexist through all nature, and to move in obedience to some fixed law.\nWe know that through the superficial strata electric currents circulate\nfreely, whether they are composed of clay, sand, or any mixture of\nthese with decomposed organic matter; indeed, that with any substance\nin a moist state they suffer no interruption.\n\nThe electricity of mineral veins has attracted much attention, and\nnumerous investigations into the phenomena which these metalliferous\nformations present, have been made from time to time.[157]\n\nBy inserting into the mass of a copper _lode_, or vein, in situ, a\nmetallic wire, which shall be connected with a measurer of galvanic\naction, a wire also from the instrument being brought into contact with\nanother _lode_, an immediate effect is generally produced, showing\nthat a current is traversing through the wires from one _lode_ to the\nother, and completing the circulation probably over the dark face of\nthe rock in which the fissures forming the mineral veins exist.[158]\nThe currents thus detected are often sufficiently active to deflect\na magnetic needle powerfully, to produce, slowly, electro-chemical\ndecomposition, and to render a bar of iron magnetic. These currents\nmust not be confounded with the great electrical movements around the\nearth. They are only to be detected in those mineral formations in\nwhich there is evidence of chemical action going on, and, the greater\nthe amount of this chemical operation, the more energetic are the\nelectrical currents.[159] We have, however, very good evidence that\nthese local currents have, of themselves, many peculiar influences. It\nnot unfrequently happens that owing to some great disturbance of the\ncrust of the earth, a mineral vein is dislocated, and one part either\nsinks below, or is lifted above its original position; the fissures\nformed between the two being usually filled in with clay or with\ncrystalline masses of more recent formation than the fissure itself. It\nis frequently found that these \u201c_cross courses_,\u201d as they are called in\nmining language, contain ores of a different character from those which\nconstitute the mineral vein; for instance, in them nickel, cobalt, and\nsilver are not unfrequently discovered. When these metals are so found,\nthey almost invariably occur between the ends of the dislocated lode,\nand often take a curvilinear direction, as if they were deposited along\na line of electrical force.[160]\n\nIn the laboratory such an arrangement has been imitated, and in a\nmass of clay fixed between the galvanic plates, after a short period\na distinct formation of a mineral vein has taken place.[161] By the\naction, too, of weak electrical currents, Becquerel, Crosse, and\nothers, have been successful in imitating nature so far as to produce\ncrystals of quartz and other minerals. In addition to this evidence, in\nsupport of the electrical theory of the origin of mineral veins, it\ncan be experimentally shown that a schistose structure may be given to\nclays and sandstone by voltaic action.[162]\n\nThere is often a very remarkable regularity in the direction of mineral\nveins: throughout Cornwall, for instance, they most commonly have a\nbearing from the E. of N. to the W. of S. It has hence been inferred\nthat they observe some relation to the magnetic poles of the earth.\nHowever this may be, it is certain that the ore in any lodes which\nare in a direction at right angles, or nearly so, to this main line,\ndiffers in character from that found in these, so called, east and west\nlobes.[163]\n\nThe sources of chemical action in the earth are numerous. Water\npercolating through the soil, and finding its way to great depths\nthrough fissures in the rocks, carries with it oxygen and various\nsalts in solution. Water again rising from below, whether infiltrated\nfrom the ocean or derived from other sources, is usually of a high\ntemperature, and it always contains a large quantity of saline\nmatter.[164] By these causes alone chemical action must be set\nup. Chemical change cannot take place without a development of\nelectricity: and it has been proved that the quantity of electricity\nrequired for the production of any change is equal to that contained\nin the substances undergoing such change. Thus a constant activity is\nmaintained within the caverns of the rock by the agency of the chemical\nand electrical elements, and mutations on a scale of great grandeur are\nconstantly taking place under some directive force.\n\nThe mysterious gnome, labouring--ever labouring--in the formation of\nmetals, and the mischievous Cobalus of the mine, are the poor creations\nof superstition. A vague fear is spread amongst great masses of mankind\nrelative to the condition of the dark recesses of the earth; a certain\nunacknowledged awe is experienced by many on entering a cavern, or\ndescending a mine: not the natural fear arising from the peculiarity of\nthe situation, but the result of a superstitious dread, the effect of a\ndepraved education, by which they have been taught to refer everything\na little beyond their immediate comprehension to supernatural causes.\nThe spirit of demon worship, as well as that of hero worship, has\npassed from the early ages down to the present; and under its influence\nthe genii of the East and the demons of the West have preserved their\ntraditionary powers.\n\nFiction has employed itself with the utmost license in giving glowing\npictures of treasures hidden in the earth\u2019s recesses. The caverns\nof Chilminar, the cave of Aladdin, the abodes of the spirits of the\nHartz, and the dwellings of the fairies of England, are gem-bespangled\nand gold-glistening vaults, to which man has never reached. The\npictures are pleasing; but although they have the elements of poetry\nin them, and delight the young mind, they want the sterling character\nof scientific truth; and the wonderful researches of the plodding\nmineralogist have developed more beauty in the caverns of the dark rock\nthan ever fancy painted in her happiest moments.\n\nIn all probability the action of the sun\u2019s rays upon the earth\u2019s\nsurface, producing a constantly varying difference of temperature,\nand also the temperature which has been observed as existing at great\ndepths, give rise to thermo-electrical currents, which may play an\nimportant part in the results thus briefly described.\n\nIn connection with these great natural operations, explaining them,\nand being also, to some extent, explained by them, we have the very\nbeautiful application of electricity to the deposition of metals,\ncalled the Electrotype.\n\nApplying the views we have adopted to this beautiful discovery,[165]\nthe whole process by which these metallic deposits are produced will\nbe yet more clearly understood. By the agency of the electric fluid,\nliberated in the galvanic battery, a disturbance of the electricity of\nthe solution of copper, silver, or gold, is produced, and the metal is\ndeposited; but, instead of allowing the acid in combination to escape,\nit has presented to it some of the same metal as that revived, and,\nconsequently, it combines with it, and this compound, being dissolved,\nmaintains the strength of the solution.[166] A system of revival, or\ndecomposition, is carried on at one pole, and one of abrasion, or more\ncorrectly speaking, of composition and solution, at the other. By\ntaking advantage of this very extraordinary power of electricity, we\nnow form vessels for ornament or use, we gild or silver all kinds of\nutensils, and give the imperishability of metal to the most delicate\nproductions of nature--her fruits, her flowers, and her insects;--and\nover the finest labours of the loom we may throw coatings of gold or\nsilver to add to their elegance and durability. Nor need we employ the\nsomewhat complex arrangement of the battery: we may take the steel\nmagnet, and, by mechanically disturbing the electricity it contains, we\ncan produce a current through copper wires, which may be used, and is\nextensively employed, for gilding and silvering.[167] The earth itself\nmay be made the battery, and, by connecting wires with its mineral\ndeposits, currents of electricity have been secured, and used for the\nproduction of electrotype deposit.[168]\n\nThe electrotype is but one of the applications of electricity to the\nuses of man. This agent has been employed as the carrier of thought;\nand with infinite rapidity, messages of importance, communications\ninvolving life, and intelligences outstripping the speed of coward\ncrime, have been communicated. There will be no difficulty in\nunderstanding the principle of this, although many of the nice\nmechanical arrangements, to ensure precision, are of a somewhat\nelaborate character. The entire action depends on the deflection of a\ncompass-needle by the passage of an electric current along its length.\nIf at a given point we place a galvanic battery, and at twenty or one\nhundred miles distance from it a compass-needle, between a wire brought\nfrom, and another returning to the battery, the needle will remain true\nto its polar direction so long as the wires are unexcited; but the\nmoment connection is made, and the circuit is complete, the electricity\nof the whole extent of wire is disturbed, and the needle is thrown at\nright angles to the direction of the current. Provided a connection\nbetween two points can be secured, however remote they are from each\nother, we thus, almost instantaneously, convey any intelligence. The\neffects of an electric current would appear at a distance of 576,000\nmiles in a second of time; and to that distance, and with that speed,\nit is possible, by Professor Wheatstone\u2019s beautiful arrangements, to\nconvey whispers of love or messages of destruction.\n\nThe enchanted horse of the Arabian magician, the magic carpet of the\nGerman sorcerer, were poor contrivances, compared with the copper\nwires of the electrician, by which all the difficulties of time and\nthe barriers of space appear to be overcome. In the Scandinavian\nmythology we find certain spiritual powers of evil enabled to pass\nwith imperceptible speed from one remote point to another, sowing the\nseeds of a common ruin amongst mankind. Such is the morbid creation\nof a wild yet highly endowed imagination. The spirit of evil diffuses\nitself in a remarkable manner, and, indeed, we might almost assign to\nit the power of ubiquity; but in reality its advance is progressive,\nand time enters as an element into any calculation on its diffusion.\nElectricity is instantaneous in action; as a spirit of peace and\ngood-will it can overtake the spirit of evil, and divert it from its\ndesigns. May we not hope that the electrical telegraph, making, as it\nmust do, the whole of the civilized world enter into a communion of\nthought, and, through thought, of feeling with each other, will bind us\nup in one common brotherhood, and that, instead of misunderstanding and\nof misinterpreting the desires and the designs of each other, we shall\nlearn to know that such things as \u201cnatural enemies\u201d do not exist? To\nhope to break down the great barrier of language is perhaps too much;\nbut assuredly we may hope that, as we must do when closer and more\nintimate relations are secured by the aids of science, the barrier of\nprejudice may be razed to the ground, and not one stone left to stand\nupon another? Our contentions, our sanguinary wars, consecrated to\nhistory by the baptism of blood, have in every, or in nearly every,\ninstance sprung from the force of prejudice, or the mistakes of\npoliticians, whose minds were narrowed to the limits of a convention\nformed for perpetuating the reign of ignorance.\n\nAnd can anything be more in accordance with the spirit of all that we\nrevere as holy, than the idea that the elements employed by the All\nInfinite in the works of physical creation shall be made, even in the\nhands of man, the ministering angels to the great moral redemption of\nthe world? Associate the distant nations of the earth, and they will\nfind some common ground on which they may unite. Mortality compels a\ndependence; and there are charities which spring up alike in the breast\nof the savage and the civilized man, which will not be controlled by\nthe cold usages of pride, but which, like all truths, though in a still\nsmall voice, speak more forcibly to the heart than errors can, and\nserve as links in the great chain which must bind mankind in a common\nbrotherhood. \u201cNone are all evil,\u201d and the best have much to learn of\nthe amenities of life from him who yet lives in a \u201cstate of nature,\u201d or\nrather from him whose sensualities have prevailed over his intellectual\npowers, but who still preserves many of the noblest instincts, to give\nthem no higher term, which other races, proud of their intelligence,\nhave thrown aside. Time and space have hitherto prevented the\naccomplishment of this; electricity and mechanics promise to subdue\nboth; and we have every reason to hope those powers are destined to\naccelerate the union of the vast human family.\n\nElectrical power has also been employed for the purpose of measuring\ntime, and by its means a great number of clocks can be kept in a state\nof uniform correctness, which no other arrangement can effect. A\nbattery being united with the chief clock, which is itself connected\nby wires with any number of clocks arranged at a distance from each\nother, has the current continually and regularly interrupted by the\nbeating of the pendulum, which interruption is experienced by all the\nclocks included in the electric circuit; and, in accordance with this\nbreaking and making contact, the indicators or hands move over the dial\nwith a constantly uniform rate. Instead of a battery the earth itself\nhas supplied the stream of electric fluid, with which the rate of its\nrevolutions has been registered with the utmost fidelity.[169]\n\nElectricity, which is now employed to register the march of time,\nrushes far in advance of the sage who walks with measured tread,\nwatching the falling sands in the hour-glass.\n\nThe earth is spanned and the ocean pierced by the wires of the electric\ntelegraph. Already, from the banks of the Thames to the shores of the\nAdriatic, our electric messenger will do our bidding. The telegraph\nis making its way through Italy, and it is dipping its wires in the\nMediterranean, soon to reach the coast of Africa. They will then run\nalong the African shores to Egypt and Turkey, and still onward until\nthey unite with the telegraphs of India, of which three thousand miles\nare in progress. From Hindostan these wondrous wires will run from\nisland to island in the Indian Archipelago, and thus connect Australia\nand New Zealand with Europe.\n\nIn a few years we may expect to have an instantaneous report in London\nof the extraordinary \u201cnugget\u201d discovered by some fortunate gold-digger;\nand the exile from his native land in the Islands of the South Pacific\nOcean, may learn every hour, if he will, of the doings of his family\nand friends in some village home of England.\n\n\nFOOTNOTES:\n\n[136] _Trait\u00e9 de Physique_: M. Biot, vol. vii. Becquerel: Annales\nde Chimie, vol. xlvi.-xlix. Faraday\u2019s _Experimental Researches in\nElectricity_, 2 vols., 1830-1844. _A Speculation touching Electric\nConduction and the Nature of Matter_: by Michael Faraday, D.C.L.,\nF.R.S.; Philosophical Magazine, vol. xxiv., 1836. _Objections to the\ntheories severally of Franklin, Dufay, and Amp\u00e8re, with an attempt to\nexplain Electrical Phenomena by statical or undulatory polarization_:\nby Robert Hare, M.D., Emeritus Professor of Chemistry in the University\nof Pennsylvania.\n\n[137] \u201cA good piece of gutta percha will insulate as well as an equal\npiece of shell-lac, whether it be in the form of sheet, or rod, or\nfilament; but being tough and flexible when cold, as well as soft\nwhen hot, it will serve better than shell-lac in many cases where the\nbrittleness of the latter is an inconvenience. Thus it makes very good\nhandles for carriers of electricity in experiments on induction; not\nbeing liable to fracture in the form of thin band or string, it makes\nan excellent insulating suspender; a piece of it in sheet makes a\nmost convenient insulating basis for anything placed on it. It forms\nexcellent insulating plugs for the stems of gold-leaf electrometers,\nwhen they pass through sheltering tubes, and larger plugs form good\ninsulating feet for electrical arrangements; cylinders of it, half an\ninch or more in diameter, have great stiffness, and form excellent\ninsulating pillars. In these and in other ways its power as an\ninsulator may be useful.\u201d--_On the use of Gutta Percha in Electrical\nInsulation_: by Dr. Faraday; Philosoph. Mag., March, 1848.\n\nThe following deductions have been given by Faraday, in his _Researches\nin Electricity_, a work of most extraordinary merit, being one of the\nmost perfect examples of fine inductive philosophy which we possess in\nthe English language:--\n\n\u201cAll bodies conduct electricity in the same manner from metals to lacs\nand gases, but in very different degrees.\n\n\u201cConducting power is in some bodies powerfully increased by heat, and\nin others diminished, yet without one perceiving any accompanying\nessential electrical difference, either in the bodies, or in the change\noccasioned by the electricity conducted.\n\n\u201cA numerous class of bodies insulating electricity of low intensity,\nwhen solid, conduct it very freely when fluid, and are then decomposed\nby it.\n\n\u201cBut there are many fluid bodies which do not sensibly conduct\nelectricity of this low intensity; there are some which conduct it and\nare not decomposed; nor is fluidity essential to decomposition.\n\n\u201cThere are but two bodies (sulphuret of silver and fluoride of lead)\nwhich, insulating a voltaic current when solid, and conducting it when\nfluid, are not decomposed in the latter case.\n\n\u201cThere is no strict electrical distinction of conduction which can as\nyet be drawn between bodies supposed to be elementary, and those known\nto be compounds.\u201d\n\n[138] Faraday\u2019s _Speculation on the Nature of Matter_, already referred\nto.\n\n[139] _Experimental Researches_: by Dr. Faraday. _Chemical\nDecomposition_, p. 151.\n\n[140] Karsten; Poggendorff\u2019s _Annalen_, vol. lvii.\n\n[141] _Trait\u00e9 Exp\u00e9rimental de l\u2019\u00c9lectricit\u00e9 et du Magn\u00e9tisme_:\nBecquerel, 1834, Priestley\u2019s _Introduction to Electricity_. _On\nElectricity in Equilibrium_: Dr. Young\u2019s Lectures.\n\n[142] Faraday\u2019s _Experimental Researches on Electricity_. This\nphilosopher has shown, by the most conclusive experiments, \u201cthat\nthe electricity which decomposes, and that which is evolved by the\ndecomposition of, a certain quantity of matter, are alike. What an\nenormous quantity of electricity, therefore, is required for the\ndecomposition of a single grain of water! We have already seen that\nit must be in quantity sufficient to sustain a platinum wire 1/104\nof an inch in thickness, red hot, in contact with the air, for three\nminutes and three quarters. It would appear that 800,000 charges of a\nLeyden battery, charged by thirty turns of a very large and powerful\nplate machine, in full action--a quantity sufficient, if passed at once\nthrough the head of a rat or cat, to have killed it as by a flash of\nlightning--are necessary to supply electricity sufficient to decompose\na single grain of water; or, if I am right, to equal the quantity of\nelectricity which is naturally associated with the elements of that\ngrain of water, endowing them with their mutual chemical affinity.\u201d\n\n[143] _Experimental Researches_: Faraday.\n\n[144] The appearance of acid and alkaline matter, in water acted on\nby a current of electricity, at the opposite electrified metallic\nsurfaces, was observed in the first chemical experiments made with\nthe column of Volta--(see Nicholson\u2019s Journal, vol. iv. p. 183, and\nvol. iv. p. 261, for Mr. Cruickshank\u2019s Experiments; and Annales de\nChimie, tom. xxxvii. p. 233, for those of M. Desormes): _On some\nChemical Agencies in Electricity_: by Sir Humphry Davy.--Philosophical\nTransactions for 1807. The various theories of electro-chemical\ndecomposition are carefully stated by Faraday, in his fifth series\nof _Experimental Researches on Electricity_, in which he thus states\nhis own views:--\u201cIt appears to me that the effect is produced by an\n_internal corpuscular action_ exerted according to the direction of\nthe electric current, and that it is due to a force either _superadded\nto_ or _giving direction to the ordinary chemical affinity_ of the\nbodies present. The body under decomposition may be considered as a\nmass of acting particles, all those which are included in the course\nof the electric current contributing to the final effect; and it is\nbecause the ordinary chemical affinity is relieved, weakened, or partly\nneutralized by the influence of the electric current in one direction\nparallel to the course of the latter, and strengthened or added to in\nthe opposite direction, that the combining particles have a tendency to\npass in opposite courses.\u201d\n\n[145] \u201cThis capital discovery (chemical decomposition of electricity)\nappears to have been made in the first instance by Messrs. Nicholson\nand Carlisle, who observed the decomposition of water so produced. It\nwas speedily followed up by the still more important one of Berzelius\nand Hisinger, who ascertained it as a general law, that, in all the\ndecompositions so effected, the acids and oxygen become transferred and\naccumulated around the positive, and hydrogen, metals, and alkalies\naround the negative, pole of a voltaic circuit; being transferred in\nan invisible, and, as it were, a latent or torpid state, by the action\nof the electric current, through considerable spaces, and even through\nlarge quantities of water or other liquids, again to reappear with all\ntheir properties at their appropriate resting-places.\u201d--_Discourse on\nthe Study of Natural Philosophy_: by Sir John Herschel, Bart., F.R.S.\n\n[146] Numerous beautiful illustrations of this fact will be found in\nBecquerel\u2019s _Trait\u00e9 Exp\u00e9rimental de l\u2019\u00c9lectricit\u00e9 et du Magn\u00e9tisme_.\n\n[147] See _Le Feu \u00e9l\u00e9mentaire_ of l\u2019Abb\u00e9 Nollet; Le\u00e7ons de\nPhysique, tom. vi. p. 252; _Du Pouvoir thermo-\u00e9lectrique_, by M.\nBecquerel--Annales de Chimie, vol. xli. p. 353; also a Memoir by\nNobili, Biblioth\u00e8que Universelle, vol. xxxvii. p. 15; _Experimental\nContributions towards the theory of Thermo-Electricity_ by Mr. J.\nPrideaux--Philosophical Magazine, vol. iii., Third Series; _On the\nThermo-Magnetism of Homogeneous Bodies, with illustrative experiments_,\nby Mr. William Sturgeon--Philosophical Magazine, vol. x. p. 1-116,\nNew Series. Botto made magnets and obtained chemical decomposition.\nAntinori produced the spark. Mr. Watkins heated a wire in Harris\u2019s\nThermo-Electrometer.\n\n[148] A very ingenious application of the knowledge of this fact\nwas suggested by Mr. Solly, by which the heat of a furnace could be\nconstantly registered at a very considerable distance from it. See\n_Description of an Electric Thermometer_: by E. Solly, Jun., Esq.\nPhilosophical Magazine, vol. xx. p. 391. New Series.\n\n[149] Humboldt; _Personal Narrative_, Chap. xvii.--Annales de Chimie,\nvol. xiv. p. 15.\n\n[150] _Experimental Researches on Electricity._ Series xv.\nConsult Sir Humphry Davy: _An Account of some Experiments on the\nTorpedo_.--Philosophical Transactions, 1829, p. 15. John Davy, M.D.,\nF.R.S.: _An Account of some Experiments and Observations on the\nTorpedo_, ibid., 1832, p. 259; and the same author\u2019s _Observations on\nthe Torpedo, with an Account of some Additional Experiments on its\nElectricity_; and Matteucci, Biblioth\u00e8que Universelle, 1837, vol. xii.\np. 174.\n\n[151] _On Lightning Conductors_, by Sir William Snow Harris;\n_Observations on the Action of Lightning Conductors_, by W. Snow\nHarris, Esq., F.R.S.--London Electrical Society\u2019s Transactions.\nNumerous valuable papers _On Electricity_, by Sir William Harris, will\nbe found in the Philosophical Transactions.\n\n[152] Adopting, to a certain extent, this view, Faraday, in his\n_Electrical Nomenclature_, proposed for the word pole to substitute\n_anode_ (\u03b1\u03bd\u03c9, _upwards_, and \u1f41\u03b4\u03bf\u03c2, _a way_), the way which the sun\nrises; and _cathode_ (\u03ba\u03b1\u03c4\u03b1, _downwards_, and \u1f41\u03b4\u03bf\u03c2, _a way_), the way\nwhich the sun sets. The hypothesis belongs essentially to Amp\u00e8re.\n_Objections to the Theories severally of Franklin, Dufay, and Amp\u00e8re,\nwith an Effort to Explain Electrical Phenomena by Statical or\nUndulatory Polarisation_, by Robert Hare, M.D., Pennsylvania, will well\nrepay an attentive perusal.\n\n[153] _Inquiry into the Laws of the Vital Functions._--Philosophical\nTransactions, 1815, 1822; _Some Observations relating to the Functions\nof Digestion_, ibid., 1829: _On the Powers on which the Functions of\nLife in the more perfect animals depend, and on the manner in which\nthey are associated in the production of their more complicated\nresults_, by A. P. W. Philip, M.D., F.R.S., L. and E.--The following\nextract from the last-quoted of Dr. Philip\u2019s Memoirs, will give a\ngeneral view of the conclusions of that eminent physiologist:--\u201cWith\nrespect to the nature of the powers of the living animal which we have\nbeen considering, the sensorial and muscular powers, and the powers\npeculiar to living blood, we have found belong to the living animal\nalone, all their peculiar properties being the properties of life. The\nfunctions of life may be divided into two classes, those which are\naffected by the properties of this principle alone, and those, by far\nthe most numerous class, which result from the co-operation of these\nproperties with those of the principles which operate in inanimate\nnature. The nervous power we have found to be a modification of one\nof the latter principles, because it can exist in other textures than\nthose to which it belongs in the living animal, and we can substitute\nfor it one of those principles without disturbing the functions of life.\n\n\u201cLate discoveries have been gradually evincing how far more extensive\nthan was supposed, even a few years ago, is the dominion of\nelectricity. Magnetism, chemical affinity, and (I believe from the\nfacts stated in the foregoing paper, it will be impossible to avoid\nthe conclusion) the nervous influence, the leading power in the vital\nfunctions of the animal frame, properly so called, appear all of them\nto be modifications of this apparently universal agent; for I may add\nwe have already some glimpses of its still more extensive dominion.\u201d\n\nRefer to Dr. Reid\u2019s papers.\n\n[154] _Electro-physiological Researches_: by Signor Carlo Matteucci;\nPhil. Trans. 1845, p. 293, and subsequent years.\n\n[155] Electro-Biology: by Alfred Smee, Esq.\n\n[156] _Observations of Electric Currents in Vegetable Structures_: by\nGolding Bird, Esq., F.L.S.; Magazine of Natural History, vol. x. p.\n240. In this paper Dr. Bird remarks that his experiments lead to the\nconclusion that vegetables cannot become so charged with electricity\nas to afford a spark; that electrical currents of feeble tension are\nalways circulating in vegetable tissues; and that electrical currents\nare developed during germination from chemical action.\n\n[157] _On Mineral Veins_: by Robert Were Fox, Esq.; Fourth Report\nof the Royal Cornwall Polytechnic Society. _On the Electro-magnetic\nProperties of Metalliferous Veins in the mines of Cornwall_: by Robert\nW. Fox, Esq.; Phil. Trans. 1830, p. 399.\n\n[158] _Experiments and Observations on the Electricity of Mineral\nVeins_: by Robert Hunt and John Phillips; Reports of the Royal Cornwall\nPolytechnic Society for 1841-42. _On the Electricity of Mineral Veins_:\nby Mr. John Arthur Phillips; Ibid., 1843.\n\n[159] In the lead lodes of _Lagylas_ and _Frongoch_, electrical\ncurrents were detected by Mr. Fox, but none in those of _South Mold_\nand _Milwr_, in Flintshire: Cornwall Geological Transactions, vol. iv.\nIn the lead veins of _Coldberry_ and _Skeers_, in Teasdale, Durham, the\ncurrents detected were very feeble: Reports of the Bristol Association,\n1838. Von Strombeck could detect no electric currents in the veins\nworked in the clay slate near Saint Goar, on the Rhine: Archiv. f\u00fcr\nMineralogie, Geognosie, &c., von Dr. C. J. B Karsten, 1833. Professor\nReich, however, obtained very decided results at _Frisch Gl\u00fcck_,\n_Neue Hoffnung_, _Gottlob_, and in other mineral veins in the mining\ndistricts of Saxony: Edinburgh New Philosophical Journal, vol. xxviii.\n1839. The irregularities are all to be explained by the presence or\nabsence of chemical excitation.\n\n[160] This was remarkably the case at _Huel Sparnon_, near Redruth,\nwhere the cobalt was discovered between two portions of a dislocated\nlode; and the same was observed by Mr. Percival Johnson in a small mine\nworked for nickel, near St. Austell.\n\n[161] _On the process used for obtaining artificial veins in clay_: by\nT. B. Jordan; Sixth Annual Report of the Royal Cornwall Polytechnic\nSociety. See also my memoir, already referred to, in the Memoirs of the\nGeological Survey and Museum of Practical Geology, vol. i.\n\n[162] See Becquerel, _Trait\u00e9 Experimental de l\u2019Electricit\u00e9, &c.\nElectrical Experiments on the formation of Artificial Crystals_: by\nAndrew Crosse, Esq.; British Association Reports, vol. v., 1836. The\nlamination of clay and other substances is described in my memoir\nreferred to, Note p. 226.\n\n[163] Report on the Geology of Cornwall, Devon, and West Somerset, by\nSir Henry T. De la Beche: _Theoretical observations on the formation\nand filling of Mineral Veins and Common Faults_, p. 349.\n\n[164] The following analyses of waters from deep mines were made by me\nin 1840, and, with many others, published in the Reports of the Royal\nCornwall Polytechnic Society.\n\n    Consolidated Mines, Gwennap,\n               Cornwall.            In 1,000 grains of water.\n        Muriate of soda                        1\u00b75\n        Sulphate of lime                        \u00b75\n        Sulphate of iron                        \u00b715\n        Sulphate of copper                     1\u00b725\n        Silica                                  \u00b715\n        Alumina                                 \u00b73\n                                               ----\n            Total                              3\u00b77\n\n    United Mines, Gwennap.\n        Muriate of soda                        1\u00b710\n        Muriate of lime                         \u00b715\n        Sulphate of soda                        \u00b750\n        Sulphate of lime                       1\u00b75\n        Sulphate of iron                        \u00b775\n        Alumina                                 \u00b75\n        Silica                                  \u00b715\n                                               ----\n            Total                              4\u00b765\n\n    Great St. George.\n        Muriate of soda                        1\u00b735\n        Sulphate of lime                        \u00b774\n        Carbonate of iron                       \u00b770\n        Alumina                                 \u00b750\n        Carbonate of lime                       \u00b710\n                                               ----\n            Total                              3\u00b74\n\n[165] The discovery of the electrotype has been disputed, as all\nvaluable discoveries are. Without, however, at all disparaging the\nmerits of what had been done by Mr. Jordan, I am satisfied, after\nthe most careful search, that the first person who really employed\nelectro-chemical action for the precipitation of metals in an\nornamental form, was Mr. Spencer, of Liverpool.\n\n[166] See Spencer, _Instructions for the Multiplication of works of Art\nin Metal by Voltaic Electricity. Novelties in Experimental Science_:\nGriffin, Glasgow, _Elements of Electro-Metallurgy_: by Alfred Smee, Esq.\n\n[167] The magneto-electrical machine is employed in Birmingham for this\npurpose; but I am informed by Messrs. Elkington that they do not find\nit economical, or rather that the electro-precipitation is carried on\ntoo slowly.\n\n[168] This has been done by Mr. Robert Were Fox, at a mine near\nFalmouth. By connecting two copper wires with two lodes, and bringing\nthem, at the surface, into a cell containing a solution of sulphate\nof copper, this gentleman obtained an electrotype copy of an engraved\ncopper-plate.\n\n[169] This has been most effectually accomplished by Mr. Bain. Mr.\nHobson has had an electric clock, thus excited, in action for several\nyears.\n\n\n\n\nCHAPTER X.\n\nMAGNETISM.\n\n  Magnetic Iron--Knowledge of, by the Ancients--Artificial\n    Magnets--Electro-Magnets--Electro-Magnetism--Magneto-\n    Electricity--Theories of Magnetism--The Magnetic Power of soft Iron\n    and Steel--Influence of Heat on Magnetism--Terrestrial\n    Magnetism--Declination of the Compass-needle--Variation of the\n    Earth\u2019s Magnetism--Magnetic Poles--Hansteen\u2019s Speculations--Monthly\n    and Diurnal Variation--Dip and Intensity--Thermo-Magnetism--Aurora\n    Borealis--Magnetic Storms--Magnetic conditions of\n    Matter--Diamagnetism, &c.\n\n\nAgreeably with the view now generally received, that magnetism and\nelectricity are but modifications of one force, since they are found to\nstand to each other in the relation of cause and effect, the separation\nwhich is here adopted, of the consideration of their several phenomena,\nmay appear inappropriate. The importance, however, of all that is\nconnected with magnetism, and the very decided difference which is\npresented by true magnetic action, and that of frictional or chemical\nelectricity, is so great that it has been thought advantageous to adopt\nthe present arrangement in reviewing the influence of terrestrial\nmagnetism with which science has made us acquainted.\n\nFrom a very early period a peculiar attractive force has been observed\nin some specimens of iron ore. Masses of this kind were found in\nMagnesia, and from that locality we derive the name given to iron in\nits polar condition. This is confirmed by the following lines by\nLucretius:--\n\n    Quod superest agere incipiam, quo f\u0153dere fiat\n    Natura lapis hic ut ferrum ducere possit,\n    Quem magn\u00eata vocant patrio de nomine Graii\n    Magn\u00eatum, quia sit patriis in finibus ortus.\n\nAgain we find Pliny employing the term _magnetic_, to express this\nsingular power. It was known to the ancients that the magnetic power\nof iron, and the electric property of amber, were not of the same\ncharacter, but they were both alike regarded as miraculous. The Chinese\nand Arabians seem to have known Magnetism at a period long before\nthat at which Europeans became acquainted with either the natural\nloadstone or the artificial magnet. Previously to A.D. 121, the magnet\nis distinctly mentioned in a Chinese dictionary; and in A.D. 419 it\nis stated in another of their books that ships were steered south by\nit.[170]\n\nThe earliest popularly received account of its use in Europe is, that\nVasco de Gama employed a compass in 1427, when that really adventurous\nnavigator first explored the Indian seas. It is highly probable,\nhowever, that the knowledge of its important use was derived from some\nof the Oriental nations at a much earlier period.\n\nWe have some curious descriptions of the _leading stone_ or loadstone,\nin the works of an Icelandic historian, who wrote in 1068. The\nmariner\u2019s compass is described in a French poem of the date of 1181;\nand from Torf\u00e6us\u2019s History of Norway, it appears to have been known to\nthe northern nations certainly in 1266.\n\nWe have not to deal with the history of magnetic discovery, but so\nfar as it tells of the strange properties which magnets are found to\npossess, and the application of this knowledge to the elucidation of\neffects occurring in nature.\n\nA brown stone, in no respect presenting anything by which it shall be\ndistinguished from other rude stones around it, is found, upon close\nexamination, to possess the power of drawing light particles of iron\ntowards it. If this stone is placed upon a table, and iron filings\nare thrown lightly around it, we discover that these filings arrange\nthemselves in symmetric curves, proceeding from some one point of the\nmass to some other; and upon examining into this, we shall find that\nthe iron which has once clung to the one point will be rejected by the\nother. If this stone is freely suspended, we shall learn also that\nit always comes to rest in a certain position,--this position being\ndetermined by these points, and some attractive force residing in the\nearth itself. These points we call its poles; and it is now established\nthat this rude stone is but a small representative of our planet. Both\nare magnetic: both are so in virtue of the circulation of currents\nof electricity, or of lines of magnetic force, as seen in the curves\nformed by the iron dust, and the north pole of the one attracts the\nsouth pole of the other, and the contrary. By a confusion of terms we\nspeak of the north pole of a compass-needle, meaning that point which\nis always opposite to the north pole of the earth: the truth being\nthat the pole of the compass-needle, which is so forcibly drawn to the\nnorth, is a point in a contrary state, or, as we may express it, really\na south pole.\n\nThere is a power of a peculiar kind, differing from gravitation, or any\nother attracting or aggregating force with which we are acquainted,\nwhich exists permanently in the magnetic iron stones, and also in the\nearth. What is this power?\n\nMagnetism may be produced in any bar of steel, either by rubbing it\nwith a loadstone, or by placing it in a certain position in relation to\nthe magnetic currents of the earth, and, by a blow or any other means,\ndisturbing its molecular arrangement. This principle appears to involve\nthe iron as with an atmosphere, and to interpenetrate it. By one magnet\nwe may induce magnetism in any number of iron bars without its losing\nany of its original force. As we have observed of the electrical forces\nalready considered, the magnet constantly presents two points in\nwhich there is a difference manifested by the circumstance that they\nare always drawn with considerable power towards the north or south\npoles of the earth. That this power is of the same character as the\nelectricity which we have been considering, is now most satisfactorily\nproved. By involving a bar of soft iron which, being without any\nmagnetic power, is incapable of sustaining even an ounce weight, with a\ncoil of copper wire, through which a galvanic current is passing, the\nbar will receive, by induction from the current, an enormous accession\nof power, and will, so long as the current flows around it, sustain\nmany hundred pounds weight, which, the moment the current is checked,\nfall away from it in obedience to the law of gravity. Thus the mere\nflow of this invisible agent around a mass of metal possessing no\nmagneto-attractive power, at once imparts this life-like influence to\nit, and as long as the current is maintained, the iron is endowed with\nthis surprising energy.\n\nThis discovery, which we owe to the genius of Oersted, and which has,\nindeed, given rise to a new science, electro-magnetism, may be regarded\nas one of the most important additions made to our knowledge.\n\nCurrent electricity is magnetic; iron is not necessary to the\nproduction of magnetic phenomena, although by its presence we secure a\ngreater amount of power. The copper wires which complete the circuit\nof a galvanic battery, will attract and hold up large quantities of\niron filings, and the wires of the electric telegraph will do the same,\nwhile any signal is being conveyed along them. Again, all the phenomena\ncommon to galvanic electricity can be produced by merely disturbing the\npower permanently secured in the ordinary magnet. It was thought that\nmagnets would become weakened by this constant disturbance of their\nmagnetism; but, since its application to the purpose of manufacture,\nand magneto-electricity has been employed in electro-plating, it has\nbeen found that continued action for many years, during which enormous\nquantities of electricity have been thus given out and employed in\nproducing chemical decomposition, has not, in the slightest degree,\naltered their powers. Thus a small bar of metal is shown to be capable\nof pouring out, for any number of years, the principle upon which the\nphenomena of magnetism depend.\n\nThere are, however, differences, and striking ones, between ordinary\nand magnetic electricity. In the magnet we have a power at rest, and in\nthe electrical machine or galvanic battery, a power in motion. Ordinary\nelectricity is stopped in its passage by a plate of glass, of resin,\nand many other substances; but magnetism passes these with freedom, and\ninfluences magnetic bodies placed on the other side. It would appear,\nthough we cannot explain how, that magnetism is due to some lateral\ninfluence of the electric currents. A magnetic bar is placed over a\ncopper wire, and it hangs steadily in the direction of its length;\nan electric current is passed along it, and the magnet is at once\ndriven to place itself across the wire. Upon this experiment, in the\nmain, Amp\u00e8re founds his theory of terrestrial magnetism. He supposes\nelectrical currents to be traversing our globe from east to west, and\nthus, that the needle takes its direction, not from the terrestrial\naction of any fixed magnetic poles, but from the repulsion of these\ncurrents, as is the case with the wire.\n\nIt has been found that wires, freely suspended, along which currents\nwere passing in opposite directions, revolve about each other, or have\nan inclination to place themselves at right angles; thus exhibiting\nthe same phenomenon as the magnet and the conducting wire. So far the\nhypothesis of Amp\u00e8re leads us most satisfactorily. We see in the magnet\none form of electricity, and in the machine or battery another. But why\nshould not the electricity of the magnet, electricity at rest, exhibit\nthe same powers as this force in motion?\n\nOersted, whose theory led him to the discovery of the fact of the\nmagnetic power of an electric current, of the establishment indeed of\nthe new science--ELECTRO-MAGNETISM, regards the phenomena of a current\npassing a wire, and its action on a needle, as evidence of two fluids,\npositive and negative, traversing in opposite directions, and mutually\nattracting and repelling. He conceives that they pass the wires in a\nseries of spirals; that in the magnet, by some peculiar property of the\niron, this conflict of the currents is reduced to an equilibrium, and\nits power becomes manifested in its attractive force.[171] This does\nnot, however, convey a clear idea to the mind.\n\nIt is curious that iron becomes magnetic in a superior degree to any\nother metal; that steel retains permanently any magnetism imparted\nto it; but that soft iron rapidly loses its magnetic power. This\nmust be in virtue of some peculiar arrangement of the molecules, or\nsome unknown physical condition of the atoms of the mass, by which a\ncontinued influence is retained by the steel, probably in a state of\nconstant internal circulation. It has, however, been shown that soft\niron, under certain circumstances, may be made to retain a large amount\nof magnetic force.[172]\n\nIf a horse-shoe shaped bar of soft iron is rendered magnetic by the\ncirculation of an electric current around it, while its two ends are\nunited by an armature of soft iron, so that it is capable of supporting\nmany hundred pounds weight; and we then, by breaking the circuit, stop\nthe current, taking care the armature is kept in contact, the iron will\nnot lose its magnetic property, but will retain this power for many\nyears. If the connecting piece of iron, the armature, is removed, the\nbar immediately loses all its magnetism, and will not support even the\narmature itself. This fact appears to confirm the idea that magnetism\nis due to the retention of electricity, and that steel possesses\nthe property of equalizing the opposing forces, or of binding this\nprinciple to itself like an atmosphere.\n\nThe influence of heat on magnetism is so remarkable a proof of the\ndependence of this power upon molecular arrangement, that it must not\nescape our notice. To select but one of many experiments by Mr. Barlow,\nit was found that in a bar of malleable iron, in which, when cold, the\nmagnetic effect was + 30\u00b0 0', all polarity ceased at a white heat, that\nit was scarcely appreciable at a red heat, but that at a blood-red heat\nit was equal to + 41\u00b0 0'.[173]\n\nThe more closely we examine the peculiarities of the magnetic power,\nand particularly as they are presented to us in its terrestrial action,\nthe more surprising will its influence appear to be. We have discovered\na natural cause which certainly exercises a very remarkable power\nover matter, and we have advanced so far in our investigations as to\nhave learnt the secret of converting one form of force into another,\nor of giving to a principle, produced by one agency, a new character\nunder new conditions; of changing, in fact, electricity into magnetism,\nand from magnetism again evolving many of the effects of electrical\ncurrents.\n\nIf a magnetic bar is freely suspended above the earth, it takes,\nin virtue of some terrestrial power, a given direction, which is\nan indication of the earth\u2019s magnetic force. Whether this is the\nconsequence of the currents of electricity, which Amp\u00e8re supposes to\ncirculate around the globe, from east to west, or the result of points\nof attraction in the earth itself, the phenomenon is equally wonderful.\nTo whatever cause we may refer the visible effects, it appears certain\nthat this earth is composed of particles in a magnetic state, the\ncharacter varying with physical conditions, and that terrestrial\nmagnetic force is the collective action of all the atoms of this\nplanetary mass.[174]\n\nThe remarkable connexion which has been observed between the changes\nin the physical condition of the surface of the sun and terrestrial\nphenomena, must not escape our notice. Sir William Herschel thought\nhe perceived a link connecting the dark spots on the sun\u2019s face with\nthe variations of the earth\u2019s temperature. This has not, however, been\nconfirmed by the observations which have been made since the time\nof Herschel. The careful examinations of the solar spots which have\nbeen made by Schwabe,[175] prove a well-defined order of progress in\nthem. He has discovered that they move in cycles of ten years--from\nthe smallest number visible in a given year, they regularly increase\nfor five years, when they reach their maximum; they then as regularly\ndecrease, and at the end of another five years they are at their\nmaximum number. The magnetic observations which have been carried on by\nthe British and other governments for some years, over every part of\nthe world, have elicited the fact that the order of variation in the\nearth\u2019s magnetic intensity is in cycles of ten years, and the law of\nincrease and decrease which is found to prevail with the solar spots\ndistinctly marks the variations of terrestrial magnetism. Few more\ninteresting facts than this are within the range of our knowledge,\nproving as it does the direct dependence of terrestrial phenomena on\nsolar force.\n\nThe constancy with which a magnetised needle points along a certain\nline which varies a little from the earth\u2019s axial line, renders it one\nof the most important instruments to the practical and the scientific\nman. The wanderer of the ocean or of the desert is enabled, without\nfear of error, to pursue his path, and in unknown regions to determine\nthe azimuth of objects. The miner or the surveyor finds in the\nmagnetic compass the surest guide in his labours, and the experiment is\nfor ever studying its indications.\n\n    \u201cTrue as the needle to the pole,\u201d\n\nhas passed into a proverb among mankind, but the searching inquiry\nof modern observers has shown that the expression is correct only\nwith certain limitations. There are two lines on the surface of the\nearth along which the needle points true north, or where the magnetic\nand the geographical north correspond. These are called lines of _no\nvariation_, or, as they have also been designated, _agonic lines_, and\none is found in the eastern and the other in the western hemisphere.\nThe American line is singularly regular, passing in a south-east\ndirection from the latitude 60\u00b0 to the west of Hudson\u2019s Bay, across the\nAmerican lakes, till it reaches the South Atlantic ocean, and cuts the\nmeridian of Greenwich in about 65\u00b0 south latitude. The Asiatic line\nof _no variation_ is very irregular, owing, without doubt, to local\ninterferences; it begins below New Holland, in latitude 60\u00b0 south,\nit bends westward across the Indian ocean, and from Bombay has an\ninflection eastward through China, and then northward across the sea\nof Japan, till it reaches the latitude of 71\u00b0 north, when it descends\nagain southward, with an immense semicircular bend, which terminates in\nthe White Sea.\n\nHansteen has thought that there are two points in each hemisphere which\nmay be regarded as stronger and weaker poles on opposite sides of the\npoles of revolution. These are called the magnetic poles of the earth,\nor by Hansteen _magnetic points of convergence_. These four points are\nconsidered to have a regular motion round the globe, the two northern\nones from west to east, and the two southern ones from east to west. By\nthe assistance of recorded observations, Hansteen has calculated the\nperiods of these revolutions to be as follows:--\n\n    The weakest north pole in 860 years.\n    The strongest north pole in 1746 years.\n    The weakest south pole in 1304 years.\n    The strongest south pole in 4609 years.\n\nThere are some points of speculation on which Hansteen has ventured\nwhich have been smiled at as fanciful; but they may rather indicate\nan amount of knowledge in the Brahminical and Egyptian priesthood,\nbeyond what we are usually disposed to allow them, and prove that their\nobservations of nature had led them to an appreciation of some of the\nmost remarkable harmonies of this mysterious creation.\n\nThe above terms are exceedingly near 864, 1246, 1728, 4320, and those\nnumbers are equal to the mystic number of the Indians, Greeks, and\nEgyptians, 432 multiplied by 2, 3, 4, and 10. On these the ancients\nbelieved a certain combination of natural events to depend, and,\naccording to Brahminical mythology, the duration of the world is\ndivided into four periods, each of 432,000 years. Again, the sun\u2019s mean\ndistance from the earth is 216 radii of the sun, and the moon\u2019s mean\ndistance 216 radii of the moon, each the half of 432. Proceeding with\nthis very curious examination, Hansteen says, 60 multiplied by 432\nequals 15,920, the smallest number divisible at once by all the four\nperiods of magnetic revolution, and hence the shortest time in which\nthe four poles can complete a cycle, and return to their present state,\nand _which coincides exactly with the period in which the precession\nof the equinoxes will amount to a complete circle_, reckoning the\nprecession at a degree in seventy-two years.[176]\n\nWhen we consider the phenomena of terrestrial magnetism carefully, it\nappears to indicate the action of a power external to the earth itself,\nand, as Hansteen conceives, having its origin from the action of the\nsun, heating, illuminating, and producing a magnetic tension, in the\nsame manner as it produces electrical excitation and actino-chemical\naction.\n\nThe movements of these magnetic poles have been the subject of\nextensive and most accurate observation in every quarter of the globe.\nIn London, during 1657-1662, there was no magnetic variation; the\nagonic line passing through it. The variation steadily increased,\nuntil, in 1815, it amounted to 24\u00b0 15' 17\", since which time it has\nbeen slowly diminishing. In addition to this great variation, we\nhave a regular annual change dependent on the position of the sun,\nin reference to the equinoctial and solstitial points, which was\ndiscovered by Cassini, and investigated by Arago and others. Also a\ndiurnal variation, which movement appears to commence early in the\nmorning, moving eastward until half-past seven, A.M., when it begins\nto move westward until two, P.M., when it again returns to the east,\nand in the course of the night reaches the point from which it started\ntwenty-four hours before.\n\nWe have also remarkable variations in what is termed the _dip_ of\nthe needle. It is well known that a piece of unmagnetized steel, if\ncarefully suspended by its centre, will swing in a perfectly horizontal\nposition, but, if we magnetize this bar, it will immediately be drawn\ndownwards at one end. The force of the earth\u2019s polarity, attracting the\ndissimilar pole, has caused it to _dip_.\n\nThere is, in the neighbourhood of the earth\u2019s equator, and cutting it\nat four points, an irregular curve, called the magnetic equator, or\n_aclinic_ line, where the needle balances itself horizontally. As we\nproceed from this line towards either pole the dip increases, until,\nat the north and south poles, the needle takes a vertical position.\nThe _intensity_ of the earth\u2019s magnetism is also found to vary with\nthe position, and to increase in a proportion which corresponds very\nclosely with the dip. But the _intensity_ is not a function of the\ndip, and the lines of equal intensity, _isodynamic lines_, are not\nparallel to those of equal dip. We have already remarked on the diurnal\nvariation of the declination of the needle; we know, also, that there\nexists a regular monthly and daily change in the magnetic intensity.\nThe greatest monthly change appears when the earth is in its perihelion\nand aphelion, in the months of December and June,--a maximum then\noccurs; and about the time of the equinoxes a minimum is detected.[177]\n\nThe daily variation of intensity is greatest in the summer, and least\nin the winter. The magnetism is generally found to be at a minimum when\nthe sun is near the meridian; its intensity increasing until about six\no\u2019clock, when it again diminishes.[178]\n\nWhat striking evidences all these well-ascertained facts give of the\ndependence of terrestrial magnetism on solar influence! and in further\nconfirmation of this view, we find a very remarkable coincidence\nbetween the lines of equal temperature--the isothermal lines, and those\nof equal dip and magnetic intensity.\n\nSir David Brewster first pointed out that there were in the northern\nhemisphere two poles of maximum cold; these poles agree with the\nmagnetic points of convergence; and the line of maximum heat, which\ndoes not run parallel to the earth\u2019s equator, is nearly coincident with\nthat of magnetic power. Since Seebeck has shown us that electrical\nand magneto-electrical phenomena can be produced by the action of heat\nupon metallic bars, we have, perhaps, approached towards some faint\nappreciation of the manner in which the solar calorific radiations may,\nacting on the surface of our planet, produce electrical and magnetic\neffects. If we suppose that the sun produces a disturbance of the\nearth\u2019s electricity along any given line, in all directions at right\nangles to that line, we shall have magnetic polarity induced.[179] That\nsuch a disturbance is regularly produced every time the sun rises, has\nbeen sufficiently proved by many observers.\n\nIn 1750, Wargentin noticed that a very remarkable display of _Aurora\nborealis_ was the cause of a peculiar disturbance of the magnetic\nneedle; and Dr. Dalton[180] was the first to show that the luminous\nrays of the Aurora are always parallel to the dipping-needle,\nand that the Auroral arches cross the magnetic meridian at right\nangles. Hansteen and Arago have attended with particular care to\nthese influences of the northern lights, and the results of their\nobservations are:--\n\nThat as the crown of the Aurora quits the usual place, the\ndipping-needle moves several degrees forward:--\n\nThat the part of the sky where all the beams of the Aurora unite, is\nthat to which a magnetic needle directs itself, when suspended by its\ncentre of gravity:--\n\nThat the concentric circles, which show themselves previously to the\nluminous beams, rest upon two points of the horizon equally distant\nfrom the magnetic meridian; and that the most elevated points of each\narch are exactly in this meridian.[181]\n\nIt does not appear that every Aurora disturbs the magnetic needle; as\nCaptains Foster and Back both describe very splendid displays of the\nphenomenon, which did not appear to produce any tremor or deviation\nupon their instruments.[182]\n\nSome sudden and violent movements have been from time to time observed\nto take place in suspended magnets; and since the establishment of\nmagnetic observatories in almost every part of the globe, a very\nremarkable coincidence in the time of these agitations has been\ndetected. They are frequently connected with the appearance of Aurora\nborealis; but this is not constantly the case. These disturbances\nhave been called _magnetic storms_; and over the Asiatic and European\ncontinent, the islands of the Atlantic and the western hemisphere, they\nhave been proved to be simultaneous.\n\nFrom observations made at Petersburg by Kupffer, and deductions drawn\nfrom the observations obtained by the Magnetic Association, it appears\nprobable that these _storms_ arise from a sudden displacement in the\nmagnetic lines of the earth\u2019s surface; but the cause to which this may\nbe due is still to be sought for.\n\nIn the brief and hasty sketch which has been given of the phenomena\nof terrestrial magnetism, enough has been stated to show the vast\nimportance of this very remarkable power in the great operations\nof nature. We are gradually reducing the immense mass of recorded\nobservations, and arriving at certain laws which are found to prevail.\nStill, the origin of the force, whether it is strictly electrical,\nwhether it is the circulation of a magnetic fluid, or whether it is\nmerely a peculiar excitation of some property of matter, are questions\nwhich are open for investigation.\n\nIn the beautiful Aurora borealis, with its trembling diffusive lights,\nand its many-coloured rays, we have what may be regarded as a natural\nexhibition of magnetism, and we appear to have within our grasp the\nexplanation we desire. But we know not the secret of even these\nextraordinary meteorological displays. If we pass an electric spark\nfrom a machine through a long cylinder, exhausted of air as far as\npossible, we have a mimic representation of the Northern Lights--the\nsame attenuation of brightness, almost dwindling into phosphorescence;\nand by the slightest change of temperature we may produce that play\nof colours which is sometimes so remarkably manifested in Aurora. Dr.\nDalton considered Aurora borealis _as a magnetic phenomenon, and that\nits beams are governed by the earth\u2019s magnetism_. We know that the arc\nof light produced between the poles of a powerful galvanic battery is\nreadily deflected by a good magnet; and we have lately learned that\nevery vapour obeys the magnetic force.[183] It is, therefore, yet a\nquestion for our consideration, does the earth\u2019s magnetism produce\nthe peculiar phenomena of Aurora by acting upon electricity in a\nstate of glow? or have we evidence in this display of the circulation\nof the magnetic fluid around our globe, manifesting itself by its\naction on the ferruginous and other metallic matter, which Fusinieri\nhas proved to exist in the upper regions of our atmosphere.[184] That\nmagnetic radiations do exist, has been proved by Faraday, and that they\nform lines of force perpendicular to the earth\u2019s surface, has been\nexperimentally shown. Parallelograms of wire moved upon a central axis,\nand connected with a galvanometer, give at every revolution indication\nof an electric disturbance in all respects analogous to the production\nof a current by moving wires in front of a steel magnet.\n\nThe alteration in the properties of heat, when it passes from the\nradiant state into combination with matter, exhibits to us something\nlike what we may suppose occurs in the conversion of magnetism into\nelectricity or the contrary. We have a subtile agent, which evidently\nis for ever busy in producing the necessary conditions of change in\nthis our earth: an element to which is due the development of many of\nthe most active powers of nature; performing its part by blending with\nthose principles which we have already examined; associating itself\nwith every form of matter; and giving, as we shall presently see, in\nall probability, the first impulses to combination, and regulating the\nforms of aggregating particles.\n\nAs electricity has the power of altering the physical conditions of\nthe more adherent states of matter, thus giving rise to variations\nof form and modes of combination, so gross matter appears to alter\nthe character of this agency, and thus disposes it to the several\nmodifications under which we have already detected its presence.\nWe have mechanical electricity and chemical electricity, each\nperforming its great work in nature; yet both manifesting conditions\nso dissimilar, that tedious research was necessary before they could\nbe declared identical. Magnetic electricity is a third form; all its\ncharacteristics are unlike the others, and the office it appears to\nperform in the laboratory of creation is of a different order from\nthat of the other states of electrical force. In the first two we have\ndecomposing and recombining powers constantly manifested--in fact,\ntheir influences are always of a chemical character; but in the last it\nappears we have only a directive power. It was thought that evidence\nhad been detected of a chemical influence in magnetism; it did appear\nthat sometimes a retarding force was exerted, and often an accelerating\none. This has been again denied, and we have arrayed in opposition to\neach other some of the first names among European experimentalists.\nThe question is not yet to be regarded as settled; but, from long and\ntedious investigation, during which every old experiment has been\nrepeated, and numerous new ones tried, we incline to the conclusion\nthat chemical action is not directly affected by magnetic power. It\nis highly probable that magnetism may, by altering the structural\narrangement of the surface, vary the rate of chemical action; but this\nrequires confirmation.[185]\n\nThere is no substance to be found in nature existing independently of\nmagnetic power. But it influences bodies in different ways: one set\nacting with relation to magnetism, like iron, and arranging themselves\nalong the line of magnetic force,--these are called magnetic bodies;\nanother set, of which bismuth may be taken as the representative,\nalways placing themselves at right angles to this line,--these are\ncalled _diamagnetic bodies_.[186] This is strikingly shown by means of\npowerful electro-magnets; but the magnetism of the earth is sufficient,\nunder proper care, to exhibit the phenomena.\n\nEvery substance in nature is in one or other of these conditions. The\nrocks, forming the crust of the earth, and the minerals which are\ndiscovered in them; the surface soil, which is by nature prepared as\nthe fitting habitation of the vegetable world, and every tree, shrub,\nand herb which finds root therein, with their carbonaceous matter, in\nall its states of wood, leaf, flower, and fruit; the animal kingdom,\nfrom the lowest monad through the entire series up to man,--have, all\nof them, distinct magnetic or diamagnetic relations.\n\n\u201cIt is a curious sight,\u201d says Dr. Faraday, \u201cto see a piece of wood or\nof beef, or an apple, or a bottle of water repelled by a magnet, or,\ntaking the leaf of a tree, and hanging it up between the poles, to\nobserve it take an equatorial position. Whether any similar effects\noccur in nature among the myriads of forms which, upon all parts of its\nsurface, are surrounded by air, and are subject to the action of lines\nof magnetic force, is a question which can only be answered by future\nobservation.\u201d[187]\n\nAt present, the bodies which are known to exhibit decided\nferro-magnetic properties are the following, which stand arranged in\nthe order of their intensity:--\n\n    Iron, Nickel, Cobalt, Manganese,\n    Chromium, Cerium, Titanium,\n    Palladium, Platinum, Osmium.\n\nIt is interesting to know that there are evidences that two bodies\nwhich, when separate, are not magnetic, as iron is, become so when\ncombined. Copper and zinc are both of the diamagnetic class, but many\nkinds of brass are discovered to be magnetic.\n\nThe salts of the above metals are, to a greater or less extent,\nferro-magnetic, but they may be rendered neutral by water, which is a\ndiamagnetic body, being repelled by the magnet. It will be unnecessary,\nhere, to enumerate the class of bodies which are diamagnetic; indeed,\nall not included in the preceding list may be considered as belonging\nto that class, with the exception of gases and vapours, which appear\nto exist, relatively to each other, sometimes in the one, and sometimes\nin the other condition.[188]\n\nTo endeavour to reduce our knowledge of these facts to some practical\nexplanation, we must bear in mind that particular spaces around the\nnorth and south geographical poles of the earth, are regarded as\ncircles to which all the magnetic lines of force converge. Under\ncircumstances which should prevent any interference with what is called\nferro-magnetic action, all bodies coming under that class would arrange\nthemselves according to the laws which would regulate the disposition\nof an infinite number of magnets, free to move within the sphere of\neach other\u2019s influence. The north and south pole of one magnetic body\nwould attach itself to the south and north pole of another, until we\nhad a line of magnets of any extent; the two ends being in opposite\nstates, like the magnetic points of convergence of the earth.\n\nEvery body, not ferro-magnetic, places itself across such a line of\nmagnetic force as we have conceived; and if the earth were made up of\nseparate layers of ferro-magnetic and diamagnetic bodies, the result\nwould be the formation of bands at right angles to each other. This\nis not the case, by reason of the intermingling of the two classes\nof substances. Out of the known chemical elements we find only about\nten which are actively ferro-magnetic; the others combining with\nthese give rise to either a weaker state, a neutral condition, or\nthe balance of action is turned to the diamagnetic side. Sulphate of\niron, for instance, is a magnetic salt; but in solution, water being\ndiamagnetic, it loses its property. The yellow prussiate of potash\ndissolved in water is a diamagnetic body; but the red prussiate, which\ncontains an atom less of potassium, is magnetic: but in the solid state\nthey are both diamagnetic.[189]\n\nFrom this it would appear that the chemical composition of a body\nregulated its relation to magnetism. The following facts will show,\nhowever, that the molecular structure is more particularly concerned in\ndetermining the molecular condition of substances.\n\nM. Pl\u00fccker, being desirous of finding the extent to which the\n_direction of the fibres_ in organic bodies might influence their\nmagnetic or diamagnetic properties, was led to inquire whether in\ncrystals the direction of the optic axes, which itself depends upon the\narrangement of the particles, might not also exercise some influence.\nThe first submitted to the action of the electro-magnet a thin plate\nof tourmaline, such as is employed in experiments upon polarization,\nhaving its optic axis parallel to its longest length. It was very\nquickly perceived that the plate was magnetic, by the effect of the\niron that it contains; but it was suspended successively in three\nways,--first, so that its longest side was vertical, then as that the\nshortest side was vertical, and finally so that the plate itself was\nhorizontal. In the first case it is directed between the two points\nof the conical curvatures of the poles like a magnetic body; but, in\nthe other two cases, on the contrary, it took the direction assumed by\ndiamagnetic bodies--that is to say, a direction such that its longest\nlength was perpendicular to the line joining the poles. This direction\nindicated that the optical axis was repelled by the two poles, and that\nthis repulsion outweighed the magnetic properties of the crystal.[190]\n\nThe relation of structure to physical phenomena of essentially\ndifferent characters is remarkable. Savart, when making crystalline\nplates of quartz and carbonate of lime vibrate, succeeded in\ndetermining a relation between the acoustic figures that are\nproduced in them, and the particular mode of the crystallization of\nthe substance. He found that the direction of the optical axis is\nconstantly connected with that of the principal forms of the acoustic\nfigures.\n\nMitscherlich has remarked that crystals do not expand uniformly by\nheat, but that this dilatation is greater in one direction than in\nanother; and that this difference is connected with their crystalline\nform. M. de S\u00e9narmont has shown that conductibility for heat,\nwhich is equal in all directions for the crystals of the regular\nsystem, acquires in others a maximum or a minimum value, according\nto directions parallel to the crystallographic axes; so that the\nisothermic surfaces, which are spheres in the former case, are, in the\nother, ellipsoids elongated or flattened in the same direction. The\noptical axes do not altogether coincide with the principal axes of\nconductibility for heat; but this appears to be due merely to slight\ndifferences in the rate of progression, or the refrangibility of the\nluminous and calorific rays.\n\nWiedemann, by employing a fine point through which he made electricity\narrive upon a surface that he had powdered with licopodium or red lead,\nsucceeded in determining, by means of the form assumed by this light\npowder, the conductibility of crystals in different directions.\n\nOn a surface of glass, the powder which disperses itself around the\npoints, in consequence of electric repulsion, forms a circular\nfigure traversed by radii. When a plate of gypsum is used instead of\nglass the figure is found to be elliptical, and the great axis of\nthe ellipse forms a right angle with the principal crystallographic\naxis, which proves that the electricity distributes itself more\neasily in a direction perpendicular to the axis than in any other.\nM. Wiedemann comes to the conclusion that crystals which possess a\nbetter conductibility in the direction of the principal axis, all\nbelong to the class of negative crystals: while those which have a\nbetter conductibility in the direction perpendicular to the axis are\npositive, which indicates that the direction of best conductibility\nfor electricity is also that according to which light is propagated\nrelatively with greater velocity.\n\nTyndale has shown, that if gutta percha which has been rendered fibrous\nin manufacture is cut so that the fibres are in the direction of this\ngreatest length, or in a direction perpendicular to this greatest\nlength, and placed under the influence of a magnet, they direct\nthemselves equatorially. Ivory cut in the same direction manifests the\nsame conditions, though both these substances are diamagnetic.\n\nThe fibrous structure, and the planes of cleavage, thus determine the\nmagnetic condition of a substance. The special properties presented by\ncrystals, in regard to the action exercised upon them by magnets, is\ndue to a particular mode of grouping their particles. This is also the\ncause of unequal dilatability, and of unequal conductibility for heat\nand for electricity.\n\nHow curiously, therefore, does molecular structure determine the\nrelation of a body to any of the forms of physical force!\n\nWe still search in the dark, and see but dimly the evidences; yet it\nbecomes almost a certainty to us, that this stone of granite, with its\ncurious arrangement of felspar, mica, and quartz, presents its peculiar\ncondition in virtue of some law of magnetic force. The crystal, too,\nof quartz, which we break out of the mass, and which presents to us a\nbeautifully regular figure, is, beyond a doubt, so formed, because the\natoms of silica are each one impelled in obedience to one of these two\nconditions of magnetism to set themselves in a certain order to each\nother, which cannot be altered by human force without destruction.\n\nAll the laws which regulate the forms of crystals and amorphous bodies\nare, to the greatest degree, simple. In nature the end is ever attained\nby the easiest means; and the complexity of operation, which appears\nsometimes to the observer, is only so because he cannot see the spring\nby which the machine is moved.\n\nThe gaseous envelope, our atmosphere, is in a neutral state. Oxygen is\nstrikingly magnetic in relation to hydrogen gas, whilst nitrogen is as\nsingularly the contrary; and the same contrasts present themselves when\nthese gases are examined in their relation to common air. Thus, oxygen\nbeing magnetic, and nitrogen the contrary, we have an equilibrium\nestablished, and the result is a compound neutral in its relations to\nall matter. All gases and vapours are found to be diamagnetic, but in\ndifferent degrees.[191] This is shown by passing a stream of the gas,\nrendered visible by a little smoke, within the influence of a powerful\nmagnet.\n\nThese bodies are, however, found relatively to each other,--or even\nto themselves, under different thermic conditions,--to change their\nstates, and pass from the magnetic to the diamagnetic class. Heat has a\nvery remarkable influence in altering these relations; and atmospheric\nair at one temperature is magnetic to the same fluid at another: thus,\nby thermic variations, attraction or repulsion may be alternately\nmaintained. By this it must be understood that a stream of air, at a\ntemperature elevated but a few degrees above that of an atmosphere of\nthe same kind into which it is passing, is deflected in one way by a\nmagnet; whereas, if the stream is colder than the bulk through which\nit flows, it is bent in another way by the same force. In this respect\nmagnetism and diamagnetism show equally the influence of another\nphysical force, heat; and we may safely refer many meteorological\nphenomena to similar alterations of condition in the atmosphere,\nrelative to the magnetic relations of the a\u00ebrial currents.\n\nThat magnetism has a directive power is satisfactorily shown by\nthe formation of crystals in the neighbourhood of the poles of\npowerful magnets. The common iron salt, the protosulphate, ordinarily\ncrystallizes so that the crystals unite by their faces; but when\ncrystallizing under magnetic influence, they have a tendency to arrange\nthemselves with regard to each other so that the acute angle of one\ncrystal unites with one of the faces of another crystal, near to, but\nnever actually at, its obtuse angle. In addition to this, if a magnet\nof sufficient power is employed, the crystals arrange themselves in\nmagnetic curves from one pole to the other, a larger crop of crystals\nbeing always formed at the north than at the south pole. Here we have\nevidence of an actual turning round of the crystal, in obedience to the\ndirective force of the magnet; and we have the curious circumstance of\na difference in some way, which is not clearly explained, between the\ntwo opposite poles. If, instead of an iron or a ferro-magnetic salt,\nwe employ one which belongs to the other, or diamagnetic, class, we\nhave a curious difference in the result. If into a glass dish, fixed\non the poles of a strong electro-magnet, we pour a quantity of a\nsolution of nitrate of silver, and place in the fluid, over the poles\nof the magnet, two globules of mercury (an arrangement by which that\narborescent crystallization, called the _Arbor Dian\u00e6_, is produced,) we\nhave the long needle-shaped crystals of silver, arranging themselves in\ncurves which would cut the ordinary magnetic lines at right angles.[192]\n\nIn the first example given we have an exhibition of magnetic force,\nwhile in the last we have a striking display of the diamagnetic power.\n\nThe large majority of natural formations appear to group themselves\nunder the class of diamagnetics. These bodies are thought to possess\npoles of mutual repulsion among themselves, and which are equally\nrepelled by the magnetic points of convergence. Confining our ideas to\nsingle particles in one condition or the other, we shall, to a certain\nextent, comprehend the manifold results which must arise from the\nexercise of these two modes of force. At present, our knowledge of the\nlaws of magnetism is too limited to allow of our making any general\ndeductions relative to the disposition of the molecules of matter; and\nthe amount of observation which has been given to the great natural\narrangements, is too confined to enable us to infer more than that it\nis probable many of the structural conditions of our planet are due to\npolarity.\n\nMountain ranges observe a singular uniformity of direction, and\nthe cleavage planes of rock are evidently determined by some\nall-pervading power. Mineral bodies are not distributed in all\nrocks indiscriminately. The primary formations hold one class of\nmetalliferous ores, and the more recent ones another. This is not\nto be regarded as in any way connected with their respective ages,\nbut with some peculiar condition of the stone itself. The granite\nand slate rocks, at their junctions, present the required conditions\nfor the deposit of copper ore, while we find the limestones have the\ncharacteristic physical state for accumulating lead ore. Again, on\nexamining any mineral vein, it will be at once apparent that every\nparticle of ore, and every crystal of quartz or limestone, is disposed\nin a direction which indicates the exercise of some powerful directive\nagency.[193]\n\nIt appears, from all the results hitherto obtained, that the magnetic\nand diamagnetic condition of bodies is equally due to some peculiar\nproperty of matter in relation to the other forms of electricity. We\nhave not yet arrived at the connecting link, but it does not appear to\nbe far distant.\n\nWe have already referred to the statement made by talented\nexperimentalists, that magnetism has a powerful influence in either\nretarding or accelerating chemical combination. Beyond a doubt chemical\naction weakens the power of a magnet; but the disturbance which it\noccasions in soft iron, on the contrary, appears to tend to its\nreceiving magnetism more readily, and retaining it more permanently.\nFurther investigations are, however, required, before we can decide\nsatisfactorily either of these problems, both of which bear very\nstrongly upon the subject we have just been considering.\n\nWe have seen that heat and electricity act strangely on magnetic force,\nand that this statical power reacts upon them: and thus the question\nnaturally arises, Do light and magnetism in any way act upon each other?\n\nMorichini and Carpi on the continent, and Mrs. Somerville in England,\nhave stated that small bars of steel can be rendered magnetic by\nexposing them to the influence of the violet rays of light. These\nresults have been denied by others, but again repeated and apparently\nconfirmed. In all probability, the rays to which the needles were\nexposed, being those in which the maximum actinic power is found,\nproduced an actual chemical change; and then, if the position were\nfavourable, it is quite evident that magnetism would be imparted.\nIndeed we have found this to be the case when the needles, exposed to\nsolar radiations, were placed in the direction of the dip. The supposed\nmagnetization of light by Faraday has already been mentioned. If the\ninfluence in one case is determined, it will render the other more\nprobable.[194]\n\n\u201cIn seeking for a cause,\u201d writes Sir David Brewster, \u201cwhich is capable\nof inducing magnetism on the ferruginous matter of our globe, whether\nwe place it within the earth, or in its atmosphere, we are limited to\nthe SUN, to which all the magnetic phenomena have a distinct reference;\nbut, whether it acts by its heat, or by its light, or by specific\nrays, or influences of a magnetic nature, must be left to future\ninquiry.\u201d[195]\n\nWe have learnt that magnetism is not limited to ferruginous matter; we\nknow that the ancient doctrine of the universality of the property is\ntrue. Kircher, in his strange work on Magnetism, published in the early\npart of the seventeenth century[196]--a curious exemplification of the\nmost unwearying industry and careful experiment, combined with the\ninfluences of the credulity and superstitions of his age--attributes to\nthis power nearly all the cosmical phenomena with which, in his time,\nmen were acquainted. He curiously anticipates the use of the supposed\nvirtue of magnetic traction in the curative art; and as the titles of\nhis concluding chapters sufficiently show, he was a firm believer in\nanimal magnetism.[197] But it is not with any reference to these that\nwe refer to the work of _Athanasii Kircheri, Societatis Jesu, Magnes,\nsive de Magnetiv\u00e2 Arte_, but to show that two hundred years since,\nman was near a great truth; but the time of its development being not\nyet come, it was allowed to sleep for more than two centuries, and\nthe shadow of night had covered it. In speaking of the vegetable\nworld, and the remarkable processes by which the leaf, the flower,\nand the fruit are produced, this sage brings forward the fact of the\ndiamagnetic character of the plant, which has been, within the last two\nyears, re-discovered; and he refers the motions of the Sun-flower, the\nclosing of the Convolvulus, and the directions of the spiral, formed by\ntwining plants, to this particular influence.\n\nThis does not appear as a mere speculation, a random guess, but is\nthe result of deductions from experiment and observation. Kircher\ndoubtless leaped over a wide space to come to his conclusion; but the\nresult is valuable in a twofold sense. In the first it shows us that,\nby neglecting a fact which is suggestive, we probably lose a truth\nof great general application; and secondly, it proves to us, that by\nstepping beyond the point to which inductive logic leads, and venturing\non the wide sea of hypothesis, we are liable to sacrifice the true to\nthe false, and thus to hinder the progress of human knowledge.\n\nMagnetism, in one or other of its forms, is now proved to be universal,\nand to its power we are disposed to refer the structural conditions\nof all material bodies, both organic and inorganic. This view has\nscarcely yet been recognised by philosophers; but as we find a certain\nlaw of polarity prevailing through every atom of created matter, in\nwhatever state it may be presented to our senses, it is evident that\nevery particle must have a polar and directing influence upon the mass,\nand every coherent mass becomes thus only a larger and more powerful\nrepresentative of the magnetic unit. Thus we see the speculation of\nHansteen, that the sun is, to us, a magnetic centre, and that it\nis equally influenced by the remoter suns of the universe,[198] is\nsupported by legitimate deductions from experiment.\n\nThe great difficulty is not, however, got rid of by this speculation;\nthe cause by which the earth\u2019s magnetism is induced is only removed\nfurther off.\n\nThe idea of a magnetic fluid is scarcely tenable; and the ferruginous\nnature of the Aurora borealis receives no proof from any investigation;\nindeed, we have procured evidence to show that iron is not at all\nnecessary for the production of magnetic phenomena. The leaf of a\ntree, a flower, fruit, a piece of animal muscle, glass, paper, and a\nvariety of similar substances, have the power of repelling the bar of\niron which we call a magnet, and of placing it at right angles to the\ndirection of the force exerted by them. This is a point which must be\nconstantly borne in mind when we now consider the mysteries of magnetic\nphenomena.\n\nAny two masses of matter act upon each other according to this law,\nand although by the power of cohesion the force may be brought to an\nequilibrium, or to its zero point, it is never lost, and may be readily\nand rapidly manifested by any of the means employed for electrical\nexcitation.\n\nReasoning by analogy, the question fairly suggests itself: If two\nsystems of inorganic atomic constitution are thus invested with a\npower of influencing each other through a distance, why may not\ntwo more highly developed organic systems equally, or to a greater\nextent, produce an influence in like manner? Upon such reasoning as\nthis is founded the phenomenon known as Animal Magnetism. There is no\ndenying the fact that one mass of blood, muscle, nerves, and bone,\nmust, magnetically, influence another similar mass. This is, however,\nsomething totally different from that abnormal condition which is\nproduced through some peculiar and, as yet, unexplained physiological\ninfluences.\n\nWith the mysterious operations of vital action, the forces which we\nhave been considering have nothing whatever in common. The powers\nwhich are employed in the arrangements of matter are, notwithstanding\ntheir subtile character, of far too gross a nature to influence the\npsychological mysteries which present themselves to the observant\nmind. It cannot be denied that, by placing a person of even moderate\nnervous sensibility in a constrained position, and under an unnatural\ninfluence of the mind, as acquired by the disciples of Mesmer, a torpor\naffecting only certain senses is produced. The recognised and undoubted\nphenomena are in the highest degree curious--but in these the marvels\nof charlatanry and ignorance are not included;--and the explanation\nmust be sought for by the physiologist among those hidden principles\nupon which depends all human sensation.[199]\n\nMan, like a magician, stands upon a promontory, and surveying the great\nocean of the physical forces which involve the material creation,\nand produce that infinite variety of phenomena which is unceasingly\nexhibited around him, he extends the wand of intelligence, and bids the\n\u201cspirits of the vasty deep\u201d obey his evocation.\n\nThe phenomena recur--the great processes of creation go on--the\nexternal manifestations of omnipotent power proceed--effects are\nagain and again produced; but the current of force passes undulating\nonwards;--and to the proud bidding of the evocator there is no reply\nbut the echo of his own vain voice, which is lost at last in the vast\nimmensity of the unknown which lies beyond him.\n\nWe see how powerfully the physical forces, in their various modes of\naction, stir and animate this planetary mass; and amongst these the\ninfluence of magnetism appears as a great directing agent, though its\norigin is unknown to us.\n\n    That power which, like a potent spirit, guides\n    The sea-wide wanderers over distant tides,\n    Inspiring confidence where\u2019er they roam,\n    By indicating still the pathway home;--\n    Through nature, quicken\u2019d by the solar beam,\n    Invests each atom with a force supreme,\n    Directs the cavern\u2019d crystal in its birth,\n    And frames the mightiest mountains of the earth;\n    Each leaf and flower by its strong law restrains,\n    And binds the monarch Man within its mystic chains.\n\n\nFOOTNOTES:\n\n[170] _Treatise on Magnetism_, by Sir David Brewster. _Cosmos: a\nSketch of a Physical description of the Universe_; by Alexander Von\nHumboldt.--Ott\u00e9\u2019s Translation.\n\n[171] _Exp\u00e9rience Electro-Magn\u00e9tique._ par M. \u0152rsted.--Annales de\nChimie, vol. xxii. p. 201. De la Rive, _Recherches sur la Distribution\nde l\u2019Electricit\u00e9 dyn. dans les Corps_.--Gen\u00e8ve, 1825.\n\n[172] _On the Magnetic power of Soft Iron_: by Mr.\nWatkins.--Philosophical Transactions, 1833.\n\n[173] Cavallo, _On Magnetism_.--Cavallo was the first who noticed the\ninfluence of heat on Magnetism. Consult _On the anomalous Magnetic\nAction of Hot Iron between the white and blood-red heat_: by Peter\nBarlow, Esq.--Philosophical Transactions, 1822, p. 124. _Treatise on\nMagnetism_: by Barlow.--Encyclop\u00e6dia Metropolitana.\n\n[174] \u201cThe foundation of our researches is the assumption that the\nterrestrial magnetic force is the collective action of all the\nmagnetised particles of the earth\u2019s mass. We represent to ourselves\nmagnetisation as the separation of the magnetic fluids. Admitting the\nrepresentation, the mode of action of the fluids (repulsion of similar,\nand attraction of dissimilar, particles inversely as the square of the\ndistance) belongs to the number of established truths. No alteration\nin the results would be caused by changing this mode of representation\nfor that of Amp\u00e8re, whereby, instead of magnetic fluids, magnetism is\nheld to consist in constant galvanic currents in the minutest particles\nof bodies. Nor would it occasion a difference if the terrestrial\nmagnetism were ascribed to a mixed origin, as proceeding partly from\nthe separation of the magnetic fluids in the earth, and partly from\ngalvanic currents, in the same; inasmuch as it is known that for each\ngalvanic current may be substituted such a given distribution of the\nmagnetic fluids in a surface bounded by the current, as would exercise\nin each point of external space precisely the same magnetic action as\nwould be produced by the galvanic current itself.\u201d--_General Theory\nof Terrestrial Magnetism_, by Professor Carl Friedrich Gauss, of the\nUniversity of G\u00f6ttingen.--Scientific Memoirs, vol. ii. p. 188.\n\n[175] Humboldt\u2019s _Cosmos_.--Ott\u00e9\u2019s translation.\n\n[176] Hansteen: _Untersuchungen \u00fcber den Magnetismus der\nErde_, Christ\u00efana, 1819. Humboldt: _Expos\u00e9 des Variations\nMagn\u00e9tiques_.--Gilbert\u2019s Annales. Brewster\u2019s Magnetism: Encyclop\u00e6dia\nMetropolitana.\n\n[177] Hansteen; as above.\n\n[178] _On the effects of temperature on the intensity of magnetic\nforces, and on the diurnal variations of the terrestrial magnetic\nintensity_; by Samuel Hunter Christie, Esq.--Philosophical\nTransactions, vol. cxv. 1825.\n\n[179] It has been observed by Mr. Barlow, in England, and some eminent\nobservers in Austria, that an electric current constantly traverses\nthe wires of the electric telegraph wherever there are two earth\nconnections.\n\n[180] _Meteorological Observations and Essays_: by Dr. Dalton. _On the\nHeight of the Aurora Borealis above the surface of the Earth_: by John\nDalton, F.R.S.--Philosophical Transactions, vol. cxiv. p. 291.\n\n[181] Arago: Annales de Chimie, vol. xxxix. p. 369. _On the variable\nIntensity of Terrestrial Magnetism and the Influence of the Aurora\nBorealis upon it_; by Robert Were Fox.--Philosophical Transactions,\n1831, p. 199.\n\n[182] \u201cBrilliant and active coruscations of the Aurora Borealis,\u201d says\nCaptain Back, \u201cwhen seen through a hazy atmosphere, and exhibiting\nthe prismatic colours, almost invariably affected the needle. On the\ncontrary, a very bright Aurora, though attended by motion, and even\ntinged with a dullish red and a yellow in a clear blue sky, seldom\nproduced any sensible change, beyond, at the most, a tremulous motion.\nA dense haze or fog, in conjunction with an active Aurora, seemed\nuniformly favourable to the disturbance of the needle, and a low\ntemperature was favourable to brilliant and active coruscations. On\nno occasion during two winters was any sound heard to accompany the\nmotions. The Aurora was frequently seen at twilight, and as often to\nthe eastward as to the westward; clouds, also, were often perceived\nin the day-time, in form and disposition very much resembling the\nAurora.\u201d--_Narrative of the Arctic Land Expedition._\n\n[183] Faraday: _On the Diamagnetic character of Flame and Gases_.\n\n[184] \u201cThe Aurora Borealis is certainly in some measure a magnetical\nphenomenon; and if iron were the only substance capable of exhibiting\nmagnetic effects, it would follow that some ferruginous particles\nmust exist in the upper regions of the atmosphere. The light usually\nattending this magnetical meteor may possibly be derived from\nelectricity, which may be the immediate cause of a change in the\ndistribution of the magnetic fluid, contained in the ferruginous\nvapours which are imagined to float in the air.\u201d--Lecture on Magnetism:\nYoung\u2019s _Lectures on Natural Philosophy_, p. 533.\n\n[185] _On the supposed influence of Magnetism and Chemical Action_; by\nRobert Hunt.--Philosophical Magazine, vol. xxxii. No. 215, 1849.\n\n[186] Those bodies which are attracted by a magnet, as iron is, are\ncalled _magnetic bodies_. Those which are, on the contrary, repelled by\nthe same power, are termed _diamagnetic bodies_. On these Dr. Faraday\nremarks:--\u201cOf the substances which compose the crust of the earth, by\nfar the greater portion belong to the diamagnetic class; and though\nferruginous and other magnetic matters, being more energetic in their\naction, are more striking in their phenomena, we should be hasty in\nassuming that, therefore, they over rule entirely the effect of the\nformer bodies. As regards the ocean, lakes, rivers, and the atmosphere,\nthey will exert their peculiar effect almost uninfluenced by any\nmagnetic matter in them, and as respects the rocks and mountains, their\ndiamagnetic influence is perhaps greater than might be anticipated.\nI mentioned that by adjusting water and a salt of iron together, I\nobtained a solution inactive in air; that is, by a due association\nof the forces of a body, from each class, water and a salt of iron,\nthe magnetic force of the latter was entirely counteracted by the\ndiamagnetic force of the former, and the mixture was neither attracted\nnor repelled: To produce this effect, it required that more than 48\u00b76\ngrains of crystallised protosulphate of iron should be added to ten\ncubic inches of water (for these proportions gave a solution which\nwould set equatorially), a quantity so large, that I was greatly\nastonished on observing the power of the water to overcome it. It\nis not, therefore, at all unlikely that many of the masses which\nform the crust of this our globe, may have an excess of diamagnetic\npower, and act accordingly.\u201d--_On new magnetic actions, and on the\nmagnetic condition of all matter_; by Michael Faraday, D.C.L., F.R.S.,\n&c.--Philosophical Transactions, Jan. 1846, vol. cxxxvii. p. 41.\n\n[187] Ibid.\n\n[188] _On the Diamagnetic conditions of Flame and Gases_, by Michael\nFaraday. F.R.S.; and _On the motions presented by Flame when under\nElectro-Magnetic Influence_, by Professor Zantedeschi.--Philosophical\nMagazine, 1847, pp. 401-421.\n\n[189] _On Diamagnetism_; by Professor Pl\u00fccker, of Bonn.--Philosophical\nMagazine, July, 1848.\n\n[190] For a detailed account of the experiments of Faraday, Pl\u00fccker,\nBecquerel, Tyndale, and Knoblauch, see De La Rive\u2019s _Treatise on\nElectricity in Theory and Practice_.\n\n[191] A few examples taken from Dr. Faraday\u2019s paper will show this:--\n\nNitrogen being acted on was manifestly diamagnetic in relation to\ncommon air when both were of the same temperature. Oxygen appears to\nbe magnetic in common air. Hydrogen proved to be clearly and even\nstrongly diamagnetic. Its diamagnetic state shows, in a striking\npoint of view, that gases, like solids, have peculiar and distinctive\ndegrees of diamagnetic force. Carbonic acid gas is diamagnetic in air.\nCarbonic oxide was carefully freed from carbonic acid before it was\nused, and it appears to be more diamagnetic than carbonic acid. Nitrous\noxide was moderately, but clearly, diamagnetic in air. Olefiant gas\nwas diamagnetic. The coal gas of London is very well diamagnetic, and\ngives exceedingly good and distinct results. Sulphurous acid gas is\ndiamagnetic in air. Muriatic acid gas was decidedly diamagnetic in\nair.--_On the Diamagnetic Conditions of Flame and Gases_: Philosophical\nMagazine, 1847, p. 409.\n\n[192] For illustration of this I must refer to my own Memoir,\n_Researches on the Influence of Magnetism and Voltaic Electricity on\nCrystallization, and other conditions of matter_, in the Memoirs of the\nGeological Survey of Great Britain, &c., vol. i.\n\n[193] In a work published by Mr. Evan Hopkins, entitled _On the\nConnexion of Geology with Terrestrial Magnetism_, will be found many\nvaluable practical observations made in this country and the gold and\nsilver districts of America; but the views taken by the author are open\nto many objections.\n\n[194] See a notice by Faraday of Morichini\u2019s Experiments in _Relations\nof Light to Magnetic Force_--Philosophical Transactions, vol. cxxxvii.\np. 15. See also Mr. Christie _On Magnetic Influence in the Solar\nRays_--Philosophical Transactions, vol. cvii. p. 219; vol. cxix. p. 379.\n\n[195] Sir David Brewster _On Magnetism_; republished from the\nEncyclop\u00e6dia Britannica.\n\n[196] The whole of the title of Kircher\u2019s book will convey some idea\nof the subjects embraced:--Athanasii Kircheri Societatis Jesu Magnes,\nsive de Arte Magnetic\u00e2; opus tripartitum, quo Universa Magnetis Natura\nejusque in omnibus Scientiis et Artibus usus nov\u00e2 methodo explicatur:\nac pr\u00e6terea e viribus et prodigiosis effectibus Magneticarum aliarumque\nabditarum Natur\u00e6 Motionum in Elementis, Lapidibus, Plantis, Animalibus\nelucescentium: multa hucusque incognita Natur\u00e6 Arcana, per Physica,\nMedica, Chymica, et Mathematica omnis generis Experimenta recluduntur\nEditio Tertia: ab ipso Authore recognita emendataque, ac multis novorum\nExperimentorum Problematibus aucta. Rom\u00e6, 1654.\n\n[197] The following are the titles of the concluding chapters of\nKircher\u2019s book:--_De magnetismo solis et lun\u00e6 in maria._ _De magnetic\u00e2\nvi plantarum._ _De insitionis magneticis miraculis._ _De magnetismo\nvirgul\u00e6 aurifer\u00e6 seu divinatori\u00e6._ _De plantis heliotropiis eorumque\nmagnetismo._ _De magnetismo rerum medicinalium._ _De vi attractiv\u00e2\npotenti\u00e6 imaginativ\u00e6._ _De magnetismo music\u00e6._ _De magnetismo amoris._\n\n[198] \u201cFor these reasons it appears most natural to seek their origin\nin the sun, the source of all living activity, and our conjecture gains\nprobability from the preceding remarks on the daily oscillations of\nthe needle. Upon this principle the sun may be conceived as possessing\none or more magnetic axes, which, by distributing the force, occasion\na magnetic difference in the earth, in the moon, and all those planets\nwhose internal structure admits of such a difference. Yet, allowing\nall this, the main difficulty seems not to be overcome, but merely\nremoved from the eyes to a greater distance; for the question may still\nbe asked, with equal justice, whence did the sun acquire its magnetic\nforce? And if from the sun we have recourse to a central sun, and from\nthat again to a general magnetic direction throughout the universe,\nhaving the Milky Way for its equator, we but lengthen an unrestricted\nchain, every link of which hangs on the preceding link, no one of them\non a point of support. All things considered, the following mode of\nrepresenting the subject appears to me most plausible. If a single\nglobe were left to move alone freely in the immensity of space, the\nopposite forces existing in its material structure would soon arrive\nat an equilibrium conformable to their nature, if they were not so at\nfirst, and all activity would soon come to an end. But if we imagine\nanother globe to be introduced, a mutual relation will arise between\nthe two; and one of its results will be a reciprocal tendency to\nunite, which is designated and sometimes thought to be explained by\nthe merely descriptive word Attraction. Now would this tendency be\nthe only consequence of this relation? Is it not more likely that the\nfundamental forces, being drawn from their state of indifference or\nrest, would exhibit their energy in all possible directions, giving\nrise to all kinds of contrary action? The electric force is excited,\nnot by friction alone, but also by contact, and probably also, though\nin smaller degrees, by the mutual action of two bodies at a distance;\nfor contact is nothing but the smallest possible distance, and that,\nmoreover, only for a few small particles. Is it not conceivable that\nmagnetic force may likewise originate in a similar manner? When the\nnatural philosopher and the mathematician pay regard to no other effect\nof the reciprocal relation between two bodies at a distance, except\nthe tendency to unite, they proceed logically, if their investigations\nrequire nothing more than a moving power; but should it be maintained\nthat no other energy can be developed between two such bodies, the\nassertion will need proof and the proof will be hard to find.\u201d--The\nabove is a translation from Hansteen\u2019s work _On Magnetism_.\n\n[199] See article _Animal Magnetism_, Encyclop\u00e6dia Britannica, and Mr.\nBraid\u2019s papers _On Hypnotism_, published in the \u201cMedical Times.\u201d\n\n\n\n\nCHAPTER XI.\n\nCHEMICAL FORCES.\n\n  Nature\u2019s Chemistry--Changes produced by Chemical Combination--Atomic\n    Constitution of Bodies--Laws of Combination--Combining\n    Equivalents--Elective Affinity--Chemical Decomposition--Compound\n    Character of Chemical Phenomena--Catalysis or action\n    of Presence--Transformation of Organic Bodies--Organic\n    Chemistry--Constancy of Combining Proportions--The Law of Volumes,\n    the Law of Substitutions, Isomeric States, &c.\n\n\nAll things on the earth are the result of chemical combination. The\noperations by which the commingling of molecules and the interchange\nof atoms take place, we can imitate in our laboratories; but in nature\nthey proceed by slow degrees, and, in general, in our hands they are\ndistinguished by suddenness of action. In nature chemical power is\ndistributed over a long period of time, and the process of change is\nscarcely to be observed. By art we concentrate chemical force, and\nexpend it in producing a change which occupies but a few hours at most.\nMany of the more striking phenomena of nature are still mysterious to\nus, and principally because we do not, or cannot, take the element time\ninto calculation. The geologist is compelled to do this to explain the\nprogress of the formation of the crust of the earth, but the chemist\nrarely regards the effects of time in any of his operations. The\nchemical change which within the fissure of the rock is slowly and\nsilently at work, displacing one element or molecule, and replacing it\nby another, is in all probability the operation of a truly geological\nperiod. Many, however, of the changes which are constantly going on\naround us, are of a much more rapid character, and in these nature is\nno slower in manipulating than the chemist.\n\nHad it been that the elements which are now found in combination\ncould exist in a free state, the most disastrous consequences would\nnecessarily ensue. There must have been a period when many of the\ncombinations known to us were not yet created. Their elements either\nexisted in other forms, or were uncombined. Our rocks are compounds of\noxygen with certain peculiar metals which unite with oxygen so rapidly\nthat incandescence is produced by their combination. Let us suppose\nthat any of these metals existed in purity, and that they were suddenly\nbrought into contact with water, the atmospheric air, or any body\ncontaining oxygen, the result would be a convulsion of the most fearful\nkind; the entire mass of metal would glow with intensity of heat, and\nthe impetuosity of the action would only be subdued when the whole\nof the metal had become oxidized. Volcanic action has been referred\nto some such cause as this, but there is not sufficient evidence to\nsupport the hypothesis; indeed, it is contrary to the opinion of most\nphilosophers.[200] Such a condition may possibly have existed at one\ntime, during that period when darkness was upon the face of the deep,\nwhen the earth was a chaos; but it is only adduced here as an example\nof the violent nature of some chemical changes. Potassium thrown on\nwater bursts into flame, and sodium does so under certain conditions.\nIf these, or the metals proper in a state of fine division, are brought\ninto an atmosphere of chlorine, the intensity of chemical action is so\ngreat that they become incandescent, many of them glowing with extreme\nbrilliancy. If hydrogen gas is mixed with this element (chlorine)\nthey unite, under the influence of light, with explosive violence,\ngiving rise to a compound, muriatic acid, which combines with water\nin an almost equally energetic manner. Nitrogen, as it exists in the\natmosphere, mixed with oxygen, appears nearly inert; with hydrogen it\nforms the pungent compound, ammonia; with carbon, the poisonous one,\ncyanogen, the base of prussic acid; with chlorine it gives rise to a\nfluid, oily in its appearance, but which, when merely touched by an\nunctuous body, explodes more violently than any other known compound,\nshivering whatever vessel it may be contained in, to atoms; with iodine\nit is only slightly less violent; and in certain combinations with\nsilver, mercury, gold, or platinum, it produces fulminating compounds\nof the most dangerous character.[201] Here we have elements harmless\nwhen uncombined, exhibiting the most destructive effects if their\ncombinations are at all disturbed; and in the other case we have inert\nmasses produced from active and injurious agents.\n\nWe regard a certain number of substances as _elementary_; that is to\nsay, not being able, in the present state of our knowledge, to reduce\nthem to any more simple condition, they are considered as the elements\nwhich by combination produce the variety of substances found in the\nthree kingdoms of nature.\n\nWe have already spoken of the atomic constitution of bodies. It remains\nnow to explain the simplicity and beauty which mark every variety of\ncombination under chemical force. As a prominent and striking example,\nwater is a compound of two gaseous bodies, oxygen and hydrogen:--\n\nIf we decompose water by means of galvanic electricity, or determine\nits composition by direct chemical analysis, we shall find it consists\nof two volumes of hydrogen gas, united to one volume of oxygen, or, by\nweight, of one part of hydrogen combined with eight of oxygen. In 100\nparts, therefore, we should find--\n\n    Oxygen        88\u00b79\n    Hydrogen      11\u00b70\n\nIt is found in the same way that the theoretical weight of the atom\nof carbon is 6, and that of nitrogen 14; whilst the atom of iron is\n28, that of silver 108, of gold 199, and that of platinum and iridium\neach 98.[202] Now, as these are the relative weights of the ultimate\nindivisible atom, it follows that all combinations must be either atom\nto atom, or one to two, three, or four; but that in no case should\ncombination take place in any other than a multiple proportion of the\nequivalent or atomic number. This is found to be the case. Oxygen,\nfor instance, combines as one, two, or three atoms; its combination\npresenting some multiple of its equivalent number 8, as 16, or 24:\nand in like manner the combining quantity of carbon is 6, or some\nmultiple of that number. Where this law is not found strictly to agree\nwith analytical results, of which some examples are afforded by the\nsesquioxides, it may be attributed, without doubt, to some error of\nanalysis or in the method of calculation.\n\nNothing can be more perfect than the manner in which nature regulates\nthe order of combination. We have no uncertain arrangement; but,\nhowever great the number of the atoms of one element may be, over those\nof another, those only combine which are required, according to this\ngreat natural law, to form the compound, all the others still remaining\nfree and uncombined. These results certainly appear to prove that the\nelementary particles of matter are not of the same specific gravities.\nDo they not also indicate that any alteration in the specific gravity\nof the atom would give rise to a new series of compounds, thus\napparently producing a new element? Surely there is nothing irrational\nin the idea that the influences of heat or electricity, or of other\npowers of which as yet we know nothing, may be sufficient to effect\nsuch changes in the atomic constituents of this earth.\n\nThe combination of elementary atoms takes place under the influence\nof an unknown force which we are compelled to express by a figurative\nterm, _affinity_. In some cases it would appear that the disposition\nof two bodies to unite, is determined by the electrical condition; but\na closer examination of the question than it is possible to enter into\nin this place, clearly shows that some physical state, not electrical,\ninfluences combining power.\n\nChemical affinity or attraction is the peculiar disposition which one\nbody has to unite with another. To give some instances in illustration.\nWater and spirit combine most readily: they have a strong affinity for\neach other. Water and oil repel each other: they have no affinity;\nthey will not enter into combination. If carbonate of potash is added\nto the spirit and water in sufficient quantity, the water is entirely\nseparated, and the pure spirit will float over the hydrated potash. If\npotash is added to the oil and water, it combines with the oil, and,\nforming soap, they all unite together; but, if we now add a little acid\nto the mixture, the potash will quit the oil to combine with the acid,\nand the oil will be repelled as before and float on the liquid. This\nhas been called single elective affinity. These elections were regarded\nas constant, and chemists drew up tables for the purpose of showing the\norder in which these decompositions occur.[203] Thus, ammonia, it was\nshown, would separate sulphuric acid from magnesia, lime remove it from\nammonia, potash or soda from lime, and barytes from potash or soda. It\nwas thought the inverse of this order would not take place, but recent\nresearches have shown that the results are modified by quantity and\nsome other conditions.\n\nIt often happens that we have a compound action of this kind in which\ndouble election is indicated. Sulphate of lime and carbonate of ammonia\nin solution are brought together, and there result a carbonate of lime\nand a sulphate of ammonia. Now, in such cases nothing more than single\nelective attraction most probably occurs, and the carbonic acid is\nseized by the lime, by the great affinity of that earth for carbonic\nacid, only after it has been set free from the ammonia, and then, by\nthe force of cohesion acting with the combining powers, the insoluble\nsalt is precipitated.[204] There is a curious fact in connection with\nthis decomposition. If carbonate of lime and sulphate of ammonia\nare mixed together dry, and exposed, in a closed vessel, to a red\nheat, sulphate of lime and carbonate of ammonia are formed. These\nopposite effects are not very easily explained. The action of heat is\nto set free the carbonic acid; and it can only be by supposing that\nconsiderable differences of temperature reverse the laws of affinity,\nthat we can at all understand this phenomenon. That different effects\nresult at high temperatures from those which prevail at low ones,\nrecent experiments prove to us, particularly those of Boutigny, already\nquoted when considering decomposition by calorific action.\n\nUnder the term chemical affinity, which we regard as a power acting\nat insensible distances, and producing a change in bodies, we are\ncontent to allow ourselves to believe that we have explained the\ngreat operations of nature. We find that the vegetable and animal\nkingdoms are composed of carbon, hydrogen, oxygen, and nitrogen. The\ngranite mountains of the earth, and its limestone hills, and all its\nother geological formations, are found to be metals and oxygen, and\ncarbon and sulphur, disposed to settle in harmonious union in their\nproper places by chemical affinity. But what really is the power which\ncombines atom to atom, and unites molecule to molecule? Can we refer\nthe process to heat? The influence of caloric, although by changing\nthe form of bodies it sometimes assists combination, is to be regarded\nrather as in antagonism to the power of cohesion. Can it be thought\nthat electricity is active in producing the result? During every change\nof state, those phenomena which we term electrical are manifested; but\nwe thereby only prove the general diffusion of the electric principle,\nand by no means show that electricity is the cause of the chemical\nchange. Can light determine these changes? It is evident, although\nlight may be a disturbing power, that it cannot be the effective one;\nfor many of these decompositions and recompositions are constantly\ngoing on within the dark and silent depths of the earth, to which a\nsunbeam cannot reach. That the excitation on the surface of the earth,\nproduced by solar influence, may modify those changes, is probable. It\nis, however, certain that we must regard all manifestations of chemical\nforce as dependent upon some secret principles common to all matter,\ndiffused throughout the universe, but modified by the influences of the\nknown imponderable elements, and by the mechanical force of aggregative\nattraction.\n\nBodies undergo remarkable changes of form, and present very different\ncharacters, by reactions, which are of several kinds. We suppose\nthat a permanent corpuscular arrangement is maintained so long as\nthe equilibrium of the molecular forces is undisturbed. Water, for\ninstance, remains unchanged so long as the balance of affinity is kept\nup between the oxygen and hydrogen of which it is composed, or so long\nas the oscillations of force between these combining elements are\nequal; but disturb this force, or set up a new vibratory action, as by\npassing an electric current through the water, or by presenting another\nbody, which has the power of reacting upon one of these corpuscular\nsystems, and the water is decomposed, the hydrogen and oxygen gases\nbeing set free, or one alone is liberated, and the other combined with\nthe molecules of the agent employed, and a new compound produced. This\nis chemistry, by which science we discover all the combinations of\nmatter.\n\nHaving reason to conclude that atom combines with atom, according to\na system most harmoniously arranged, there can be no difficulty in\nconceiving that molecule unites with molecule, in a manner regulated\nby some equally well-marked law. It was, indeed, a discovery by\nWenzel, of Fribourg, that, in salts which decompose each other, the\nacid which saturates one base will also saturate the other base;\nand the subsequent observations of Richter, of Berlin, who attached\nproportional numbers to the acids and bases, and who remarked that the\nneutrality of metallic salts does not change during the precipitation\nof metals by each other, which led the way to the atomic theory of Dr.\nDalton, to whom entirely belongs the observation, that the equivalent\nof a compound body is the sum of the equivalents of its constituents,\nand the discovery of combination in multiple proportions.\n\nThe elements of a molecule can take a new arrangement amongst\nthemselves, without any alteration in the number of the atoms or of\ntheir weight, and thus give rise to a body of a different form and\ncolour, although possessing the same chemical constitution. This is the\ncase with many of the organic compounds of carbon and hydrogen.\n\nThe elements of a compound may be disassociated, and thus the\ndissimilar substances of which it is composed set free. A piece\nof chalk exposed to heat is, by the disturbance of its molecular\narrangement, changed in its nature; a gaseous body, carbonic acid,\nis liberated, and quick-lime (oxide of calcium) is left behind. If\nthis carbonic acid is passed through red-hot metal tubes, or brought\nin contact with heated potassium, it is resolved into oxygen and\ncharcoal--the oxygen combining with the metal employed. The oxide of\ncalcium (lime), if subjected to the action of a powerful galvanic\ncurrent, is converted into oxygen and a metal, calcium. Thus we learn\nthat chalk is a body consisting of two compound molecules,--carbonic\nacid, which is formed by the combination of an atom of carbon with two\natoms of oxygen,--and lime, which results from the union of an atom of\ncalcium with one of oxygen.\n\nThe condition requisite to the production of chemical action between\nbodies is that they should be dissimilar. Two elementary atoms\nare placed within the spheres of each other\u2019s influences, and a\ncompound molecule results. Oxygen and hydrogen form water; oxygen\nand carbon give rise to carbonic acid; nitrogen and hydrogen unite\nto form ammonia; and chlorine and hydrogen to produce hydrochloric\nacid. In all these cases an external force is required to bring the\natoms within the range of mutual affinity: flame,--the electrical\nspark,--actinism,--or the interposition of a third body, is necessary\nin each case. There are other examples in which no such influence is\nrequired. Potassium and oxygen instantly unite: chlorine, iodine, and\nbromine immediately, and with much violence, combine with the metals to\nform chlorides, iodides, or bromides.\n\nWith compound molecules the action is in many cases equally active,\nand combination is readily effected, as in the cases of the acids and\nthe oxides of some metals, which are all instances of the most common\nchemical attraction.\n\nAn elementary or simple molecule and molecules of a compound and\ndifferent constitution are brought together, and a new compound\nresults from an interchange of their atoms, whilst an element is\nliberated. These are essentially illustrations of analytical chemistry.\nSulphuretted hydrogen is mixed with chlorine; the chlorine combines\nwith the hydrogen, and sulphur is set free. Potassium is put into\nwater, and it combines with the oxygen of the water, whilst the\nhydrogen is liberated.\n\nTwo compound molecules being brought together may decompose each other,\nand form two new compounds by an interchange of their elements.\n\nOne element may be substituted for another under certain circumstances.\nGold may be replaced by mercury; copper will take the place of silver;\nand iron will occasion the separation of copper from its solutions,\nthe iron itself being dissolved to supply its place; chlorine will\nsubstitute hydrogen in the carburetted hydrogen gases; and many other\nexamples might be adduced.\n\nChemical phenomena very frequently become of a complex character;\nand one, two, or three of these cases may be occurring at the same\ntime in the decomposition of one compound by another. Such are the\ngeneral features of chemical science. Many peculiarities and remarkable\nphenomena connected with chemical investigations will be named, as\nthe examination of the elementary composition of matter is proceeded\nwith; but, although the philosophy of chemical action is of the highest\ninterest, it must not be allowed to detain us with its details, which\nare, indeed, more in accordance with a treatise on the science than\none which professes to do no more than sketch out those prevailing\nand striking features which, whilst they elucidate the great truths\nof nature, are capable of being employed as suggestive examples of\nthe tendency of scientific investigation to enlarge the boundaries of\nthought, and give a greater elevation to the mind, leading us from\nthe merely mechanical process of analysis up to the great synthetical\noperations, by which all that is found upon the earth for its ornament,\nor our necessities, is created.\n\nAmong the most remarkable phenomena within the range of physical\nchemistry are those of _Catalysis_, or, as it has also been called, the\n\u201c_Action of presence_.\u201d[205] There are a certain number of bodies known\nto possess the power of resolving compounds into new forms, without\nundergoing any change themselves. Kirchoff discovered that the presence\nof an acid, at a certain temperature, converted starch into sugar and\ngum, no combination with the acid taking place. Thenard found that\nmanganese, platinum, gold, and silver, and, indeed, almost any solid\norganic body, had the power of decomposing the binoxide of hydrogen by\ntheir presence merely, no action being detected on these bodies. Edmund\nDavy found that powdered platinum, moistened with alcohol, became\nred-hot, fired the spirit, and converted it into vinegar, without\nundergoing, itself, any chemical change. D\u00f6bereiner next discovered\nthat spongy platinum fired a current of hydrogen gas directed upon\nit, which, by combining with the oxygen of the air, formed water.\nDulong and Thenard traced the same property, differing only in degree,\nthrough iridium, osmium, palladium, gold, silver, and even glass.\nFurther investigation has extended the number of instances; and it has\neven been found that a polished plate of platinum has the power of\ncondensing hydrogen and oxygen so forcibly upon its surface, that these\ngases are drawn into combination and form water, with a development of\nheat sufficient to ignite the metal.\n\nThis power, whatever it may be, is common in both organic and inorganic\nnature, and on its important purposes Berzelius has the following\nremarks:--\n\n\u201cThis power gives rise to numerous applications in organic nature;\nthus, it is only around the eyes of the potato that diastase exists:\nit is by means of catalytic power that diastase, and that starch,\nwhich are insoluble, are converted into sugar and into gum, which,\nbeing soluble, form the sap that rises in the germs of the potato.\nThis evident example of the action of catalytic power in an organic\nsecretion, is not, probably, the only one in the animal and vegetable\nkingdom, and it may hereafter be discovered that it is by an action\nanalogous to that of catalytic power, that the secretion of such\ndifferent bodies is produced, all which are supplied by the same\nmatter, the sap in plants, and the blood in animals.\u201d[206]\n\nIt is, without doubt, to this peculiar agency that we must attribute\nthe abnormal actions produced in the blood of living animals by the\naddition of any gaseous miasma or putrid matter, of which we have, in\nall probability, a fearful example in the progress of Asiatic cholera;\ntherefore the study of its phenomena becomes an important part of\npublic hygi\u00e8ne.\n\nPhysical research has proved to us that all bodies have peculiar\npowers, by which they condense with varying degrees of force gases\nand vapours upon their surfaces; every body in nature may, indeed, be\nregarded as forming its own peculiar atmosphere. To this power, in all\nprobability, does catalysis belong. Different views have, however,\nprevailed on this subject, and Dr. Lyon Playfair[207] argues that the\ncatalytic force is merely a modified form of chemical affinity, exerted\nunder peculiar conditions.\n\nWhatever may be the power producing chemical change, it acts in\nconformity with some fixed laws, and in all its transmutations, an\nobedience to a most harmonious system is apparent.\n\nIt is curious to observe the remarkable character of many of these\nnatural transmutations of matter, but we must content ourselves with a\nfew examples only. For instance:--\n\nSugar, oxalic acid, and citric acid are very unlike each other, yet\nthey are composed of the same elements; the first is used as a general\ncondiment, the second is a destructive poison, and the third a grateful\nand healthful acid: sugar is readily converted into oxalic acid, and\nin the process of ripening fruits nature herself converts citric acid\ninto sugar. Again, starch, sugar, and gum would scarcely be regarded\nas alike, yet their only difference is in the mode in which carbon,\nhydrogen, and oxygen combine. They are composed of the same principles,\nin the following proportions:--\n\n              Carbon.  Hydrogen.  Oxygen.\n    Starch      12        10        10\n    Sugar       12        11        11\n    Gum         12        11        11\n\nThese _isomeric_ groups certainly indicate some law of affinity which\nscience has not yet discovered. Similar and even more remarkable\ninstances might be adduced of the same elements producing compounds\nvery unlike each other; but the above have been selected from their\nwell-known characters. Indeed, we may state with truth that all the\nvarieties of the vegetable world--their woody fibre--their acid or\nalkaline juices--the various exudations of plants--their flowers,\nfruit, and seeds, and the numerous products which, by art, they are\nmade to yield for the uses of man, are, all of them, compounds of these\nthree elements, differing only in the proportions in which they are\ncombined with nitrogen, or in some peculiar change of state in one\nor other of the elementary principles. The chemist is now enabled by\nsimple processes, from the refuse of manufactories to produce fruit\nessences which are equal in flavour to the natural production; and from\nbenzoic acid, which is obtained in great abundance from the houses in\nwhich cows are kept, the most delicate essences are produced, which\nare given to the world as the distillations of a thousand flowers.\nBy the impulse given to organic chemistry by Liebig, our knowledge\nof the almost infinite variety of substances, in physical character\nexceedingly dissimilar, which result from the combination of oxygen,\nhydrogen, and carbon, in varying proportions, has been largely\nincreased. And the science is now in that state which almost causes\na regret that any new organic compounds should be discovered, until\nsome industrious mind has undertaken the task of reducing to a good\ngeneral classification the immense mass of valuable matter which has\nbeen accumulated, but which, for all practical purposes, remains nearly\nuseless and unintelligible.\n\nThese combinations, almost infinitely varied as they are, and so\nreadily produced and multiplied as to be nearly at the will of the\norganic analyst, are not, any of them, accidental: they are the result\nof certain laws, and atom has united with atom in direct obedience\nto principles which have been through all time in active operation.\nThey are unknown; the researches of science have not yet developed\nthem, and the philosopher has not yet made his deductions. They are\nto be referred to some secret fixed principles of action, to a force\nwhich has impressed upon every atom of the universe its distinguishing\ncharacter. Chemistry makes us familiar with a system of order. The\nresearches of analysts have proved that every body has a particular\nlaw of combination, to which it is bound by a mathematical precision;\nbut it is not proportional combination alone we have to consider. If\n_allotrophy_ is evidenced in the mineral world, it is certainly far\nmore strikingly manifested in the vegetable and animal kingdoms.\n\nThere are some cases in which bodies appear to combine without any\nlimitation, as spirit of wine and water, sulphuric acid and water;\nbut these must be considered as conditions of mixture rather than of\nchemical combination.\n\nThe composition of bodies is fixed and invariable, and a compound\nsubstance, so long as it retains its characteristic properties, must\nconsist of the same elements united in the same proportions. Thus,\nsulphuric acid is invariably composed of 16 parts of sulphur and 24\nparts of oxygen. Chalk, whether formed by nature or by the chemist,\nyields 43\u00b771 parts of carbonic acid, and 56\u00b729 parts of lime. The rust\nwhich forms upon the surface of iron by the action of the atmosphere,\nis as invariable in its composition as if it had been formed by the\nmost delicate adjustment of weight by the most accurate manipulator,\nbeing 28 parts of iron and 12 parts of oxygen. This law is the basis of\nall chemical inquiry, all analytical investigations depending upon the\nknowledge it affords us, that we can only produce certain undeviating\ncompounds as the results of our decompositions. We are not in a\nposition to offer any explanation which will account for these constant\nquantities in combination. The forces of cohesion and elasticity\nhave been advanced in explanation, on the strength of the fact that\nthe solubility of a salt in water is regulated by cohesion, and that\nof a gas by its elasticity. Although it may appear that some cases\nof chemical combination are due to these powers,--as, for instance,\nwhen the union of oxalic acid or sulphuric acid with lime produces\nan insoluble salt,--we cannot thus explain the constant proportions\nin which the metals, sulphur, oxygen, and similar bodies, unite. It\nis quite certain there is a power or principle, which we have not\nyet reached, upon which are dependent all the phenomena which we now\nembrace under the term chemical affinity.\n\nAnother law teaches us that when compound bodies combine in more than\none proportion, every additional union represents a multiple of the\ncombining proportion of the first. With the difficulty which arises\nfrom the sub-multiple compounds we cannot deal:--further research may\nrender their laws less obscure. We have seen that 8 parts of oxygen\nunite with 1 of hydrogen and 14 of nitrogen. It also unites with 110 of\nsilver, 96 of platinum, 40 of potassium, 36 of chlorine, and 200 parts\nof mercury, giving rise to--\n\n    Water                    9\n    Nitrous oxide           22\n    Oxide of silver        118\n    Oxide of platinum      104\n    Potash                  48\n    Oxide of chlorine       44\n    Oxide of mercury       208\n\nIn these proportions, or in multiples of them, and in no others, will\nthese bodies unite with the acids or other compounds. It will, of\ncourse, be understood that any other numbers may be adopted, provided\nthey stand in the same relation to each other.[208]\n\nFrom the discovery of these harmonious arrangements was deduced the\nbeautiful atomic theory to which allusion has been already made.\nIndeed, there does not appear to be any other way of explaining these\nphenomena than by the hypothesis that the ultimate atoms of bodies have\n_relatively_ the weights which we arbitrarily assign to them, as their\ncombining quantities. These views are further confirmed by the fact,\nthat gaseous bodies unite together by volume in very simple definite\nproportions:--100 measures of hydrogen and 200 measures of oxygen form\nwater; 100 measures of oxygen and 100 measures of vapour of sulphur\nform sulphurous acid gas. Ammoniacal gas consists of 300 volumes of\nhydrogen and 100 volumes of nitrogen, condensed by combination into 200\nvolumes; consequently, we are enabled most readily to calculate the\nspecific gravity of ammoniacal gas. The specific gravity of nitrogen\nis 0\u00b79722, that of hydrogen 0\u00b70694. Now, three volumes of hydrogen are\nequal to 0\u00b72082: this added to 0\u00b79722 is equal to 1\u00b71804, which is\nexactly the specific gravity obtained by experiment.\n\nThere is no doubt, from the generality with which this law of volumes\nprevails, that it would be found to extend through all substances,\nprovided they could be rendered gaseous; in other words, there is\nabundant proof to convince us that throughout nature the process of\ncombination, in the most simple ratio of volumes, is in operation to\nproduce all the forms of matter known to us.\n\nIt has been shown, by the investigations of Dr. Dalton, in 1840, that\nsalts, containing water of crystallization, dissolve in water without\nincreasing the bulk of the fluid more than is due to the liquefaction\nof the water which these salts contain; while Joule and Playfair\nhave shown that the anhydrous salts take up no space in solution.\nFrom this we are naturally led to conclude that the volume occupied\nby a salt in the solid state has a certain relation to the volume of\nthe same salt when in solution, and has also a fixed relation to the\nvolume occupied by any other salt. The law appears to be:--the atomic\nvolume of any salt whatever (anhydrous or hydrated) is a multiple of\n11, or of a number near 11, or a multiple of 9\u00b78 (the atomic volume\nof ice), or the sum of a multiple of 11 or 9\u00b78. Marignac, who has\nalso paid much attention to the subject, does not think these numbers\nabsolutely correct, but approximately so.[209] It would be a beautiful\nexemplification of the simplicity of Nature\u2019s operations, if it should\nbe clearly proved that the atomic volume of solid water (ice) regulated\nthe combining proportions by volume of all other bodies,--that it was\nthe standard by which chemical combination and ordinary solution were\ndetermined.\n\nIn addition to the laws already indicated, there appear to be some\nothers of which, as yet, we have a less satisfactory knowledge, and,\nas a remarkable case, we may adduce the phenomena of _substitution_,\nor that power which an elementary body, under certain conditions,\npossesses, of turning out one of the elements of a compound, and of\ntaking its place.[210] Thus, the hydrogen of a compound radical, as\ncarburetted hydrogen, may be replaced by chlorine, equivalent for\nequivalent, and form a chloride of carbon, which being constructed\non the same type as the original, will have the same general laws of\ncombination.\n\nUnder the influence of these laws, all the combinations which we\ndiscover in nature take place. The metals, and oxygen, and sulphur,\nand phosphorus unite. The elements of the organic type, entering into\nthe closest relations, give rise to every form of vegetable life. The\nacids, the gums, the resins, and the sugar which plants produce; and\nthose yet more complicated animal substances, bone, muscle, blood, and\nbile; albumen, casein, milk, with those compounds which, under the\ninfluence of vital power, resolve themselves into substances which are\nessential to the existence, health, and beauty of the animal fabric,\nare all dependent on these laws. But these metamorphoses must be\nfurther considered in our examination of the more striking cases of\nchemical action. The changes which result from organic combination are\nso remarkable, and withal they show how completely the whole of the\nmaterial world is in subjection to chemical force, and every variety\nof form the result of mysterious combination, that some particular\nreference to these metamorphoses is demanded.\n\nIn nearly all cases of decided chemical action, all trace of the\ncharacters of the combining bodies disappear. We say decided chemical\naction, because, although sulphuric acid and water combine, and\nsalts dissolve in water, we may always recognize their presence, and\ntherefore these and similar cases cannot be regarded as strict examples\nof the phenomena under consideration.\n\nHydrogen and oxygen, in combining, lose their gaseous forms, and are\ncondensed into a liquid--water. Sulphuric acid is intensely sour and\ncorrosive; potash is highly caustic; but united they form a salt\nwhich is neither: they appear to have destroyed the distinguishing\ncharacters of each other. Combined bodies frequently occupy less space\nthan they did previously to combination, of which numerous particular\ninstances might be adduced. Gases in many cases undergo a remarkable\ncondensation when chemically combined. In slaking lime, the water\nbecomes solid in the molecules of the hydrate of lime formed, and the\nintense heat produced arises from the liberation of that caloric which\nhad been employed to keep the water liquid. When a solid passes into\nthe liquid state, cold is produced by the abstraction from surrounding\nobjects of the heat required to effect fluidity. An alteration of\ntemperature occurs whenever chemical change takes place, as we have\nalready shown, with a few trivial and uncertain exceptions. The\ndisturbance caused by the exercise of the force of affinity frequently\nleads to the development of several physical powers.\n\nChanges of colour commonly arise; indeed, there does not appear to be\nany relation between the colour of a compound and that of its elements.\nIodine is of a deep iron-grey colour; its vapour is violet; yet it\nforms beautifully white salts with the alkalies, a splendid red salt\nwith mercury, and a yellow one with lead. The salts of iron vary from\nwhite and yellow to green and dark brown. Those of copper, a red metal,\nare of a beautiful blue and green colour, and the anhydrous sulphate is\nwhite.\n\nIsomorphism, which appears in a very remarkable manner among the\norganic compounds, has, under the head of crystallization, already had\nour attention. There is also a class of bodies which are said to be\n_isomeric_; that is, to have the same composition, although different\nin their physical characters. But the idea that bodies exist, which,\nalthough of a decidedly different external character, are of exactly\nthe same chemical composition and physical condition, is not tenable;\nand in nearly all the examples which have been carefully examined, a\ndifference in the aggregate number of atoms, or in the mode in which\nthose atoms have respectively arranged themselves, or that peculiar\nphysical difference designated by the term _allotropy_, has been\ndetected.\n\nOil of turpentine and oil of lemons have the same composition, each\nbeing composed of five equivalents of carbon and four of hydrogen.\nThese substances form, from the striking difference perceptible in\ntheir external characters, a good example of isomerism.\n\nThe laws of organic chemistry are not, however, the same as those\napplying to inorganic combinations. Organic chemistry is well defined\nby Liebig, as the chemistry of compound radicals; and under the\ninfluence of vitality, nature produces compounds which have all the\nproperties of simple elements.[211]\n\nWhen we reflect upon the conditions which prevail throughout nature,\nwith a few of which only has science made us acquainted, we cannot fail\nto be struck with the various phases of being which are presented to\nour observation, and the harmonious system upon which they all appear\nto depend.\n\nWhen we discover that bodies are formed of certain determinate atoms,\nwhich unite one with another, according to an arithmetical system, to\nform molecules, which, combining with molecules, observe a similar law,\nwe see at once that all the harmonies of chemical combination--the\ndefinite proportions, laws of volume, and the like--are but the\nnecessary consequences of these simple and guiding first principles.\nIn the pursuit of truth, investigators must discover still further\narrangements, which, from their perfection, may be compared to the\nmelodious interblending of sweet sounds, and many of the apparently\nindeterminate combinations will, beyond a doubt, be shown to be as\ndefinite as any others. But we cannot reflect upon the fact that these\natoms and these molecules are guided in their combinations by impulses,\nwhich we can only explain by reference to human passions, as the term\n_elective affinity_ implies, without feeling that an impenetrable\nmystery of a grand and startling character in its manifestations\nsurrounds each grain of dust which is hurried along upon the wind.\n\nWe now, habitually, speak of attraction and repulsion--of the affinity\nand non-affinity of bodies. We are disposed, from the discovery of the\nattractive and repelling poles of electrified substances, to regard\nthese powers in all cases as depending upon some electrical state, and\nwe write learnedly upon the laws of these forces. After all, it would\nbe more honest to admit, that we know no more of the secret impulses\nwhich regulate the combinations of matter, than did those who satisfied\nthemselves by referring all phenomena of these kinds to sympathies\nand antipathies: terms which have a poetic meaning, conveying to the\nmind, with considerable distinctness, the fact, and giving the idea\nof a feeling--a passion--involving and directing inanimate matter,\nsimilar to that which stirs the human heart, and certainly calculated\nto convey the impression that there is working within all things a\nliving principle, and pointing, indeed, to \u201cthe soul of the world.\u201d The\nanimated marble of ancient story is far less wonderful than the fact,\nproved by investigation, that every atom of matter is penetrated by a\nprinciple which directs its movements and orders its positions, and\ninvolved by an influence which extends, without limits, to all other\natoms, and which determines their union, or otherwise.\n\nWe have gravitation, drawing all matter to a common centre, and\nacting from all bodies throughout the wide regions of unmeasured\nspace upon all. We have cohesion, holding the particles of matter\nenchained, operating only at distances too minute for the mathematician\nto measure; and we have chemical attraction, different from either\nof these, working no less mysteriously within absolutely insensible\ndistances, and, by the exercise of its occult power, giving determinate\nand fixed forms to every kind of material creation.\n\nThe spiritual beings, which the poet of untutored nature gave to the\nforest, to the valley, and to the mountain, to the lake, to the river,\nand to the ocean, working within their secret offices, and moulding\nfor man the beautiful or the sublime, are but the weak creations\nof a finite mind, although they have for us a charm which all men\nunconsciously obey, even when they refuse to confess it. They are like\nthe result of the labours of the statuary, who, in his high dreams of\nlove and sublimated beauty, creates from the marble block a figure\nof the most exquisite moulding which mimics life. It charms us for a\nseason; we gaze and gaze again, and its first charms vanish; it is ever\nand ever still the same dead heap of chiselled stone. It has not the\npower of presenting to our wearying eyes the change which life alone\nenables matter to give; and we admit the excellence of the artist, but\nwe cease to feel at his work. The creations of poetry are pleasing, but\nthey never affect the mind in the way in which the poetic realities\nof nature do. The sylph moistening a lily is a sweet dream; but the\nthoughts which rise when first we learn that its broad and beautiful\ndark-green leaves, and its pure and delicate flower, are the results\nof the alchemy which changes gross particles of matter into symmetric\nforms,--of a power which is unceasingly at work under the guidance of\nlight, heat, and electrical force,--are, after our incredulity has\npassed away--for it is too wonderful for the untutored to believe at\nonce--of an exalting character.\n\nThe flower has grown under the impulse of principles which have\ntraversed to it on the solar beam, and mingled with its substance. A\nstone is merely a stone to most men. But within the interstices of\nthe stone, and involving it like an atmosphere, are great and mighty\ninfluences, powers which are fearful in their grander operations, and\nwonderful in their gentler developments. The stone and the flower hold,\nlocked up in their recesses, the three great known forces--light, heat,\nand electricity: and, in all probability, others of a more exalted\nnature still, to which these powers are but subordinate agents. Such\nare the facts of science, which, indeed, are the true \u201csermons in\nstones,\u201d and the most musical of \u201ctongues in trees.\u201d How weak are the\ncreations of romance, when viewed beside the discoveries of science!\nOne affords matter for meditation, and gives rise to thoughts of a most\nennobling character; the other excites for a moment, and leaves the\nmind vacant or diseased. The former, like the atmosphere, furnishes\na constant supply of the most healthful matter; the latter gives\nan unnatural stimulus, which compels a renewal of the same kind of\nexcitement, to maintain the continuation of its pleasurable sensations.\n\n\nFOOTNOTES:\n\n[200] All the phenomena connected with volcanic action, and the\ntheories connected therewith, will be found in Dr. Daubeny\u2019s work, _A\ndescription of active and extinct Volcanoes, of Earthquakes, and of\nThermal Springs_. 1848.\n\n[201] Graham\u2019s _Elements of Chemistry_. New Edition.\n\n[202] Graham\u2019s _Elements of Chemistry_; and Brande\u2019s _Manual_.\n\n[203] Of these _tables of attraction_ the following may be taken as a\nspecimen:--\n\n    SULPHURIC ACID.\n    Baryta.\n    Strontia.\n    Potassa.\n    Soda.\n    Lime.\n    Magnesia.\n    Ammonia.\n\nIt thus appears that baryta separates sulphuric acid from its compounds\nwith all inferior substances, and that ammonia is separated from the\nacid by all that are above it.\n\n[204] Berthollet: _Essai de Statique Chimique_, 1803. Sir Humphry Davy,\nin his _Elements of Chemical Philosophy_, has given an excellent review\nof the views of Berthollet.\n\n[205] _On certain combinations of a new acid, formed of Azote, Sulphur,\nand Oxygen_; by J. Pelouze. Translated from Annales de Chimie, vol.\nxvi., for Scientific Memoirs, vol. i. p. 470. _Some ideas of a new\nforce acting in the combinations of Organic Compounds_, by Berzelius:\nAnnales de Chimie, vol. lxi. The conclusion come to by this eminent\nchemist is expressed in the following translation:--\u201cThis new power,\nhitherto unknown, is common both in organic and inorganic nature.\nI do not believe that it is a power which is entirely independent\nof the electro-chemical affinities of the substance. I believe, on\nthe contrary, that it is merely a new form of it; but so long as we\ndo not see their connection and mutual dependence, it will be more\nconvenient to describe it by a separate name. I shall, therefore, call\nit _catalytic power_: I shall also call _catalysis_, the decomposition\nof bodies by this force--in the same way as the decomposition of bodies\nby chemical affinity is termed analysis.\u201d\n\n[206] Berzelius: _Annales de Chimie_, vol. lxi.\n\n[207] _On Transformations produced by Catalytic Bodies_: by Lyon\nPlayfair, Esq.; Phil. Mag., vol. xxxi. p. 191, 1847.--\u201cFacts have been\nbrought forward to show that there is at least as much probability in\nthe view that the catalytic force is merely a modified form of chemical\naffinity exerted under peculiar conditions, as there is in ascribing\nit to an unknown power, or to the communication of an intestine motion\nto the atoms of a complex molecule. Numerous cases have been cited,\nin which the action results when the assisting or catalytic body is\nnot in a state of change; and attempts have been made to prove, by new\nexperiments, that the catalytic power exercises its peculiar power by\nacting in the same direction as the body decomposing, or entering into\nunion, but under conditions in which its own affinity cannot always be\ngratified.\u201d\n\n[208] Consult Graham\u2019s Chemistry, _On Combining Proportions_.\n\n[209] _Memoir on Atomic Volume and Specific Gravity._ Messrs. Lyon\nPlayfair and Joule.--Philosophical Magazine, vol. xxvii. p. 453, or\nTransactions of Chemical Society of London. _Observations_ on the\nabove, by Professor de Marignac.--Biblioth\u00e8que Universelle, Feb. 1846.\n_On the Relation of the Volumes of bodies in the solid state, to their\nequivalents, or atomic weights_: by Professor Otto. _Studies on the\nconnection between the atomic weights, crystalline form, and density\nof bodies_: by M. Filhol. Translated for the Cavendish Society, and\npublished in their Chemical Reports and Memoirs.\n\n[210] _Comptes Rendus de l\u2019Acad\u00e9mie des Sciences_, 1840, No. 5. A good\ntranslation of Dumas\u2019s Memoir appeared in the Philosophical Magazine,\nfrom which I extract the following familiar exposition of the laws of\nsubstitution:--\u201cLet me make a comparison drawn from a familiar order of\nideas. Let us put ourselves in the place of a man overlooking a game at\nchess without the slightest knowledge of the game. He would soon remark\nthat the pieces must be used according to positive rules. In chemistry,\nthe equivalents are our pieces, and the law of substitutions one of the\nrules which preside over their moves. And as in the oblique move of the\npawns one pawn must be substituted for another, so in the phenomena\nof substitution one element must take the place of another. But this\ndoes not hinder the pawn from advancing without taking anything, as the\nlaw of substitution does not hinder an element from acting on a body\nwithout displacing or taking the place of any other element that it may\ncontain.\u201d--_Memoir on the Law of Substitutions, and Theory of Chemical\nTypes._\n\n[211] Liebig\u2019s _Chemistry in its application to Agriculture and\nPhysiology_: translated by Lyon Playfair, Ph. D. _Animal Chemistry, or\nChemistry in its application to Physiology and Pathology_: by Justus\nLiebig; translated by Wm. Gregory.\n\n\n\n\nCHAPTER XII.\n\nCHEMICAL PHENOMENA.\n\n  Water--Its Constituents--Oxygen--Hydrogen--Peroxide\n    of Hydrogen--Physical Property of Water--Ice--Sea\n    Water--Chlorine--Muriatic Acid--Iodine--Bromine--Compounds\n    of Hydrogen with Carbon--Combustion--Flame--Safety\n    Lamp--Respiration--Animal Heat--The Atmosphere--Carbonic\n    Acid--Influence of Plants on the Air--Chemical Phenomena of\n    Vegetation--Compounds of Nitrogen--Mineral Kingdom, &c. &c.\n\n\nWithout attempting anything which shall approach even to the character\nof a sketch of chemical science, we may be allowed, in our search\nafter exalting truths, to select such examples of the results of\ncombination as may serve to elucidate any of the facts connected with\nnatural phenomena. In doing this, by associating our examination with\nwell-known natural objects or conditions, the interpretation afforded\nby analysis will be more evident, and the operation of the creative\nforces rendered more striking and familiar, particularly if at the same\ntime we examine such physical conditions as are allied in action, and\nare sufficiently explanatory of important features.\n\nA large portion of this planet is covered by the waters of the ocean,\nof lakes and rivers. Water forms the best means of communication\nbetween remote parts of the earth. It is in every respect of the\nutmost importance to the animal and vegetable kingdom; and, indeed, it\nis indispensable in all the great phenomena of the inorganic world.\nThe peculiarities of saltness or freshness in water are dependent\nupon its solvent powers. The waters of the ocean are saline from\nholding dissolved various saline compounds, which are received in\npart from, and imparted also to, the marine plants. Perfectly pure\nwater is without taste: even the pleasant character of freshly-drawn\nspring-water is due to the admixture of atmospheric air and carbonic\nacid. The manner in which water absorbs air is evidently due to a\npeculiar physical attractive force, the value of which we do not at\npresent clearly perceive or correctly estimate. It is chemically\ncomposed of two volumes of hydrogen gas--the lightest body known, and\nat the same time a highly inflammable one--united with one volume of\noxygen, which excites combustion, and continues that action,--producing\nheat and light,--with great energy. By weight, one part of hydrogen\nis united with eight of oxygen, or in 100 parts of water we find 88\u00b79\noxygen, and 11\u00b71 of hydrogen gas. That two such bodies should unite to\nfurnish the most refreshing beverage, and indeed the only natural drink\nfor man and animals, is one of the extraordinary facts of science.\nHydrogen will not support life--we cannot breathe it and live; and\noxygen would over-stimulate the organic system, and, producing a kind\nof combustion, give rise to fever in the animal frame; but, united,\nthey form that drink, for a drop of which the fevered monarch would\nyield his diadem, and the deprivation of which is one of the most\nhorrid calamities that can be inflicted upon any living thing. Water\nappears as the antagonist principle to fire, and the ravages of the\nlatter are quenched by the assuaging powers of the former; yet a\nmixture of oxygen and hydrogen gases, in the exact proportion in which\nthey form water, explodes with the utmost violence on the contact of\nflame, and, when judiciously arranged, produces the most intense degree\nof heat known;--such is the remarkable difference between a merely\nmechanical mixture and a chemical combination. Beyond this, we have\nalready noticed the remarkable fact that water deprived of air is\nexplosive at a comparatively low temperature, less than 300\u00b0; gunpowder\nrequiring a temperature of nearly 1000\u00b0 F.\n\nIf we place in a globe, oxygen and hydrogen gases, in the exact\nproportions in which they combine to form water, they remain without\nchange of state. They appear to mix intimately; and, notwithstanding\nthe difference in the specific gravities of the two gases, the lighter\none is diffused through the heavier in a curious manner, agreeably to\na law which has an important bearing on the conditions of atmospheric\nphenomena.[212] The moment, however, that an incandescent body, or\nthe spark from an electric machine, is brought into contact with the\nmixed gases, they ignite, explode violently, and combine to form water.\nThe discovery of the composition of water was thus synthetically made\nby Cavendish--its constitution having been previously theoretically\nannounced by Watt.[213]\n\nIf, instead of combining oxygen and hydrogen in the proportions in\nwhich they form water, we compel the hydrogen to combine with an\nadditional equivalent of oxygen, we have a compound possessing many\nproperties strikingly different from water. This--peroxide of hydrogen,\nas it is called--is a colourless liquid, less volatile than water,\nhaving a metallic taste. It is decomposed at a low temperature, and,\nat the boiling point, the oxygen escapes from it with such violence,\nthat something like an explosion ensues. All metals, except iron, tin,\nantimony, and tellurium, have a tendency to decompose this compound,\nand separate it into oxygen and water. Some metals are oxidized during\nthe decomposition, but gold, silver, platinum, and a few others,\nstill retain their metallic state. If either silver, lead, mercury,\ngold, platinum, manganese, or cobalt, in their highest states of\noxidation, are put into a tube, containing this peroxide of hydrogen,\nits oxygen is liberated with the rapidity of an explosion, and so\nmuch heat is excited that the tube becomes red hot. These phenomena,\nto which we have already referred in noticing catalysis, are by no\nmeans satisfactorily explained, and the peculiar bleaching property\npossessed by the peroxide of hydrogen sufficiently distinguishes it\nfrom water. There are few combinations which show more strikingly than\nthis the difference arising from the chemical union of an additional\natom of one element. Similar instances are numerous in the range\nof chemical science; but scarcely any two exhibit such dissimilar\nproperties. During the ordinary processes of combustion, it has been\nlong known that water is formed by the combination of the hydrogen of\nthe burning body with the oxygen of the air. The recent researches of\nSch\u00f6nbein have shown that a peculiar body, which has been regarded as\na peroxide of hydrogen, to which he has given the name of OZONE, is\nproduced at the same time, and that it is developed in a great many\nways, particularly during electrical changes of the atmosphere. Thus\nwe obtain evidence that this remarkable compound, which was considered\nas a chemical curiosity merely, is diffused very generally through\nnature, and produced under a great variety of circumstances. During\nthe excitation of an electrical machine, or the passage of a galvanic\ncurrent through water by the oxidation of phosphorus, and probably\nin many similar processes--in particular those of combustion, and we\nmay therefore infer also of respiration--this body is formed. From\nobservations which have been made, it would appear that, during the\nnight, when the activity of plants is not excited by light, they act\nupon the atmosphere in such a way as to produce this ozone; and its\npresence is said to be indicated by its peculiar odour during the\nearly hours of morning. We are not yet acquainted with this body\nsufficiently to speculate on its uses in nature: without doubt, they\nare important, perhaps second to those of water only. It is probable,\nas we have already had occasion to remark, that ozone may be the active\nagent in removing from the atmosphere those organic poisons to which\nmany forms of pestilence are traceable; and it is a curious fact, that\na low electrical intensity, and a consequent deficiency of atmospheric\nozone, marks the prevalence of cholera, and an excess distinguishes the\nreign of influenza.[214]\n\nSome interesting researches appear to show the probability that ozone\nis simply oxygen in a state of high activity. It has been found,\nindeed, that perfectly dry oxygen, which will not bleach vegetable\ncolours in the dark, acquires, by exposure to sunshine, the power of\ndestroying them. Becquerel has proved that this ozonous state may be\nproduced in dry oxygen by passing a succession of electric sparks\nthrough it. Fremy passed the electric sparks on the outside of a tube\nwhich contained perfectly dry oxygen, and it was found to have acquired\nthe properties of ozone. In this case, and probably in the experiments\nof Becquerel, the light of the spark, rather than the electricity,\nappears to have been the active agent in producing this change.\nSch\u00f6nbein himself does not appear disposed to regard ozone as being\neither peroxide of hydrogen, or an allotropic oxygen. He leans to his\nfirst view of its being an entirely new chemical element. The energy\nof this ozone is so great, that it has been found to destroy almost\ninstantaneously the Indian-rubber union joints of the apparatus in\nwhich it is formed.[215]\n\nWater, from the consideration of which a digression has been indulged\nin, to consider the curious character of one of its elements,--water is\none of the most powerful chemical agents, having a most extensive range\nof affinities, entering directly into the composition of a great many\ncrystallizable bodies and organic compounds. In those cases where it is\nnot combined as water, its elements often exist in the proportions in\nwhich water is formed. Gum, starch, and sugar, only differ from each\nother in the proportions in which the elements of water are combined\nwith the carbon.\n\nIn saline combinations, and also in many organic forms, we must regard\nthe water as condensed to the solid form; that is, to exist as ice. We\nwell know that, by the abstraction of heat, this condition is produced;\nbut, in chemical combinations, this change must be the result of the\nmechanical force exerted by the power of the agency directing affinity.\n\nIn the case of water passing from a liquid to a solid state, we have a\nmost beautiful exemplification of the perfection of natural operations.\nWater conducts heat downwards but very slowly; a mass of ice will\nremain undissolved but a few inches under water, on the surface of\nwhich, ether, or any other inflammable body, is burning. If ice (solid\nwater) swam beneath the surface, the summer sun would scarcely have\npower to thaw it; and thus our lakes and seas would be gradually\nconverted into solid masses at our ordinary winter temperatures.\n\nAll similar bodies contract equally during the process of cooling,\nfrom the highest to the lowest points to which the experiments have\nbeen carried. It has been thought that if this applied to water,\nthe result would be the sudden consolidation of the whole mass. A\nmodification of the law has been supposed to take place to suit the\npeculiar circumstances of water. Nature never modifies a law for a\nparticular purpose; we must, therefore, seek to explain the action of\nthe formation of ice, as we know it, by some more rational view.\n\nWater expands by heat, and contracts by cold; consequently, the\ncoldest portions of this body occupy the lower portions of the fluid;\nbut it must be remembered that these parts are warmed by the earth.\nRoss, however, states that at the depth of 1,000 fathoms the sea\nhas a constant temperature of 39\u00b0. Water is said to be at its point\nof greatest density at 40\u00b0 of Fahrenheit\u2019s thermometer; in cooling\nfurther, this fluid appears to expand, in the same way as if heated:\nand, consequently, water colder than this point, instead of being\nheavier, is lighter, and floats on the surface of the warmer fluid.\nIt does not seem that any modification of the law is required to\naccount for this phenomenon. Water cooled to 40\u00b0 still retains its\npeculiar corpuscular arrangement; but immediately it passes below that\ntemperature, it begins to dispose itself in such a manner that visible\ncrystals may form the moment it reaches 32\u00b0. Now, if we conceive\nthe particles of water, at 39\u00b0, to arrange themselves in the manner\nnecessary for the assumption of the solid form, by the particular\ngrouping of molecules in an angular instead of a spheroidal shape,\nit will be clear, from what we know of the arrangement of crystals\nof water--ice--that they must occupy a larger space than when the\nparticles are disposed, side by side, in minute spheres. Even the\nescape of air from the water in which it is dissolved is sufficient to\ngive an apparent lightness to the colder water. This expansion still\ngoes on increasing, from the same cause, during the formation of ice,\nso that the specific gravity of a mass of frozen water is less than\nthat of water at any temperature below 40\u00b0. It must not be forgotten\nthat ice always contains a large quantity of air, by which it is\nrendered buoyant.\n\nWater, at rest, may be cooled many degrees below the freezing point\nwithout becoming solid. This is easily effected in a thin glass flask;\nbut the moment it is agitated, it becomes a firm mass. Here we have the\nindication of another cause aiding in producing crystals of ice on the\nsurface of water, under the influence of the disturbance produced by\nthe wind, which does not extend to any depth.\n\nAs oxygen and hydrogen gases enter largely into other chemical\ncompounds besides water, it is important to consider some of the forms\nof matter into the composition of which these elements enter. To\nexamine this thoroughly, a complete essay on chemical philosophy would\nbe necessary; we must, therefore, be content with referring to a few of\nthe more remarkable instances.\n\nThe waters of the ocean are salt: this arises from their holding, in\nsolution chloride of sodium (_muriate of soda_--_common culinary salt_)\nand other saline bodies. Water being present, this becomes muriate of\nsoda,--that is, a compound of muriatic acid and soda: muriatic acid\nis hydrogen, combined with a most remarkable gaseous body, called,\nfrom its yellow colour, _chlorine_; and soda, oxygen in union with\nthe metal sodium,--therefore, when anhydrous, culinary salt is truly\na chloride of sodium. Chlorine in some respects resembles oxygen; it\nattacks metallic bodies with great energy; and, in many cases, produces\nthe most vivid incandescence, during the process of combination. It\nis a powerful bleaching agent, is destructive to animal life, and\nrapidly changes all organic tissues. There are two other bodies in\nmany respects so similar to chlorine, although one is at the ordinary\ntemperatures solid, and the other fluid, and which are also discovered\nin sea-water, or in the plants growing in it, that it is difficult to\nconsider them otherwise than as different forms of the same principle.\nThese are iodine and bromine, and they both unite with hydrogen to\nform acids. The part which chlorine performs in nature is a great and\nimportant one. Combined in muriate of soda, we may trace it in large\nquantities through the three kingdoms of nature, and the universal\nemployment of salt as a condiment indicates the importance to the\nanimal economy of the elements composing it. Iodine has been traced\nthrough the greater number of marine plants, existing, apparently as\nan essential element of their constitution; in some land plants it has\nalso been found, particularly in the Armeria maritima, when this plant\ngrows near the sea:[216] it has been detected in some mineral springs,\nand in small quantities in the mineral kingdom[217] combined as iodide\nof silver, and in the aluminous slate of Latorp in Sweden.[218] Bromine\nis found in sea-water, although in extremely minute quantities, in a\nfew saline springs, and in combination with silver; but we have no\nevidence to show that its uses are important in nature.\n\nHydrogen, again, unites with carbon in various proportions, producing\nthe most dissimilar compounds. The air evolved from stagnant water,\nand the fire-damp of the coal mine, are both carburetted hydrogen; and\nthe gas which we employ so advantageously for illumination, is the\nsame, holding an additional quantity of carbon in suspension. Naphtha,\nand a long list of organic bodies, are composed of these two chemical\nelements.\n\nThese combinations lead us, naturally, to the consideration of the\ngreat chemical phenomena of combustion, which involve, indeed, the\ninfluences of all the physical powers. By the application of heat,\nwe produce an intense action in a body said to be combustible; it\nburns,--a chemical action of the most energetic character is in\nprogress, the elements which constitute the combustible body are\ndecomposed, they unite with some other elementary principles, and new\ncompounds are formed. A body burns--it is entirely dissipated, or it\nleaves a very small quantity of ashes behind unconsumed, but nothing\nis lost. Its volatile parts have entered into new arrangements, the\nform of the body is changed, but its constituents are still playing an\nimportant purpose in creation.\n\nThe ancient notion that fire was an empyreal element, and the Stahlian\nhypothesis of a phlogistic principle on which all the effects of\ncombustion depended,[219] have both given way to the philosophy of the\nunfortunate Lavoisier--which has, indeed, been modified in our own\ntimes--who showed that combustion is but the development of heat and\nlight under the influence of chemical combination.\n\nCombustion was, at one period, thought to be always due to the\ncombination of oxygen with the body burning, but research has shown\nthat vivid combustion may be produced where there is no oxygen. The\noxidizable metals burn most energetically in chlorine, and some of\nthem in the vapour of iodine and bromine, and many other unions take\nplace with manifestations of incandescence. Supporters of combustion\nwere, until lately, regarded as bodies distinct from those undergoing\ncombustion. For example, hydrogen was regarded as a combustible body,\nand oxygen as a supporter of combustion. Such an arrangement is a\nmost illogical one, since we may _burn_ oxygen in an atmosphere of\nhydrogen, in the same manner as we burn hydrogen in one of oxygen; and\nso, in all the other cases, the supporter of combustion may be burnt\nin an atmosphere formed of the, so called, combustible. The ordinary\nphenomena of combustion are, however, due to the combination of oxygen\nwith the body burning; therefore every instance of oxidization may be\nregarded as a condition of combustion, the difference being only one of\ndegree.\n\nCommon iron, exposed to air and moisture, _rusts_; it combines with\noxygen. Pure iron, in a state of fine division, unites with oxygen so\neagerly, that it becomes incandescent, and in both cases oxide of iron\nis formed. This last instance is certainly a case of combustion; but\nin what does it differ from the first one, except in the intensity of\nthe action? The cases of spontaneous combustion which are continually\noccurring are examples of an analogous character to the above.\nOxygen is absorbed, it enters more or less quickly, according to\natmospheric conditions, into chemical combination; heat is evolved, and\neventually,--the action continually increasing,--true combustion takes\nplace. In this way our cotton-ships, storehouses of flax, piles of\noiled-cloth, sawdust, &c., frequently ignite; and to such an influence\nis to be attributed the destruction of two of our ships of war, a few\nyears since, in Devonport naval arsenal.[220]\n\nIn the economic production of heat and light, we have the combination\nof hydrogen and carbon with the oxygen of common air, forming water\nand carbonic acid. In our domestic fires we employ coal, which is\nessentially a compound of carbon and hydrogen containing a little\noxygen and some nitrogen, with some earthy matters which must be\nregarded as impurities; the taper, whether of wax or tallow, is made up\nof the same bodies, differing only in their combining proportions, and,\nlike coal gas, these burn as carburetted hydrogen. All these bodies\nare very inflammable, having a tendency to combine energetically with\noxygen at a certain elevation of temperature.\n\nWe are at a loss to know how heat can cause the combination of those\nbodies. Sir Humphry Davy has shown that hydrogen will not burn, nor\na mixture of it with oxygen explode, unless directly influenced by a\nbody heated so as to _emit light_.[221] May we not, therefore, conclude\nthat the chemical action exhibited in a burning body is a development\nof some latent force, with which we are unacquainted, produced by the\nabsorption of light;--that a repulsive action at first takes place,\nby which the hydrogen and carbon are separated from each other;--and\nthat in the nascent state they are seized by the oxygen, and again\ncompelled, though in the new forms of water and carbonic acid, to\nresume their chains of combining affinity?\n\nEvery equivalent of carbon and of hydrogen in the burning body unites\nwith two equivalents of oxygen, in strict conformity with the laws\nof combination. The flame of hydrogen, if pure, gives scarcely any\nlight, but combined with the solid particles of carbon, it increases\nin brightness. The most brilliant of the illuminating gases is the\nolefiant gas, produced by the decomposition of alcohol, and it is\nonly hydrogen charged with carbon to the point of saturation. Flame\nis a cone of heated vapour, becoming incandescent at the points of\ncontact with the air; a mere superficial film only being luminous. It\nis evident that all the particles of the gas are in a state of very\nactive repulsion over the surface, since flame will not pass through\nwire gauze of moderate fineness. Upon this discovery is founded the\ninimitable safety-lamp of Davy, by means of which the explosive gases\nof a mine are harmlessly ignited within a cage of wire gauze. This\neffect has been attributed to a cooling influence of the metal; but,\nsince the wires may be brought to a degree of heat but little below\nredness without igniting the fire-damp, this does not appear to be the\ncause. The conditions of the safety lamp may be regarded as presenting\nexamples exactly the converse of those already stated with reference to\nthe spheroidal state of water; and it affords additional evidence that\nthe condition of bodies at high temperatures is subject to important\nphysical changes.\n\nThe principle upon which the safety lamp is constructed is, that a\nmixture of the fire-damp and atmospheric air in certain proportions\nexplodes upon coming in contact with a flame.\n\nThis mixture passes readily through a wire gauze, under all\ncircumstances, and it, of course, thus approaches the flame of the lamp\nenclosed within such a material, and it explodes. But, notwithstanding\nthe mechanical force with which the exploding gas is thrown back\nagainst the bars of its cage, it cannot pass them. Consequently, the\nelement of destruction is caught and caged; and notwithstanding its\nfierceness and energy, it cannot impart to the explosive atmosphere\nwithout, any of its force. No combustion can be communicated through\nthe wire gauze.\n\nThe researches which led to the safety-lamp may be regarded as among\nthe most complete examples of correct inductive experiment in the range\nof English science, and the result is certainly one of the proudest\nachievements of physico-chemical research. By merely enveloping the\nflame of a lamp with a metallic gauze, the labourer in the recesses of\nthe gloomy mine may feel himself secure from that outpouring current\nof inflammable gas, which has been so often the minister of death; he\nmay walk unharmed through the explosive atmosphere, and examine the\nintensity of its power, as it is wasted in trifling efforts within the\nlittle cage he carries. Accidents have been attributed to the \u201cDavy,\u201d\nas the lamp is called among the colliers; but they may in most cases be\ntraced to carelessness on the part of those whose duty it has been to\nexamine the lamps, or to the recklessness of the miners themselves.\n\nThat curious metal, platinum, and also palladium, possesses a property\nof maintaining a slow combustion, which the discoverer of the\nsafety-lamp proposed to render available to a very important purpose.\nIf we take a coil of platinum wire, and, having made it red-hot, plunge\nit into an explosive atmosphere of carburetted hydrogen and common\nair, it continues to glow with considerable brightness, producing,\nby this very peculiar influence, a combination of the gases, which\nis discovered by the escape of pungent acid vapours. Over the little\nflame of the safety-lamp, it was proposed by Davy to suspend a coil\nof platinum which would be thus kept constantly at a red heat. If the\nminer became accidentally enveloped in an atmosphere of fire-damp,\nalthough the flame of his lamp might be extinguished, the wire would\ncontinue to glow with sufficient brightness to light him from his\ndanger, through the dark winding passages which have been worked in the\nbed of fossil fuel. This very beautiful arrangement has not, however,\nbeen adopted by our miners.\n\nIt is thus that the discoveries of science, although they may appear\nof an abstract character, constantly, sooner or later, are applied to\nuses by which some branch of human labour is assisted, the necessities\nof man\u2019s condition relieved, and the amenities of life advanced.\n\nThe respiration of animals is an instance of the same kind of chemical\nphenomena as we discover in ordinary combustion. In the lungs the blood\nbecomes charged with oxygen, derived from the atmospheric air, with\nwhich it passes through the system, performing its important offices,\nand the blood is returned to the lungs with the carbonic acid formed\nby the separation of carbon from the body which is thrown off at every\nexpiration. It will be quite evident that this process is similar to\nthat of ordinary combustion. In man or animals, as in the burning\ntaper,--which is aptly enough employed by poets as the symbol of\nlife,--we have hydrogen and carbon, with some nitrogen superadded; the\nhydrogen and oxygen form water under the action of the vital forces;\nthe carbon with oxygen produces carbonic acid, and, by a curious\nprocess, the nitrogen and hydrogen also combine, to form ammonia.[222]\n\nAll the carbon which is taken into the animal economy passes, in\nthe process of time, again into the atmosphere, in combination with\noxygen, this being effected in the body, under the _catalytic_ power of\ntissues, immediately influenced by the excitation of nervous forces,\nwhich are the direct manifestations of vital energy. The quantity of\ncarbonic acid thus given out to the air is capable of calculation,\nwith only a small amount of error. It appears that upwards of fifty\nounces of carbonic acid must be given off from the body of a healthy\nman in twenty-four hours. On the lowest calculation, the population of\nLondon must add to the atmosphere daily 4,500,000 pounds of carbonic\nacid. It must also be remembered that in every process for artificial\nillumination, and in all the operations of the manufactures in which\nfire is used, and also in our arrangements to secure domestic comfort,\nimmense quantities of this gas are formed. We may, indeed, fairly\nestimate the amount, if we ascertain the quantity of wood and coal\nconsumed, of all the carbon which combines with oxygen while burning,\nand escapes into the air, either as carbonic acid or carbonic oxide.\nThe former gas, the same as that which accumulates in deep wells\nand in brewers\u2019 vats, is highly destructive to life, producing very\ndistressing symptoms, even when mixed with atmospheric air, in but\nslight excess over that proportion which it commonly contains. The\noppressive atmosphere of crowded rooms is in a great measure due to the\nincreased proportion of carbonic acid given off from the lungs of those\nassembled, and collected in the almost stagnant air of badly ventilated\napartments. It will be evident to every one, that unless some provision\nwas made for removing this deleterious gas from the atmosphere as\nspeedily as it formed, consequences of the most injurious character to\nthe animal races would ensue. It is found, however, that the quantity\nin the atmosphere is almost constantly about one per cent. The peculiar\nproperties of carbonic acid in part ensure its speedy removal. It is\namong the heaviest of gaseous bodies, and it is readily absorbed by\nwater; consequently, floating within a short distance from the surface\nof the earth, a large quantity is dissolved by the waters spread\nover it. A considerable portion is removed by the vegetable kingdom;\nindeed, the whole of that produced by animals, and by the processes\nof combustion, eventually becomes part of the vegetable world, being\nabsorbed with water by the roots, and separated from the air by the\npeculiar functions of the leaves. However, this heavy gas unites with\nthe lighter atmospheric fluid in obedience to that law which determines\nthe diffusion of different specific gravities through each other.\n\nThe leaves of plants may be regarded as performing similar offices\nto the lungs of animals. They are the breathing organs. In the animal\neconomy a certain quantity of carbon is necessarily retained, in\ncombination with nitrogen and other elements, to form muscle; but this\nis constantly undergoing change; the entire system being renewed within\na comparatively limited period. The conditions with plants are somewhat\ndifferent. For instance, the carbon is fixed in a tree, and remains\nas woody fibre until it decays, even though the life of the plant may\nextend over centuries.\n\nAnimals, then, are constantly supplying carbonic acid; plants are as\nconstantly feeding on it; thus is the balance for ever maintained\nbetween the two kingdoms. Another condition is, however, required to\nmaintain for the uses of men and animals the necessary supply of oxygen\ngas. This is effected by one of those wonderful operations of nature\u2019s\nchemistry which must strike every reflecting mind with admiration.\nDuring the night plants absorb carbonic acid; but there is a condition\nof repose prevailing then in their functions, and consequently their\npowers of effecting the decomposition of this gas are reduced to their\nminimum. The plant sleeps, and vital power reposes; its repose being as\nnecessary to the plant as to the animal. With the first gleam of the\nmorning sun the dormant energies of the plant are awakened into full\naction; it decomposes this carbonic acid, secretes the carbon, to form\nthe rings of wood which constitute so large a part of its structure,\nand pour out oxygen gas to the air. The plant is, therefore, an\nessential element in the conditions necessary for the support of animal\nlife.\n\nThe animal produces carbonic acid in an exact proportion to the\nquantity of carbonaceous matter which it consumes. Fruit and herbage\ncontain a small quantity of carbon in comparison with muscle and fat.\nBut let us confine our attention to the human race. Man within the\nTropics, where the natural temperature is high, does not require so\ngreat an amount of chemical action to go on within him for the purpose\nof maintaining the requisite animal heat; consequently his Maker has\nsurrounded him with fruits and grains which constitute his food.\n\nAs we advance to the colder regions of the earth man becomes a\nflesh-eater, and his carnivorous appetite increases as the external\ntemperature diminishes. Eventually we reach the coldest zones, and the\nhuman being there devours enormous quantities of fat to supply the\nnecessities of his condition.\n\nIt must necessarily follow, that the inhabitants of the tropics do not\nproduce so much carbonic acid as those who dwell in colder regions. In\nthe first place, their habits of life are different, and they are not\nunder the necessity of maintaining animal heat by the use of artificial\ncombustion, as are the people of colder climes. The vegetation of\nthe regions of the tropics is much more luxuriant than that of the\ntemperate and arctic zones. Hence an additional supply of carbonic acid\nis required between the torrid zones, and a less quantity is produced\nby its animals. These cases are all met by the great a\u00ebrial movements.\nA current of warmed air, rich in oxygen, moves from the equator towards\nthe poles, whilst the cooler air, charged with the excess of carbonic\nacid, sets in a constant stream towards the equator. By this means the\nmost perfect equalization of the atmospheric conditions is preserved.\n\nThe carbonic acid poured out from the thousand mouths of our fiery\nfurnaces,--produced during the laborious toil of the hard-working\nartizan,--and exhaled from every populous town of this our island\nhome,--is borne away by this our a\u00ebrial currents to find its place\nin the pines of the Pacific Islands, the spice-trees of the Eastern\nArchipelago, and the cinchonas of Southern America. The plants of\nthe valley of the Caucasus, and those which flourish amongst the\nHimalayas, equally with the less luxuriant vegetation of our temperate\nclimes, are directly dependent upon man and the lower animals for their\nsupply of food.\n\nIf all plants were removed from the earth, animals could not exist.\nHow would it be if the animal kingdom was annihilated?--would it\nbe possible for vegetation to continue? This question is not quite\nso easily answered; but, if we suppose all the carbon-producing\nmachines--the animals--to be extinct, from whence would the plants\ndraw their supply? It has been supposed that during the epoch of\nthe coal formation a luxuriant vegetation must have gone on over\nthe earth\u2019s surface, when the existence of animal life was regarded\nas problematical. It is supposed that the air was then charged with\ncarbonic acid, and that the calamites, lepidodendra, and sigilaria,\nwere employed to remove it, and fit the earth for the oxygen-breathing\nraces. The evidence upon these points is by no means satisfactory; and\nalthough at one time quite disposed to acquiesce in a conjecture which\nappears to account so beautifully for the observed geological phenomena\nof carboniferous periods, we do not regard the necessities for such\na condition of the atmosphere as clearly made out.[223] Geological\nresearch, too, has shown that the immense forests from which our coal\nis formed teemed with life. A frog as large as an ox existed in the\nswamps, and the existence of insects proves the high order of organic\ncreation at this epoch.\n\nIn all probability the same mutual dependence which now exists between\nthe animal and vegetable kingdoms existed from the beginning of time,\nand will continue to do so under varying circumstances through the\ncountless ages of the earth\u2019s duration.\n\nThere is yet another very important chain of circumstances which binds\nthese two great kingdoms together. This is the chain of the animal\nnecessities. A large number of races feed directly upon vegetables;\nherbs and fruits are the only things from which they gain those\nelements required to restore the waste of their systems.\n\nThese herbivorous animals, which must necessarily form fat and muscle\nfrom the elements of their vegetable diet, are preyed on by the\ncarnivorous races; and from these the carbon is again restored to the\nvegetable world. Sweep off from the earth the food of the herbivora,\nthey must necessarily very soon perish, and with their dissolution,\nthe destruction of the carnivora is certainly ensured. To illustrate\nthis on a small scale, it may be mentioned that around the coasts of\nCornwall, pilchards were formerly caught in very great abundance, in\nthe shallow water within coves, where these fish are now but rarely\nseen. From the investigations of the Messrs. Couch, whose very accurate\nobservations on the Cornish fauna have placed both father and son\namongst the most eminent of British naturalists,[224] it appears that\nthe absence of these fish is to be attributed entirely to the practice\nof the farmers, who cut the sea-weed from the rocks for the purpose\nof manuring their lands. By this they destroy all the small crustacea\ninhabiting these immature marine forests feeding on the alg\u00e6, and as\nthese, the principal food of the pilchards, have perished they seek\nfor a substitute in more favourable situations. Mr. Darwin remarks,\nthat if the immense sea-weeds of the Southern Ocean were removed by any\ncause, the whole fauna of these seas would be changed.\n\nWe have seen that animals and vegetables are composed principally of\nfour elementary principles,--oxygen, hydrogen, nitrogen, and carbon.\nWe have examined the remarkable manner in which they pass from one\ncondition--from one kingdom of nature--into another. The animal,\nperishing and dwindling by decomposition into the most simple forms of\nmatter, mingling with the atmosphere as mere gas, gradually becomes\npart of the growing plant, and by like changes vegetable organism\nprogresses onward to form a portion of the animal structure.\n\nA plant exposed to the action of natural or artificial decomposition\npasses into air, leaving but a few grains of solid matter behind it.\nAn animal, in like manner, is gradually resolved into \u201cthin air.\u201d\nMuscle, and blood, and bones, having undergone the change, are found to\nhave escaped as gases, leaving only \u201ca pinch of dust,\u201d which belongs\nto the more stable mineral world. Our dependency on the atmosphere\nis therefore evident. We derive our substance from it--we are, after\ndeath, resolved again into it. We are really but fleeting shadows.\nAnimal and vegetable forms are little more than consolidated masses of\nthe atmosphere. The sublime creations of the most gifted bard cannot\nrival the beauty of this, the highest and the truest poetry of science.\nMan has divined such changes by the unaided powers of reason, arguing\nfrom the phenomena which science reveals in unceasing action around\nhim. The Grecian sage\u2019s doubts of his own identity, were only an\nextension of a great truth beyond the limits of our reason. Romance and\nsuperstition resolve the spiritual man into a visible form of extreme\nethereality in the spectral creations, \u201cclothed in their own horror,\u201d\nby which their reigns have been perpetuated.\n\nWhen Shakespeare made his charming Ariel sing--\n\n    \u201cFull fathom five thy father lies,\n      Of his bones are coral made,\n    Those are pearls that were his eyes:\n      Nothing of him that doth fade,\n    But doth suffer a sea change\n    Into something rich and strange,\u201d\n\nhe painted, with considerable correctness, the chemical changes\nby which decomposing animal matter is replaced by a siliceous or\ncalcareous formation.\n\nBut the gifted have the power of looking through the veil of nature,\nand they have revelations more wonderful than even those of the\nphilosopher, who evokes them by perpetual toil and brain-racking\nstruggle with the ever-changing elements around him.\n\nThe mysteries of flowers have ever been the charm of the poet\u2019s song.\nImagination has invested them with a magic influence, and fancy has\nalmost regarded them as spiritual things. In contemplating their\nsurpassing loveliness, the mind of every observer is improved, and\nthe sentiments which they inspire, by their mere external elegance,\nare great and good. But in examining the real mysteries of their\nconditions, their physical phenomena, the relations in which they stand\nto the animal world, \u201cstealing and giving odours\u201d in the marvellous\ninterchange of carbonic acid and ammonia for the soul-inspiring\noxygen--all speaking of the powers of some unseen, in-dwelling\nprinciple, directed by a supreme ruler--the philosopher finds subjects\nfor deep and soul-trying contemplation. Such studies lift the mind into\nthe truly sublime of nature. The poet\u2019s dream is the dim reflection of\na distant star: the philosopher\u2019s revelation is a strong telescopic\nexamination of its features. One is the mere echo of the remote whisper\nof nature\u2019s voice in the dim twilight; the other is the swelling music\nof the harp of Memnon, awakened by the sun of truth, newly risen from\nthe night of ignorance.\n\nTo return from our long, but somewhat natural digression, to a\nconsideration of the chemical phenomena connected with the atmosphere,\nand its curious and important element, nitrogen, we must first examine\nthe evidence we have of the condition of the air itself.\n\nThe mean pressure exerted upon the surface of the earth, as indicated\nby the barometer, is equal to a column of mercury thirty inches\nhigh; that is, the column of air from the surface of the ocean to\nits highest limits exactly balances that quantity of mercury. If our\ntube of mercury had the area of one square inch, the columns would\nweigh fifteen pounds, which represents a pressure of fifteen pounds\nupon every square inch of the earth\u2019s surface. This pressure, it must\nbe remembered, is the compound weight of the gaseous envelope, and\nthe elastic force of the aqueous vapour contained in it.[225] If the\natmosphere were of uniform condition, its height, as inferred from\nthe barometer, would be about five miles and a half. The density of\nthe air, however, diminishes with the pressure upon it, so that at the\nheight of 11,556 feet, the atmosphere is of half density; or one volume\nof air, as taken at the surface of the earth, is expanded into two at\nthat height. Thus the weight is continually diminishing; but this is\nregularly opposed by the decreasing temperature, which diminishes the\nrate of about one degree for every 352 feet of ascent, although in all\nprobability it is less rapid at great distances from the earth.\n\nIt has been calculated from certain phenomena of refraction, that our\natmosphere must extend to about forty miles from the surface of the\nearth. It may, in a state of extreme tenuity, extend still further;\nbut it is probable that the intense cold produced by rarefaction sets\nlimits to any extension much beyond this elevation.\n\nThe uses of the atmosphere are many. It is the medium for regulating\nthe dispersion of watery vapours over the earth. If there were no\natmosphere, and that, as now, the equatorial climes were hot and the\npoles cold, evaporation would be continually going on at the equator,\nand condensation in the colder regions. The sky of the tropical climes\nwould be perpetually cloudless, whilst in the temperate and arctic\nzones we should have constant rain and snow. By having a gaseous\natmosphere, a more uniform state of things is produced; the vapours\narising from the earth become intimately mixed with the air, and are\nborne by it over large tracts of country, and only precipitated when\nthey enter some stratum much colder than that which involves them.\nThere are opposite tendencies in an atmosphere of air and one of\nvapour. The air circulates from the colder to the warmer parts, and\nthe vapour from the warmer to the colder regions; and as the currents\nof the air, from the distribution of land and sea--the land, from its\nlow conducting power, being more quickly heated than the sea--are\nvery complicated, and as some force is employed in keeping the vapour\nsuspended in the air, water is less suddenly deposited on the earth\nthan it would have been, had not these tendencies of the air and its\nhygrometric peculiarities been such as we find them.\n\nThe blue colour of the sky, which is so much more agreeable to the eye\nthan either red or yellow, is due to a tendency of the mixed gas and\nvapour to reflect the blue rays rather than red or yellow. The white\nlight which falls upon the surface of the earth, without absorption or\ndecomposition in its passage from the sun, is partially absorbed by,\nand in part reflected back from, the earth. The reflected rays pass\nwith tolerable freedom through this transparent medium, but a portion\nof the blue rays are interrupted and rendered visible to us. That it\nis reflected light, is proved by the fact of its being in a polarized\nstate.[226] Clouds of vapour reflect to us again, not isolated rays,\nbut the undecomposed beam, and consequently they appear white as snow\nto our vision.\n\nThe golden glories of sunset,--when, \u201clike a dying dolphin,\u201d heaven\nputs on the most gorgeous hues, which are continually changing,--depend\nentirely upon the quantity of watery vapour which is mixed with air,\nand its state of condensation. It has been observed, that steam at\nnight, issuing into the atmosphere under a pressure of twenty or thirty\npounds to the square inch, transmits and reflects orange-red light.\nThis we may, therefore, conclude to be the property of such a condition\nof mixed vapour and air, as prevails when the rising or the setting\nsun is shedding over the eastern or the western horizon the glory of\nits coloured rays.[227]\n\nThus science points out to us the important uses of the air. We learn\nthat life and combustion are entirely dependent on it, and that it\nis made the means for securing greater constancy in the climates\nof the earth than could otherwise be obtained. The facts already\ndwelt upon are sufficient to convince every thinking mind that the\nbeautiful system of order which is displayed in the composition of\nthe atmosphere, in which the all-exciting element, oxygen, is subdued\nto a tranquil state by another element, nitrogen, (which, we shall\nhave presently to show, is itself, under certain conditions, one of\nthe most energetic agents with which we are acquainted,) indicates a\nsupreme power, omniscient in the adaptation of things to an especial\nend. Oxygen and nitrogen are here _mixed_ for the benefit of man;\nman _unites_ them by the aid of powers with which he is gifted, and\nthe consequences are of a fatal kind. The principles which the great\nChemist of Nature renders mild are transformed into sources of evil by\nthe chemist of art.\n\nBeyond all this, the atmosphere produces effects on light which add\ninfinitely to the beauty of the world. Were there no atmosphere, we\nshould only see those objects upon which the sun\u2019s rays directly fell,\nor from which they were reflected. A ray falling through a small hole\ninto a dark room, illuminating one object, which reflects some light\nupon another, is an apt illustration of the effect of light upon\nthe earth, if it existed without its enveloping atmosphere. By the\ndispersive powers of this medium, sunlight is converted into daylight;\nand instead of unbearable, parallel rays illuminating brilliantly,\nand scorching up with heat those parts upon which they directly\nfall, leaving all other parts in the darkness of night, we enjoy the\nblessings of a diffusion of its rays, and experience the beauties of\nsoft shades and slowly-deepening shadows. Without an atmosphere, the\nsun of the morning would burst upon us with unbearable brilliancy, and\nleave us suddenly, at the close of day, at once in utter darkness. With\nan atmosphere we have the twilight with all its tempered loveliness,--a\n\u201ctime for poets made.\u201d\n\nIn chemical character, atmospheric air is composed of twenty-one\nvolumes of oxygen, and seventy-nine volumes of nitrogen: or one hundred\ngrains of air consist of 23\u00b71 grains of the former, and 76\u00b79 grains\nof the latter. Whether the air is taken from the greatest depths or\nthe most exalted heights to which man has ever reached, an invariable\nproportion of the gases is maintained. The air of Chimborazo, of the\narid plains of Egypt, of the pestilential delta of the Niger, or\neven of the infected atmosphere of an hospital, all give the same\nproportions of these two gases as we find existing on the healthful\nhills of Devonshire, or in the air of the city of London. This\nconstancy in constitution leads to the supposition that the oxygen\nand nitrogen are chemically combined; but many eminent philosophers\nhave contended that they are merely mechanically mixed; and they have\nshown that some peculiar properties prevail amongst gaseous bodies,\nwhich very fully explain the equal admixture of two gases the specific\ngravities of which are different. This is particularly exemplified in\nthe case of carbonic acid, of which gas one per cent. can be detected\nin all regions of the air to which the investigations of man have\nreached. This gas, although so heavy, is, by the law of diffusion,\nmixed with great uniformity throughout the mass.[228] Every exhalation\nfrom the earth, of course, passes into the air; but these are generally\neither so light that they are carried into the upper regions, and\nthere perform their parts in the meteorological phenomena, or they\nare otherwise very readily absorbed by water or growing plants, and\nthus is the atmosphere preserved in a state of purity for the uses of\nanimals. Again, the quantity of oxygen contained in the air, and its\nvery peculiar character, ensures the oxidation of all the volatile\norganic matters which are constantly passing off,--as the odoriferous\nprinciples of plants, the miasmata of swamps, and the products of\nanimal putrefaction; these are rapidly converted into water, carbonic\nacid, or nitric acid, and quickly enter into new and harmless\ncombinations. The elements of contagion we are unacquainted with; but\nsince the attention of inquirers has been of late directed to this\nimportant and delicate subject, some light may possibly be thrown upon\nit before long.\n\nNothing, shows more strikingly the admirable adaptation of all things\nfor their intended uses than the atmosphere. In it we find the source\nof life and health; and chemistry teaches us, most indisputably,\nthat it is composed of certain proportions of oxygen and nitrogen\ngases; and experience informs us that it is on the oxygen that we\nare dependent for all that we enjoy. So beautifully is the atomic or\nmolecular constitution ordered, that it is impossible to produce any\nchange in the air without rendering it injurious to the vegetable and\nanimal economy. It might be thought, from the well-known exhilirating\ncharacter of oxygen gas, that, if a larger quantity existed in the\natmosphere than that which we find there, the enjoyments of life would\nbe of a more exciting kind; but the consequences of any increase would\nbe exceedingly injurious; and, by quickening all the processes of life\nto an unnatural extent, the animal fabric would soon decay: excited\ninto fever, it would be destroyed by its own fires. Chemistry has made\nus acquainted with six other compounds of oxygen and nitrogen, neither\nof them fitted for the purposes of vitality, of which the following are\nthe most remarkable:--\n\nNitrous oxide, or the, so called, _laughing gas_, which contains two\nvolumes of nitrogen to one of oxygen, would prove more destructive than\neven pure oxygen, from the delirious intoxication which it produces.\n\nNitric oxide is composed, according to Davy, of two volumes of nitrogen\nand two of oxygen. It is of so irritating a nature, that the glottis\ncontracts spasmodically when any attempt is made to breathe it; and the\nmoment it escapes into the air it combines with more oxygen, and forms\nthe deep red fumes of nitrous acid.\n\nNitrous acid and the peroxide of nitrogen each contains an additional\nproportion of oxygen, and they are still more destructive to all\norganization.\n\nNitric acid contains five volumes of oxygen united to two of nitrogen;\nand the well-known destructive properties of aqua fortis it is\nunnecessary to describe.\n\nThe atmosphere, and these chemically active compounds, contain the same\nelements, but their mode of combining is different; and what is, in the\none case, poisonous to the highest degree, is, in the other, rendered\nsalubrious, and essential to all organized beings.\n\nNitrogen gas may be regarded in the light of a diluent to the oxygen.\nIn its pure state it is only characterised by its negative properties.\nIt will not burn, or act as a supporter of combustion. Animals speedily\nperish if confined in it; but they die rather through the absence\nof oxygen than from any poisonous property of this gas. Yet, in\ncombination, we find nitrogen exhibiting powers of a most energetic\ncharacter. In addition to the fulminating compounds and the explosive\nsubstances already named, which are among the most remarkable instances\nof unstable affinity with which we are acquainted, we have also the\nwell-known pungent body, ammonia. From the analogous nature of this\nvolatile compound, and the fixed alkalies soda and potash, it was\ninferred that it must, like them, be an oxide of a metallic base. Davy\nexposed ammonia to the action of potassium, and to the influence of the\nvoltaic arc produced from 2,000 double plates, without at all changing\nits character. From its slight tendency to combination, and from its\nbeing found abundantly in the organs of animals feeding on substances\nthat do not contain it, it is, however, probably a compound body. A\nphenomenon of an obscure and mysterious character is presented in the\nformation of the \u201cammoniacal amalgam,\u201d as it is called.\n\nMercury, being mixed with an ammoniacal salt, is exposed to powerful\ngalvanic action; and a compound, maintaining its metallic appearance,\nbut of considerable lightness and very porous, presents itself.[229]\nThis preparation has been carefully examined by Davy, Berzelius, and\nothers. It is always resolved into ammonia and mercury; and, although\nthe latter chemist is strongly inclined to regard it as affording\nevidence of the compound nature of nitrogen,--and he has, indeed,\nproposed the name _nitricum_ for its hypothetical base,--yet, to the\npresent time, we have no satisfactory explanation of this apparent\nmetallization of ammonia.\n\nNo attempt will be made to describe the various elementary substances\nwhich come under the class of metallic bodies, much less to enumerate\ntheir combinations. Many of the metals, as silver and copper, are found\nsometimes in a native state, or nearly pure; but, for the most part,\nthey exist, in nature, in combination with oxygen or sulphur; gold\nfurnishing a remarkable exception. They are occasionally found combined\nwith other bodies,--as oxidized carbon, phosphorus, chlorine, &c.; but\nthese cases are by no means so common. Those substances called metals\nare generally found embedded in the rocks, or deposited in fissures\nformed through them; but it is one of the great discoveries of modern\nscience, that those rocks themselves are metallic oxides. With metals\nwe generally associate the idea of great density; but potassium and\nsodium, the metallic bases of potash and soda, are lighter than water,\nand they consequently float upon that fluid. We learn, therefore, from\nthe researches of science, that the crust of this earth is composed\nentirely of metals, combined with gaseous elements; and there is\nreason for believing that one, or perhaps two, of the gases we have\nalready named are also of a metallic character. Strange as it may\nappear, there is nothing, as will be seen on attentive consideration,\nirrational in this idea. Many of the metals proper, under the influence\nof such heat as we can, by artificial means, command, are dissipated\nin vapour, and may be maintained in this state perfectly invisible.\nIndeed, the transparent space above the surface of the mercury in the\ntube of a barometer, known as the Torricellian vacuum, is filled with\nthe vapour of mercury. There is, therefore, no reason why nitrogen,\nor even hydrogen, should not be metallic molecules kept by the force\nof the repulsive powers of heat, or some other influence, at a great\ndistance from each other. The peculiar manner in which nitrogen unites\nwith mercury, and the property which hydrogen possesses of combining\nwith antimony, zinc, arsenic, potassium, sodium, and possibly other\nmetals, besides its union with sulphur and carbon--in all which cases\nthere is no such change of character as occurs when they combine with\noxygen--appear to indicate bodies which, chemically, are not very\ndissimilar to those metals themselves, although, physically, they have\nnot the most remote resemblance.\n\n\u201cWe know nothing,\u201d says Davy, \u201cof the true elements belonging to\nnature; but, so far as we can reason from the relations of the\nproperties of matter, hydrogen is the substance which approaches\nnearest to what the elements may be supposed to be. It has energetic\npowers of combination, its parts are highly repulsive as to each\nother, and attractive of the particles of other matter; it enters into\ncombination in a quantity very much smaller than any other substance,\nand in this respect it is approached by no known body.\u201d[230]\n\nMany of the elements are common to the three kingdoms of nature:\nmost of those found in one condition of organization are discovered\nin another. The carbonates are an abundant mineral class. In the\nvegetable kingdom we find carbon combining with oxygen, hydrogen, and\nnitrogen: these elements, also, constitute the substance of animals,\nthe proportion of nitrogen being, however, much larger. If one element,\nmore than another, belongs especially to the animal economy, it is\nphosphorus, although this is not wanting in the vegetable world; and\nit is not uncommon in the mineral. Sulphur is common to the three\nkingdoms: it is abundant in the mineral, being one of the products of\nvolcanic action; it is united with the metals, forming sulphurets;\nand is found in our rocks in the state of sulphuric acid or oxidized\nvapour, combined with the metallic bases of lime and other earths. In\nthe vegetable kingdom we discover sulphur in all plants of the onion\nkind, in the mustard, and some others; it enters into the composition\nof vegetable albumen, and appears always combined with albumen,\nfibrine, and caseine, in the animal economy.\n\nChlorine is found most abundantly in combination with sodium, as common\nsalt: in this state, in particular, we may trace it from the depths\nof the earth, its waters, and its rocks, to the plants and animals\nof the surface. Iodine is most abundant in marine plants; but it has\nbeen found in the mineral world, traced to plants, and it is indicated\nin the flesh of some animals. Bromine is known to us as a product of\ncertain saline waters, and a few specimens of natural bromide of silver\nhave been examined. Fluorine, the base of the acid which, combining\nwith lime, forms fluor-spar, is found to exist to some considerable\nextent in bones; it has been discovered in milk and blood; and\ninvestigations have proved its existence in the vegetable world. It\nmust not be forgotten that the earths, lime and magnesia, enter into\nthe composition of the more solid parts of plants and animals. Lime is\none of the principal constituents of animal bone and shells, and it is\nfound in nearly all vegetables.\n\nSilica, or the _earth_ of flints, is met with in beautiful transparent\ncrystals, in the depths of the mine; in all rock and soils we find it.\nIn the bark of many plants, particularly the grasses, it is discovered,\nforming the hard supporting cuticle of the stalk, in wheat, the Dutch\nrush, the sugar-cane, the bamboo, and many other plants.\n\nIt is thus that we find the same elementary principle presenting itself\nin every form of matter, under the most Protean shapes. Numerous\nphenomena of even a more striking character than those selected, are\nexhibited in every department of chemistry; but within the limits of\nthis essay it is impracticable to speak of any beyond those which\ndirectly explain natural phenomena.\n\nThe chemical elements, which actually exist in nature as simple\nbodies, are probably but few. Most of the gases are in all probability\ncompounds of some ethereal ultimate principles; and with the advance of\nscience we may fairly hope to discover the means of reducing some of\nthem to a yet more simple state.\n\nCurious relations, which can be traced through certain bodies, lead us\nto believe that they may be only modified conditions of one element.\nFlint and charcoal do not at first appear allied; but carbon in some\nof its states approaches very near to the condition of silicon, the\nmetallic base of flint. When we remember the differences which are\nevident in three forms of one body--coke, graphite, and diamond--the\ndissimilitude between flint, a quartz crystal, and carbon, will cease\nto be a strong objection to the speculation.\n\nPhosphorus, sulphur, and selenium, have many properties in common.\nIodine, bromine, chlorine, and fluorine, appear to belong to the same\ngroup. Iron and nickel, and cobalt, have a close relation. Silver and\nlead are usually combined, and exhibit a strong relationship. Gold,\nplatinum, and the rarer metals, have so many properties in common, that\nthey may form a separate group from all the others.\n\nIndeed, a philosophical examination of the elements now supposed to\nconstitute the material world, enables us to divide them into about six\nwell-defined groups. Wide differences exist within these groups; but\nstill we find a sufficient number of common properties to warrant our\nclassing them in one family.\n\nThe dream of the alchemists, in the vain endeavour to realise which\nthey exhausted their lives and dissipated their wealth, had its\nfoundation in a natural truth. The transmutation of one form of matter\ninto another may be beyond the power of man, but it is certainly\ncontinually taking place in the laboratory of nature, under the\ndirecting law of the great Creator of this beautiful earth.\n\nThe speculations of men, through all ages, have leaned towards this\nidea, as is shown by the theory of the four elements,--Air, Fire,\nEarth, and Water,--of the ancients, the three,--Salt, Sulphur, and\nMercury,--of the alchemists, and the refined speculations of Newton\nand Boscovich on the ultimate constitution of matter. All experimental\ninquiry points towards a similar conclusion. It is true we have no\ndirect evidence of any elementary atom actually undergoing a change\nof state; but when we regard the variations produced by electrical\ninfluence, the changes of state which arise from the power of heat, and\nthe physical alterations produced by light, it will be difficult to\ncome to any other conclusion than that the particles of matter known\nto us as ultimate are capable of change, and consequently must be far\nremoved from positively simple bodies, since the real elementary atom,\npossessing fixed properties, cannot be supposed capable of undergoing\nany transmutation. Allotropism could not occur in any absolutely simple\nbody.\n\nIt will now be evident that in all chemical phenomena we have the\ncombined exercise of the great physical forces, and evidences of some\npowers which are, as yet, shrouded in the mystery of our ignorance. The\nformation of minerals within the clefts of the rocks, the decomposition\nof metallic lodes, the germination of seeds, the growth of the plant,\nthe development of its fruit and its ultimate decay, the secret\nprocesses of animal life, assimilation, digestion, and respiration, and\nall the changes of external form, which take place around us, are the\nresult of the exercise of that principle which we call chemical.\n\nBy chemical action plants take from the atmosphere the elements of\ntheir growth; these they yield to animals, and from these they are\nagain returned to the air. The viewless atmosphere is gradually formed\ninto an organized being, the lordly tree upon whose branches the fowls\nof the air have their homes, and the human animal, exalted by being\ncharged with a spiritual soul: yet the tree and the man alike are\ngradually resolved again into thin air. The changes of the mineral\nworld are of an analogous character; but we cannot trace them so\nclearly in all their phenomena.\n\nThe planet on which we live began its course charged with a fixed\nquantity of physical force, and this has remained constant to the\npresent moment, and will do so to the end of time. By influences\nexternal to this earth the balance of these forces is continually\ndisturbed; and in the effort to restore the equilibrium, we have the\nproduction of all the varied forms of matter, and the manifestation of\neach particular physical principle or power. As motion and attraction,\nbalanced against each other, maintain the earth in her elliptical\norbit, so the opposition of forces determines the existence of the\namorphous rock, the light-refracting crystal, the fixed and flowering\nplant, and the locomotive animal.\n\nAn eternal round of chemical action is displayed in nature. Life and\ndeath are but two phases of its influences. Growth and decay are\nequally the result of its power.\n\n\nFOOTNOTES:\n\n[212] Dr. Priestley appears to have been the first to observe the\npeculiar property of the diffusion of gases. Dr. Dalton, however,\nfirst drew attention to the important bearing of this fact on natural\nphenomena, and he published his views on _The Miscibility of Gases_ in\nthe Manchester Memoirs, vol. v. The following extract from his memoir\n_On the Constitution of the Atmosphere_ will exhibit its bearings:--\n\nIt may be worth while to contrast this view of the constitution of the\natmosphere with the only other one, as far as I know, that has been\nentertained.\n\n    According to one view,        | According to the other view,\n                                  |\n    1. The volumes of each gas    | 1. The volume of each gas\n    found at the surface of the   | found at the surface of\n    earth are proportional to     | the earth, _multiplied by\n    the whole weights of the      | its specific gravity_, is\n    respective atmospheres.       | proportional to the whole\n                                  | weight of the respective\n                                  | atmospheres.\n                                  |\n        Azote           79        |     Azote           76\u00b76\n        Oxygen          21        |     Oxygen          23\u00b74\n        Aqueous vapour   1\u00b733     |     Aqueous vapour   0\u00b783\n        Carbonic acid    1\u00b70      |     Carbonic acid    0\u00b715\n                      -------     |                    ------\n                      101\u00b743      |                    100\u00b788\n                                  |\n    2. The altitude of each       | 2. The altitude of each\n    atmosphere differs from that  | atmosphere is the same, and\n    of every other, and the       | the proportion of each in the\n    proportions of each in the    | compound atmosphere, is the\n    compound atmosphere gradually | same at all elevations.\n    vary in the ascent.           |\n                                  |\n    3. When two atmospheres are   | 3. When two atmospheres\n    mixed, they take their places | are mixed, they continue\n    according to their specific   | so without the heavier\n    gravity, not in separate      | manifesting any disposition to\n    strata, but intermixedly.     | separate and descend from the\n    There is, however, a separate | lighter.\n    stratum of the specifically   |\n    lighter atmosphere at the     |\n    summit over the other.        |\n\n[213] The discussion of this question, commenced by Arago in his\n_Eloge_, was continued by Lord Brougham in his _Lives of Watt and\nCavendish_, and by Mr. Vernon Harcourt, in his address as President\nof the British Association, and more recently in his _Letter to Lord\nBrougham_. Watt\u2019s _Letters_ on the subject have been since published\nunder the superintendence of Mr. Muirhead.\n\n[214] See several papers _On Ozone_, by Professor Sch\u00f6nbein, in the\nPhilosophical Magazine, and in the Reports of the British Association.\nConsult a paper by the Author: _Athen\u00e6um_, September, 1849.\n\n[215] Memoire _sur l\u2019Ozone_; B\u00e0le 1849. Poggendorff\u2019s _Annalen_,\nlxxvii., p. 592. Ibid, lxxviii. p. 162.\n\n[216] _Chemical Gazette_, 1849.\n\n[217] Iodide of silver has been found at Albarradon, near Mazapil, in\nMexico. Iodide of mercury, of a fine lemon-yellow colour, has been\ndiscovered in the sandstone of Casas, Viegas, Mexico. Algers; Phillips\u2019\n_Mineralogy_.\n\n[218] GENTELE\u2019S Reports of the Stockholm Academy.\n\n[219] Stahl, taking up the obscure notions of Becher and Van Helmont,\nsupposed the phenomena of combustion to be due to phlogiston. He\nimagined that by combination with phlogiston, a body was rendered\ncombustible, and that its disengagement occasioned combustion, and\nafter its evolution there remained either an acid or an earth: thus\nsulphur was, by this theory, supposed to be composed of phlogiston and\nsulphuric acid, and lead of the calx of lead and phlogiston, &c.\n\n[220] Being called upon by the Solicitor for the Admiralty to examine\ninto the causes of the fire which destroyed the _Imogene_ and\n_Talavera_, in Devonport Arsenal, I discovered a bin under the roofing\nwhich covered these ships, in which there had been accumulating for a\nlong period all the refuse of the wheelwrights\u2019 and painters\u2019 shop; and\nit was quite evident that spontaneous combustion had taken place in the\nmass of oiled oakum, sawdust, anti-attrition, and old sail-cloth, there\nallowed to accumulate.\n\n[221] _Researches on Flame_: Sir H. Davy\u2019s Collected Works.\n\n[222] See note, _ante_, _On the Chemical Theory of Respiration_.\n\n[223] At the request of the British Association, a committee undertook\nthe investigation of this subject. Experiments were carried on by Dr.\nDaubeny, in the Botanic Gardens at Oxford, and by the Author, at his\nresidence, Stockwell. Dr. Daubeny, in his report made at the meeting\nof the British Association at Birmingham, appears disposed to consider\nten per cent. of carbonic acid in excess as destructive to the growth\nof ferns. I found, however, that, by gradually increasing the quantity,\nthe ferns would live in an atmosphere still more highly charged with\ncarbonic acid.\n\n[224] See memoir _On the Pilchard_, by Mr. Couch, in the Reports of the\nRoyal Cornwall Polytechnic Society.\n\n[225] \u201cThis scale, in which the humidity of the air is expressed,\nis the simple natural scale in which air at its maximum of humidity\n(_i.e._, when it is saturated with vapour) is reckoned as = 100, and\nair absolutely deprived of moisture as = 0; the intermediate degrees\nare given by the fraction 100 \u00d7 actual tension of vapour \u00f7 tension\nrequired for the saturation of the air at its existing temperature.\nThus, if the air at any temperature whatsoever contains vapour of half\nthe tension, which it would contain if saturated, the degree is 50; if\nthree-fourths, then 75; and so forth. Air of a higher temperature is\ncapable of containing a greater quantity of vapour than air of less\ntemperature; but it is the proportion of what it does contain, to what\nit would contain if saturated, which constitutes the measure of its\ndryness or humidity. The capacity of the air to contain moisture being\ndetermined by its temperature, it was to be expected that an intimate\nconnection and dependence would be found to exist between the annual\nand diurnal variations of the vapour and of the temperature.\u201d--Sabine,\n_On the Meteorology of Toronto_; Reports of the British Association,\nvol. xiii. p. 47. _The Temperature Tables_: by Prof. W. H. Dove;\nReports for 1847 should be consulted.\n\n[226] Sir David Brewster\u2019s _Optics_, and Memoirs in the Philosophical\nTransactions. Sir John Herschel\u2019s Treatise on _Light_, Encyclop\u00e6dia\nMetropolitana.\n\n[227] _On the Colour of Steam under certain circumstances_: by\nProfessor Forbes; Philosophical Magazine, vol. xiv. p. 121, vol. xv.\np. 25. In the first paper the following remarks occur:--\u201cI cannot\ndoubt that the colour of watery vapour under certain circumstances\nis the principal or only cause of the red colour observed in clouds.\nThe very fact that that colour chiefly appears in the presence of\nclouds is a sufficient refutation of the only explanation of the\nphenomena of sunset and sunrise, having the least plausibility, given\nby optical writers. If the red light of the horizontal sky were simply\ncomplementary to the blue of a pure atmosphere, the sun ought to set\nred in the clearest weather, and then most of all; but experience shows\nthat a lurid sunrise or sunset is _always_ accompanied by clouds or\ndiffused vapours, and in a great majority of cases occurs when the\nchanging state of previously transparent and colourless vapour may be\ninferred from the succeeding rain. In like manner, terrestrial lights\nseen at a distance grow red and dim when the atmosphere is filled\nwith vapour soon to be precipitated. Analogy applied to the preceding\nobservations would certainly conduct to a solution of such appearances;\nfor I have remarked that the existence of vapour of high tension is\nby no means essential to the production of colour, though of course\na proportionally greater thickness of the medium must be employed to\nproduce a similar effect when the elasticity is small.\u201d\n\n[228] _On the Law of Diffusion of Gases_: by Thomas Graham, M.A.,\nF.R.S., &c.; Edinburgh Philosophical Transactions, 1832. _Sur l\u2019Action\nCapillaire des Fissures, &c._: by D\u00f6bereiner; Annales de Chimie, xxiv.\n332.\n\n[229] _Electro-chemical Researches on the Decompositions of the Earths,\nwith observations on the Metals obtained from the Alkaline Earths,\nand on the Amalgam procured from Ammonia_: by Sir Humphry Davy;\nPhilosophical Transactions, 1808, and collected works, vol. v. p. 102.\n\n[230] _Elements of Chemical Philosophy_: by Sir H. Davy.\n\n\n\n\nCHAPTER XIII.\n\nTIME.--GEOLOGICAL PHENOMENA.\n\n  Time, an element in Nature\u2019s Operations--Geological\n    Science--Its Facts and Inferences--Nebular Hypothesis\n    applied--Primary Formations--Plutonic and Metamorphic\n    Rocks--Transition Series--Pal\u00e6ozoic Rocks--Commencement of\n    Organic Arrangements--Existence of Phosphoric Acid in Plutonic\n    Rocks--Fossil Remains--Coal Formation--Sandstones--Tertiary\n    Formations--Eocene, Miocene, and Pliocene Formations--Progressive\n    changes now apparent--General Conclusions--Physics applied in\n    explanation.\n\n\nThe influence of time, as an element, in producing certain structural\narrangements, by modifying the operations of physical force, under\nwhatever form it may be exerted, has scarcely been sufficiently\nattended to in the examination of cosmical phenomena. Every particle\nof matter is, as it were, suspended between the agencies to which\nwe have been directing our attention. Under the influences of the\nphysical powers, sometimes exerted in common, but often with a great\npreponderance in favour of one of them, every accumulated heap of mud\nor sand is slowly cohering, and assuming the form of a rock possessing\ncertain distinguishing features, as it regards lamination, cleavage, &c.\n\nThe minute particles of matter are necessarily but slightly influenced\nby the physical forces: their action in accordance with the laws which\ndetermine physical condition is manifested in an exceedingly modified\ndegree. But in all the operations of nature, what is deficient in\npower is made up in time, and effects are produced during myriads\nof ages, by powers far too weak to give satisfactory results by any\nexperiments which might be extended even over a century.\n\nIf, with the eye of a geologist, we take but a cursory glance over the\nEarth, we shall discover that countless ages must have passed during\nthe progress of this planet to its present state. This is a fact\nwritten by the finger of nature, in unmistakeable characters, upon the\nmighty tablets of her mountains.\n\nThe superficial crust of the earth,--by which is meant only that film,\ncompared with its diameter, which is represented by a few miles in\ndepth--is composed of distinct mineral masses, exhibiting peculiar\nphysical conditions and a certain order of arrangement. These rocks\nappear to have resulted from two dissimilar causes; in one class the\naction of heat is evident, and in the other we have either the slow\ndeposition of matter suspended in water, or crystallization from\nsolution; an aqueous origin is indicated by peculiarities of formation\nin all the more recent rocks.\n\nThere are few branches of science which admit of speculation to the\nextent to which we find it carried in geology. The consequences of this\nare shown in the popular character of the science. A few observations\nare made over a limited area, and certain structural conditions are\nascertained, and at once the mind, \u201cfancy free,\u201d penetrates the\nprofound depths of the earth, and imagination, having \u201cample room\nand verge enough,\u201d creates causes by which every effect is to be\ninterpreted. Such students, generally ignorant of the first principles\nof physics, knowing little of mineralogy, and less of chemistry, to\nsay nothing of pal\u00e6ontology, having none of the requisites for an\nobserver, boldly assume premises which are untenable, and think they\nhave explained a phenomenon,--given to the world a truth,--when they\nhave merely promulgated an unsubstantiated speculation, which may have\noccasional marks of ingenuity, and but little else.\n\nThe carefully-made observations of those who, with unwearying industry,\nhave traversed hill and valley, marked and measured the various\ncharacters, thicknesses, inclinations, and positions of rocks; who have\nwatched the influences of heat in changing, of water in wearing, and\nthe results of precipitation in forming, strata; who have traced the\nmechanical effects of earthquake strugglings and of volcanic eruptions,\nand, reasoning from an immense mass of accumulated facts, deduced\ncertain general conclusions,--are, however, of a totally different\ncharacter; and it is such observers as these who induced Herschel to\nsay truly, that \u201cgeology, in the magnitude and sublimity of the objects\nof which it treats, undoubtedly ranks, in the scale of the sciences,\nnext to astronomy.\u201d[231]\n\nThe origin of this planet is involved in great obscurity, which the\npowers of the most gifted are unable to penetrate. It stands the work\nof an Almighty and Eternal mind, the beginning of which we cannot\ncomprehend, nor can we define the period of its termination.\n\nIt may, probably, be safe to speculate that there was a time when\nthis globe consisted of only one homogeneous stratum. Whether\nthis remains,--whether, in our plutonic rocks, our granites, or\nour porphyries, we have any indications of the primitive state of\nthe world, or whether numerous changes took place before even our\nunstratified formations had birth, are questions we cannot answer. The\ngeologist looks back into the vista of time, and reckons, by phenomena,\nthe progress of the world\u2019s mutations. The stratified formations\nmust have occupied thousands of ages; but before these were, during\na period extending over countless thousands, the unstratified rocks\nmay have been variously metamorphosed. It matters not whether we admit\nthe nebular hypothesis or not,--a time must have been when all these\nbodies which now form the mass of this globe existed in the most simple\nstate. We have already shown that very remarkable changes in external\ncharacter and in chemical relations are induced, in the same simple\nelement, by its having been exposed to some peculiar and different\nconditions; and already have we speculated on the probability that\nthe advance of science will enable us to reduce the numerous elements\nwe now reckon, to two or three. It is, therefore, by no means an\nirrational thought (which must, however, be held in the light of a\npure conjecture), to suppose that at the beginning a mighty mass of\nmatter, in the most attenuated state, was produced in space, and was\ngradually, under the influence of gravitation, of cohesive force, and\nof chemical aggregation, moulded into the form of a sphere. Ascending\nto the utmost refinement of physics, we may suppose that this mass was\nof one uniform character, and that it became in dissimilar parts--its\nsurfaces and towards its centre--differently constituted, under the\ninfluences of the same powers which we now find producing, out of the\nsame body, charcoal and the diamond, and creating the multitudinous\nforms of organized creations. These conditions being established, and\ncarried to an extent of which, as yet, science has afforded us no\nevidence, chemical intermixture may have taken place, and a new series\nof compounds have been formed, which, by again combining, gave rise to\nanother and more complex class of bodies.\n\nThe foundation of the superficial crust of the earth appears to be\nformed of a class of rocks which have resulted from the slow cooling\nof an immense mass of heated matter. These rocks have been called\n_igneous_; but are now more generally termed _Plutonic_ (such as\ngranites, syenites, &c.) Immediately above these, we find rocks which\nhave resulted by deposition from water. These masses, having been\nexposed to the action of the heat below, have been considerably changed\nin their character, and hence they are often called _metamorphic_;\nbut metamorphic rocks may, however, be of any age. The rocks formerly\ntermed the _transition_ series--from their forming the connecting link\nbetween the earlier formations--are now, from the circumstance of their\nbeing fossiliferous, classed under the general term of pal\u00e6ozoic rocks,\nto distinguish them from the rocks in which no organic remains have\nbeen found. Above these are found the secondary strata, and, still more\nrecently produced, we have a class now usually denominated the tertiary\nformations. \u201cEternal as the hills\u201d is a poetic expression, implying a\nlong duration; but these must, from the nature of things, eventually\npass away. The period of time necessary for the disintegration of a\ngranite hill is vastly beyond the powers of computation, according\nto our conception of the ordinary bounds of finite things. But a\nconsideration of the results of a few years,--under the influence of\nthe atmosphere and the rains,--as shown in quantity of solid matter\ncarried off by the rivers, and deposited at their mouths, will tend to\ncarry conviction to every mind, that a degrading process is for ever in\naction on the surface of the earth. The earth itself may be eternal,\nbut the surface is continually undergoing mutation, from various\ncauses, many of which we must briefly consider.[232]\n\nIn regarding geological phenomena, the absence of any fossil remains\nhas often been supposed to indicate a period previous to any organic\nformations. The inorganic constituents of matter are probably of\nprior origin to the organic combinations; the vessel was constructed,\nupon which the organic creation was to float in space before any\nvital organisms were created. The supposed evidences in favour of the\nassumption that there was no organic life during the formation of the\noldest rocks we know, are in some respects doubtful; and we can well\nunderstand that changes may have been induced in the earlier rock\nformations, by heat or by other powers, quite sufficient to destroy all\ntraces of organized forms. It was long thought that phosphoric acid was\nnot to be detected in rocks which are regarded as of igneous origin;\nand since this acid is peculiarly a constituent of organic bodies, this\nhas been adduced as a proof that the plutonic rocks must have existed\npreviously to the appearance of vegetable or animal life upon the\nsurface of the globe. The researches of modern chemists have, however,\nshown that phosphoric acid is to be found in formations of granitic\norigin, in porphyry, basalt, and hornblende rocks.[233] If, therefore,\nwe are to regard this substance as of organic origin, the rational\ninference is against the speculation; but there is no more necessity\nfor supposing phosphorus to be formed in the animal economy than in\nthe mineral kingdom, from which it will probably be found the animal\nobtained it.\n\nWithout attempting to enter into any account of the apparent progress\nof life over the earth, it appears desirable that some description\nshould be given of the kinds of plants and animals which we know to\nhave existed at different epochs. We shall thus learn, at least, some\nof the prevailing characteristics of the earth during its transitions,\nand be in a better condition for applying our knowledge of physical\npower to the explanation of the various geological phenomena.\n\nAmong the earliest races we have those remarkable forms, the\ntrilobites, inhabiting the ancient ocean.\n\nThese crustacea bear some resemblance, although a very remote one, to\nthe common wood-louse, and, like that animal, they had the power of\nrolling themselves into a ball when attacked by an enemy. The eye of\nthe trilobite is a most remarkable organ; and in that of one species,\n_Phacops caudatus_, not less than two hundred and fifty lenses have\nbeen discovered. This remarkable optical instrument indicates that\nthese creatures lived under similar conditions to those which surround\nthe crustacea of the present day.\n\nAt the period of the trilobites of the Silurian rocks, all the animals\ncontemporaneous with them had the organs necessary for the preservation\nof life in the waters.\n\nNext in order of time to the trilobite, the most singular animals\ninhabiting those ancient seas, whose remains have been preserved,\nare the _Cephalopoda_, possessing some traces of organs which belong\nto vertebrated animals. There are numerous arms for locomotion and\nprehension, arranged in a centre round the head, which is furnished\nwith a pair of sharp, horny mandibles, embedded in powerful muscles.\nThese prehensile arms are provided with a double row of suckers, by\nwhich the animal seized its prey. Of these cephalopodous animals there\nare many varieties, but all of them appear to be furnished with powers\nof rapid locomotion, and those with shells had an hydraulic arrangement\nfor sinking themselves to any depth of the seas in which, without\ndoubt, they reigned the tyrants.\n\nPassing by without notice the numerous fishes, which appear to have\nexhibited a similar order of progression to the other animals, we must\nproceed to the more remarkable period when the dry land first began to\nappear.\n\nAll the animals found in the strata we have mentioned are such as would\ninhabit the seas; but we gradually arrive at distinct evidence of the\nseparation of the land from the water, and the \u201cgreen tree yielding\nseed\u201d presents itself to our attention; not that the strata earlier\nthan this are entirely destitute of any remains indicating vegetable\ngrowth, but those they exhibit are such as, in all probability, may be\nreferred to marine plants.\n\nThose plants, however, which are found in the carboniferous series\nare most of them distinguished by all the characteristics of those\nwhich grow upon the land; we, therefore, in the mutilated remains of\nvegetation left us in our coal-formations, read the history of our\nearly world.\n\nThen the reed-like calamite bowed its hollow and fragile stems over\nthe edges of the lakes the tree-ferns grew luxuriantly in the shelter\nof the hills, and gave a wild beauty to the humid valleys; the\nlepidodendrons spread themselves in mighty forests along the plains,\nwhich they covered with their curious cones; whilst the sigillari\u00e6\nextended their multitudinous branches, wreathing like serpents amongst\nthe luxurious vegetation, and embraced, with their roots (stigmari\u00e6), a\nmost extensive space on every side.[234]\n\nThe seas and lakes of this period abounded with minute animals nearly\nallied to the coral animals, which are now so actively engaged in the\nformation of islands in the tropical and southern seas. During the ages\nwhich passed by without any remarkable disturbance of the surface of\nthe earth, the many bands of mountain limestone were formed by the\nceaseless activity of these minute architects. Encrinites (creatures\nin some respects resembling star-fish) existed in vast numbers in the\noceans of this time; and the great variety of bivalve shells, and those\nof a spiral character, discovered in the rocks of this period, show the\nwaters of the newer pal\u00e6ozoic period to have been instinct with life.\n\nIn the world then, as it does now, water acting on the dry land\nproduced remarkable changes. We have evidence of extensive districts\nover which the most luxuriant vegetation must have spread for\nages,--from the remains of plants in every state of decay,--which we\nfind went to form our great coal-fields. These, by some changes in the\nrelative levels of land and water, became covered with this fluid;\nand over this mass of decaying organic matter, sand and mud were for\nages being deposited. At length, rising above the surface, it becomes\ncovered with vegetation, which is, after a period, submerged; the same\ndeposition of sand and mud again takes place, it is once more fitted\nfor vegetable growth, and thus, cycle after cycle, we see the dry land\nand the water changing places with each other. This will be evident\nto every one who will carefully contemplate a section of one of the\ncoal-fields of Great Britain. We find a stratum of coal lying upon\na bed of under clay, and above it an extensive stratum of shale or\nsandstone, probably formed by the denudation of the neighbouring hills;\nand in this manner we have many strata of coal, shale, clay, ironstone,\nand sandstone alternating with each other; the coal-formations of the\nSouth Wales coal-field having the extraordinary thickness of 1500 feet.\nThe lowest bed of this extensive series must at one time have been\nexposed as the surface of the country.\n\nAscending in the series, we have now formations of a more recent\ncharacter, in which fishes of a higher order of organization, creeping\nand flying saurians, crocodiles and lizards, tortoises, serpents, and\nfrogs, are found. The lias formations (a term corrupted from _layers_),\nconsisting of strata in which an argillaceous character prevails, stand\nnext in series. In these we have animals preserved in a fossil state,\nof a distinguishingly different character from those of the inferior\nstrata. We meet with extended beds of pentacrinites, some inches in\nthickness; and their remains are often so very complete that every part\nof the skeleton can be made out, although so complicated that it cannot\nconsist of less than 150,000 parts. In these formations we often find\nthe curiously beautiful remains of the ammonites, of which a great\nvariety have been discovered. Of the belemnites--animals furnished with\nthe shell and the ink-bag of the cuttle-fish, with which it darkened\nthe water to hide itself from enemies, numerous varieties have also\nbeen disentombed, with the ink-bag so well preserved, that the story of\nthe remarkable fossil has been written with its own ink. In addition to\nthese we find nautili; and sixty species of extinct fishes have been\ndescribed by Agassiz from the lias of Lyme Regis alone.\n\nWhen these rocks were in the progress of formation, there existed the\nichthyosaurus, or fish-lizard, which appears, in many respects, to have\nresembled the crocodile of the Nile. It was a predatory creature of\nenormous power, and must have been the tyrant and terror of the seas\nwhich it inhabited. Its alligator-like jaws, its powerful eye, its\nfish-like fins, and turtle-like paddles, were all formed to facilitate\nits progress as a destructive minister. The plesiosaurus was, if\npossible, a still more extraordinary creation. To the head of a lizard\nwas united an enormously long neck, a small and fish-like body, and the\ntail of a crocodile: it appears formed for existence in shallow waters,\nso that, when moving at the bottom, it could lift its head above the\nsurface for air, or in search of its food. The flora of this period\nmust have been extensive; and it resembled the vegetation which exists\nat present in Tropical regions.\n\nWe pass now to a new epoch, which is well distinguished by its animals\nfrom all that had preceded it. Races of reptiles still have place upon\nthe earth, and we have now the megalosaurian remains; these animals\npossessing a strength and rapacity which would render them objects of\nterror as well as astonishment, could they be restored to the world\nwhich they once ravaged. An enormous bat-like creature also existed\nat this time--the pterodactyl--which, in the language of Cuvier, was,\n\u201cundoubtedly, the most extraordinary of all the beings of whose former\nexistence a knowledge is granted to us, and that which, if seen alive,\nwould appear most unlike anything that exists in the present world.\u201d\n\u201cYou see before you,\u201d says the same writer, \u201can animal which, in all\npoints of bony structure, from the teeth to the extremities of the\nnails, presents the well-known saurian characteristics, and of which no\none can doubt that its integuments and soft parts, its scaly armour and\nits organs of circulation and reproduction, are likewise analogous. But\nit was, at the same time, an animal provided with the means of flying;\nand, when stationary, its wings were probably folded back like those\nof a bird, although, perhaps, by the claws attached to its fingers, it\nmight suspend itself from the branches of trees.\u201d[235]\n\nFrom the disintegration of the older rocks have no doubt arisen those\nformations which are known as the oolitic series. In these strata are\npreserved the remains of plants and animals more resembling those which\nnow exist upon the earth; and, for the first time,--unless the evidence\nof the footsteps of birds on the new red sandstone of America be\naccepted,--we meet with the remains of the feathered tribes.\n\nIn these formations we discover animals belonging to the class\nMammalia,--the amphitherium and the phascolotherium,--which appear\nto have resembled, in many respects, the marsupial animals of New\nHolland.[236]\n\nThe wealden formations, which are the next in order of position, are a\nseries of clays and sands, with subordinate beds of limestone, grit,\nand shale. These have, in some instances, been formed in the sea; but\nthey are usually regarded as fresh-water deposits. All the older rocks\nbear evident marks of marine origin, unless some of the coal-measure\nstrata may be regarded as otherwise; but nearly all the wealden series\ncontain the remains of land, fresh-water, and estuary animals, and of\nland vegetables. The creatures which we discover, preserved, to tell\nthe history of this period, are numerous, and have marked peculiarities\nto distinguish them from those already described, or from any now\nexisting on the earth. We find land saurians of a large kind, and\nanimals of all sizes; even insects, of which a great variety are found\nin the wealds. The remarkable iguanodon was an animal which, even by\nthe cautious measurement of Professor Owen, must have been at least\ntwenty-eight feet long; and this enormous creature was suspected, by\nCuvier, and has been proved by Owen, to have been an \u201cherbivorous\nsaurian for terrestrial life.\u201d[237] Dr. Mantell calculates that no\nless than seventy individuals of the iguanodon of all ages have come\nunder his notice; and the bones of a vast number of others must have\nbeen broken up by the workmen in the few quarries of Tilgate grit;\nso that these creatures were by no means rare at the period of their\nexistence.[238]\n\nThe uppermost of these secondary formations is the cretaceous or chalk\ngroup, which spreads over a large portion of south-eastern England, and\nis met with in all parts of Europe. This chalk, which is a carbonate\nof lime, appears to have been slowly precipitated from tranquil water,\nas, according to Sir Henry De la Beche, organic remains are beautifully\npreserved in it. Substances of no greater solidity than common sponges\nretain their forms, delicate shells remain unbroken, fish even are\nfrequently not flattened, and altogether we have the appearances\nwhich justify us in concluding that, since these organic exuvi\u00e6 were\nentombed, they have been protected from pressure by the consolidation\nof the rock around them.[239]\n\nBeneath the chalk exists what has been called, from its colour--derived\nfrom a silicate of the protoxide of iron,--green sand, and was, no\ndoubt, formed by deposition from the same water in which the carbonate\nof lime was suspended,--the green sand falling to the bottom more\nreadily from its greater specific gravity. \u201cThe tranquillity,\u201d observes\nSir Henry De la Beche, \u201cwhich seems to have prevailed during this great\naccumulation of siliceo-calcareous matter, whether it may have been\na deposit from water, in which it was mechanically suspended, partly\nthe work of living creatures, or in a great measure chemical, is very\nremarkable.\u201d[240]\n\nIn the chalk, the remains of the leaves of dicotyledonous plants\nand fragments of wood are found more abundantly than in the earlier\nstrata, many of which are marked with the perforations of marine\nworms, indicating that they had floated for some time in the ocean.\nIt should, however, be remembered, that these are not the first\nindications of vegetable life,--leaves have been found in the new red\nsandstone; and the flora of the coal formation must not be forgotten.\nThe manner in which silica has deposited itself on organic bodies--such\nas the sponges--is curious; the whole of the organized tissue being\noften removed, and flint having taken its place. Flints formed by\nsuch a process as this abound in the upper chalk. The association\nof carbon and silicon, combined with oxygen, as we find them in the\ncretaceous formations, is most interesting, and naturally gives rise\nto some speculation on the relation of these two elements. Both carbon\nand silicon, as has been already shown, exist in several allotropic\nconditions; and, although the statements made by Dr. Brown relative\nto the conversion of carbon into silicon are proved to be grounded on\nexperimental error, it is not improbable that a very intimate relation\nmay exist between these elements.[241] The probability is, that the\nsponge animal has the power of secreting silica to give strength\nto its form. \u201cMany species,\u201d says Rymer Jones, speaking of recent\nsponges, \u201cexhibiting the same porous structure, have none of the\nelasticity of the officinal sponge--a circumstance which is due to the\ndifference observable in the composition of their skeletons or ramified\nframe-work. In such the living crust forms within its substance\nnot only tenacious bands of animal matter, but great quantities of\ncrystallized spicula, sometimes of a calcareous, at others of a\nsiliceous, nature.\u201d Thus, a frame of siliceous matter being formed by\nthe living animal, a deposition of the same substance is continued\nafter death.\n\nSea-urchins and star-fish, and numerous fossil shells, are found in\nthese beds, which, however, differ materially from the remains of the\nsame animals found in the earlier formations. A vast number of new\nspecies and genera of fish are also discovered in the chalk.\n\nNearly all the animals and plants which existed up to this period are\nnow extinct, although they have some imperfect representatives at the\npresent day.\n\nThe uppermost group, which has been called the supercretaceous or\ntertiary formation, appears in our island to have been formed during\nfour great eras, as we find fresh-water deposits alternating with\nmarine ones. The term _eocene_, which is the first or oldest deposit;\n_miocene_, which is the second; _pliocene_, which is the third; and the\n_newer pliocene_,--which is the fourth and last, have been applied to\nthese formations, the names referring to the respective proportions of\nexisting species found among their fossil shells.[242]\n\nAll these formations show distinct evidence of their having been\ndeposited from still or slowly-flowing deep waters. Thus the eocene\nappears in the Paris basin,--formed clearly at an estuary, in which\nare mingled some interesting fresh-water deposits;--in the lacustrine\nformations in Auvergne; also at Aix; and in the north of Italy. It\nappears probable that, in the formations generally termed eocene, both\nfresh-water and marine deposits have been confounded, and several\nformations of widely-different eras regarded as the result of one. We\nhave not yet been furnished with any distinct and clear evidence to\nshow that the deposits of the Paris basin, and those of Auvergne,\nare of the same age. At all events, it is sufficient for our present\npurpose to know that they are the result of actions which are now as\ngeneral as they were when the plastic clay of Paris, and its sulphate\nof lime, or the London clay, were slowly deposited.\n\nAs a general conclusion, we may decide that, at the eocene period,\nexisting continents were the sites of vast lakes, rivers, and\nestuaries, and were inhabited by quadrupeds, which lived upon\ntheir thickly-wooded margins. Many remains, allied to those of the\nhippopotamus, have been found in the subsidences of this period.\n\nExamples of the miocene or middle tertiary era are to be found in\nWestern France, over the whole of the great valley of Switzerland, and\nthe valley of the Danube. In these deposits we find the bones of the\nrhinoceros, elephant, hippopotamus, and the dinotherium, an extinct\nanimal, possessing many very distinguishing features.[243]\n\nThe pliocene period has been termed the age of elephants, and is most\nremarkable for the great mastodons and gigantic elks, with other\nanimals not very unlike those which are contemporaneous with man.\n\nIn the superficial layers of the earth, the diluvium, alluvium, peat\nand vegetable soil, we have a continuation of the history of the\nmutations of our globe and of its inhabitants, which has been here so\nbriefly sketched. They bring us up to the period when man appeared in\nthe world, since whose creation it is evident no very extensive change\nhas been produced upon the surface. We have viewed the phenomena of\neach great epoch, marked as they are by new creations of organized\nbeings, and it would appear as if, through the whole series, from\nthe primary rocks up to the modern alluvial deposits, a progressive\nimprovement of the earth\u2019s surface had been effected, to fit it at last\nfor the abode of the human race.\n\nThus have we preserved for us, in a natural manner, evidences which, if\nwe read them aright, must convince us that the laws by which creation\nhas ever been regulated are as constant and unvarying as the Eternal\nmind by which they are decreed. Our earth, we find, by the records\npreserved in the foundation-stones of her mountains, has existed\nthrough countless ages, and through them all exhibited the same active\nenergies that prevail at the present moment. By precisely similar\ninfluences to those now in operation, have rocks been formed, which,\nunder like agencies, have been covered with vegetation, and sported\nover by, to us, strange varieties of animal life. Every plant that\nhas grown upon the earliest rocks which presented their faces to the\nlife-giving sun, has had its influence on the subsequent changes of our\nplanet. Each trilobite, each saurian, and every one of the mammalia\nwhich exist in the fossil state, have been small laboratories in which\nthe great work of eternal change has been carried forward, and, under\nthe compulsion of the strong laws of creation, they have been made\nministers to the great end of forming a world which might be fitting\nfor the presence of a creature endued with a spark taken from the\ncelestial flame of intellectual life.\n\nFor a few moments we will return to a consideration of the operations\nat present exhibiting their phenomena, and examine what bearing they\nhave upon our knowledge of geological formations.\n\nDuring periods of immense, but unknown, duration, the ocean and the dry\nland are seen to have changed their places. Enormous deposits, formed\nat the bottom of the sea, are lifted by some mechanical, probably\nvolcanic, force, above the waters, and the land, like the ocean\nsurrounding it, teems with life. This state of things lasts for ages;\nbut the time arrives when the ocean again floods the land, and a new\nstate of things, over a particular district, has a beginning.\n\nIt must not be imagined that the changes which we have spoken of, as if\nthey were the result of slow decay and gradual deposit, were effected\nwithout occasional violent convulsions. Many of the strata which\nwere evidently deposited at the bottom of the sea, and, of course,\nas horizontal beds, are now found nearly vertical. We have evidence\nof strata of immense thickness having been subjected to forces that\nhave twisted and contorted them in a most remarkable manner. Masses of\nsolid rock, many thousand feet deep, are frequently bent and fractured\nthroughout their whole extent. Mountains have been upheaved by internal\nforce, and immense districts have suddenly sunk far below their usual\nlevel. By the expansive force due to that temperature which must be\nrequired to melt basaltic and trap rocks, the whole of the superficial\ncrust of a country has been heaved to a great height, immense fissures\nhave been formed by the breaking of the mass, and the melted matter has\nbeen forced through the opening, and overflowed extensive districts, or\nvolcanoes have been formed, and wide areas have been buried under the\nashes ejected from them. With the cause of these convulsions we are at\npresent unacquainted.\n\nWe have evidence of the extent to which these forces may be exerted, in\nthe catastrophes which have occurred within historical times, and which\nhave happened even in our own day. Herculaneum and Pompeii, buried\nunder the lava and ashes of Vesuvius, in an hour when the inhabitants\nof these cities were unprepared for such a fearful visitation,--the\nfrightful earthquakes which have, from time to time, occurred in South\nAmerica--are evidences of the existence of hidden forces which shake\nthe firm-set earth. Similar ravaging catastrophes may have often\noccurred, and, involving cataclysms, swept the surface to produce the\nchanges we detect over every part of the earth, compared with which\nthe earthquakes and floods of history are but trivial things. Evidence\nhas been adduced, to show that the mountains of the Old World may\nhave approached in height the highest of the Andes or Himalayas, and\nthese have not been destroyed by any sudden effect, but by the slow\ndisintegrating action of the elements.[244] All these phenomena are\nnow in progress: the winds and the rains wear the faces of the exposed\nrock; their _d\u00e9bris_, mixed with decayed vegetable and animal matter,\nare washed off from the surface, and borne away by the rivers, to be\ndeposited in the seas. Thus it is that the great delta of the Ganges\nis formed, and that a continual increase of matter is going on at the\nmouths of rivers. The Amazon, the Mississippi, and other great rivers,\nbear into the ocean, daily, thousands of tons of matter from the\nsurface of the earth.[245] This is, of course, deposited at the bottom\nof the sea, and it must, in the process of time, alter the relative\nlevels of the ocean and the land. Islands have been lifted by volcanic\npower from the bottom of the sea, and many districts in South America\nhave been depressed by the same causes.\n\nChanges as extensive have been, in all probability, effected by forces\n\u201cequally or more powerful, but acting with less irregularity, and so\ndistributed over time as to produce none of those interregnums of\nchaotic anarchy which we are apt to think (perhaps erroneously) great\ndisfigurements of an order so beautiful and harmonious as that of\nnature.\u201d[246] These forces are, without doubt, even now in action.\n\nHad it not been for these convulsive disturbances of the surface,\nthe earth would have presented an almost uniform plain, and it would\nhave been ill-adapted for the abode of man. The hills raised by the\ndisturbances of nature, and the valleys worn by the storms of ages,\nminister especially to his wants, and afford him the means of enjoyment\nwhich he could not possess had the surface been otherwise formed. The\n\u201ciced mountain tops,\u201d condensing the clouds which pass over them, send\ndown healthful streams to the valleys, and supply the springs of the\nearth, thus securing the fertility and salubrity of the distant plains.\nThe severities of climate are mitigated by these conditions, and both\nthe people of the tropics and those dwelling near the poles are equally\nbenefited by them.\n\nGravitation, cohesion, motion, chemical force, heat, and electricity,\nmust, from that hypothetical time when the earth floated a cloud of\nnebulous vapour, in a state of gradual condensation up to the present\nmoment, have been exercising their powers, and regulating the mutations\nof matter.\n\nWhen the dry land was beneath the waters, and when darkness was upon\nthe face of the deep, the same great operations as those which are\nnow in progress in the depths of the Atlantic, or in the still waters\nof our inland lakes, were in full activity. At length the dry land\nappears; and--mystery of mysteries--it soon becomes teeming with life\nin all the forms of vegetable and animal beauty, under the aspect of\nthe beams of a glorious sun.\n\nGeology teaches us to regard our position upon the earth as one far\nin advance of all former creations. It bids us look back through\nthe enormous vista of time, and see, shining still in the remotest\ndistance, the light which exposes to our vision many of nature\u2019s holy\nwonders. The elements which now make up this strangely beautiful fabric\nof muscle, nerves, and bone, have passed through many ordeals, ere yet\nit became fashioned to hold the human soul. No grain of matter has been\nadded to the planet, since it was weighed in a balance, and poised with\nother worlds. No grain of matter can be removed from it. But in virtue\nof those forces which seem to originate in the sun, \u201cthe soul of the\ngreat earth,\u201d a succession of new forms has been produced, as the old\nthings have passed away.\n\nUnder the forces we have been considering, acting as so many contending\narmies, matter passes from one condition to another, and what is now\na living and a breathing creature, or a delicate and sweetly-scented\nflower, has been a portion of the amorphous mass which once lay in the\ndarkness of the deep ocean, and it will again, in the progress of time,\npass into that condition where no evidences of organization can be\nfound,--again, perhaps, to arise clothed with more exalted powers than\neven man enjoys.\n\nWhen man places himself in contrast with the Intelligences beyond him,\nhe feels his weakness; and the extent of power which he can discover at\nwork, guided by a mysterious law, is such, that he is dwarfed by its\nimmensity. But looking on the past, surveying the progress of matter\nthrough the inorganic forms up to the higher organizations, until at\nlength man stands revealed as the chief figure in the foreground of the\npicture, the monarch of a world on which such elaborate care has been\nbestowed, and the absolute ruler of all things around him, he rises\nlike a giant in the conscious strength of his far-searching mind. That\nso great, so noble a being, should suffer himself to be degraded by the\nsensualities of life to a level with the creeping things, upon which he\nhas the power to tread, is a lamentable spectacle, over which angels\nmust weep.\n\nThe curious connection between the superstitions of races, the\ntraditionary tales of remote tribes, and the developments of the truths\nof science, are often of a very marked character, and they cannot but\nbe regarded as instructive. In the wonders of \u201colden time\u201d fiction has\never delighted; and a thousand pictures have been produced of a period\nwhen beings lived and breathed upon the earth which have no existence\nnow.\n\nHydras, harpies, and sea-monsters, figure in the myths of antiquity.\nIn the mythology of the northern races of Europe we have fiery flying\ndragons, and Poetry has placed these as the guardians of the \u201choarded\nspirit\u201d and protectors of the enchanted gold.\n\nThrough the whole of the romance period of European literature,\nnothing figures but serpents, \u201cwhite and red,\u201d toiling and fighting\nunderground,--thus producing earthquakes, as in the story of Merlin\nand the building of Stonehenge. Flying monsters, griffins and others,\nwhich now live only in the meaningless embellishments of heraldry,\nappear to have been conceived by the earlier races of men as the\nrepresentatives of power. Curious is it, too, to find the same class\nof ideas prevailing in the East. The monster dragons of the Chinese,\nblazoned on their standards and ornamenting their temples;--the\nBuddaical superstition that the world is supported on a vast elephant,\nwhich stands on the back of a tortoise, which again rests on a serpent,\nwhose movements produce earthquakes and violent convulsions;--the rude\ndecorations also of the temples of the Aztecs, which have been so\nrecently restored to our knowledge by the adventurous travellers of\nCentral America,--all give expression to the same mythological idea.\n\nDo not these indicate a faint and shadowy knowledge of a previous\nstate of organic existence? The process of communion between man of\nthe present, and the creations of a former world, we know not; it is\nmysterious, and for ever lost to us. But even the most ignorant and\nuncultivated races of mankind have figured for themselves the images\nof creatures which, whilst they do really bear some resemblance to\nthings which have for ever passed away, do not, in the remotest degree,\npartake of any of the peculiarities of existing creations.\n\nThe ichthyosaurus, and the plesiosaurus, and the pterodactylus, are\npreserved in the rude images of harpies, of dragons, and of griffins;\nand, although the idea of an elephant standing on the back of a\ntortoise was often laughed at as an absurdity, Captain Cautley and\nDr. Falconer at length discovered in the hills of Asia the remains of\na tortoise in a fossil state of such a size that an elephant could\neasily have performed the feat.[247]\n\nOf the ammonites, we have more exact evidence; they were observed by\nour forefathers, and called by them snake-stones. According to the\nlegends of Catholic saints they were considered as possessing a sacred\ncharacter:--\n\n    \u201cOf these and snakes, each one\n    Was changed into a coil of stone\n    When holy Hilda prayed.\u201d\n\nAnd in addition to this petrifying process, one of decapitation is said\nto have been effected; hence the reason why these _snake-stones_ have\nno heads.\n\nWe also find, in the northern districts of our island, that the name of\n\u201cSt. Cuthbert\u2019s beads\u201d is applied to the fossil remains of encrinites.\n\nThus we learn that, to a great extent, fiction is dependent upon\ntruth for its creations; and we see that when we come to investigate\nany wide-spread popular superstition, although much distorted by the\nmedium of error through which it has passed, it is frequently founded\nupon some fragmentary truth. There are floating in the minds of men\ncertain ideas which are not the result of any associations drawn from\nthings around; we reckon them amongst the mysteries of our being. May\nthey not be the truths of a former world, of which we receive the dim\noutshadowing in the present, like the faint lights of a distant Pharos,\nseen through the mists of the wide ocean?\n\nMan treads upon the wreck of antiquity. In times which are so long\npast, that the years between them cannot be numbered by the aids of\nour science, geology teaches us that forms of life existed perfectly\nfitted for the conditions of the period. These performed their offices\nin the great work; they passed away, and others succeeded to carry\non the process of building a world for man. The past preaches to\nthe present, and from its marvellous discourses we venture to infer\nsomething of the yet unveiled future. The forces which have worked\nstill labour: the phenomena which they have produced will be repeated.\n\n    Ages on ages slowly pass away,\n    And nature marks their progress by decay.\n    The plant which decks the mountain with its bloom,\n    Finds in the earth, ere long, a damp dark tomb:\n    And man, earth\u2019s monarch, howe\u2019er great and brave--\n    Toils on--to find at last a silent grave.\n    The chosen labours of his teeming mind\n    Fade by the light, and crumble \u2019neath the wind;\n    And e\u2019en the hills, whose tops appear to shroud\n    Their granite peaks deep in the vapoury cloud,\n    Worn by tempests--wasted by the rains,\n    Sink slowly down to fill wide ocean\u2019s plains.\n    The ocean\u2019s breast new lands again display,\n    And life and beauty drink the light of day:\n    The powers which work at great creation\u2019s wheel,\n    Will from the wrecks of matter still reveal\n    New forms of wondrous beauty--which will rise\n    Pure as the flame of love\u2019s young sacrifice,\n    Beaming with all the pristine hues of youth,\n    Robed by the day, and crowned by holy truth.\n\n\nFOOTNOTES:\n\n[231] _Preliminary Discourse_; Sir J. F. W. Herschel. Lardner\u2019s Cabinet\nCyclop\u00e6dia.\n\n[232] _Geological Researches_; by Sir Henry De la Beche, C.B.\n(_Degradation of Mountains_, p. 167.) _Geological Manual_, p. 184.\n_Principles of Geology_; by Sir Charles Lyell, 7th Edition, p. 150,\n686. _On the Denudation of South Wales, and the adjacent countries of\nEngland_; by Professor Andrew Ramsay; Memoirs of the Geological Survey\nand Museum of Practical Geology, vol. i. p. 297.\n\n[233] Fownes, _On the Existence of Phosphoric Acid in Rocks of Igneous\nOrigin_; Phil. Trans. 1844, p. 53. Nesbitt, _Quarterly Journal of the\nChemical Society_.\n\n[234] _On the Vegetation of the Carboniferous Period as compared\nwith that of the present day; On some peculiarities in the structure\nof Stigmaria; Remarks on the Structure and Affinities of some\nLepidostrobi_: by Dr. Hooker; Memoirs of the Geological Survey, &c.,\nvol. ii. pp. 387, 431, 440.\n\n[235] See Owen, Quarterly Journal of the Geological Society, No. 6,\np. 96. Dr. Buckland, Geological Transactions, vol. iii. p. 220. _The\nWonders of Geology_: by Dr. Mantell, vol. ii. p. 493.\n\n[236] _Report on British Fossil Mammalia_: by Richard Owen, Esq.,\nF.R.S.; British Association Reports, vols. xi. xii.\n\n[237] _Notice on the Iguanodon, a newly discovered fossil reptile from\nthe sandstone of Tilgate Forest, in Sussex_: by Gideon Mantell, Esq,\nF.R.S., &c.; Philosophical Transactions, vol. cxv. p. 179. _On the\nStructure of Teeth, &c._; by Professor Owen.\n\n[238] Dr. Mantell, _Wonders of Geology_. _Geology of the South-east of\nEngland._\n\n[239] _Geological Researches_; _Geological Manual_; by Sir Henry Thos.\nDe la Beche, C.B., &c.\n\n[240] Ibid.\n\n[241] _Experimental Researches on the production of Silicon from\nParacyanogen_: by Samuel Brown, M.D.; Transactions of the Royal Society\nof Edinburgh, vol. xv. p. 229. _Experiments on the alleged conversion\nof Carbon into Silicon_: by R. H. Brett, Ph.D., and J. Denham Smith,\nEsq.; Philosophical Magazine, vol. xix. p. 295, New Series. See also\nDr. Brown\u2019s reply to the above, ibid, p. 388.\n\n[242] _Geology, Introductory, Descriptive, and Practical_: by Prof.\nAnsted, vol. ii. p. 22.\n\n[243] _The Wonders of Geology_: by Dr. Mantell, vol. i. p. 162.\n_Bridgewater Treatise_: by Dr. Buckland. Dr. J. J. Kemp, and Dr. A.\nV. Klipstein, _On the Dinotherium_; Darmstadt, 1836. Cuvier and De\nBlainville have also carefully described the fossil remains of this\nanimal.\n\n[244] See Professor Ramsay\u2019s memoir _On Denudation_: Memoirs of the\nGeological Survey of Great Britain.\n\n[245] \u201cThe distances to which river water, more or less charged with\ndetritus, would flow over sea-water, will depend upon a variety\nof obvious circumstances. Captain Sabine found discoloured water,\nsupposed to be that of the Amazons, three hundred miles distant in\nthe ocean from the embouchure of that river. It was about 126 feet\ndeep. Its specific gravity was = 1\u00b70204, and the specific gravity of\nthe sea-water = 1\u00b70262. This appears to be the greatest distance from\nland at which river water has been detected on the surface of the\nocean. If rivers, containing mechanically suspended detritus, flowed\nover sea-water in lines which, in general terms, might be called\nstraight, the deposit of transported matter which they carried out\nwould also be in straight lines. If, however, they be turned aside\nby an ocean current, as was the case with that observed by Captain\nSabine, the detritus would be thrown, and cover an area corresponding\nin a great degree with the sweep which the river has been compelled\nto make out of the course, that its impulse, when discharged from its\nembouchure, might lead it to take: supposing the velocity with which\nthis river-water was moving has been correctly estimated at about\nthree miles per hour, it is not a little curious to consider that the\nagitation and resistance of its particles should be sufficient to keep\nfinely comminuted solid matter mechanically suspended, so that it\nwould not be disposed freely to part with it, except at its junction\nwith the sea-water over which it flows, and where, from friction, it\nis sufficiently retarded. So that a river, if it can preserve a given\namount of velocity flowing over the sea, may deposit no very large\namount of mechanically suspended detritus in its course from the\nembouchure, where it is ultimately stopped. Still, however, though the\ndeposit may not be so abundant as at first sight would appear probable,\nthe constant accumulation of matter, however inconsiderable at any\ngiven time, must produce an appreciable effect during the lapse of\nages.\u201d--Sir Henry De la Beche\u2019s _Geological Researches_, p. 72.\n\n[246] Sir J. F. W. Herschel: _Preliminary Treatise_.\n\n[247] _Fauna Antiqua Sivalensis. Being the Fossil Zoology of the\nSewalik Hills in the North of India_: by Hugh Falconer and Proby T.\nCautley. 1844.\n\n\n\n\nCHAPTER XIV.\n\nPHENOMENA OF VEGETABLE LIFE.\n\n  Psychology of Flowers--Progress of Matter towards\n    Organization--Vital Force--Spontaneous Generation--The Vegetable\n    Cell--Simplest Development of Organization--The Crystal and\n    the Cell--Primitive Germ--Progress of Vegetation--Influence\n    of Light--Morphology--Germination--Production of Woody\n    Fibre--Leaves--Chlorophylle--Decomposition of Carbonic\n    Acid--Influence of Light, Heat, and Actinism on the Phenomena of\n    Vegetable Life--Flowers and Fruits--Etiolation--Changes in the\n    Sun\u2019s Rays with the Seasons--Distribution of Plants--Electrical and\n    Combined Physical Powers\n\n\nThe variety of beautiful forms which cover the surface of this sphere,\nserve, beyond the physical purposes to which we have already alluded,\nto influence the mind, and give character to the inhabitants of every\nlocality. There are men who appear to be dead to the mild influences\nof flowers; but these sweet blossoms--the stars of our earth--exert a\npower as diffusive as their pervading odours.\n\nThe poet tells us of a man to whom\n\n    The primrose on the river\u2019s brim\n    A yellow primrose was to him,\n    And it was nothing more.\n\nBut it was something more. He, perhaps, attended not to the eloquent\nteaching of its pure, pale leaves: he might not have been conscious\nof the mysterious singing of that lowly flower: he might, perchance,\nhave crushed it beneath his rude foot rather than quaff the draught of\nwisdom which it secreted in its cell; but the flower still ministered\nto that mere sensualist, and in its strange, tongueless manner,\nreproved his passions, and kept him \u201ca wiser and a better man,\u201c than if\nit had pleased God to have left the world without the lovely primrose.\n\nThe psychology of flowers has found many students--than whom not one\nread them more deeply than that mild spirit who sang of the Sensitive\nPlant, and in wondrous music foreshadowed his own melancholy fate.[248]\nThat martyr to sensibility, Keats, who longed to feel the flowers\ngrowing above him, drew the strong inspiration of his volant muse from\nthose delicate creations which exhibit the passage of inorganic matter\ninto life; and other poets will have their sensibilities awakened by\nthe \u00e6sthetics of flowers, and find a mirror of truth in the crystal\ndew-drop which clings so lovingly to the purple violet, and draws fresh\nbeauties from its coloured petals.\n\nIf we examine carefully all the conditions of matter which we have\nmade the subject of our studies, we cannot but perceive how gradual\nis the progress of the involved action of the physical forces, as we\nadvance from the molecule--the mere particle of matter--up to the\norganic combination. At first we detect only the action of cohesion in\nforming the rude mass; then we have the influence of the crystallogenic\npowers giving a remarkable regularity to bodies; we next discover the\ninfluences of heat and electrical force in determining condition, and\nof chemical action as controlled by them. Yet, still we have a body\nwithout organization. Light exerts its mysterious powers, and the same\nelements assume an organized form; and, in addition to the recognized\nagencies, we dimly perceive others on which vitality evidently\ndepends. These empyreal influences become more and more complicated\nto us: ascending in the scale, they rise beyond our science; and, at\nlength, we find them guiding the power of intelligence, while instinct\nand reason are exhibited in immediate dependence upon them.\n\nLet it not be imagined that this view has any tendency to materialism.\nThe vital energy is regarded as a spiritualization, and reason as a\ndivine emanation; but they are connected with materialities, on which\nthey act, and by which they are themselves controlled. The organic\ncombinations, and the physical powers by which these unions of matter\nare effected and retained, have a direct action over that ethereality\nwhich is life, and the powers of life again control these more material\nforces. The spirit, in whatever state, when connected with matter, is,\nlike Prometheus chained to his rock, in a constant struggle to escape\nfrom its shackles, and assert the full power of its divine strength.\n\nWe have seen variety enough in the substances which make up the\ninorganic part of creation; but infinitely more varied are the forms\nof organization. In the vegetable world which is immediately around\nus, from the green slime of our marshes to the lustrous flowers of our\ngardens and the lordly trees of our forests, what an extraordinary\ndiversity of form is apparent! From the infusoria of an hour, to the\ngigantic elephant roaming in his greatness in the forests of Siam--the\nnoble lion of the caves of Senegal--the mighty condor of the Andes--and\nonward to man, the monarch of them all, how vast are the differences,\nand yet how complete are they in their respective conditions! In the\ncreation we have examined, we have had conclusive evidence, that from\nthe combination of _atoms_ every peculiar form has been produced. In\nthe creation we are about to examine, we shall discover that all the\nimmense diversity of form, of colour, and condition which is spread\nover the world in the vegetable and animal kingdoms, results from the\ncombination of _cells_. The atom of inorganic nature becomes a cell in\norganic creation. This cell must be regarded as the compound radical of\nthe chemist, and by decomposing it, we destroy the essential element of\norganization.\n\nWith the mysterious process by which the atom is converted into a\ncell, or a compound radical, we are unacquainted; but we must regard\nthe cell as the organic atom. It is in vain that the chemist or the\nphysiologist attempts to examine this change of the inorganic elements\nto an organized state; it is one of the mysteries of creation, which is\nto be, in all probability, hid from our eyes, until this \u201cmortal coil\u201d\nis shaken off, and we enjoy the full powers of that intelligence which\nwe are promised we shall enjoy in an immortal state.\n\nAgain and again has the attention of men been attracted to the\n_generatio \u00e6quivoca_; they have sometimes thought they have discovered\na _generatio primitiva_ or _spontanea_; but a more careful examination\nof these organisms has shown that an embryo existed--a real germination\nhas taken place.\n\nCount Rumford[249] stated that threads of silk and wool had the power\nof decomposing carbonic acid in water in the sunshine; and hence some\nhave referred organization to a mere chemical change produced by\nluminous excitation; and we have heard of animal life resulting from\npounded siliceous matter. All such statements must be regarded as\nevidences of imperfect investigation.\n\nDr. Carus, alluding to the experiments of Gruithuisen, Priestley, and\nIngenhousz,[250] says:--\u201cThese show, more than any other experiments,\nthat, in the purest water, under the influence of air, light, and heat,\nbeings are formed, which, oscillating as it were between the animal\nand the plant, exhibit the primitive germs of both kingdoms.\u201d[251]\nTreviranus[252] repeated, and appeared to confirm these results; but in\nthese experiments we have no evidence that the germ did not previously\nexist in the spring-water which was employed.\n\nSome have regarded the cell as a crystal; they see the crystal forming,\nby the accumulation of atoms, into a fixed form, under the influence\nof an \u201cinner life;\u201d and, advancing but a step, they regard the cell as\nthe result of an increased exercise of the physical influences.[253]\nWe have referred crystalline form to certain magnetic conditions; and\nit is evident that the atomic cell is influenced by similar forces;\nbut if we place a crystal in its natural fluid, though it increases in\nsize, it never alters in form: whereas, if we examine a cell in its\nnatural position, it gives indications of motion, it produces other\ncells, and we have a development of organs which are in no respect\nthe same in form as the original. From a vesicle floating invisible\nto the unaided human sense in its womb of fluid, is produced a plant\npossessing strange powers, or an animal gifted with volition. The idea,\nthat two kinds of polarity--light on one side, and gravitation on the\nother--produce the two peculiar developments of roots and branches, can\nonly be regarded as one of those fanciful analogies which prove more\nimagination than philosophy.[254]\n\nThe conditions are, however, most curious; they deserve very attentive\nstudy; but in examining the phenomena, the safest course is to allow\nthe effects as they arise to interpret to us, and not admit the love\nof hypothesis to lead us into bewildering analogies; or uncertain\nphenomena to betray us to hasty inferences. It is of this evil that\nBacon speaks, in his \u201cAdvancement of Learning.\u201d He says:--\n\n\u201cThe root of this error, as of all others, is this, that men, in\ntheir contemplations of nature, are accustomed to make too timely a\ndeparture, and too remote a recess from experience and particulars, and\nhave yielded and resigned themselves over to the fumes of their own\nfancies and popular argumentations.\u201d\n\nWithout venturing, therefore, to speculate on the origin of the\nprimitive cell, or unit of organic life, which involves the problem\nof the metamorphosis of a rude mass--the primitive transformation\nof the rudimentary atoms into organic form,--we must admit that the\nhighly organized plant or animal is but an aggregation of cells; their\narrangement being dependent upon certain properties peculiar to them,\nand the exercise of forces such as we have been studying,--all of which\nappear to act externally to the plant or animal itself.\n\nExperiments have been brought forward, in which it appeared that, after\nall organization which could by any possibility have existed, had\nbeen destroyed by the action of fire, solutions of flint and metallic\nsalts, have, under the influence of electric currents, exhibited\nsigns of organic formations, and that, indeed, insects--a species\nof acari--have been developed in them. The experiments were said to\nhave been made with care, and many precautions taken to shut out\nall chances of any error, but not all the precautions required in a\nmatter of such exceeding delicacy; and we are bound not to receive the\nevidence afforded as the true expression of a fact without much further\ninvestigation. All experience,--setting aside the experiment named,--is\nagainst the supposition that pounded or dissolved flint could by any\nartificial means be awakened into life. Ova may have been conveyed\ninto the vessels which contained the solutions under experiment; and\nin due time, although possibly quickened by electric excitation, the\nanimals--the most common of insects--came into existence.[255]\n\nThe rapid growth of conferv\u00e6 upon water has often been brought forward\nas evidence of a spontaneous generation, or the conversion of inorganic\nelements into organic forms; but it has been most satisfactorily proved\nthat the germ must be present, otherwise no evidence of anything\nlike organization will be developed. All the conditions required for\nthe production of vegetable life appear to show, that it is quite\nimpossible for any kind of plant, even the very lowest in the scale, to\nbe formed in any other way than from an embryo in which are contained\nthe elements necessary for it, and the arrangements required for the\nvarious processes which are connected with its vitality.\n\nThe earth is now covered with vegetable life, but there must have\nexisted a time when \u201cdarkness was upon the face of the deep,\u201d and\norganization had not yet commenced tracing its lovely net-work of cells\nupon the bare surface of the ocean-buried rock. At length the mystery\nof organic creation began: into this science dares not penetrate, but\nit is privileged to begin its search a little beyond this point, and\nwe are enabled to trace the progress of organic development through a\nchain of interesting results which are constantly recurring.\n\nIf we take some water, rising from a subterranean spring, and expose\nit to sunshine, we shall see, after a few days, a curious formation\nof bubbles, and the gradual accumulation of green matter. At first we\ncannot detect any marks of organization--it appears a slimy cloud of\nan irregular and undetermined form. It slowly aggregates, and forms a\nsort of mat over the surface, which at the same time assumes a darker\ngreen colour. Careful examination will now show the original corpuscles\ninvolved in a net-work formed by slender threads, which are tubes of\ncirculation, and may be traced from small points which we must regard\nas the compound atom, the vegetable unit. We must not forget, here,\nthat we have to deal with four chemical elements,--oxygen, hydrogen,\ncarbon, and nitrogen, which compose the world of organized forms, and\nthat the water affords us the two first as its constituents, gives us\ncarbon in the form of carbonic acid dissolved in it, and that nitrogen\nis in the air surrounding it, and frequently mixed with it also.\n\nUnder the influence of sunshine, we have now seen these elements\nuniting into a mysterious bond, and the result is the formation of a\ncellular tissue, which possesses many of the functions of the noblest\nspecimens of vegetable growth. But let us examine the progress. The\nbare surface of a rock rises above the waters covered over with this\ngreen slime, a mere veil of delicate net-work, which, drying off,\nleaves no perceptible trace behind it; but the basis of a mighty growth\nis there, and under solar influence, in the process of time, other\nchanges occur.\n\nAfter a period, if we examine the rock, we shall find upon its face\nlittle coloured cups or lines with small hard discs. These, at first\nsight, would not be taken for plants, but on close examination they\nwill be found to be lichens. These minute vegetables shed their seed\nand die, and from their own remains a more numerous crop springs into\nlife. After a few of these changes, a sufficient depth of soil is\nformed, upon which mosses begin to develope themselves, and give to\nthe stone a second time a faint tint of green, a mere film still, but\nindicating the presence of a beautiful class of plants, which, under\nthe microscope, exhibit in their leaves and flowers many points of\nsingular elegance. These mosses, like the lichens, decaying, increase\nthe film of soil, and others of a larger growth supply their places,\nand run themselves the same round of growth and decay. By and by,\nfunguses of various kinds mingle their little globes and umbrella-like\nforms. Season after season plants, perish and add to the soil, which is\nat the same time increased in depth by the disintegration of the rock\nover which it is laid, the cohesion of particles being broken up by the\noperations of vegetable life. The minute seeds of the ferns floating on\nthe breeze, now find a sufficient depth of earth for germination, and\ntheir beautiful fronds, eventually, wave in loveliness to the passing\nwinds.\n\nVegetable forms of a higher and a higher order gradually succeed each\nother, each series perishing in due season, and giving to the soil\nadditional elements for the growth of plants of their own species or\nthose of others. Flowering herbs find a genial home on the once bare\nrock; and the primrose pale, the purple foxglove, or the gaudy poppy,\nopen their flowers to the joy of light. The shrub, with its hardy roots\ninterlaced through the soil, and binding the very stones, grows rich\nin its bright greenery. Eventually the tree springs from the soil,\nand where once the tempest beat on the bare cold rock, is now the\nlordly and branching monarch of the forest, with its thousand leaves,\naffording shelter from the storm for bird and beast.\n\nSuch are the conditions which prevail throughout nature in the progress\nof vegetable growth; the green matter gathering on a pond, the mildew\naccumulating on a shaded wall, being the commencement of a process\nwhich is to end in the development of the giant trees of the forest,\nand the beautifully tinted flower of nature\u2019s most chosen spot.\n\nWe must now consider closely the phenomena connected with the growth of\nan individual plant, which will illustrate the operation of physical\ninfluences throughout the vegetable world. The process by which the\nembryo, secured in the seed, is developed, is our first inquiry.\n\nA seed is a highly carbonized body, consisting of integuments and\nembryo: between these, in most seeds, lies a substance called the\n_albumen_, or _perisperm_. The embryo contains the elements of the\nfuture plant--the cotyledons, the plumule, and the radicle; the\nformer developing into stalk and leaves, the latter into roots. This\nembryo hides the living principle, for the development of which it\nis necessary that the starch and gluten undergo a chemical change,\nand that an elevation of temperature is produced. The vital power\nis dormant--it sleeps--in the seed until the proper conditions are\nproduced. It has been proved, that the powers of maintaining life\nin the seed are very great; excessive cold, sufficiently intense to\nfreeze mercury, will not kill seed, and they resist a comparatively\nhigh temperature. It is probable that heat only destroys seeds by\ndrying them too completely. The temperature at which seeds germinate is\nexceedingly varied,--those belonging to our own clime will germinate\nwhen the thermometer rises above 40\u00b0 F., but the seeds of tropical\nplants demand that a temperature of from 70\u00b0 to 84\u00b0, or even to 90\u00b0,\nbe steadily applied to them. In some cases it has been found that\neven boiling the seeds has been advantageous to the future process of\ngermination in the soil. But let us take the seed of some ordinary\nplant, and trace its progress.\n\nAn apparently dead grain is placed in the soil. If the temperature is a\nfew degrees above the freezing point, and the soil holds a due quantity\nof water, the integument of the seed imbibes moisture and swells; the\ntissue is softened, and the first effort of vital force begins. The\nseed has now the power of decomposing water, the oxygen combines with\nsome of the carbon of the seed, and is expelled as carbonic acid.\nSaussure\u2019s experiments prove this. The air above the soil in which\na horse-bean was placed to germinate, gave, before the experiment,\nnitrogen 210\u00b726, and oxygen 56\u00b729, and after germination, nitrogen\n209\u00b741, oxygen 44\u00b738, and carbonic acid 11\u00b727. This part of the process\nis but little removed from the merely chemical changes which we have\nalready considered. We find the starch of the seed changed into gum and\nsugar, which affords nutritive food for the developing embryo. The seed\nnow lengthens downwards by the radicle, and upwards by the cotyledons,\nwhich, as they rise above the earth, acquire a green colour. Here the\nfirst stage of vegetable life ends, the chemically exciting process is\nat an end, and a new stimulus is required to continue in full activity\nthe vital powers. Carbonic acid is no longer given off.\n\nThe cotyledons, which are two opposite roundish leaves, act as the\nlungs; by them carbonic acid taken from the atmosphere is absorbed\nand carried by a circulating process, now in full activity, through\nthe young plant. The carbonic acid, a compound of carbon and oxygen,\nis decomposed; it is deprived of its carbon, which is retained by the\nplant, and oxygen is exhaled. The plant at this period is little more\nthan an arrangement of cellular tissue, a very slight development\nof vascular and fibrous tissue appearing as a cylinder lying in the\ncentre of the sheath. At this point, however, we begin more distinctly\nto trace the operations of the new power; the impulses of life are\nstrikingly evident.\n\nThe young root is now lengthening, and absorbing from the moisture in\nthe soil, which always contains some soluble salts, a portion of its\nnutriment, which is impelled upwards by a force--probably capillary\nattraction and endosmose action combined--to the point from which the\nplumule springs. Capillary force raises the fluids through the tubes\nin the stalk, and conveys them to the veins in the leaves, while\nthe endosmose force diffuses them through the vegetable tissues.\nThe plumule first ascends as a little twig, and, at the same time,\nby exerting a more energetic action on the carbonic acid than the\ncotyledons have done, the carbon retained by them being only so much\nas is necessary to form chlorophylle, or the green colouring matter of\nleaves, some wood is deposited in the centre of the radicle. From this\ntime the process of lignification goes on through all the fabric,--the\nincrease, and indeed the life, of the plant depending upon the\ndevelopment of a true leaf from the plumule.\n\nIt must not be imagined that the process consists, in the first place,\nof a mere oxidation of the carbon in the seed,--a slow combustion by\nwhich the spark of life is to be kindled;--the hydrogen of the water\nplays an important part, and, combining also with the carbon, forms\nnecessary compounds, and by a secondary process gives rise again to\nwater by combination with oxygen in the cells of the germinating grain.\nNor must we regard the second class of phenomena as mere mechanical\nprocesses for decomposing carbonic acid, but the result of the combined\ninfluences of all the physical powers and life superadded.\n\nThis elongating little twig, the plumule, at length unfolds itself, and\nthe branch is metamorphosed into a leaf. The leaf a\u00ebrates the sap it\nreceives, effects the decomposition of the carbonic acid, the water,\nand in all probability the ammonia which it derives from the air,\nand thus returns to the pores, which communicate with the pneumatic\narrangements of the plant, the necessary secretions for the formation\nof bark, wood, and the various proximate principles which it contains.\n\nAfter the first formation of a leaf, others successively appear, all\nconstructed alike, and performing similar functions. The leaf is the\nprincipal organ to the tree; and, indeed, Linn\u00e6us divined, and Goethe\ndemonstrated, the beautiful fact, that the tree was developed from this\ncuriously-formed organ.\n\n\u201cKeeping in view,\u201d says the poet-philosopher, \u201cthe observations that\nhave been made, there will be no difficulty in discovering the leaf in\nthe seed-vessel, notwithstanding the variable structure of that part\nand its peculiar combinations. Thus the pod is a leaf which is folded\nup and grown together at its edges, and the capsules consist of several\nleaves grown together, and the compound fruit is composed of several\nleaves united round a common centre, their sides being opened so as to\nform a communication between them, and their edges adhering together.\nThis is obvious from capsules which, when ripe, split asunder, at which\ntime each portion is a separate pod. It is also shown by different\nspecies of one genus, in which modifications exist of the principle\non which their fruit is formed; for instance, the capsule of _nigella\norientalis_ consists of pods assembled round a centre, and partially\nunited; in _nigella damascena_ their union is complete.\u201d[256]\n\nProfessor Lindley thus explains the same view:--\u201cEvery flower, with\nits peduncle and bracteol\u00e6, being the development of a flower-bud, and\nflower-buds being altogether analogous to leaf-buds, it follows as a\ncorollary that every flower, with its peduncle and bracteol\u00e6, is a\nmetamorphosed branch.\n\n\u201cAnd, further, the flowers being abortive branches, whatever the laws\nare of the arrangement of branches with respect to each other, the same\nwill be the laws of the flowers with respect to each other.\n\n\u201cIn consequence of a flower and its peduncle being a branch in a\nparticular state, the rudimentary or metamorphosed leaves which\nconstitute bracte\u00e6, floral envelopes, and sexes, are subject to exactly\nthe same laws of arrangement as regularly-formed leaves.\u201d[257]\n\nThe idea that the leaf is the principal organ of the plant, and that\nfrom it all the other organs are probably developed, is worthy the\ngenius of the great German poet.\n\nEvery leaf, a mystery in itself, is an individual gifted with peculiar\npowers; they congregate in families, and each one ministers to the\nformation of the branch on\n\nwhich it hangs, and to the main trunk of the tree of which it is a\nmember. The tree represents a world, every part exhibiting a mutual\ndependence.\n\n    \u201cThe one red leaf, the last of its clan,\n    That dances as often as dance it can;\n    Hanging so light and hanging so high,\n    On the topmost twig that looks up at the sky,\u201d\n\nis influenced by, and influences, the lowest root which pierces\nthe humid soil. Like whispering voices, the trembling leaves sing\nrejoicingly in the breeze and summer sunshine, and they tremble alike\nwith agony when the equinoctial gale rends them from the parent stalk.\nThe influences which pervade the whole, making up the sum of vital\nforce, are disturbed by every movement throughout the system; a wound\non a leaf is known to disturb the whole, and an injury inflicted on the\ntrunk interferes with the processes which are the functions of every\nindividual leaf.[258]\n\nThe consideration of the physical circumstances necessary to\ngermination and vegetable growth, brings us acquainted with many\nremarkable facts. At a temperature below the freezing point, seeds will\nnot germinate; at the boiling point of water, a chemical change is\nproduced in the grain, and its power of germinating is destroyed. Heat,\ntherefore, is necessary to the development of the embryo, but its power\nmust only be exerted within certain prescribed limits: these limits are\nonly constant for the same class of seeds, they vary with almost every\nplant. This is apparent to every one, in the different periods required\nfor germination by the seeds of dissimilar vegetables.\n\nThe seed is placed in the soil; shade is always--absolute darkness\nsometimes--necessary for the success of the germinating process. We\nhave seen that the first operation of nature is purely a chemical one,\nbut this manifestation of affinity is due to an exertion of force,\nwhich is directly dependent upon solar power. The seed is buried in the\nsoil, when the genial showers of spring, and the increasing temperature\nof the earth, furnish the required conditions for this chemistry of\nlife, and the plant eventually springs into sunshine. Thus we obtain\nevidence that even through some depth of soil the solar power, whatever\nit may be, is efficient, and that under its excitement the first spring\nof life, in the germ, is effected.\n\nThe cotyledons and the plumule being formed, the plant undergoes a\nremarkable change. The seed, like an animal, absorbed oxygen and\nexhaled carbonic acid; the first leaves secrete carbon from carbonic\nacid inspired, and send forth, as useless to the plant, an excess of\noxygen gas.\n\nThis power of decomposing carbonic acid is a vital function which\nbelongs to the leaves and bark. It has been stated, on the authority\nof Liebig, that during the night the plant acts only as a mere bundle\nof fibres,--that it allows of the circulation of carbonic acid and\nits evaporation, unchanged. In his eagerness to support his chemical\nhypothesis of respiration, the able chemist neglected to inquire\nif this was absolutely correct. The healthy plant never ceases to\ndecompose carbonic acid during one moment of its existence; but during\nthe night, when the excitement of light is removed, and the plant\nreposes, its vital powers are at their minimum of action, and a much\nless quantity is decomposed than when a stimulating sun, by the action\nof its rays, is compelling the exertion of every vital function.\n\nDuring this process, we have another example of natural organic\nchemistry. The four inorganic elements of which the vegetable kingdom\nis composed--oxygen, hydrogen, nitrogen, and carbon--are absorbed as\nair or moisture by the leaves and through the roots, and the great\nphenomenon of vegetable life is the conversion of these to an organic\ncondition. Sugar and gum are constantly produced, and from these, by\ncombination with atmospheric nitrogen, a proteine compound is formed,\nwhich is an essential element in the progress of development.[259]\n\nPlants growing in the light are beautifully green, the intensity of\ncolouring increasing with the brilliancy of the light. Those which are\ngrown in the dark are etiolated, their tissues are weak and succulent,\ntheir leaves of a pale yellow. It is, therefore, evident that the\nformation of this chlorophylle--as the green colouring matter of leaves\nis called--results from some action determined by the sun\u2019s rays.\n\nChlorophylle is a carbonaceous compound formed in the leaves, serving,\nit would appear, many purposes in the process of assimilation. In the\ndark the plant still requires carbon for its further development,\nand growing slowly, it removes it from the leaves, decomposing the\nchlorophylle, and supports its weak existence by preying on parts of\nits own structure, until at length, this being exhausted, it actually\nperishes of starvation.\n\nPlants always turn towards the light: the guiding power we know not,\nbut the evidence of some impulsive or attracting force is strong; and\nthe purpose for which they are constituted to obey it, is proved to be\nthe dependence of vegetable existence upon luminous power.\n\nLight is not, however, alone sufficient to perfect the plant: another\nagent is required to aid in the production of flowers and fruits,\nand this power is proved to be heat--and heat, perhaps, in some\npeculiar condition. Having reached that point of development when\nthe reproductive functions are, by another change in the chemical\noperations going on within the vegetable structure, to be called forth,\nit has been found that the heat rays become in a remarkable manner\neffective. It has also been observed that plants bend from the red,\nor calorific rays, instead of towards them, as they are found to do\nto every other ray of the spectrum. From this we may argue that the\ninfluence of these rays is to check the vegetation, and thus to ensure\nthe perfection of the reproductive processes.\n\nIt has already been stated that we have the means of separating, to\na considerable extent, the three principles which we discover in the\nsunbeam, from each other, by the use of absorbent media.\n\nBy a peculiar yellow glass we cut off the chemical principle of the\nsunbeam, and admit the passage of the _luminous rays_ only--LIGHT.\n\nBy a cobalt blue glass we obstruct the _light_, but allow the chemical\nagent to pass through freely, without, indeed, any loss--ACTINISM.\n\nBy a glass coloured deep blood-red by oxide of gold we obstruct\nthe chemical principle and much of the light, but such a medium is\nperfectly transparent to HEAT.\n\nTherefore, this gives us the means of experimenting with either of\nthese principles, and of examining the parts which they respectively\nplay in the work of organization.\n\nSome seeds being placed in the soil, in every respect in their natural\nconditions, duly supplied with moisture, and a uniform and proper\ntemperature maintained, we place above the soil the three media\nabove named, and allow one portion to be exposed to all the ordinary\ninfluences of the solar rays.\n\nThe result will be, that the seeds under the blue glass will germinate\nlong before those which are exposed to the combined influences of the\nsunshine: a few of the seeds will struggle into day under the red\nglass, but the process of germination is entirely checked under the\nyellow glass. Here we see that the chemical radiations have quickened\nthe chemical changes, and accelerated the process, under the red glass,\nthrough which rays having some peculiar chemical action pass; the\ngerminating process, though checked, is not entirely stopped. Whereas,\nit would appear that under the influences of light which has been\ndeprived of chemical power, this conversion of the starch into gum and\nsugar, which appears to be necessary, is entirely prevented.\n\nIf the experiment is continued, it will be found that under the\nblue glass the plants grow rapidly, but weakly; and that instead of\nproducing leaves and wood they consist chiefly of stalk, upon which\nwill be seen here and there some abortive attempts to form leaves.\nWhen the process of germination has terminated, if the young plant is\nbrought under the yellow glass, it grows most healthfully, and forms an\nabundance of wood, the leaves having an unusually dark green colour,\nfrom the formation of a large quantity of chlorophylle. Plants do not,\nhowever, produce flowers with readiness under this medium; but if, at\nthe proper period, they are brought under the red glass, the flowering\nand fruiting processes are most effectively completed.[260]\n\nThese experiments, simple as they are, prove to us the importance of\nlight: the _luminous principle_ of the sunbeam is exciting the vital\npowers of the plant to decompose carbonic acid and form wood; and the\ncalorific agent, possibly under those modifications which have already\nbeen noticed as belonging to the parathermic rays, is essential to the\nproduction of flower and fruit.\n\nObservations, which have been extended over many years, prove that\nwith the seasons these solar powers are, relatively to each other,\nsubject to an interesting change. In the spring, the actinic or\nchemical power prevails, and during this period its agency is required\nfor the vitalization of the germ. As the summer comes on, the actinic\nrays diminish, and those of light increase. Perhaps it would be more\nstrictly correct to say that the luminous intensity being increased,\nthe chemical power was retarded; the former expression implies a\nvariation in quantity, which may not be correct. We see the necessity\nfor this, since luminous power is required for the secretion of\nthe carbon, with which the woody fibre is formed, and also for the\nelaboration of the proximate principles of the plant. Autumn, the\nseason of fruit, is characterized by an increase of the heat rays, and\na diminution of the others: this change being necessary, as science now\nteaches us, for the due production of flower and fruit.\n\nThe calorific rays of the solar beam, to which the autumnal phenomena\nof vegetation appear particularly to belong, are of a peculiar\ncharacter. They have been called, the Parathermic rays, and exhibit a\ncurious compound nature. To these rays we may refer the ripening of\nfruit and grain, and the browning of the leaf before its fall. May not\nthe rise of the sap in spring be traced to the excitement of either\nlight or actinism, and its recession, in the autumn, to that power\nfrom which the plant is found to bend, and which appears to be their\nmodified form of heat?\n\nThere can be no doubt that the varieties of climate and the\npeculiarities of countries, as it regards their animal and vegetable\nproductions, are dependent on the same causes. The distribution of\nspecies has been referred by some to specific centres of creation\naround which the plants and animals have spread, without reference to\nphysical conditions. Although centres of creation may be admitted,\nthese centres themselves have been determined by the physical\nfitness of each centre to the conditions of the creation, and in\nlike manner the migration of tribes is solely due to these physical\nforces we have been considering. In every zone we find that vegetable\norganization is peculiarly fitted for the considerations by which it\nis surrounded. Under the equator we have the spice-bearing trees, the\nnutmeg, the clove, the cinnamon, and the pepper-tree; there we have\nalso the odoriferous sandal, the ebony, the banyan, and the teak: we\nhave frankincense, and myrrh, and other incense-bearing plants; the\ncoffee-tree, the tea-plant, and the tamarind.\n\nA little further north we have the apricot, the citron, the peach,\nand the walnut. In Spain, Sicily, and Italy, we have the orange and\nlemon-tree blooming rich with perfume, and the pomegranate and the\nmyrtle growing wild upon the rocks. Beyond the Alps the vegetation\nagain changes; instead of the cypress, the chesnut, and the cork-tree,\nwhich prevail to the south of them, we have the hardier oak, the beech,\nand the elm. Still further north, we have the Scotch and spruce fir\nand larch. On the northern shores of the Baltic, and in that line of\nlatitude, the hazel alone appears; and beyond this the hoary alder,\nthe sycamore, and the mountain ash. Within the Arctic circle we find\nthe mezereum, the water-lilies, and the globe-flowers; and, when the\nweakness of the solar radiations becomes too great even for these,\nthe reindeer moss still lends an aspect of gladness to the otherwise\nsterile soil.\n\nThe cultivation of vegetables depends on the temperature of the clime.\nThe vine flourishes where the mean annual temperature ranges between\n50\u00b0 and 73\u00b0, and it is only cultivated profitably within 30\u00b0 S. and 50\u00b0\nN. of the equator. To the same limits is confined the cultivation of\nmaize and of olives. Cotton is grown profitably up to latitude 46\u00b0 in\nthe Old World, but only up to 40\u00b0 in the New. We have evidence derived\nfrom photographic phenomena, that the constitution of the solar rays\nvaries with the latitude. The effects of the sun\u2019s rays in France and\nEngland in producing chemical change are infinitely more decided than,\nwith far greater splendour of light, they are found to be in the lands\nunder or near the equator. Indeed, the remarks made on the variations\nin the character of the sunbeam with the changing seasons, may apply\nequally to the variations in latitude.\n\nFungals are among the lowest forms of vegetation, but in these we have\npeculiarities which appear to link them with the animal kingdom. Marcet\nfound that mushrooms absorbed oxygen, and disengaged carbonic acid.\nIn all probability this is only a chemical phenomenon of a precisely\nsimilar character to that which we know takes place with decaying\nwood. In the conversion of wood into _humus_, oxygen is absorbed, and\ncombining with the carbon, it is evolved as carbonic acid. Of course we\nhave the peculiar condition of vitality to modify the effect, and we\nhave, too, in this class of plants, the existence of a larger quantity\nof nitrogen than is found in any other vegetating substance.\n\nThese few sketches of remarkable phenomena connected with vegetation\nare intended to show merely the operations of the physical powers of\nthe universe, so far as we know them, upon these particular forms\nof organization. During the process of germination, electricity is,\naccording to Pouillet, evolved; and again, in ripening fruits, there\nappears to be some evidence of electrical currents. Vegetables are,\nhowever, in the growing state, such good conductors of electricity,\nthat it is not, according to the laws of this force, possible that\nthey should accumulate it; so that the luminous phenomena stated to\nhave been observed cannot be due to this agency. We know, however,\nthat under every condition of change, whether induced by chemical or\ncalorific action, electricity is set in motion; and we have reasons\nfor believing that the excitation of light will also give rise to\nelectrical circulation.\n\nThe question, whether plants possess sensation, whether they have\nany disposition of parts at all analogous to the nervous system of\nanimals, has been often put forward, but as yet the answers have been\nunsatisfactory. The point is one well worthy all the attention of\nthe vegetable physiologist; but regarding plants as the link between\nthe animal and the mineral kingdom,--looking upon phyto-chemistry,\nas exhibited by them, as the means employed to produce those more\ncomplex organizations which exist in animals,--we necessarily consider\nplants as mere natural machines for effecting organic arrangements,\nand, as such, that they cannot possess any nervous sensibility.\nMuscular contraction may be represented in many of their marvellous\narrangements; and any disturbance produced by natural or artificial\nmeans would consequently effect a change in the operations of those\nforces which combine to produce vegetable life. Indeed, the experiments\nof Carlo Matteucci, already referred to, prove that an incision across\na leaf, the fracture of a branch, or the mere bruising of any part of\nthe plant, interferes with the exercise of that power which, under the\noperation of luminous agency, decomposes carbonic acid, and effects the\nassimilation of the other elements.\n\nTo recapitulate. A plant is an organized creation; it is so in virtue\nof certain strange phyto-chemical operations, which are rendered active\nby the solar influences involved in the great phenomena of light, and\nby the excitation of caloric force mid electrical circulation. It is\na striking exemplification of the united action of certain empyreal\npowers, which give rise to the combination, of inorganic principles\nunder such forms that they become capable of obeying the mysterious\nimpulses of life.\n\nThe poet has imaged the agency of external powers in various shapes\nof spiritualized beauty. From the goddess Flora, and her attendant\nnymphs, to the romantic enchantress who called up flowers by the light\ntouch of her wand, we have, in all these creations, foreshadowings of\nthe discovery of those powers which science has shown are essential\nto vegetable life. A power from without influences the plant; but the\nanimal is dependent upon a higher agency which is potent within him.\n\nThe poet\u2019s dream pleases the imaginative mind; and, associating in our\nideas all that is graceful and loveable in the female form, with that\ndiviner feeling which impresses the soul with the sense of some unseen\nspirituality, we perceive in the goddess, the enchantress, or the\nsylph, pure idealizations of the physical powers. The spirit floating\nover these forms of beauty, and adorning them with all the richness\nof colour--painting the rose, and giving perfume to the violet--is,\nin the poet\u2019s mind, one which ascends to nearly the highest point of\netherealization, and which becomes, indeed, to him a spirit of light;\nthey ride upon the zephyrs, and they float, in all the luxury of an\nempyreal enjoyment, down to the earth upon a sunbeam. Such is the\nwork of the imagination. What is the result of the search of plodding\nscience after truth? The sunbeam has been torn into rays, and every ray\ntasked to tell of its ministry.\n\nNature has answered to some of the interrogations; and, passing over\nall the earth, echoed from plant to plant, we have one universal cry\nproclaiming that every function of vegetable life is due to the spirits\nof the sun.\n\nThe mighty Adansonia of Senegal, hoary with the mosses of five\nthousand years,--the Pohon upas in their deadly valleys,--the climbing\nlianas of the Guiana forests,--the contorted serpent-cactus on the\nburning hills,--the oaks, which spread their branches in our tempered\nclimes,--the glorious flowers of the inter-tropical regions, and\nthose which gem our virent plains,--the reindeer lichen of northern\nlands, and the conferv\u00e6 of the silent pool,--the greatest and humblest\ncreations of the vegetable world,--all proclaim their direct\ndependence upon the mysterious forces which are bound together in the\nsilver thread of Light.\n\nThese undulations, pulsations too refined for mortal ears, which\nquicken and guide these wonderful organisms, may be indeed regarded\nas sphered music for ever repeating the Divine command, \u201c_Let there\nbe Light_,\u201d by the creation of which, a dark and dreary chaos was\nmoulded into a star of beauty, capable of radiating brightness to other\nspace-wandering worlds.\n\n\nFOOTNOTES:\n\n[248] Percy Bysshe Shelley.\n\n[249] _Experiments on the production of dephlogisticated air from water\nwith various substances_: by Lieut.-General Sir Benjamin, Count of\nRumford; Phil. Trans., vol. lxxvii. p. 84.\n\n[250] _Experiments upon Vegetables, discovering their great power of\npurifying the common air in the Sunshine, and of injuring it in the\nShade and at Night; to which is joined, A new method of examining the\naccurate degrees of Salubrity of the Atmosphere_, by John Ingenhousz,\nCouncillor of the Court, and Body Physician to their Imperial and Royal\nMajesties, F.R.S., &c. London: printed for P. Elmsley, in the Strand,\nand H. Payne, Pall Mall, 1779.\n\n[251] _The Kingdoms of Nature, their life and affinity_: by Dr. C. G.\nCarus; Scientific Memoirs, vol. i. p. 223.\n\n[252] In _Biologie_, by G. R. Treviranus, vol. ii. p. 302, the\nfollowing passage occurs:--\u201cIf we expose spring water to the sun in\nopen or even closed transparent vessels, after a few days bubbles\nrise from the bottom, or from the sides of the vessel, and a green\ncrust is formed at the same time. Upon observing this crust through\na microscope, we discover a mass of green particles, generally of a\nround or oval form, very minute, and overlaid with a transparent mucous\ncovering, some of them moving freely, whilst others, perfectly similar\nto these, remain motionless and attached to the sides of the vessel.\nThis motion is sometimes greater than at others. The animalcules\nfrequently lie as if torpid, but soon recover their former activity.\u201d\n\n[253] _On the Structure of the Vegetable Cell_: by Mohl.--Scientific\nMemoirs, vol. iv. p. 113. _Outlines of Structural and Physical Botany_:\nby Henfrey.\n\n[254] Dr. Carus, in the memoir already quoted, says:--\u201cBut since, in\nthe organization of the earth, light and air, as constituting a second\nintegrant part, stand opposed to gravitation, and since the plant\nbears a relation, not only to gravitation, but to light also, when its\nformation is complete it will necessarily present a second anatomical\nsystem, namely, that of the spiral vessels, which have been very justly\nconsidered, of late, as the organs that perform in plants the functions\nof nerves.\u201d\n\n[255] Mr. Crosse\u2019s Experiments in the Journal of the London Electrical\nSociety, and Mr. Weekes in the Electrical Magazine, and a communication\nappended to _Explanations: a Sequel to the Vestiges of the Natural\nHistory of Creation_.\n\n[256] _Die Metamorphose der Pflanzen_: Goethe, sect. 78.\n\n[257] Lindley\u2019s _Elements of Botany_.\n\n[258] See the very curious experiments of C. Matteucci. Traduit et\nextrait du \u201c_Cimento_.\u201d--Archives des Sciences Physiques et Naturelles;\n_Quelques Exp\u00e9riences sur la Respiration des Plantes_. Nov. 1846.\n\n[259] Consult _Rural Economy_, by J. B. Boussingault; _The Chemical and\nPhysiological Balance of Organic Nature_, by Dumas and Boussingault;\nand _Agricultural Chemistry_, by Liebig.\n\n[260] The practical value of the discovery now described, will be best\nunderstood from the following letter from Mr. Lawson, of Edinburgh:--\n\nEdinburgh, 1, George the Fourth\u2019s Bridge, Sept. 8, 1853.\n\nMY DEAR SIR,--I am favoured with yours of the 5th, relative to my\npractical experience in the effect of the chemical agency of coloured\nmedia on the germination of seeds and the growth of plants.\n\nI must first explain that it is our practice to test the germinating\npowers of all seeds which come into our warehouses before we send\nthem out for sale; and, of course, it is an object to discover, with\nas little delay as possible, the extent that the vital principle is\nactive, as the value comes to be depreciated in the ratio it is found\nto be dormant. For instance, if we sow 100 seeds of any sort, and the\nwhole germinate, the seed will be the highest current value; but if\nonly 90 germinate, its value is 10 per cent. less; if 80, then its\nvalue falls 20 per cent.\n\nI merely give this detail to show the practical value of this test, and\nthe influence it exerts on the fluctuation of prices.\n\nOur usual plan formerly was to sow the seeds to be tested in a hot-bed\nor frame, and then watch the progress and note the results. It was\nusually from eight to fourteen days before we were in a condition to\ndecide on the commercial value of the seed under trial.\n\nMy attention was, however, directed to your excellent work, \u201cOn the\nPhysical Phenomena of Nature,\u201d about five years ago, and I resolved to\nput your theory to a practical test. I accordingly had a case made,\nthe sides of which were formed of glass coloured blue or indigo, which\ncase I attached to a small gas stove for engendering heat; in the case\nshelves were fixed in the inside, on which were placed small pots\nwherein the seeds to be tested were sown.\n\nThe results were all that could be looked for: the seeds freely\ngerminated in from two to five days only, instead of from eight to\nfourteen days as before.\n\nI have not carried our experiments beyond the germination of seeds, so\nthat I cannot afford practical information as to the effect of other\nrays on the after culture of plants.\n\nI have, however, made some trials with the yellow ray in preventing the\ngermination of seeds, which have been successful; and I have always\nfound the violet ray prejudicial to the growth of the plant after\ngermination.--I remain, my dear Sir,\n\nVery faithfully yours, CHARLES LAWSON.\n\n\n\n\nCHAPTER XV.\n\nPHENOMENA OF ANIMAL LIFE.\n\n  Distinction between the Kingdoms of Nature--Progress of Animal\n    Life--Sponges--Polypes--Infusoria--Animalcula--Phosphorescent\n    Animals--Annelidans--Myriapoda--Animal\n    Metamorphoses--Fishes--Birds--Mammalia--Nervous System--Animal\n    Electricity--Chemical Influences--Influence of Light on Animal\n    Life--Animal Heat--Mechanical Action--Nervous Excitement--Man and\n    the Animal Races, &c.\n\n\n\u201cA stone grows; plants grow and live; animals grow, live, and feel.\u201d\nSuch were the distinctions made by Linn\u00e6us, between the conditions\nof the three kingdoms of nature. We cannot, however, but regard them\nas in all respects illogical. The stone--a solid mass of unorganized\nparticles--enlarges, if placed in suitable conditions, by the accretion\nof other similar particles around it; but it does not, according to any\nmeaning in which we use the word, _grow_. Plants and animals grow; and\nthey differ, probably, only in the phenomena of sensation. Yet, the\ntrembling mimosa, and several other plants, appear to possess as much\nfeeling as sponges and some of the lower classes of animals. By this\ndefinition, however, of the celebrated Swedish naturalist, we have a\npopular and simple expression of a great fact.\n\nAs we have only to examine the question of the agency of the physical\nforces upon animal life, we must necessarily confine our attention to\nthe more striking phenomena with which science has made us acquainted;\nand, having briefly traced the apparent order in which the advance of\norganization proceeded, we must direct our few concluding remarks to\nthe physico-physiological influences, which we must confess to know but\ntoo imperfectly.\n\nWe learn that, during the states of progress which geology, looking\ninto the arcana of time, has made us acquainted with, a great variety\nof animal forms were brought into existence. They lived their periods.\nThe conditions of the surface of the earth, the sea, or the atmosphere,\nwere altered; and, no longer fitted for the enjoyments of the new life,\nthese races passed away, and others occupied their places, which, in\nturn, went through all the stages of growth, maturity, and decay;\nuntil at length, the earth being constituted for the abode of the\nhighest order of animals, they were called into existence; and man,\nthe intellectual monarch of the world, was placed supreme amongst them\nall. Types of nearly all those forms of life which are found in the\nfossil state are now in existence; and if we examine the geographical\ndistribution of animals--the zones of elevation over the surface of\nthe earth, and the zones of depth in the ocean,--we shall find, now\nexisting, animal creations strikingly analogous to the primitive forms\nand conditions of the earth\u2019s inhabitants. From the depths of the ocean\nwe may even now study--as that most indefatigable naturalist, Professor\nEdward Forbes, has done--the varying states of organization under the\ncircumstances of imperfect light and varying temperature.[261]\n\nThe gradual advance of animal life in the ascending strata has led\nto many speculations, ingenious and refined, on the progressive\ndevelopment of animals. That the changes of the inorganic world have\nimpressed new conditions on the organic structures of animals, to meet\nthe necessities of their being, must be admitted. Comparative anatomy\nhas demonstrated that such supposed differences really existed between\nthe creatures of secondary formations--those of the tertiary and the\npresent periods. It has been imagined, but upon debatable foundations,\nthat the atmosphere, during the secondary periods, was highly charged\nwith carbonic acid; and, consequently, that though beneficial to the\ngrowth of plants, and peculiarly fitted for the conditions required\nby those which the fossil flora makes us acquainted with, it was not\nadapted to support any animals above the slow-breathing, cold-blooded\nfishes and reptiles. Under the action of the super-luxuriant vegetation\nof these periods, this carbonic acid is supposed to have been removed,\nan addition of oxygen furnished; and thus, consequently, the earth\ngradually fitted for the abode of warm-blooded and quick-breathing\ncreatures. We do, indeed, find a very marked line between the fossil\nremains of the lias formations which enclose the saurians, and the\nwealden, in which birds make their appearance more numerously than in\nany previous formation.\n\nFounded upon these facts, speculations have been put forth on the\ngradual development of animals from the lowest up to the highest\norders. Between the polype and man a continuous series has been\nimagined, every link of the chain being traced into connection with\nthe one immediately succeeding it; and, through all the divisions,\nzoophytes, fishes, amphibia, reptiles, birds, and mammalia are seen,\naccording to this hypothesis, to be derived by gradual advancement from\nthe preceding orders. The first having given rise to amphibia,--the\namphibion gives birth to the reptile,--the reptile advances to\nthe bird,--and from this class is developed the mammal. A slight\ninvestigation will convince us that this view has no foundation.\nAlthough a certain relationship may be found between some of the\nmembers of one class, and those of the other immediately joining it,\nyet this is equally discovered to exist towards classes more remote\nfrom each other; and in no one instance can we detect anything like\nthe passage of an animal of one class into an animal of another. Until\nthis is done, we cannot but regard the forms of animal life as distinct\ncreations, each one fitted for its state of being, springing from the\ncommand of the great First Cause.[262]\n\nBut it is time to quit these speculative questions, and proceed to the\nexamination of the general conditions of animal life at the present\ntime.\n\nLowest in the scale of animals, and scarcely distinguishable from a\nvegetable, we find the sponge, attached to and passing its life upon\na rock, exhibiting, indeed, less signs of feeling than many of the\nvegetable tribes. The chemical differences between vegetables and\nsponges are, however, very decided; and we find in the tissues of the\nsponge a large quantity of nitrogen, a true animal element, which\nexists, but in smaller quantities, in vegetables.\n\nThese creations, standing between vegetable and animal life, possess\nthe singular power of decomposing carbonic acid, as plants do; and the\nwater in which they live always contains an excess of free oxygen.\n\nThe polypes are a remarkably curious class. \u201cFixed in large arborescent\nmasses to the rocks of tropical seas, or in our own climate attached\nto shells or other submarine substances, they throw but their\nramifications in a thousand beautiful and plant-like forms; or,\nincrusting the rocks at the bottom of the ocean with calcareous earth,\nseparated from the water which bathes them, they silently build up\nreefs and shoals, justly dreaded by the navigator; and sometimes giving\norigin, as they rise to the surface of the sea, to islands, which\nthe lapse of ages clothes with luxuriant verdure, and peoples with\nappropriate inhabitants.\u201d[263]\n\nMost of the polypes are fixed and stationary; but the hydra and some\nothers have the power of changing their positions, which they do in\nsearch of the light of the sun. They do not appear to have organs of\nsight requiring light; but still they delight in the solar influences.\nThe most extraordinary fact connected with the hydra is its being\nmultiplied by division. If an incision be made in the side of a hydra,\na young polype soon developes itself; and if one of these creatures be\ndivided, it quickly restores the lost portion of its structure. The\nvarieties of the polypes are exceedingly numerous, and many of them are\nin the highest degree curious, and often very beautiful. The actini\u00e6,\nlike flowers, appear to grow from the rocks, unfolding their tentacula\nto the light; and, in the excitement due to their eagerness for prey,\nthey exhibit a beautiful play of colours and most interesting forms.\nMicroscopic zoophytes of the most curious shapes are found,--all of\nwhich attest, under examination, the perfection of all created things.\n\nInfusoria and animalcula,--animals, many of them, appearing under the\nmicroscope as little more than a transparent jelly,--must be recognized\nas the most simple of the forms of life. They exist in all waters in\nuncountable myriads; and, minute creatures as they are, it has been\ndemonstrated that many of the great limestone hills are composed\nentirely of their remains.\n\nThe acaleph\u00e6, or the phosphorescent animals of the ocean, are no less\ncurious. From creatures of the most minute size, they extend to a\nconsiderable magnitude, yet they appear to be little more than animated\nmasses of sea-water. If any one of these sea-jellies, or jelly-fishes\nas they are often called (even the largest varieties of them), is cast\nupon the shore, it is soon, by the influence of the sun, converted into\na mere fibre no thicker than a cobweb: an animal weighing seven or\neight pounds is very soon reduced to as many grains. There are numerous\nkinds of these singular creatures, most of which are remarkable for\nthe powerful phosphorescent light they emit. The _beroes_ and the\n_pulmonigrade_ shine with an intense white light many feet below the\nsurface, whilst the _Cestum Veneris_, or girdle of Venus, gliding\nrapidly along, presents, on the edge of the wave, an undulating riband\nof flame of considerable length. There can be no doubt that this arises\nfrom the emission of phosphorescent matter of an unknown kind from the\nbodies of these animals.\n\nThe microscope has made us familiar with the mysteries of a minute\ncreation which we should not otherwise have comprehended. These\ncreatures are found inhabiting the waters and the land, and they exist\nin the intestinal structure of plants and animals, preying upon the\nnutritive juices which pass through their systems. Although these\nbeings are so exceedingly small that even the most practised observer\ncannot detect them with the naked eye, they are proved, by careful\nexamination under the microscope, to be in many cases elaborately\norganized. Ehrenberg has discovered in them filamentary nerves and\nnervous masses, and even vessels appropriated to the circulation\nof fluids, showing that they belong really to a high condition of\nexistence.\n\nPassing over many links in that curious chain which appears to bind\nthe animal kingdom into a complete whole, we come to the articulata of\nCuvier--the homogangliata of Owen.\n\nAll those creatures which we have been hitherto considering are too\nimperfect in the construction of their simple organizations to maintain\na terrestrial existence; they are, therefore, confined to a watery\nmedium. In the articulata, we have evidences of higher attributes,\nand indications of instincts developed in proportion to the increased\nperfection of organization. Commencing with the annelidans, all of\nwhich, except the earthworms, are inhabitants of the waters, we\nproceed to the myriapoda, presenting a system intermediate in every\nrespect between that of worms and insects; we then find embraced in\nthe same order, the class insecta, which includes flies and beetles\nof all kinds; and, as the fourth division of articulated beings, the\narachnidans or spiders; and, lastly, the marine tribe of crustaceans.\n\nThe most remarkable phenomena connected with these animals are the\nmetamorphoses which they undergo. The female butterfly, for instance,\nlays eggs, which, when hatched, produce caterpillars: these live in\nthis state for some time, feeding upon vegetables, and, after casting\ntheir skins as they increase in size, at last assume an entirely\ndifferent state, and, dormant in their oblong case, they appear like\ndead matter. This chrysalis, or pupa, is generally preserved from\ninjury by being embedded in the earth, from which, after a season, a\nbeautifully perfect insect escapes, and, floating on the breeze of\nsummer, enjoys its sunshine, and revels amidst its flowers.\n\nNo less remarkable is the metamorphosis of the caducibranchiate\namphibia, passing through the true fish condition of the tadpole to the\nperfect air-breathing and four-footed animal, the frog.\n\nA metamorphosis of the crustaceans, somewhat similar to that which\ntakes place in insects, has been of late years creating much discussion\namongst naturalists: but the question appears to be now settled by the\ncareful and long-continued observations of Mr. Thompson and Mr. R. C.\nCouch.\n\nA wide line of demarcation marks the separation of the invertebrata\nfrom the four great classes of vertebrate animals--fishes, reptiles,\nbirds, and mammalia. Every part of the globe,--the ocean and the inland\nlake,--the wide and far-winding river, and the babbling stream,--the\nmountain and the valley,--the forest with its depth of shade, and\nthe desert with its intensity of light,--the cold regions of the\nfrost-chained north, and the fervid clime within the tropics--presents\nfor our study innumerable animals, each fitted for the conditions to\nwhich it is destined; and through the whole we find a gradual elevation\nin the scale of intelligence, until at last, separated from all by\npeculiar powers, we arrive at man himself.\n\nIn each of these four classes the animals are furnished with a bony\nskeleton, which is in the young animal little more than cartilage;\nbut, as growth increases, lime becomes deposited, and a sufficient\ndegree of hardness is thus produced to support the adult formation.\nSome anatomists have endeavoured to show that even in the mechanical\nstructure of the bony fabrics of animals, we are enabled to trace a\ngradual increase in the perfection of arrangement, from the fish until\nthe most perfect is found in man. Many of the mammalia, however, are\nfurnished with skeletons which really surpass that of man. These belong\nto animals which depend for subsistence upon their muscular powers, and\nwith whom man is, in this particular, on no equality. What is the lord\nof the creation, compared with the antelope for fleetness, or with the\nelephant and many other animals for strength?\n\nAs we ascend the scale of animal life we find a more perfectly\ndeveloped nervous system; and the relative size of the brain, compared\nwith that of the brute, is found progressively to increase, until it\narrives at the utmost perfection in man. On the system of nerves\ndepends sensation, and there can be no doubt that the more exalted the\norder of intelligence displayed, the more exquisitely delicate is the\nnervous system. Thus, in this world, refined genius must necessarily be\nattended with a condition of sensibility which, too frequently, to the\npossessor is a state of real disease.\n\nIt must be evident to every reader that but very few of the striking\nfeatures of animal life have been mentioned in the rapid survey which\nhas been taken of the progress of animal organization. The subject\nis so extensive that it would be quite impossible to embrace it\nwithin any reasonable limits; and it furnishes matter so curious and\nso instructive, that, having once entered on it, it would have been\ndifficult to have made any selection, and we must have devoted a volume\nto the \u00e6sthetics of natural science. Passing it by, therefore, with the\nmere outline which has been given, we must proceed to consider some of\nthe conditions of vitality.\n\nBell has proved that one set of nerves is employed in conveying\nsensation to the brain, and another set in transferring the desires of\nthe will to the muscles. By the separation of a main branch of one of\nthe nerves of sensation, although all the operations of life will still\nproceed, the organ to which that nerve goes is dead to its particular\nsense. In like manner, if one of the nerves of volition is divided,\nthe member will not obey the inclination of the brain. It is evident,\ntherefore, although many of the great phenomena of vital force are\ndependent on the nervous system, and the paralysis of a member ensues\nupon the separation or the disease of a nerve, that the nerves are but\nthe channels through which certain influences are carried. The _vis\nvit\u00e6_ or vital principle--for we are compelled by the imperfection of\nour knowledge to associate under this one term the ultimate causes of\nmany of the phenomena of life--is a power which, although constantly\nemployed, has the capability of continually renewing itself by\nsome inexplicable connection existing between it and many external\ninfluences. We know that certain conditions are necessary to the health\nof animals. Diseased digestion, or any interruption in the circulation\nof the blood, destroys the vital force, and death ensues. The processes\nof digestion and of the circulation are perfectly understood, yet we\nare no nearer the great secret of the living principle.\n\nAnimals are dependent on several external agents for the support of\nexistence. The oxygen of the air is necessary for respiration. Animal\nheat, as will be shown presently, is in a great measure dependent\nupon it. The external heat is so regulated that animal existence is\ncomfortably supported. Electricity is without doubt an essential\nelement in the living processes; and, indeed, many physiologists have\nbeen inclined to refer vital force to the development of electricity\nby chemical action in the brain. This view has, however, no foundation\nin experiment beyond that afforded by the appearance of electric\ncurrents, when the brain is excited. This proves no more than that the\noperations of mind develope physical power in the matter with which it\nis mysteriously connected.\n\nThe phenomena of the Torpedo and Gymnotus we have already noticed,[264]\nand there are other creatures which certainly possess the power of\nsecreting and discharging electricity. Galvani\u2019s experiments, and\nthose of Aldini, appear to show--and the more delicate researches of\nMatteucci have satisfactorily determined--that currents of electricity\nare always circulating in the animal frame;--that positive electricity\nis constantly passing from the interior to the exterior of a muscle.\nMatteucci, by arranging a series of muscles, has formed an electric\npile of some energy.[265] These currents have been detected in man, in\npigeons, fowls, eels, and frogs.\n\nIn the human body it is evident a large quantity of electricity\nexists in a state of equilibrium. Du Bois Raymond has shown that we\nmay by mere muscular motion give rise to electric currents which can\nbe measured by the galvanometer. This, however, may be said of every\nsubstance. It is perhaps more easily disturbed in the human system;\nindeed, the manifestation of sparks from the hair and other parts of\nthe body by friction is not uncommon. Every chemical action, it has\nbeen already shown, gives rise to electrical manifestations; and the\nanimal body is a laboratory, beautifully fitted with apparatus, in\nwhich nearly every chemical process is going on. It has been proved\nthat acid and alkaline principles are constantly acting upon each\nother through the tissues of the animal frame; and we have the curious\nphenomena of endosmose and exosmose in constant effort, and catalysis\nor _surface force_, operating in a mysterious manner.[266]\n\nWith the refined physiological questions connected with the phenomena\nof sensation we cannot deal, nor will any argument be adduced for or\nagainst the hypothesis which would refer these phenomena to some\nextraordinary development of electric force in the brain. The entire\nsubject appears to stand beyond the true limits of science, and every\nattempt to pass it is invariably found to lead to a confused mysticism,\nin which the real and the ideal are strangely confounded. Science stops\nshort of the phenomena of vital action.\n\nWe cannot, however, but refer to the idea entertained by many that the\nbrain is an electric battery, and the nerves a system of conductors.\nOn this view Sir John Herschel remarks:--\u201cIf the brain be an electric\npile constantly in action, it may be conceived to discharge itself\nat regular intervals, when the tension of the electricity reaches a\ncertain point, along the nerves which communicate with the heart, and\nthus excite the pulsation of that organ.\u201d Priestley, however, appears\nto have been the first to promulgate this idea.\n\nLight is an essential element in producing the grand phenomenon of\nlife, though its action is ill understood. Where there is light,\nthere is life, and any deprivation of this principle is rapidly\nfollowed by disease of the animal frame, and the destruction of the\nmental faculties. We have proof of this in the squalor of those whose\nnecessities compel them to labour in places to which the blessings\nof sunshine never penetrate, as in our coal-mines, where men having\neverything necessary for health, except light, exhibit a singularly\nunhealthy appearance. The state of fatuity and wretchedness to which\nthose individuals have been reduced who have been subjected for\nyears to incarceration in dark dungeons, may be referred to the same\ndeprivation. Again, in the peculiar aspect of those people who inhabit\ndifferent regions of the earth under varying influences of light, we\nsee evidence of the powerful effects of solar action. Other forces, as\nyet undiscovered, may, in all probability do, exert decided influences\non the animal economy; but, although we recognize many effects which we\ncannot refer to any known causes, we are perfectly unable to imagine\nthe sources from which they spring.\n\nIt will be interesting now to examine the phenomena of animal heat, the\nconsideration of which naturally leads us to consider the digestive\nsystem, the circulatory processes, and the effects of nervous\nexcitation.\n\nThe theory, which attributes animal heat to the combination of the\ncarbon of the food taken into the stomach with the oxygen of the air\ninspired through the lungs, has become a very favourite one. It must,\nhowever, be remembered that it is by no means new. The doctrines of\nBrown, known as the Brunonian system, and set forth in his _Elementa\nMedicin\u00e6_, are founded upon similar hasty generalizations. Although,\nwithout doubt, true in a certain degree, it is not so to the extent\nto which its advocates would have us believe. That the carbonaceous\nmatter received into the stomach, after having undergone the process\nof digestion, enters into combination with the oxygen breathed through\nthe lungs or absorbed by the skin, and is given off from the body in\nthe form of carbonic acid, and that, during the combination, heat is\nproduced, by a process similar to that of ordinary combustion, is an\nestablished fact; but the idea of referring animal heat entirely to\nthis chemical source, when there are other well-known causes producing\ncalorific effects, is an example of the errors into which an ingenious\nmind may be led, when eagerly seeking to establish a favourite\nhypothesis.\n\nAnimal and vegetable diet, which is composed largely of carbon and\nhydrogen, passes into the digestive system, and becomes converted into\nthe various matters required for the support of the animal structure.\nThe blood is the principal fluid employed in distributing over the\nsystem the necessary elements of health and vigour, and for restoring\nthe waste of the body. This fluid, in passing through the lungs,\nundergoes a very remarkable change, and not merely assumes a different\ncolour, but really acquires new properties, from its exposure to the\nair with which the cells of these organs are filled. By a true chemical\nprocess, the oxygen is separated from the air, that oxygen is made to\ncombine with the carbon and hydrogen, and carbonic acid and water are\nformed. These are liberated and thrown off from the body either through\nthe lungs or by the skin. In the processes of life, as far as we are\nenabled to trace them, we see actions going on which are referred to\ncertain causes which we _appear_ to explain. Thus, the combination of\nthe oxygen of the air with the carbon of the blood is truly designated\na case of chemical affinity; and we find that in endeavouring to\nimitate the processes of nature in the laboratory, we are, to a certain\nextent, successful. We can combine carbon and oxygen to produce\ncarbonic acid; and we know that the result of that combination is the\ndevelopment of certain definite quantities of heat. Let us examine the\nconditions of this chemical phenomenon, and we shall find that in the\nnatural and artificial processes,--for we must be allowed to make that\ndistinction,--there are analogous circumstances. If we place a piece of\npure carbon, a lump of charcoal or a diamond, in a vessel of air, or\neven of pure oxygen gas, no change will take place in either of these\nelements, and, however long they may be kept together, they will still\nbe found as carbon or diamond, and oxygen gas. If we apply heat to the\ncarbon until it becomes incandescent, it immediately begins to combine\nwith the oxygen gas,--it burns;--after a little time all the carbon has\ndisappeared, and we shall find, if the experiment has been properly\nmade, that a gas is left behind which is distinguished by properties\nin every respect the reverse of those of oxygen, supporting neither\nlife nor combustion, whereas oxygen gives increased vigour to both.\nWe have now, indeed, carbonic acid gas formed by the union of the two\nprinciples.\n\nA dead mass of animal matter may be placed in oxygen gas, and, unless\nsome peculiar conditions are in some way brought about, no change will\ntake place; but, if it were possible to apply the _spark of life_ to\nit, as we light up the spark in the other case, or if, as that is\nbeyond the power of man, we substitute a living creature, a combination\nbetween the carbon of the animal and the gas will immediately begin,\nand carbonic acid will be formed by the waste of animal matter, as in\nthe other case it is by the destruction of the carbon; and, if there is\nnot a fresh supply given, the animal must die, from the exhaustion of\nits fabric. Now, in both these cases, it is clear that, although this\nchemical union is a proximate cause of heat, there must be existing\nsome power superior to it, as the ultimate cause thereof.\n\nThe slow combustion (_eremacausis_) of vegetable matter, decomposing\nunder the influence of moisture and the air, does not present similar\nconditions to those of the human body, although it has been insisted\nupon to be in every respect analogous. That the results resemble each\nother is true, but we must carefully distinguish between effects and\ncauses; and the results of chemical decomposition in inert matter\ndiffer from those in the living organism. The vegetable matter has lost\nthe principle of organic life, and, that gone, the tendency of all\nthings being to be resolved into their most simple forms, a disunion of\nthe elements commences: oxygen, hydrogen, and carbon pass off either\nin the gaseous state or as water, whilst some carbon is liberated in\na very finely-divided condition, and enters slowly into combination\nwith oxygen supplied by the water or the air. Hydrogenous compounds\nare at the same time formed, and, under all these circumstances, as in\nall other chemical phenomena, an alteration of temperature results.\nHeat results from the chemical changes, and eventually true combustion\nbegins.\n\nThe animal tissue may act in the same way as platina has already\nbeen shown to act in producing combination between gases; but of this\nwe have no proof. We know that electricity is capable of producing\nthe required conditions, and we also learn, from the beautiful\nresearches of Faraday, that the quantity of electricity developed\nduring decomposition is exactly equal to that required to effect the\ncombination of the same elements. Thus it is quite clear that, during\nthe combination of the carbon of the blood with the oxygen of the air,\na large amount of electricity must become latent in the compound. The\nsource of this we know not: it may be derived from some secret spring\nwithin the living structure, or it may be gathered from the matter\nsurrounding it. There is much in nervous excitation which appears like\nelectrical phenomena, and attempts have been frequently made to refer\nsensation to the agency of electricity. But these are the dreams of the\ningenious, for which there is but little waking reality.\n\nEvery mechanical movement of the body occasions the development of\nheat; every exertion of the muscles produces sensible warmth; and,\nindeed, it can be shown by experiment that every expansion of muscular\nfibre is attended with the escape of caloric, and its contraction\nwith the absorption of it. There are few operations of the mind which\ndo not excite the latent caloric of the body, and frequently we find\nit manifested in a very remarkable manner by a suddenly-awakened\nfeeling. The poet, in the pleasure of creation, glows with the ardour\nof his mind, and the blush of the innocent is but the exhibition\nof the phenomenon under some nervous excitation, produced by a\nspirit-disturbing thought. Thus we see that the processes of digestion\nand respiration are not the only sources of animal heat, but that many\nothers exist to which much of the natural temperature of the body must\nbe referred.\n\nSo much that is mysterious belongs to the phenomena of life, that\nsuperstition has had a wide scope for the exercise of its influence;\nand through all ages a powerful party of mankind have imagined that\nthe spirit of human curiosity must be checked before it advances to\nremove the veil from any physiological causes. Hence it is that even at\nthe present day so much that stands between what, in our ignorance, we\ncall the real and the supernatural, remains uninvestigated. Even those\nmen whose minds are sceptical upon any development of the truths of\ngreat natural phenomena,--who, at all events, will have proof before\nthey admit the evidence, are ready to give credit to the grossest\nabsurdities which may be palmed upon them by ingenious charlatans,\nwhere the subject is man and his relations to the spiritual world.\n\nMan, and the races of animals by which he is surrounded, present a\nvery striking group, consider them in whatever light we please. The\ngradual improvement of organic form, and the consequent increase of\nsensibility, and eventually the development of reason, are the grandest\nfeature of animated creation.\n\nThe conditions as to number even of the various classes are not the\nleast remarkable phenomena of life. In the lowest orders of animals,\ncreatures of imperfect organization,--consequently those to whom the\nconditions of pain must be nearly unknown,--increase by countless\nmyriads. Of the infusoria and other beings, entire mountains have\nbeen formed, although microscopes of the highest powers are required\nto detect an individual. Higher in the scale, even among insects, the\nsame remarkable conditions of increase are observed. Some silkworms lay\nfrom 1,000 to 2,000 eggs; the wasp deposits 3,000; the ant from 4,000\nto 5,000. The queen bee lays between 5,000 and 6,000 eggs according to\nBurmeister; but Kirby and Spence state that in one season the number\nmay amount to 40,000 or 50,000. But, above all, the white ant (_Termes\nfatalis_) produces 86,400 eggs each day, which, continuing for a\nlunar month, gives the astonishing number of 2,419,200, a number far\nexceeding that produced by any known animal.\n\nThese may appear like the statements in which a fictionist might\nindulge, but they are the sober truths discovered by the most\npains-taking and cautious observers. And it is necessary that such\nconditions should prevail. These insects, and all the lower tribes of\nthe animal kingdom, furnish food for the more elevated races. Thousands\nare born in an hour, and millions upon millions perish in a day. For\nthe support of organic life, like matter is required; and we find that\nthe creatures who are destined to become the prey of others are so\nconstituted that they pass from life with a perfect unconsciousness of\nsuffering. As the animal creation advances in size and strength, their\nincrease becomes limited; and thus they are prevented from maintaining\nby numbers that dominion over the world which they would be enabled\nfrom their powers to do, were their bands more numerous than we now\nfind them.\n\nThe comparative strength, too, of the insect tribes has ever been a\nsubject of wonder and of admiration to the naturalist. The strength of\nthese minute creatures is enormous; their muscular power, in relation\nto their size, far exceeds that of any other animal. The grasshopper\nwill spring two hundred times the length of its own body. The\ndragonfly, by its strength of wing, will sustain itself in the air for\na long summer day with unabated speed. The house-fly makes six hundred\nstrokes with its wings, which will carry it five feet, every second.\nThe stag-beetle, were it the size of the elephant, would be able to\ntear up the largest mountains.\n\nSuch are the wonders of the natural world; from the zoophyte, growing\nlike a flowering plant[267] upon an axis filled with living pith--a\nsmall remove from the conditions of vegetable life, upwards through the\nmyriads of breathing things--to man, we see the dependence of all upon\nthese physical powers which we have been considering.\n\nTo trace the effects of those great causes through all their mysterious\nphases is the work of inductive science; and the truths discovered tend\nto fit us for the enjoyment of the eternal state of high intelligence\nto which every human soul aspires.\n\nThat which the ignorant man calls the supernatural, the philosopher\nclasses amongst natural phenomena. The ideal of the credulous man\nbecomes the real to him who will bend his mind to the task of inquiry.\nTherefore to attempt to advance our knowledge of the unknown, to add\nto the stores of truth, is an employment worthy the high destiny of\nthe human race. Remembering that the revelations of natural science\ncannot in any way injure the revelation of eternal truth, but, on\nthe contrary, aid to establish in the minds of the doubting a firm\nconviction of its Divine origin and of man\u2019s high position, we need\nnever fear that we are proceeding too far with any inquiry, so long as\nwe are cautious to examine the conditions of our own minds, that they\nbe not made the dupe of the senses.\n\nIn the fairies of the hills and valleys, in the gnomes of the caverns,\nin the spirits of the elements, we have the attempts of the mind, when\nthe world was young, to give form to the dim outshadowings of something\nwhich was then felt to be hidden behind external nature.\n\nIn the Oread, the Dryad, and the Nereid, we have, in like manner, an\nembodiment of powers which the poet-philosopher saw in his visions\npresiding over the mountain, the forest, and the ocean. Content with\nthese, invested as they were with poetic beauty, man for ages held\nthem most religiously sacred; but the progress of natural science\nhas destroyed this class of creations. \u201cGreat Pan is dead,\u201d but the\nmountains are not voiceless; they speak in a more convincing tone; and,\ninstead of the ear catching the dying echo of an obscure truth, it is\ngladdened with the full, clear note of nature in the sweetest voice\nproclaiming secrets which were unknown to the dreams of superstition.\n\n\nFOOTNOTES:\n\n[261] _Reports of the Fauna of the \u00c6gean_: by Professor\nForbes.--Reports of the British Association. _On the Physical\nConditions affecting the Distribution of Life in the Sea and the\nAtmosphere, &c._: by Dr. Williams. Swansea.\n\n[262] _The Vestiges of the Natural History of Creation._\n\n[263] _General Outline of the Animal Kingdom_: by Professor Thomas\nRymer Jones, F.Z.S.\n\n[264] In addition to the memoirs already referred to, Note p. 211,\nsee Carlisle, _On the battery of the Torpedo, governed by a voluntary\nmuscle_.--Phil. Trans., vol. xcv. p. 11. Todd, _Experiments on the\nTorpedo of the Cape of Good Hope_.--Ibid., vol. cvi. p. 120. Todd,\n_Experiments on the Torpedo Electricus at La Rochelle_.--Ibid., vol.\ncvii. p. 32.\n\n[265] For a concise account of these experiments see _Elements of\nNatural Philosophy_: by Golding Bird, A.M., M.D., &c. 3rd Edition,\nchap, xx p. 336. In this work all the most recent researches are given,\nand the authorities referred to; see also Matteucci\u2019s interesting\npapers already quoted.\n\n[266] _On the laws according to which the mixing of fluids, and their\npenetration into permeable substances, occurs, with special reference\nto the processes in the Human and Animal Organism_, by Julius Vogel, of\nGiessen: translated for the Cavendish Society. Liebig, _On the Motion\nof the Juices in the Animal Body_.\n\n[267] _A General Outline of the Animal Kingdom_: by Thomas Rymer Jones,\np. 54, et seq.\n\n\n\n\nCHAPTER XVI.\n\nGENERAL CONCLUSIONS.\n\n  The Changes produced on Physical Phenomena by the Movement of\n    the Solar System considered--Exertion of the Physical Forces\n    through the Celestial Spaces--The Balance of Powers--Varieties\n    of Matter--Extension of Matter--Theory of Nonentity--A Material\n    Creation an indisputable fact--Advantages of the Study of\n    Science--Conclusion.\n\n\nWe have examined terrestrial phenomena under many of the harmonious\nconditions which, with our limited intelligence, we can reach by the\naid of science. From the first exhibition of force, in the cohesion\nof two atoms, onward to the full development of organic form in the\nhighest order of animals, we have observed strange influences. We\nhave seen the solitary molecule invested with peculiar properties,\nand regulated by mighty forces; we have learned that the modes of\nmotion given to this beautiful sphere produce curious changes in the\noperation of these powers; and we may with safety infer that every atom\nconstituting this globe is held in wonderful suspension against every\natom of every star, in the celestial spaces, even to that bright orb in\nthe centre of the Pleiades, around which the entire system of created\nworlds is supposed to roll.\n\nAs we move around our own sun--in the limited period of 365 days, and\nround our own axis in 24 hours--we experience transitions from heat to\ncold, dependent upon our position in regard to that luminary and the\nlaws which regulate the reception and retention of certain physical\nforces. May we not therefore conclude, without being charged with\nmaking any violent deduction, that in the great revolution of our\nsystem around the centre of space, we are undergoing gradual changes\nwhich are essential to the great scheme of creation, though at present\nincomprehensible to us?\n\nIn our consideration of the influence of time on the structure of\nthe earth as we find it, we discovered that, in ages long past, the\nvegetation of the tropics existed upon these northern parts of the\nglobe; and geological research has also proved that over the same lands\nthe cold of an arctic winter must have long prevailed--the immense\nglaciers of that period having left the marks of their movements upon\nthe face of the existing rocks.[268] We know that during 3,000 years\nno change of temperature has taken place in the European climate.\nThe children of Israel found the date and the vine flourishing in\nCanaan; and they exist there still. Arago has shown that a trifling\nalteration of temperature would have destroyed one or the other of\nthese fruit-bearing trees, since the vine will not ripen where the mean\ntemperature of the year is higher than 84\u00b0, or the date flourish where\nit sinks below that degree.\n\nHow immense, then, the duration of time since these changes must have\ntaken place! The 432,000 years of Oriental mythology is a period\nscarcely commensurable with these effects; yet, to the creature of\nthree-score years, that period appears an eternity. The thirty-three\nmillions of geographical miles which our solar system traverses\nannually, if multiplied by three thousand years, during which we know\nno change has taken place, give us 99,000,000,000 as the distance\npassed over in that period. How wide, then, must have been the journey\nof the system in space to produce the alteration in the physical\npowers, by which these changes have been effected!\n\nWe have an example, and a striking one, of the variations which may\nbe produced in all the physical conditions of a world, in those\ndisturbances of Uranus which led to the discovery of Neptune. For\nthirty years or more certain perturbations were observed in this\ndistant planet, the discovery of Sir William Herschel, and calculation\npointed to some still more remote mass of matter as the cause, which\nhas been verified by its actual discovery. But now Uranus is at\nrest;--quietly that star progresses in its appointed orbit,--Neptune\ncan no longer, for the present, cause it to move with greater or less\nrapidity--they are too remote to produce any sensible influence upon\neach other. Consequently, for thirty years, it is evident, phenomena\nmust have occurred on the surface of Uranus, which can be no longer\nrepeated until these two planets again arrive at the same positions\nin their respective paths which they have occupied since 1812. These\nconsiderations assist us in our attempts to comprehend infinite time\nand space; but the human mind fails to advance far in the great\nsublimity.\n\nThrough every inch of space we have evidence of the exercise of such\nforces as we have been considering. Gravitation chains world to world,\nand holds them all suspended from the mystic centre. Cohesion binds\nevery mass of matter into a sphere, while motion exerts a constant\npower, which tends to alter the form of the mass. The earth\u2019s form--a\nflattened spheroid--the rings of Saturn and of Neptune are the\nconsequences of motion in antagonism to cohesion. Heat, radiating\nfrom one planet to another, does its work in all, giving variety to\nmatter. Light seeks out every world--each trembling star tells of the\nmystery of its presence. Where light and heat are, chemical action,\nas an associated power, must be present; and electricity must do its\nwondrous duties amongst them all. Modified by peculiar properties of\nmatter, they may not manifest themselves in phenomena like those of our\nterrestrial nature; but the evidence of light is a sufficient proof of\nthe presence of its kindred elements; and it is difficult to imagine\nall these powers in action without producing some form of organization.\nIn the rounded pebble which we gather from the sea-shore, in the medusa\nfloating bright with all the beauty of prismatic colour in the sun-lit\nsea,--in the animal, mighty in his strength, roaming the labyrinthine\nforests, or, great in intelligence, looking from this to the mysteries\nof other worlds,--in all created things around us, we see direct\nevidence of a beautiful adjustment of the balance of forces, and the\nharmonious arrangement of properties.\n\nOne atom is removed from a mass and its character is changed; one\nforce being rendered more active than another, and the body, under its\ninfluence, ceases to be the same in condition. The regulation which\ndisposes the arrangements of matter on this earth, must exist through\nthe celestial spaces, and every planet bears the same relation to every\nother glittering mass in heaven\u2019s o\u2019erarching canopy, as one atom\nbears to another in the pebble, the medusa, the lion, or the man. An\nindissoluble bond unites them all, and the grain of sand which lies\nburied in the depth of one of our primary formations, holds, chained\nto it by these all-pervading forces, the uncounted worlds which, like\nluminous sand, are sprinkled by the hand of the Creator through the\nuniverse. Thus we advance to a conception of the oneness of creation.\n\nThe vigorous mind of that immortal bard who sang \u201cof man\u2019s first\ndisobedience,\u201d never, in the highest rapture, the holiest trance of\npoetic conception, dreamed of any natural truths so sublime as those\nwhich science has revealed to us.\n\nThe dependence of all the systems of worlds upon each other, every\ndust composing each individual globe being \u201cweighed in a balance,\u201d the\nadjustment of the powers by which every physical condition is ordered,\nthe disposition of matter in the mass of the earth, and the close\nrelation of the kingdoms of nature,--are all revelations of natural\ntruths, exalting the mind to the divine conception of the universe.\n\nThere is a remarkable antagonism displayed in the operation of many\nof these forces. Gravitation and cohesion act in opposition to the\nrepellent influences of caloric. Light and heat are often associated\nin a very remarkable manner; but they are certainly in their radiant\nstates in antagonism to chemical action, whether produced by the direct\nagency of actinic force, or through the intermediate excitement of\nthe electrical current.[269] And in relation to chemical force, as\nmanifested in organic combinations, we have the all-powerful operation\nof LIFE preventing any exercise of its decomposing power.[270] As world\nis balanced against world in the universe, so in the human fabric, in\nthe vegetable structure, in the crystallized gem, or in the rude rock,\nforce is weighed against force, and the balance hangs in tranquillity.\nLet but a slight disturbance occasion a vibration of the beam, and\nelectricity shakes the stoutest heart with terror, at the might of its\ndevastating power.[271] Heat melts the hardest rocks, and the earth\ntrembles with volcanic strugglings; and actinic agency, being freed\nfrom its chains, speedily spreads decay over the beautiful, and renders\nthe lovely repulsive.\n\nWe know matter in an infinite variety of forms, from the most ponderous\nmetal to the lightest gas; and we have it within our power to render\nthe most solid bodies invisible in the condition of vapour. Is it not\neasy, then, to understand that matter may exist equally attenuated\nin relation to hydrogen, as that gas itself is, when compared with\nthe metal platinum? A doubt has been raised against this view, from\nthe difficulty of accounting for the passage of the physical elements\nthrough solid masses of matter. If we, however, remember that the known\ngases have the power of transpiration through matter in a remarkable\ndegree,[272] and that the passage of water through a sieve may be\nprevented by heat, it will be at once apparent that the permeation of\nany radiant body through fixed solid matter is entirely a question of\nconditions.\n\nWe can form no idea of the size of the ultimate atom; we cannot\ncomprehend the degree of etherealization to which matter may be\nextended. Our atmosphere, we have seen, is only another condition of\nthe same elements which compose all the organized forms of matter\nupon the earth, and, at the height reached by man, it is in a state\nof extreme attenuation. What must be its condition at the distance\nof forty miles from the earth? According to known laws, certain\nphenomena of refraction have led us to set these bounds to the matter\nconstituting our globe: but it may exist in such a state of tenuity,\nthat no philosophical instrument constructed by human hands could\nmeasure its refracting power; and who shall declare with certainty that\nmatter itself may not be as far extended as we suppose its influences\nto be?\n\n\u201cHast thou perceived the breadth of the earth? declare if thou knowest\nit all.\n\n\u201cKnowest thou the ordinances of heaven? Canst thou set the dominion\nthereof in the earth?\u201d\n\nA cheerless philosophy, derived from the transcendentalism of the\nGerman schools, by an unhappy metaphysical subtlety, and grafted\nupon what professes to be a positive philosophy, but which is not\nso, is spreading amongst us, and would teach us to regard all things\nas the mere exhibition of properties, a manifestation of powers; it\nbelieves not in a material creation. The grandeur of the earth, and\nthe beautiful forms adorning it, are not entities. Yonder exquisite\nspecimen of the skill of man, in which mind appears to shine through\nthe marble,--that distant mountain which divides the clouds as they are\ndriven by the winds across it,--those trees, amid whose branches the\nbirds make most melodious music,--this flower, so redolent of perfume,\nso bright in colour, and so symmetric in form,--and that lovely being\nwho, a model of beauty and grace, walks the earth an impersonation\nof love and charity blended, making, indeed, \u201ca sunshine in a shady\nplace,\u201d are not realities. Certain forces combine to produce effects,\nall of which unite to deceive poor man into the belief that he is a\nmaterial being, and the inhabitant of a material world. There may be\ningenuity in the philosophy of this school; its metaphysics may be of\na high order; but it evidently advances from the real to the ideal\nwith such rapidity, that every argument is based on an assumption\nwithout a proof; every assumption being merely a type of the philosophy\nitself,--a baseless fabric, a transcendental vision.\n\nA material creation surrounds us. This earth, all that it contains, and\nthe immense hosts of stellar worlds, are absolute entities, surrounded\nwith, and interpenetrated by, certain exhibitions of creative\nintelligence, which perform, according to fixed laws, the mighty\nlabours upon which depend the infinite and eternal mutations of matter.\nThe origin of a grain of dust is hidden from our finite comprehensions;\nbut its existence should be a source of hope, that those minds which\nare allowed the privilege of tracing out its marvellous properties,--of\nexamining the empyreal principles upon which its condition, as a grain\nof dust, depends,--and even of reducing these giant elements to do our\nhuman bidding,--may, after a period of probation, be admitted to the\nenjoyment of that infinite power to which the great secrets of creation\nwill be unveiled.\n\nEvery motion which the accurate search of the experimentalist has\ntraced, every principle or power which the physicist has discovered,\nevery combination which the chemist has detected, every form which the\nnaturalist has recorded, involves reflections of an exalting character,\nwhich constitute the elements of the highest poetry. The philosophy of\nphysical science is a grand epic, the record of natural science a great\ndidactic poem.\n\nTo study science for its useful applications merely, is to limit its\nadvantages to purely sensual ends. To pursue science for the sake of\nthe truths it may reveal, is an endeavour to advance the elements\nof human happiness through the intelligence of the race. To avail\nourselves of facts for the improvement of art and manufactures, is\nthe duty of every nation moving in the advance of civilization. But\nto draw from the great truths of science intelligible inferences and\nmasterly deductions, and from these to advance to new and beautiful\nabstractions, is a mental exercise which tends to the refinement and\nelevation of every human feeling.\n\nThe mind thus exercised during the mid-day of life, will find in the\ntwilight of age a divine serenity; and, charmed by the music of nature,\nwhich, like a vesper hymn poured forth from pious souls, proclaims\nin devotion\u2019s purest strain the departure of day, he will sink into\nthe repose of that mysterious night which awaits us all, tranquil in\nthe happy consciousness that the sun of truth will rise in unclouded\nbrilliancy, and place him in the enjoyment of that intellectual light,\nwhich has ever been among the holiest aspirations of the human race.\n\nThe task of wielding the wand of science,--of standing a scientific\nevocator within the charmed circle of its powers, is one which leads\nthe mind through nature up to nature\u2019s God.\n\nExperiment and observation instruct us in the discovery of a\nfact;--that fact connects itself with natural phenomena,--the ultimate\ncause of which we learn from Divine revelation, and receive in full\nbelief,--but the proximate causes are reserved as trials of man\u2019s\nintelligence; and every natural truth, discovered by induction,\nenables the contemplative mind to deduce those perfect laws which are\nexemplifications of the fresh-springing and all enduring POETRY OF\nSCIENCE.\n\n\nFOOTNOTES:\n\n[268] \u201cAs to the polishing and grooving of hard rocks, it has lately\nbeen ascertained that glaciers give rise to these effects when pushing\nforward sand, pebbles, and rocky fragments, and causing them to grate\nalong the bottom. Nor can there be any doubt that icebergs, when they\nrun aground on the floor of the ocean, imprint similar marks upon\nit.\u201d--_Principles of Geology, or the modern changes of the Earth and\nits Inhabitants considered as illustrative of Geology_: by Charles\nLyell, M.A., F.R.S. _Travels through the Alps of Savoy, and other parts\nof the Pennine Chain, with Observations on the Phenomena of Glaciers_:\nby James D. Forbes, F.R.S.\n\n[269] This may be readily proved by the following simple but\ninstructive experiment:--Take two pairs of watch-glasses; into one pair\nput a solution of nitrate of silver, into the other a weak solution\nof iodide of potassium; connect the silver solution of each pair with\nthe potash one by a film of cotton, and carry a platina wire from one\nglass into the other. Place one series in sunshine, and the other\nin a dark place. After a few hours it will be found that the little\ngalvanic arrangement in the dark will exhibit, around the platina\nwire, a very pretty crystallization of metallic silver, but no such\nchange is observable in the other exposed to light. If a yellow glass\nis interposed between the glass and the sunshine, the action proceeds\nas when in the dark. This experiment is naturally suggestive of many\nothers, and it involves some most important considerations.\n\n[270] In cases of violent death it is often found the gastric juice\nhas, in a few hours, dissolved portions of the stomach.--Dr. Budd\u2019s\nLecture before the College of Physicians.\n\n[271] Faraday\u2019s _Experimental Researches_, vol. i.; from which a\nquotation has already been made, showing the enormous quantity of\nelectricity which is latent in matter.\n\n[272] _On the Motion of Gases_: by Professor Graham, F.R.S.--Phil.\nTrans., vol. cxxxvi. p. 573.\n\n\n\n\nINDEX.\n\n\n  Absorption of heat by air, water, and earth, 74.\n\n  ---- of light, 125.\n\n  Acaleph\u00e6, or phosphorescent animals, 387.\n\n  Actinism, 166.\n\n  ---- producing chemical change, 174.\n\n  ---- and light antagonistic, 177.\n\n  ----, influence of, on plants, 372.\n\n  Action of presence--_Catalysis_, 280.\n\n  \u201cActive principles\u201d of Newton, 11.\n\n  Adams on planet Neptune, 32.\n\n  Adiathermic bodies, 95.\n\n  A\u00ebrial currents dependent on heat, 80.\n\n  ---- chemical, 274.\n\n  Affinity, 292.\n\n  Age of the world, 404.\n\n  Aggregation, attraction of, 48.\n\n  ----, crystalline, 58.\n\n  Agonic lines, 244.\n\n  Air, absorption of heat by, 74.\n\n  ---- density of the, 319.\n\n  Alchemy, Nature\u2019s, 293.\n\n  Aldini on animal electricity, 393.\n\n  Allotropic conditions of atoms, 43.\n\n  Allotropism, 330.\n\n  Allotropy, 291.\n\n  Alum, opacity to heat rays, 65.\n\n  Alpinus\u2019 theory of matter, 47.\n\n  Ammonites of the lias, 341.\n\n  Ammoniacal amalgam, 325.\n\n  Amp\u00e8re\u2019s theory of magnetism, 239.\n\n  Analogy, dangers of reasoning by, 152.\n\n  Ancients\u2019 knowledge of magnetism, 235.\n\n  Animals, phosphorescence of, 154.\n\n  ---- respiration of, 310.\n\n  ---- articulated, 388.\n\n  Animal magnetism, 267.\n\n  ---- electricity, 211, 392.\n\n  ---- life, progress of, 338.\n\n  ----, phenomena of, 383.\n\n  Arago on the surface of the sun, 123.\n\n  ---- on copying the Egyptian temples, 177.\n\n  ---- on magnetic variation, 246.\n\n  _Arbor Dian\u00e6_--silver tree, 261.\n\n  Aristotle on motion, 10.\n\n  Atmosphere, uses of the, 319.\n\n  Atmospheric refraction, 322.\n\n  Atomic theory, 278.\n\n  ---- volumes, 287.\n\n  Atoms, allotropic state of, 43.\n\n  Atom, the organic, 360.\n\n  ----, ultimate size of, 408.\n\n  ----, the, and its powers, 3.\n\n  Attraction, chemical, 275.\n\n  Aurora of the sun, 186.\n\n\n  Back\u2019s account of Aurora, 249.\n\n  Balance of forces, 14.\n\n  Bartholin on Iceland spar, 140.\n\n  Beccaria, Father, on phosphorescence, 160.\n\n  Becquerel\u2019s experiments on electricity, 227.\n\n  ---- on ozone, 300.\n\n  Bell on the nerves, 391.\n\n  Belemnites, 341.\n\n  Berkeley, Bishop, on motion, 10.\n\n  Berzelius on allotropy, 44.\n\n  ---- on catalysis, 281.\n\n  Biela\u2019s comet, 26.\n\n  Biot on polarization, 145.\n\n  Bolognian stone, 161.\n\n  Bouguer on the absorption of light by the atmosphere, 126.\n\n  Boutigny on heat, 107.\n\n  _Boletus igniarius_, 102.\n\n  Boyle on motion, 9.\n\n  Brain and nerves, 391.\n\n  Brahminical philosophy, 245.\n\n  Brewster, Sir D., refers magnetism to the sun, 263.\n\n  ---- on magnetism, 247.\n\n  Brown\u2019s doctrines of life, 395.\n\n  Butterfly, metamorphosis of, 389.\n\n\n  Cagniard de la Tour state, 106.\n\n  Calorific transparency, 65.\n\n  ---- influence on plants, 376.\n\n  Calotype, the, 174.\n\n  Canton\u2019s phosphorus, 161.\n\n  Carbon, allotropic state of, 43.\n\n  Carboniferous plants, fossil, 339.\n\n  Carbonic acid, solid, 111.\n\n  ---- quantity in atmosphere, 311.\n\n  Cassini on magnetic variation, 246.\n\n  Catalysis, 280.\n\n  Cell, organic, 361.\n\n  Cellini, Benvenuto, on the carbuncle, 159.\n\n  Central sun, doctrine of a, 27.\n\n  Changes, physical, 290.\n\n  Chemical phenomena developing heat, 42.\n\n  ---- decomposition producing heat, 97.\n\n  ---- combination by heat, 98.\n\n  ---- affinity suspended by heat, 109.\n\n  ---- radiations, 166.\n\n  ---- power of solar rays in the Tropics, 177.\n\n  ---- agency of luminous rays, 178.\n\n  ---- action influenced by magnetism, 252.\n\n  ---- forces, 270.\n\n  ---- elements, 272.\n\n  ---- proportions, 285.\n\n  ---- metamorphoses, 289.\n\n  ---- phenomena, 295.\n\n  ---- composition of atmosphere, 322.\n\n  ---- rays, action of, on germination, 375.\n\n  Chemistry, Electro, 206.\n\n  ---- of Nature, 270.\n\n  ---- Animal, 396.\n\n  Chinese knowledge of magnet, 236.\n\n  Chlorophylle, formation of, 373.\n\n  Chloride of sulphur, transparency of, to heat, 65.\n\n  Chlorine and hydrogen combine by light, 171.\n\n  Chlorine in the ocean, 303.\n\n  Cholera and electricity, 215.\n\n  Choroid coat, the, 149.\n\n  Chromatic lines on the earth, 133.\n\n  Clay converted into slate by electricity, 227.\n\n  Climate of the earth, 350.\n\n  Clock, Electrical, 233.\n\n  Coal formation, theory of, 314.\n\n  Cohesive force opposed to gravitation, 33.\n\n  Cohesion and gravitation, 49.\n\n  ---- distinguished from crystallization, 51.\n\n  Cold, extreme, 110.\n\n  Colour of bodies, 132.\n\n  ---- changes of, in chemical combinations, 290.\n\n  ---- blue, of sky, 320.\n\n  ---- of steam, 321.\n\n  Colours, Newton\u2019s theory of, 135.\n\n  Coloured heat rays, 85.\n\n  Combining equivalents, 273.\n\n  ---- forces, 292.\n\n  Combination, laws of, 286.\n\n  ---- of forces, 330.\n\n  Combustion, 305.\n\n  Comets, 26.\n\n  Condensation of gases, 290.\n\n  Conduction of heat, 69.\n\n  Conducting power of bodies for heat, 89.\n\n  Condition, change of chemical, 271.\n\n  Conversion of motion, 16.\n\n  Convection of heat, 69.\n\n  Cotyledons, use of the, 368.\n\n  Coulomb on repulsion of atoms, 47.\n\n  Creation, oneness of, 406.\n\n  Cretaceous formations, 344.\n\n  Crosse on electricity, 227.\n\n  Crustaceans, metamorphosis of, 389.\n\n  Crust of the earth, 333.\n\n  Crystals, pseudomorphous, 54.\n\n  ----, size of, 56.\n\n  Crystallogenic forces, 50.\n\n  Crystalline bodies, magnetic influence of, 260.\n\n  Cudworth\u2019s \u201cPlastic Nature,\u201d 10.\n\n  Current, electric, speed of, 231.\n\n  ----, electricity, magnetic, 239.\n\n  Crystallization, 50.\n\n  Cultivation, limits of, 379.\n\n  Currents of electricity around the earth, 224.\n\n  Cyanite, a true magnet, 48.\n\n\n  Daguerre\u2019s discovery, 170.\n\n  Daguerreotype, the, 172.\n\n  Dalton on Aurora Borealis, 248.\n\n  ---- on liquefaction, 287.\n\n  Dalton\u2019s atomic theory, 278.\n\n  Daniel on incandescence, 100.\n\n  Dark lines of spectrum, 125.\n\n  Darwin on sea-weeds of the Southern Ocean, 316.\n\n  Davy, Sir H., on the elements, 328.\n\n  ---- on flame, 307.\n\n  ---- discovers the alkaline metals, 325.\n\n  Decomposition, electro-chemical, 208.\n\n  De la Tour, Cagniard\u2019s experiments, 105.\n\n  Delaroche on heat, 93.\n\n  Density of the earth, 31.\n\n  Development, animal, 384.\n\n  Dew, formation of, 81.\n\n  Diamond, allotropic carbon, 43.\n\n  ----, phosphorescence of, 160.\n\n  Diamagnetism, 253.\n\n  Diamagnetic nature of gases, 259.\n\n  Diathermic bodies, 94.\n\n  Diffusion of gases, 323.\n\n  Digestion a cause of heat, 105.\n\n  Dip of magnetic needle, 247.\n\n  Dimorphism in crystals, 55.\n\n  Directive power of a magnet on crystals, 261.\n\n  Distribution of elements, 328.\n\n  Divisibility of matter, 38.\n\n  D\u00f6bereiner\u2019s lamp, 281.\n\n  Dispersion of light, 129.\n\n  Draper on incandescence, 100.\n\n  Dumas on atoms, 39.\n\n  Dust, a grain of, 2.\n\n\n  Earth, physical, the, 1.\n\n  ---- density of, 31.\n\n  ---- the revolution of the, 77.\n\n  ----, geological formation of, 333.\n\n  Earth\u2019s, motion, 11.\n\n  ---- temperature dependent on the sun, 63.\n\n  Effects produced by loss of heat, 69.\n\n  Eggs, number of, laid by insects, 399.\n\n  Elective affinity, 292.\n\n  Electricity, 193.\n\n  Electricity and light influencing crystallization, 57.\n\n  ----, kinds of, 195.\n\n  ---- contained in water, 203.\n\n  ---- developed by chemical action, 204.\n\n  ----, velocity of, 231.\n\n  ---- of plants, 380.\n\n  Electric condition of matter, 5.\n\n  ---- telegraph, the, 231.\n\n  ---- affinity, 275.\n\n  Electrical phosphorescence, 160.\n\n  ---- action influenced by actinism, 183.\n\n  ---- radiations, 190.\n\n  ---- clock, 233.\n\n  Electro-chemistry, 206.\n\n  Electro culture, 223.\n\n  Electrotype, the, 229.\n\n  Electro-chemical decomposition, 208.\n\n  Electro-magnetism, 240.\n\n  Electrum, 193.\n\n  Elements, chemical, 37, 272.\n\n  ----, atmospheric, 325.\n\n  ----, interchanges of, 319.\n\n  Englefield on heat rays, 67.\n\n  Eocene formations, 346.\n\n  Equinoxes, precession of the, 244.\n\n  ----, the vernal and autumnal, 77.\n\n  Epicurus\u2019 hooked atoms, 48.\n\n  Epipolic phenomena, 129.\n\n  Eremacausis, 105.\n\n  Ether, hypothesis of an, 120.\n\n  Examples of crystallization, 59.\n\n  Expansion of bodies by heat, 96.\n\n  Eye, mechanism of, 149.\n\n\n  Faraday on Magnetism of Crystals, 59.\n\n  ---- on solidification of gases, 112.\n\n  ---- on magnetization of light, 147.\n\n  ---- on the gymnotus, 211.\n\n  ---- on diamagnetism, 254.\n\n  Ferro-magnetic bodies, 255.\n\n  Fish Lizard, the, 341.\n\n  Fixed stars, light of, 122.\n\n  Flint glass, permeability to heat, 65.\n\n  Flora, fossil, 345.\n\n  Flowers, influences of, 317.\n\n  Fluid, magnetic theory of, 252.\n\n  Fluorescence of light, 130.\n\n  Forbes, Prof. Jas., on vibrations of heated metals, 97.\n\n  Forbes, Prof. Edward, on zones of life in the ocean, 127.\n\n  Forbes on colour of steam, 321.\n\n  Force producing motion, 9.\n\n  ---- a cause of motion, 17.\n\n  ----, molecular, 40.\n\n  ---- of crystallization, 61.\n\n  Forces, active, in matter, 3.\n\n  ----, balance of, 14.\n\n  ---- in antagonism, 407.\n\n  Form, change of, 2.\n\n  ---- of surface, influence of, on climate, 351.\n\n  ----, variety of vegetable, 359.\n\n  Foster describes Northern Lights, 249.\n\n  Fox, R. W., on temperature of Cornish mines, 91.\n\n  Franklin on atoms, 47.\n\n  Franklin\u2019s kite experiment, 214.\n\n  Freezing mixtures, 110.\n\n  Freezing, remarkable phenomena of, 112.\n\n  ---- of water, 302.\n\n  Friction, 17.\n\n  Frictional electricity, 199.\n\n  Fraunhofer\u2019s dark lines, 125.\n\n  Franklin\u2019s experiment on heat, 75.\n\n  Fusion influenced by pressure, 107.\n\n\n  Galvanism, 201.\n\n  Galvani\u2019s experiment, 201.\n\n  Gases, condensation of, 111, 290.\n\n  ----, magnetism of, 259.\n\n  Gaseous constitution, 317.\n\n  Gauss\u2019s theory of magnetism, 243.\n\n  Generation, spontaneous, 363.\n\n  Geological phenomena, 332.\n\n  Germ, Treviranus on the, 361.\n\n  Germination of seeds, 367.\n\n  Glass, coloured, transparency to heat, 65.\n\n  Goethe\u2019s theory of colour, 139.\n\n  Goethe on phosphorescence, 157.\n\n  ---- on the leaf, 369.\n\n  Graham\u2019s law of diffusion, 323.\n\n  Gravitation, 21.\n\n  Growth explained, 52.\n\n  ----, progress of, 364.\n\n  ---- defined, 383.\n\n  Grove decomposes water by heat, 98.\n\n  Gulf stream, the, 81.\n\n  Gulielmini on crystallisation, 50.\n\n  Gun cotton, 103.\n\n  Gymnotus electricus, 211.\n\n  Gyroscope, the, 14.\n\n\n  Hansteen and Arago on Northern Lights, 248.\n\n  Hansteen on magnetism, 244.\n\n  Heat, solar and terrestrial, 62.\n\n  ----, conductors of, 90.\n\n  ----, rays absorbed by atmosphere, 63, 73.\n\n  ---- and light, their relations, 64.\n\n  ----, radiation of, 82.\n\n  ---- rays, coloured, 85.\n\n  ---- lessens chemical affinity, 88.\n\n  ----, latent, 101.\n\n  ----, decomposition by, 109, 276.\n\n  ----, scientific knowledge of, 114.\n\n  ---- developed by combustion of wood equivalent to heat absorbed in\n      growth, 116.\n\n  ----, influence of, on magnetism, 241.\n\n  ----, action of, on water, 302.\n\n  ----, influence of on plants, 371.\n\n  ---- essential to life, 395.\n\n  Heliography of M. Niepce, 170.\n\n  Herbivorous animals, 315.\n\n  Herschel on the nebul\u00e6, 24.\n\n  Herschel, Sir W., on heat rays, 67.\n\n  Hobbes on the properties of matter, 8.\n\n  Hopkins on the temperature of fusion, 107.\n\n  Huyghens on double refraction, 140.\n\n  Hydra, the, 387.\n\n  Hydrogen, peroxide of, 298.\n\n  ---- and oxygen, 289, 297.\n\n  Hydro-carbons, 297.\n\n  Hydro-carbon compounds, 308.\n\n  Hypnotism, Mr. Braid on, 269.\n\n\n  Ice, 301.\n\n  Ichthyosaurus, the, 341.\n\n  Igneous rocks, 335.\n\n  Ignition by chemical action, 102.\n\n  Iguanodon, the, 343.\n\n  Incandescence, temperature of, 69-100.\n\n  Influences of matter on heat, 79.\n\n  Infusoria and animalcul\u00e6, 387.\n\n  Interference of light, 138.\n\n  Intensity, magnetic, 247.\n\n  Invisible light, Moser on, 188.\n\n  Iodide of silver found natural, 304.\n\n  Iodine, 304.\n\n  Iridescent paper, 137.\n\n  Iron, magnetic, 235.\n\n  ----, soft, rendered magnetic, 241.\n\n  ----, rusting, 306.\n\n  Isomeric compounds, 291.\n\n  Isomorphism, 290.\n\n  Isothermic lines, 92.\n\n  Isodynamic lines, 247.\n\n\n  Jones, Rymer, on sponges, 345.\n\n  Joule on anhydrous salts, 287.\n\n  ---- on heat and motion, 18.\n\n\n  Kircher\u2019s Magnetism, 264.\n\n  Kupffar on magnetic storms, 249.\n\n\n  Lamination of clay by electricity, 226.\n\n  Land and sea, alternations of, 340.\n\n  Laplace\u2019s theory of the universe, 23.\n\n  Latent heat, 101.\n\n  Lavoisier\u2019s theory of combustion, 305.\n\n  Law of gravitation, 30.\n\n  Lawson, letter from Mr., on germination of seeds, 375.\n\n  Leaf, the functions of the, 369.\n\n  Leaves of plants, action on air of, 311.\n\n  Le Verrier on planet Neptune, 32.\n\n  Leyden jar, the, 198.\n\n  Lias formations, 341.\n\n  Liebig and organic chemistry, 284.\n\n  Life and light, 52.\n\n  ----, influence of light on, 153.\n\n  ---- dependent on light, 164.\n\n  ----, vegetable, 362.\n\n  ----, mysteries of, 398.\n\n  Light, 118.\n\n  ---- essential to life, 39.\n\n  ---- of fixed stars, 122.\n\n  ----, transparency to, 124.\n\n  ----, transmission of, through different media, 128.\n\n  ----, absorption of, 125.\n\n  ----, interference of, 138.\n\n  ----, polarized condition of, 141.\n\n  ----, magnetization of, 146.\n\n  ----, artificial, 162.\n\n  ----, influence of, on plants, 373.\n\n  ---- and heat, correlation of, 64.\n\n  Lightning conductors, 215.\n\n  Lindley on the leaf, 370.\n\n  Lubbock, Sir J., on shooting stars, 22.\n\n  Lodes, mineral, electricity of, 225.\n\n  Luminous and actinic rays distinguished, 176.\n\n\n  Machine electricity, 209.\n\n  Magellanic clouds, 25.\n\n  Magnetic curves, 236.\n\n  ---- iron ore, 237.\n\n  ---- polarity, 237.\n\n  ---- points of convergence, 244.\n\n  ---- poles of the earth, 245.\n\n  ---- intensity, 247\n\n  ---- storms, 249.\n\n  ---- lines of no variation, 243.\n\n  Magnetism, 235.\n\n  ---- induced, 238.\n\n  ---- influenced by heat, 242.\n\n  ----, universality of, 253.\n\n  ---- of gases, 259.\n\n  ---- induced by solar rays 263.\n\n  ---- and electricity, correlation of, 239.\n\n  ---- and crystallisation, 57.\n\n  Magneto-electrical decomposition, 230.\n\n  Magnetisation of light, 146.\n\n  Malus on polarisation, 139.\n\n  Mammalia, fossil, 343.\n\n  Man, temperature of, 105.\n\n  Manganesiate of potash, 171.\n\n  Mantell, Dr., on the iguanodon, 343.\n\n  Mariotte on seat of vision, 149.\n\n  Matter, its general conditions, 1.\n\n  ----, forms of, 21.\n\n  ----, transmutation of, 37.\n\n  ----, divisibility of, 38.\n\n  ----, solid, absorption of heat by, 75.\n\n  ----, influence of, on light, 162.\n\n  ----, polarity of, 265.\n\n  ---- and its properties, 409.\n\n  ----, entity of, 410.\n\n  ----, varied condition of, 36.\n\n  Mayer\u2019s hypothesis of three colours, 138.\n\n  Mechanical force and heat, 103.\n\n  Mechanism of the eye, 149.\n\n  Media, influence of, on light, 128.\n\n  Medus\u00e6, phosphorescence of, 159.\n\n  Melloni on coloured heat rays, 85.\n\n  ---- on new nomenclature for heat, 95.\n\n  Mesmer and electricity, 222.\n\n  Metamorphic rocks, 336.\n\n  Metamorphoses of animals, 389.\n\n  Mexico, Gulf of, warmth of the, 81.\n\n  Mica, black, transparency to heat, 66.\n\n  Miller, Dr., on dark lines of the spectrum, 126.\n\n  Mineral veins, electricity of, 225.\n\n  Mines, Cornish, temperature of, 91.\n\n  Miocene formations, 346.\n\n  Mirrors, magic, 191.\n\n  Mitscherlich on expansion of crystals by heat, 257.\n\n  Molecular forces, 35, 40.\n\n  ----, compound action of, 279.\n\n  Molecules, Dumas on, 39.\n\n  ---- combination, 277.\n\n  Morichini and Carpi on magnetism of violet rays of light, 263.\n\n  Moser on invisible light, 189.\n\n  Motion, 7.\n\n  ---- a property of matter, 8.\n\n  ----, principles of, 10.\n\n  ---- of the earth, 12.\n\n  ---- round an axis shows the earth\u2019s motion, 18.\n\n  ----, influence of, on form, 32.\n\n  Mountain ranges probably determined by magnetic force, 262.\n\n  Multiplication of life, 399.\n\n  Musical notes produced by heat, 97.\n\n  Muscular contraction by electricity, 202.\n\n  Musschenbroek of Leyden, 198.\n\n  Mythology, ancient, probable origin of, 353.\n\n\n  Natural polarization, 145.\n\n  Nebulous state of matter, 23.\n\n  Neptune, discovery of, 32.\n\n  Newton on gravitating force, 49.\n\n  Newton on motion, 9.\n\n  Newton\u2019s hypothesis of matter, 4.\n\n  ---- theory of heat, 115.\n\n  ---- theory of light, 120.\n\n  ---- theory of colours, 135.\n\n  Niepce on the chemical radiations, 168.\n\n  Nitrogen, magnetic neutrality of, 259.\n\n  ----, combinations of, 324.\n\n  ----, supposed metallic nature of, 325.\n\n  Nocturnal radiation, 83.\n\n  Northern lights, the, 268.\n\n\n  Obsidian transparency to heat, 66.\n\n  Ocean, waters of, 303.\n\n  Oersted discovers electro-magnetism, 238.\n\n  Orders of animals, 386.\n\n  Organic creation, influence, 185.\n\n  ---- compounds, 283.\n\n  ---- compounds, influence of light on them, 181.\n\n  ---- chemistry, 331.\n\n  ---- cell, 360.\n\n  ---- remains, 337.\n\n  Organized forms, varieties of, 35.\n\n  ---- bodies, heat of, 104.\n\n  Organization, progress of, 385.\n\n  Oxides, metallic, 326.\n\n  Oxidizable metals, 305.\n\n  Oxygen gas magnetic, 259.\n\n  ---- and nitrogen, uses of, 321.\n\n  ---- and carbon in animals, 396.\n\n  Ozone, 299.\n\n  ---- and electricity, 217.\n\n\n  Palladium maintaining slow combustion, 309.\n\n  Parathermic rays, 74.\n\n  ---- rays, influence in nature, 377.\n\n  Particles, Dumas on, 39.\n\n  Peach on phosphorescence of the sea, 159.\n\n  Pearsall on phosphorescence, 160.\n\n  Pendulum, oscillation of, indicates the earth\u2019s motion, 13.\n\n  Perkins on repulsion of heat, 108.\n\n  Permeation of heat, 96.\n\n  Perturbations of Uranus, 31.\n\n  Pestilential diseases, 216.\n\n  Phenomena of vision, 148.\n\n  ----, natural, of electricity, 194.\n\n  ----, recent geological, 349.\n\n  Phosphorescence of animals, 154.\n\n  ---- of plants, 156.\n\n  Phosphorescent spectrum, 184.\n\n  Phosphoric acid detected in the oldest rocks, 337.\n\n  Photosphere of the sun, 123.\n\n  Photography, 170.\n\n  ----, its importance, 180.\n\n  Physiological influences of electricity, 219.\n\n  Physical forces, action of, 4, 45.\n\n  ---- forces, modes of motion, 7.\n\n  ---- properties of polarized light, 142.\n\n  Physiological influences of magnetism, 268.\n\n  Pilchard, on the, by Couch, 315.\n\n  Plants, distribution of, dependent on light, 133.\n\n  ----, phosphorescence of, 156.\n\n  ----, respiration of, 312.\n\n  ---- and animals, dependence of, 313.\n\n  ----, growth of, 368.\n\n  ---- bend to the light, 373.\n\n  ----, distribution of, 378.\n\n  ---- of the Tropics, 381.\n\n  Plane polarization, 141.\n\n  \u201cPlastic nature\u201d of Cudworth, 10.\n\n  Plateau\u2019s experiment on bodies relieved from gravitation, 33.\n\n  Platinum maintaining slow combustion, 309.\n\n  Plato on motion, 10.\n\n  ---- on light, 119.\n\n  Plesiosaurus, the, 341.\n\n  Pliocene formations, 346.\n\n  Pl\u00fccker on crystallo-magnetic force, 57.\n\n  ---- on diamagnetic bodies, 256.\n\n  Plumule, use of, 369.\n\n  Plutonic rocks, 334.\n\n  Polarization, circular and elliptical, 143.\n\n  Polarization of light, 139.\n\n  Polar condition of matter, 265.\n\n  Polypes and infusoria, 387.\n\n  Porosity of matter, 41.\n\n  Porta, Baptista--camera obscura, 149.\n\n  Powers, active, in nature, 405.\n\n  Prevost, theory of, on heat, 96.\n\n  Primary origin of our planet, 334.\n\n  Principles of motion, 10.\n\n  Prismatic refraction, 121.\n\n  ---- rays, heat of, 67.\n\n  ---- analysis of sunbeam, 134.\n\n  Principle of gravitation, 29.\n\n  ----, elementary, 38.\n\n  Properties, essential, of matter, 5.\n\n  Pseudomorphism, 54.\n\n  Psychology of flowers, 357.\n\n  Pterodactyl, the, 342.\n\n  Pythagorean doctrine of motion, 10.\n\n\n  Quinine, solution, influence of, on light, 129.\n\n\n  Radiant heat, 69.\n\n  Radiation and absorption of heat, 77.\n\n  ----, nocturnal, 83.\n\n  Raia torpedo, 211.\n\n  Raymond, Du Bois, on animal electricity, 221.\n\n  Refrangibility, rays of high, 130.\n\n  ---- of solar forces, 168.\n\n  Refraction, prismatic, 121.\n\n  Races, dependence of, 315.\n\n  Repulsion of heat, 108.\n\n  Respiration of animals, 310.\n\n  ---- plants, 312.\n\n  Rest, absolute and relative, 15.\n\n  Respiration a cause of heat, 105.\n\n  Retina, the, 149.\n\n  Revelations of nature, 401.\n\n  Revolution of magnetic poles, 246.\n\n  Robinson on decomposition by heat, 98.\n\n  Rock formations, 335.\n\n  Rocks, conducting power of, 224.\n\n  Rosse\u2019s, Lord, telescopes, 25.\n\n  Rumford, Count, experiments on heat, 18.\n\n  ---- on chemical properties of light, 99.\n\n  Rings, Newton\u2019s, 137.\n\n\n  Safety lamp of Davy, 309.\n\n  Salt rock, transparency to heat, 65.\n\n  Saturn\u2019s ring explained, 34.\n\n  Savart on vibrating plates, 257.\n\n  Seasons, influence of heat on the, 70.\n\n  Sea, phosphorescence of, 158.\n\n  Sch\u00f6nbein on ozone, 299.\n\n  Schwabe on solar spots, 243.\n\n  Seebeck on thermo-electricity, 211, 248.\n\n  Selenite and alabaster, 60.\n\n  S\u00e9narmont on conducting power of crystals for heat, 257.\n\n  Shooting stars, 21.\n\n  Silicon, allotropic state of, 43.\n\n  Silica, substitution of, 345.\n\n  Simple bodies, chemical, 329.\n\n  Sky of tropical climes, 319.\n\n  Slow combustion in animals, 397.\n\n  Smee on electricity and vitality, 219.\n\n  Solar system, motion of, 11.\n\n  ---- disc, light from, 185.\n\n  ---- influence on magnetism, 263.\n\n  Solidification of gases by Faraday, 112.\n\n  Solstices, summer and winter, 77.\n\n  Solar spots connected with magnetism, 243.\n\n  Solar phosphori, 161.\n\n  Somerville, Mrs., magnetises needles by light, 263.\n\n  Sound and light, analogy of, 151.\n\n  Spectra produced by polarization of light, 144.\n\n  Spectrum, dark lines of, 125.\n\n  Spheroidal condition of fluids, 107.\n\n  Spontaneous ignition, 307.\n\n  Stahl on phlogiston, 305.\n\n  Stars, shooting, theories of, 21.\n\n  Steel ornaments incandescent, 137.\n\n  Stereoscope, the, 151.\n\n  Stokes, Prof., on fluorescence, 130.\n\n  Stratified formations, 334.\n\n  Strength of animals, 400.\n\n  Structure, influence of, on magnetism, 256.\n\n  ----, relation of, to physical phenomena, 257.\n\n  Struv\u00e9 on motion of solar system, 12.\n\n  Substitution, chemical, 279.\n\n  ----, law of, 288.\n\n  Substances, all, electric, 197.\n\n  Subterranean temperature, 91.\n\n  Sulphuric acid, permeability to heat, 65.\n\n  Surfaces, action of, 282.\n\n  Sulzar on galvanism, 201.\n\n  Sulphuretted hydrogen, solid, 111.\n\n  Sun, the central, 28.\n\n  ----, the source of light, 121.\n\n  ----, physical state of the, 123.\n\n  ----, a magnetic centre, 265.\n\n\n  Tadpole, metamorphosis of, 389.\n\n  Talbot\u2019s sensitive photographic process, 178.\n\n  Telegraph, electric, 231.\n\n  Temperature of incandescence, 68.\n\n  Temperature, subterranean, 91.\n\n  Terrestrial currents of electricity, 224.\n\n  ---- magnetism, 255.\n\n  Thales of Miletus discovers electricity, 193.\n\n  Theories of light, 86, 118.\n\n  Thermography, 188.\n\n  Thermometric examination of the temperature of flowers, 76.\n\n  Thermo-electricity, 209.\n\n  Theory of motion producing force, 15.\n\n  Thilorier on solid carbonic acid, 111.\n\n  Time, influence of, 332.\n\n  Tissues, catalytic power of, 310.\n\n  Tourmaline, action of, on light, 142.\n\n  Trade winds, 81.\n\n  Transition series of rocks, 336.\n\n  Transparency, calorific, 67.\n\n  ----, luminous, 124.\n\n  Transmutation of matter, 37.\n\n  Transmission of light, 128.\n\n  Transcalescent bodies, 94.\n\n  Trevelyan, Mr., on vibration of heated metals, 97.\n\n  Tyndale proves the influence of structure on magnetism, 258.\n\n  Type, elements of the organic, 289.\n\n\n  Undulations producing colour, 131.\n\n  Undulatory theory of heat, 115.\n\n  ---- theory of light, 121.\n\n  Uranus, discovery of, 31.\n\n  Uranium glass, influence of, on light, 129.\n\n\n  Vapour, elastic force of, 318.\n\n  Variation, magnetic, 244.\n\n  Vegetables conductors of electricity, 379.\n\n  Vegetable life, phenomena of, 357.\n\n  Vegetation of carboniferous epoch, 339.\n\n  Velocity of electricity, 231.\n\n  Vertebrate animals, 390.\n\n  Vision, phenomena of, 148.\n\n  Vis vit\u00e6, vital principle, 391.\n\n  Vision single with a pair of eyes, 150.\n\n  Vitality superior to physical force, 53.\n\n  Vision, seat of, 149.\n\n  Volume, doctrine of, 287.\n\n  Volcanic action referred to chemical action, 271.\n\n  Volatilization of matter, 27.\n\n  Voltaic electricity, 201.\n\n\n  Water, absorption of heat by, 74.\n\n  ---- frozen free of air, 112.\n\n  ---- free of air, peculiar state of, 113.\n\n  ----, electricity in a drop of, 204.\n\n  ----, composition of, 296.\n\n  Wargentin\u2019s notice of aurora, 248.\n\n  Wave movement of heat and light, 68.\n\n  Wealden formations, 343.\n\n  Wedgwood on incandescence, 100.\n\n  Wells, Dr., on dew, 84.\n\n  Wiedemann on electrical vibrations, 257.\n\n  Wenzel\u2019s proportional numbers, 277.\n\n  Winds dependent on heat, 80.\n\n  Wollaston notices dark lines in spectrum, 125.\n\n  World, its age, 404.\n\n\n  Young on molecular forces, 49.\n\n\n  Zodiacal light, 25.\n\n  Zoophytes, microscopic, 387.\n\n\nTHE END.\n\n\nWilson and Ogilvy, 57, Skinner Street, Snowhill, London.\n\n\n\n\nBOHN\u2019S BOOKS.\n\n\nBOHN\u2019S STANDARD LIBRARY.\n\n_Post 8vo., Elegantly Printed, and bound in Cloth, at 3s. 6d. per Vol._\n\n\n  =1. THE MISCELLANEOUS WORKS AND REMAINS OF THE REV. ROBERT HALL=,\n      with Memoir by DR. GREGORY, and Essay by JOHN FOSTER. _Portrait._\n\n  =2 & 3. ROSCOE\u2019S LIFE AND PONTIFICATE OF LEO X.= Edited by his Son,\n      with the Copyright Notes, Documents, &c. In 2 Vols. _Portraits._\n\n  =4. SCHLEGEL\u2019S LECTURES ON THE PHILOSOPHY OF HISTORY.= Translated\n      from the German, with a Memoir by J. B. ROBERTSON, Esq.\n      _Portrait._\n\n  =5 & 6. SISMONDI\u2019S HISTORY OF THE LITERATURE OF THE SOUTH OF\n      EUROPE.= Translated by ROSCOE. In 2 Vols. _Portraits._\n\n  =7. ROSCOE\u2019S LIFE OF LORENZO DE MEDICI=, with the Copyright Notes, &c.\n\n  =8. SCHLEGEL\u2019S LECTURES ON DRAMATIC LITERATURE.= _Portrait._\n\n  =9 & 11. BECKMANN\u2019S HISTORY OF INVENTIONS, DISCOVERIES, AND\n      ORIGINS.= Fourth Edition, revised and enlarged. In 2 Vols.\n      _Portraits._\n\n  =10. SCHILLER\u2019S HISTORY OF THE THIRTY YEARS\u2019 WAR AND REVOLT OF THE\n      NETHERLANDS.= Translated by A. J. W. MORRISON. _Portrait._\n\n  =12. SCHILLER\u2019S WORKS.= Vol. II. [Conclusion of \u201cThe Revolt of the\n      Netherlands;\u201d \u201cWallenstein\u2019s Camp;\u201d \u201cThe Piccolomini;\u201d \u201cThe\n      Death of Wallenstein;\u201d and \u201cWilhelm Tell.\u201d] _With Portrait of\n      Wallenstein._\n\n  =13. MEMOIRS OF THE LIFE OF COLONEL HUTCHINSON.= By his Widow: with\n      an \u201cAccount of the Siege of Lathom House.\u201d _Portrait._\n\n  =14. MEMOIRS OF BENVENUTO CELLINI=, by HIMSELF. By ROSCOE. _Portrait._\n\n  =15, 18, & 22. COXE\u2019S HISTORY OF THE HOUSE OF AUSTRIA=, from the\n      foundation of the Monarchy, 1218-1792. Complete in 3 vols.\n      _Portraits._\n\n  =16, 19, & 23. LANZI\u2019S HISTORY OF PAINTING.= By ROSCOE. In 3 Vols.\n      _Portraits._\n\n  =17. OCKLEY\u2019S HISTORY OF THE SARACENS.= Revised and Completed.\n      _Portrait._\n\n  =20. SCHILLER\u2019S WORKS.= Vol. III. [\u201cDon Carlos,\u201d \u201cMary Stuart,\u201d \u201cMaid\n      of Orleans,\u201d and \u201cBride of Messina.\u201d] _Frontispiece._\n\n  =21, 26, & 33. LAMARTINE\u2019S HISTORY OF THE GIRONDISTS=; or, Memoirs\n      of the French Revolution, from _unpublished sources_. In 3 Vols.\n      _Portraits._\n\n  =24. MACHIAVELLI\u2019S HISTORY OF FLORENCE, PRINCE=, &c. _Portrait._\n\n  =25. SCHLEGEL\u2019S LECTURES ON THE PHILOSOPHY OF LIFE AND THE PHILOSOPHY\n      OF LANGUAGE.= Translated by A. J. W. MORRISON.\n\n  =27, 32, & 36. RANKE\u2019S HISTORY OF THE POPES.= Translated by E.\n      FOSTER. In 3 Vols. _Portraits._ (The only complete English\n      translation.)\n\n  =28, 30, & 34. COXE\u2019S MEMOIRS OF THE DUKE OF MARLBOROUGH.= In 3 Vols.\n      _Portraits._\n\n  *** ATLAS, of 26 fine large Maps and Plans of Marlborough\u2019s\n      Campaigns, (being all those published in the original edition at\n      \u00a312 12s.) 4to. 10s. 6d.\n\n  =29. SHERIDAN\u2019S DRAMATIC WORKS AND LIFE.= _Portrait._\n\n  =31. GOETHE\u2019S WORKS.= Vol. I. [His Autobiography. 13 Books.]\n      _Portrait._\n\n  =35. WHEATLEY ON THE COMMON PRAYER.= _Frontispiece._\n\n  =37. MILTON\u2019S PROSE WORKS.= Vol. I. _Portrait._\n\n  =38, 41, & 45. MENZEL\u2019S HISTORY OF GERMANY.= Complete in 3 Vols.\n      _Portrait._\n\n  =39. MILTON\u2019S PROSE WORKS.= Vol. II. _Frontispiece._\n\n  =40. MILTON\u2019S PROSE WORKS.= Vol. III. _Portrait of Laud._\n\n  =42. SCHLEGEL\u2019S \u00c6STHETIC AND MISCELLANEOUS WORKS.=\n\n  =43. GOETHE\u2019S WORKS.= Vol. II. [Remainder of his Autobiography, and\n      Travels.]\n\n  =44. SCHILLER\u2019S WORKS.= Vol. IV. [\u201cThe Robbers,\u201d \u201cFiesko,\u201d \u201cLove and\n      Intrigue,\u201d and \u201cThe Ghost-Seer.\u201d] Translated by HENRY G. BOHN.\n\n  =46. SCHLEGEL\u2019S LECTURES ON MODERN HISTORY.=\n\n  =47. LAMARTINE\u2019S HISTORY OF THE FRENCH REVOLUTION OF 1848.=\n\n  =48 & 50. JUNIUS\u2019S LETTERS=, with Notes, Additions, Essay, Index, &c.\n      2 Vols.\n\n  =49, 55, 60, 65, 71. VASARI\u2019S LIVES OF THE MOST CELEBRATED PAINTERS,\n      SCULPTORS, AND ARCHITECTS.= Translated by MRS. FOSTER, with\n      Notes. Complete in 5 Vols., with Index.\n\n  =51. TAYLOR\u2019S (JEREMY) HOLY LIVING AND DYING.= _Portrait._\n\n  =52. GOETHE\u2019S WORKS.= Vol. III. [\u201cFaust,\u201d \u201cIphigenia,\u201d \u201cTorquato\n      Tasso,\u201d and \u201cEgmont.\u201d] Translated by Miss SWANWICK. With \u201cGoetz\n      von Berlichingen,\u201d translated by SIR WALTER SCOTT.\n\n  =53, 56, 58, 61, 66, 67, & 75. NEANDER\u2019S CHURCH HISTORY.= Carefully\n      revised by the REV. A. J. W. 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EMERSON\u2019S ORATIONS AND LECTURES.=\n\n\n_Also, uniform with the_ STANDARD LIBRARY, 5_s._ (_except Thucydides,\n\u00c6schylus, Virgil, Horace, and Cicero\u2019s Offices, which are_ 3_s._ 6_d._\n_each_),\n\nBOHN\u2019S CLASSICAL LIBRARY.\n\nA SERIES OF LITERAL PROSE TRANSLATIONS OF THE GREEK AND LATIN CLASSICS,\nWITH NOTES.\n\n  =1. HERODOTUS.= By the REV. HENRY CARY, M.A. _Index, and\n      Frontispiece._\n\n  =2 & 3. THUCYDIDES.= By the REV. H. DALE. In 2 Vols. (3_s._ 6_d._\n      each).\n\n  =4. PLATO.= Vol. I. By CARY. [The Apology of Socrates, Crito, Ph\u00e6do,\n      Gorgias, Protagotas, Ph\u00e6drus, The\u00e6tetus, Euthyphron, Lysis.]\n\n  =5. LIVY\u2019S HISTORY OF ROME.= Vol I., Books 1 to 8.\n\n  =6. PLATO.= Vol. II. By DAVIS. [The Republic, Tim\u00e6us, and Critias.]\n\n  =7. LIVY\u2019S HISTORY OF ROME.= Vol. II., Books 9 to 26.\n\n  =8. SOPHOCLES.= The Oxford Translation, revised.\n\n  =9. \u00c6SCHYLUS.= By an OXONIAN. (Price 3_s._ 6_d._)\n\n  =10. ARISTOTLE\u2019S RHETORIC AND POETIC.= With Examination Questions.\n\n  =11. LIVY\u2019S HISTORY OF ROME.= Vol. III., Books 27 to 36.\n\n  =12 & 14. EURIPIDES.= From the Text of Dindorf. In 2 Vols.\n\n  =13. VIRGIL.= By DAVIDSON. New Edition, Revised. (Price 3_s._ 6_d._)\n\n  =15. HORACE.= By SMART. New Edition, Revised. (Price 3_s._ 6_d._)\n\n  =16. ARISTOTLE\u2019S ETHICS.= By PROF. R. W. BROWNE, of King\u2019s College.\n\n  =17. CICERO\u2019S OFFICES.= [Old Age, Friendship, Scipio\u2019s Dream,\n      Paradoxes, &c.]\n\n  =18. PLATO.= Vol. III. By G. BURGES, M.A. [Euthydemus, Symposium,\n      Sophistes, Politicus, Laches, Parmenides, Cratylus, and Meno.]\n\n  =19. LIVY\u2019S HISTORY OF ROME.= Vol. IV. (which completes the work).\n\n  =20. C\u00c6SAR AND HIRTIUS.= With Index.\n\n  =21. HOMER\u2019S ILIAD.= _Frontispiece._\n\n  =22. HOMER\u2019S ODYSSEY=, HYMNS, EPIGRAMS, AND BATTLE OF THE FROGS AND\n      MICE.\n\n  =23. PLATO.= Vol. IV. By G. 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Notes and Essays.\n      _Frontispiece._ 3_s._\n\n  =---- ODYSSEY=, (uniform). _Frontispiece._ 3_s._\n\n  =SCOTT\u2019S POETICAL WORKS=, and Life, in one volume. _Port. and\n      Frontisp._ 3_s._ 6_d._\n\n  =STURM\u2019S REFLECTIONS ON THE WORKS OF GOD.= _Frontisp._ 2_s._\n\n  =THOMPSON\u2019S SEASONS.= With his Castle of Indolence, _4 beautiful\n      Woodcuts_. 2_s._\n\n  =VATHEK, AND THE AMBER WITCH.= 2 vols. in 1. 3_s._\n\n\n\n\nTRANSCRIBER\u2019S NOTE.\n\n\nArchaic, obsolete, unusual and inconsistent spellings have been\nmaintained as in the original book. Obvious errors have been fixed as\ndetailed below.\n\nSome entries in the index were out of alphabetical order in the\noriginal book. They have been moved without noting them in the details\nbelow.\n\nThe totals in the various tables are not equal to the sum of the column\nabove them. I assume this is due to round off error, or details in the\noriginal data which are not represented here. No attempt has been made\nto correct these totals.\n\nIn the original book, half of the publisher\u2019s catalogue (Bohn\u2019s Books)\nwas in the beginnig of the book. It was moved to immediately precede\nthe other half of the catalogue at the end of the book.\n\nPreface, Contents, Introduction, Index, Bohn\u2019s Books and Transcriber\u2019s\nNote have been added to the table of contents. Only the chapters of\nthe book were in the table of contents in the original book. The title\n\"Bohn\u2019s Books\" was inserted into the beginning of the publisher\u2019s book\ncatalogue.\n\nIn the table below, the first line shows the text in this ebook, the\nsecond line shows the text in the original book.\n\n  Page vii.:  conditions of Matter--Diamagnetism, &c.    235\n  Originally: conditions of Matter--Dia-Magnetism, &c.    235\n\n  Page viii.: Time, an element in Nature\u2019s Operations--Geological\n  Originally: Time, an element in Nature\u2019s Operations==Geological\n\n  Page viii.: Progress of Matter towards Organization\n  Originally: Progress of Matter rowards Organization\n\n  Page xii.:  of external nature, evoked beautiful spiritualizations\n  Originally: of external nature, evoked beautiful spirtualizations\n\n  Footnote 1: Boscovich regarded the constitution of matter differently\n  Originally: Boscovitch regarded the constitution of matter differently\n\n  Footnote 1: full explanation of the theory of Boscovich.)\n  Originally: full explanation of the theory of Boscovitch.)\n\n  Page 8:     The views of metaphysicians regarding motion involve\n  Originally: The views of metaphyscians regarding motion involve\n\n  Page 14:    tremulous gyration upon the deck of a vast a\u00ebrial ship\n  Originally: tremulous gyration upon the deck of a vast aerial ship\n\n  Page 27:    agent of organisation and all manifestations of beauty?\n  Originally: agent of organisation and all manifestatious of beauty?\n\n  Footnote 18: fixes, est d\u00e9termin\u00e9e par ce qui pr\u00e9c\u00e8de entre certaines\n  Originally:  fixes, est determin\u00e9e par ce qui pr\u00e9c\u00e8de entre certaines\n\n  Footnote 18: est le groupe central de l\u2019ensemble du syst\u00e8me\n  Originally:  est le groupe central l\u2019ensemble du syst\u00e8me\n\n  Footnote 24: into a single mass at the bottom of the flask under\n  Originally:  into a single mass at the bottom of the flask unde\n\n  Page 42:    with which the particles combined, from interstices,\n  Originally: with which the particles combined, from insterstices,\n\n  Page 45:    bromine, &c., are the results of different _allotropic_\n  Originally: bromime, &c., are the results of different _allotropic_\n\n  Page 46:    which,--from the imperfections of science,--resisting\n  Originally: which,--from the imperfectious of science,--resisting\n\n  Page 46:    The experiments of Faraday and of Pl\u00fccker prove\n  Originally: The experiments of Faraday and of Plucker prove\n\n  Footnote 25: Young\u2019s _Natural Philosophy_; ed. by Rev. P. Kelland.\n  Originally:  Young\u2019s _Natural Philosophy_; ed. by Rev. P. Lelland.\n\n  Footnote 35: Hence the origin of compound and visible bodies; hence\n  Originally:  Hence the origin of compouud and visible bodies; hence\n\n  Page 50:    her operations, but the very processes themselves.\n  Originally: her operations, but the very processes themselvss.\n\n  Paqe 59:    combination appears to the eye in no respect different\n  Originally: combinatiou appears to the eye in no respect different\n\n  Page 61:    Those fissures formed by the first system of crystalline\n  Originally: Those fissures formed by the first sytsem of crystalline\n\n  Page 68:    luminous power are sufficiently striking to convince us\n  Originally: luminous power are sufficienlty striking to convince us\n\n  Page 109:   of temperature is experienced.[79] Professor Pl\u00fccker, of\n  Originally: of temperature is experienced.[79] Professor Plucker, of\n\n  Footnote 55: this motion. He was followed by Musschenbroek, and then\n  Originally:  this motion. He was followed by Muschenbroek, and then\n\n  Footnote 61: _regarding the internal temperature of the Earth_: by\n  Originally:  _regarding the internal temperature of tha Earth_: by\n\n  Footnote 78: _en vertu de l\u2019\u00e9tat sph\u00e9ro\u00efdal dans un creuset_\n  Originally:  _en vertu de l\u2019\u00e9tat sph\u00e9rod\u00efal dans un creuset_\n\n  Page 121:   Fraunhofer, Herschel, Brewster, and others, but proceed\n  Originally: Frauenhofer, Herschel, Brewster, and others, but proceed\n\n  Page 123:   between charcoal points at the poles of a powerful voltaic\n  Originally: between charcoal points a the poles of a powerful voltaic\n\n  Page 129:   of quinine, and the fluor spar, we obtain the same results\n  Originally: of quinine, and the flour spar, we obtain the same results\n\n  Page 140:   the first instance, by Erasmus Bartholin, in Iceland-spar,\n  Originally: the first instance, by Erasmus Bartolin, in Iceland-spar,\n\n  Page 145:   from what has been already stated, that some\n  Originally: from what has beeen already stated, that some\n\n  Page 153:   to prove that light is absolutely necessary to\n  Originally: to prove that light is absolutely neccessary to\n\n  Page 159:   of light behind them.[113] By microscopic examination\n  Originally: of light behind them.[113] By miscroscopic examination\n\n  Page 159:   Benvenuto Cellini gave a curious account of a carbuncle\n  Originally: Benvenuto Cellini give a curious account of a carbuncle\n\n  Page 160:   near a fire. From this it may be inferred that the\n  Originally: near a a fire. From this it may be infered that the\n\n  Footnote 88: Brande\u2019s _Manual of Chemistry_; or, indeed, any work\n  Originally:  Brande\u2019s _Mannal of Chemistry_; or, indeed, any work\n\n  Footnote 94: Schouw, _Grundz\u00fcge der Pflanzengeographie_. Also his\n  Originally:  Schouw, _Grund\u00fczge der Pflanzengeographie_. Also his\n\n  Footnote 95: Fraunhofer\u2019s measure of illuminating power is as\n  Originally:  Frauenhofer\u2019s measure of illuminating power is as\n\n  Footnote 99: _Sur une Propri\u00e9t\u00e9 de la Lumi\u00e8re R\u00e9fl\u00e9chie_: M\u00e9moires\n  Originally:  _Sur une Propri\u00e9t\u00e9 de la Lumi\u00e8re R\u00e9fl\u00e9chie_: Memoires\n\n  Page 176:   the strongest sunlight which has passed through\n  Originally: the strongest sun-light which has passed through\n\n  Page 179:   productions of the photographer as on those of the\n  Originally: productions of the photograper as on those of the\n\n  Page 180:   preserve the lineaments of those who have benefited\n  Originally: preserve the lineaments of those who have benefitted\n\n  Page 185:   line, over which no action takes place, is preserved at\n  Originally: line, over which no action takes plates, is preserved at\n\n  Page 185:   presented to us by a circular body: calorific action seems\n  Originally: present to us by a circular body: calorific action seems\n\n  Page 188:   piece of wood is used instead of a metal, there will, by\n  Originally: piece of wood is used instead of a medal, there will, by\n\n  Footnote 126: _dans la v\u00e9g\u00e9tation_: by Senebier; Gen\u00e8ve et Paris, 1788\n  Originally:   _dans la v\u00e9getation_: by Senebier; Gen\u00e8ve et Paris, 1788\n\n  Page 198:   Leyden phial,--so called from its inventor, Musschenbroek,\n  Originally: Leyden phial,--so called from its inventor, Muschenbrock,\n\n  Page 219:   may be made a measurer of nervous irritability.[154] There\n  Originally: may be made a measurer of nervous iritability.[154] There\n\n  Footnote 141: _Trait\u00e9 Exp\u00e9rimental de l\u2019\u00c9lectricit\u00e9 et du Magn\u00e9tisme_:\n  Originally:   _Trait\u00e9 Exp\u00e9rimental de l\u2019Electricit\u00e9 et du Magn\u00e9tisme_:\n\n  Footnote 146: _Trait\u00e9 Exp\u00e9rimental de l\u2019\u00c9lectricit\u00e9 et du Magn\u00e9tisme_.\n  Originally:   _Trait\u00e9 Exp\u00e9rimental de l\u2019Electricit\u00e9 et du Magn\u00e9tisme_\n\n  Footnote 160: where the cobalt was discovered between two portions of\n  Originally:   where the cobalt was discovered betweed two portions of\n\n  Page 235:   Storms--Magnetic conditions of Matter--Diamagnetism,\n  Originally: Storms--Magnetic conditions of Matter--Dia-Magnetism,\n\n  Page 236:   Magn\u00eatum, quia sit patriis in finibus ortus.\n  Originally: Magn\u00eatum, buia sit patriis in finibus ortus.\n\n  Page 251:   conditions of change in this our earth: an element to\n  Originally: conditions of change in this our earth: an elemeut to\n\n  Page 257:   Wiedemann, by employing a fine point through which\n  Originally: Wiedmann, by employing a fine point through which\n\n  Page 258:   than in any other. M. Wiedemann comes to the conclusion\n  Originally: than in any other. M. Wiedmann comes to the conclusion\n\n  Page 260:   salt, the protosulphate, ordinarily crystallizes so that\n  Originally: salt, the proto-sulphate, ordinarily crystallizes so that\n\n  Footnote 176: Humboldt: _Expos\u00e9 des Variations Magn\u00e9tiques_.\n  Originally:   Humboldt: _Expos\u00e9 des Variations Magnetiques_.\n\n  Footnote 188: _Electro-Magnetic Influence_, by Professor Zantedeschi.\n  Originally:   _Electro-Magnetic Influence_, by Professor Zandeteschi.\n\n  Footnote 190: detailed account of the experiments of Faraday, Pl\u00fccker,\n  Originally:   detailed account of the experiments of Faraday, Plucker,\n\n  Page 276:   light determine these changes? It is evident, although\n  Originally: light determine these change? It is evident, although\n\n  Page 281:   chemical change. D\u00f6bereiner next discovered that\n  Originally: chemical change. D\u0153bereiner next discovered that\n\n  Page 282:   a fearful example in the progress of Asiatic\n  Originally: a fearful example in the progress of Asatic\n\n  Page 300:   as being either peroxide of hydrogen, or an allotropic\n  Originally: as being either per-oxide of hydrogen, or an allotropic\n\n  Page 304:   the gas which we employ so advantageously for illumination\n  Originally: the gas which we emply so advantageously for illumination\n\n  Page 306:   increasing,--true combustion takes place. In this way\n  Originally: increasing,--true combustion takes plaee. In this way\n\n  Page 306:   sawdust, &c., frequently ignite; and to such an\n  Originally: saw-dust, &c., frequently ignite; and to such an\n\n  Page 316:   Mr. Darwin remarks, that if the immense sea-weeds of\n  Originally: Mr. Darwin remarks, that if the immense seaweeds of\n\n  Page 317:   When Shakespeare made his charming Ariel sing--\n  Originally: When Shakspeare made his charming Ariel sing--\n\n  Footnote 212: (Redundant line removed before item 2 in table.)\n  Originally: According to one view,      | According to the other view,\n\n  Page 334:   speculation, which may have occasional marks of ingenuity,\n  Originally: speculation, whieh may have occasional marks of ingenuity,\n\n  Page 337:   origin, the rational inference is against the speculation;\n  Originally: orgin, the rational inference is against the speculation;\n\n  Page 370:   capsule of _nigella orientalis_ consists of pods assembled\n  Originally: capsule of _nigilla orientalis_ consists of pods assembled\n\n  Page 370:   a centre, and partially united; in _nigella damascena_\n  Originally: a centre, and partially united; in _nigilla damascena_\n\n  Page 399:   whose minds are sceptical upon any development of the\n  Originally: whose mind are sceptical upon any development of the\n\n  Page 406:   evidence of a beautiful adjustment of the balance of\n  Originally: evidence of a beautifnl adjustment of the balance of\n\n  Page 408:   Let but a slight disturbance occasion a vibration\n  Originally: Let but a slight disturbance occcasion a vibration\n\n  Page 409:   A cheerless philosophy, derived from the transcendentalism\n  Originally: A cheerless philosophy, derived from the transendentalism\n\n  Page 410:   which are allowed the privilege of tracing out its\n  Originally: which are alowed the privilege of tracing out its\n\n  Page 413:   A\u00ebreal currents dependent on heat, 80.\n  Originally: \u00c6real currents dependent on heat, 80.\n\n  Page 413:   Animal electricity, 211, 392.\n  Originally: Magnetic electricity, 211, 392.\n\n  Page 413:   Bartholin on Iceland spar, 140.\n  Originally: Bartolin on Iceland spar, 140.\n\n  Page 414:   Cagniard de la Tour state, 106.\n  Originally: Caignard de la Tour state, 106.\n\n  Page 415:   D\u00f6bereiner\u2019s lamp, 281.\n  Originally: Doebereiner\u2019s lamp, 281.\n\n  Page 415:   Eye, mechanism of, 149.\n  Originally: Eye, mechanism of, 491.\n\n  Page 416:   ---- on diamagnetism, 254.\n  Originally: ---- on dia-magnetism, 254.\n\n  Page 418:   Musschenbroek of Leyden, 198.\n  Originally: Muschenbrock of Leyden, 198.\n\n  Page 421:   Wiedemann on electrical vibrations, 257.\n  Originally: Wiedman on electrical vibrations, 257.\n\n  Bohn\u2019s Books: =LOUDON\u2019S (MRS.) ENTERTAINING NATURALIST=,\n  Originally:   =LOUDON\u2019S (MRS.) ENTERTAING NATURALIST=,\n\n  Bohn\u2019s Books: Indexes of Scientific and Popular Names. _With_\n  Originally:   Indexes of Scientific and and Popular Names. _With_\n\n  Bohn\u2019s Books: =18. PLATO.= Vol. III. By G. BURGES, M.A. [Euthydemus,\n  Originally:   =8. PLATO.= Vol. III. By G. BURGES, M.A. [Euthydemus,\n\n  Bohn\u2019s Books: =35. JUVENAL, PERSIUS, &c.= By the REV. L. EVANS, M.A.\n  Originally:   =34. JUVENAL, PERSIUS, &c.= By the REV. L. EVANS, M.A.","title":"The Poetry of Science; or, Studies of the Physical Phenomena of Nature","tradition":"philosophy-ethics","translated_text":null,"word_count":144678}