{"collection":"scripture-revelation","full_text_available":true,"graph_url":"https://unchartedknowledge.5gfusion.net/v2/api/page/gutenberg_58222/graph","html_url":"https://unchartedknowledge.5gfusion.net/v2/page/gutenberg_58222","id":"gutenberg_58222","license":"Public Domain (US)","rights_basis":"gutenberg_metadata_copyright_false","source":"gutenberg","source_url":"https://www.gutenberg.org/ebooks/58222","summary":null,"tags":["Category: History - Ancient","Category: Philosophy & Ethics","Category: Religion/Spirituality","Category: Science - Physics","Cosmogony","Mars (Planet)","Milky Way"],"text":"Produced by ellinora, Charlie Howard, and the Online\nDistributed Proofreading Team at http://www.pgdp.net (This\nfile was produced from images generously made available\nby The Internet Archive/Canadian Libraries)\n\n\n\n\n\n\n\n\n\nTranscriber\u2019s Notes\n\n\nSuperscripts are indicated by caret symbols: 2^8 for single characters\nand 2^{1.5} for multiple characters. Italic text is enclosed in\n_underscores_. Other notes will be found at the end of this eBook.\n\n\n\n\n The\n Destinies of the Stars\n\n By\n Svante Arrhenius, Ph.D.\n\n President, Nobel Institute, Stockholm, Sweden\n (Recipient of the Nobel Prize in Chemistry, 1903)\n\n Authorized Translation from the Swedish\n By\n J.\u00a0E. Fries\n Fellow A.I.E.E.\n\n _Illustrated_\n\n G.\u00a0P. Putnam\u2019s Sons\n New York and London\n The Knickerbocker Press\n 1918\n\n\n\n\n COPYRIGHT, 1918\n BY\n G.\u00a0P. PUTNAM\u2019S SONS\n\n The Knickerbocker Press, New York\n\n\n\n\nTRANSLATOR\u2019S PREFACE\n\n\nWhen Dr. Svante Arrhenius in the year 1903 received the NOBEL PRIZE in\nChemistry it came as a fitting reward of his achievements principally\nin the electro-chemical field. It was natural, however, that a genius\nof his calibre would not limit his interest to the \u201cinfinitely\nsmall\u201d but would gradually broaden it to encompass the \u201cinfinitely\nlarge.\u201d And \u201cto take an interest\u201d means with Dr. Arrhenius to push\nthe boundaries of the unknown and of the unexplored a little farther\naway from man. His evolution in this respect runs parallel with that\nof all the great men who stand out as leaders in the history of\nscience. Wrapt up in the solution of a particular problem and fired\nwith the divine yearning to reach ultimate causes they are inevitably\ndriven to ever widening circles of research until this whole material\nuniverse, its whence and whither, becomes the overpowering passion\nof their spirits. Thus the mere titles of the works of Dr. Arrhenius,\nread in the sequence of their publication, give us, better than any\nbiography, the history of a soul, which, no matter what his unprofessed\nphilosophical faith may be, constitutes our strongest evidence in\nfavour of that theory of \u201cpurposiveness\u201d in the universe which Dr.\nArrhenius so heartily abhors (and justly so) when resorted to in\nnatural science, but which theory nevertheless (and justly so) is so\ndear to the philosopher:--_Researches in Regard to the Conductivity of\nElectrolytes; Conductivity of Extremely Diluted Solutions; Chemical\nTheory of Electrolytes; Textbook in Theoretical Electro-Chemistry;\nTextbook in Cosmological Physics; Worlds in the Making; Infinity of the\nUniverse; Life of the Universe as Conceived by Man from Earliest Ages\nto the Present Time_;--thus run the titles of a few of the works we\nalready have by Dr. Arrhenius\u2019 hand. How were it possible for him NOT\nto write _The Destinies of the Stars_? The volume came as inevitably\nas fruition follows flowering. What remains to be seen is if Dr.\nArrhenius can withstand the tremendous temptation that must be at work\nin his soul to lift, be it ever so little, the curtain that separates\nnatural science and philosophy; we hope he will give in; we admire in\nthis book how he reads \u201cThe Riddle of the Milky Way\u201d; we certainly wish\nto know how he reads--the riddle of the universe.\n\n_The Destinies of the Stars_ met with unexampled success in Sweden.\nThree editions appeared within two months when the book was published\nin November, 1915. The American version has been somewhat delayed\nprincipally due to war conditions. This, however, has not been wholly\na loss to the English-speaking world as Dr. Arrhenius by no means has\nbeen idle in the meantime. Considerable additional subject matter,\nincluding three new pictures, has been added, chiefly based on the most\nrecent astronomical discoveries some of which have been recorded as\nlate as 1917.\n\nFor valuable suggestions and for all the American equivalents of the\nmetric measures in the original, the reader as well as the translator,\nis indebted to a member of the Publishing House that presents this\nvolume in such an attractive way, Mr. E.\u00a0W. Putnam, himself an ardent\nlover of astronomy and a writer on the subject.\n\nDr. Arrhenius is justly renowned for his lucid style and polished form.\nAll that is lacking in these qualities within the covers of this volume\nis wholly due to the deficiencies of the translator, who however could\nnot resist the temptation of transferring to Anglo-Saxon soil this\nmonument to the genius of his former teacher, Dr. Svante Arrhenius.\n\n J.\u00a0E. FRIES.\n\n BIRMINGHAM, ALA., December 15, 1917.\n\n\n\n\nPREFACE\n\n\nSince I presented _Worlds in the Making_ and _Life of the Universe\nas Conceived by Man from Earliest Ages to the Present Time_ to the\npublic--which received them with far greater interest and appreciation\nthan I could foresee--I have had repeated occasions to treat new\nquestions of a cosmological nature, questions largely arisen from\nnew discoveries and observations within the scope of astronomy. Vast\nnew vistas have been opened through the study of the relation of the\nstars to the \u201cMilky Way\u201d and through observations of our neighbour\nplanets. The last mentioned give plain indications of the course of\nplanetary evolution and thus enable us to surmise the changing fate and\nfuture position of the Earth. In an earlier German publication, _Das\nSchicksal der Planeten_ (1911), I dealt with some of these problems.\nAs, further, the evolution of the solar system from the Milky Way\nnebula, to which I have devoted several lectures at home and abroad,\nmay be considered as the pre-history of the evolution of the planets, I\nhave given this collection of cosmogenic articles the common title _The\nDestinies of the Stars_. I offer as introduction a lecture delivered\nbefore the Fourth International Philosophical Congress in Bologna,\n1911, dealing with the \u201cOrigin of Star-Worship.\u201d\n\nHoping that this little book will, to a considerable extent, fill the\ngaps in my previous works, I present these treatises in remodelled form.\n\n SVANTE ARRHENIUS.\n\n STOCKHOLM,\n _November, 1915_.\n\n\n\n\nCONTENTS\n\n\n CHAPTER I\n PAGE\n ORIGIN OF STAR-WORSHIP 1\n\n Position and practical value of astronomy. Worship of stars.\n Chronology. The Australian negro\u2019s conception of the stars.\n Day and night, summer and winter. Solar year. Sun-worship.\n Changing phases of the moon in chronology. The Mexican\n \u201cTonalamatl.\u201d Moon-worship in Mesopotamia. Significance of\n the moon in astrology. The sun and the heat. Agriculture\u2019s\n demand on chronology. Worship of the planet Venus by the\n Mexicans and the Babylonians. The Church Calendar. The\n Zodiac. The seven planets. The week. Correspondence and\n sympathetic magic. The Platonic-Aristotelian philosophy.\n Astrology and alchemy. Tycho Brahe. Occult sciences.\n Aristarchos from Samos. Kopernicus. The progress of\n Astronomy.\n\n\n CHAPTER II\n\n THE MYSTERY OF THE MILKY WAY 41\n\n Primitive conceptions of the Milky Way. Anaxagoras and\n Demokritos. Ptolemaios. Galilei. Cosmogenic speculations.\n Wm. Herschel\u2019s statistical researches regarding the\n distribution of the stars. The Milky Way as the foundation\n of the stellar system. The Milky Way as a nebula.\n Classification according to age of the stars, their\n distribution and velocity. Motion in the Orion nebula.\n The planetary nebul\u00e6. Kapteyn\u2019s \u201cstar-drifts.\u201d The origin\n of the Milky Way. Comparison between the Milky Way and a\n spiral nebula in \u201cThe Dogs of Orion.\u201d A few details from\n the Milky Way. The infinitely great and the infinitely\n small. The magnitude and destiny of the Milky Way.\n\n\n CHAPTER III\n\n THE CLIMATIC IMPORTANCE OF WATER VAPOUR 84\n\n The four elements of Aristotle. Humid-warm climates. The Congo\n and Amazon basins. The carboniferous age. The effect\n of cloudiness. Desert climate. Steppes. \u201cKevirs\u201d and\n \u201cBayirs.\u201d Sand dunes. The great Kevir. Climatic changes.\n Khanikoff\u2019s description. Salt lakes. Deposits of salt\n through evaporation. Huntington about the arefaction of the\n earth. Humid period during the ice-age. Climatic changes\n during historic time. Africa, Asia, Greece, Italy, Sicily.\n West-Europe\u2019s climate has grown more marine. Present\n conditions.\n\n\n CHAPTER IV\n\n ATMOSPHERE AND PHYSICS OF THE STELLAR BODIES 119\n\n Outer envelope of the stars. The large planets. Spectra. Mars,\n Earth, Venus, Mercury. Atmosphere impossible on the moon.\n The light from the Earth. The atmosphere of Mercury. The\n atmosphere of Venus and its Clouds. Composition of air and\n its change with height. Forced circulation. Troposphere\n and Stratosphere. Hydrogen in the highest strata of the\n atmosphere. Water vapour and carbonic acid in the air.\n \u201cGeokoronium.\u201d Influence of gravity on composition of the\n atmosphere. The air on Venus and Mars.\n\n\n CHAPTER V\n\n THE CHEMISTRY OF THE ATMOSPHERE 155\n\n Inhabited Worlds. Kinship of the stellar bodies. Presence\n of life. Importance of water and carbon. Importance of\n temperature. All life evolved from existence in water.\n Necessity of oxygen. Bacteria. Reducing substances\n preponderable in the World-matter. Volcanic gases and gases\n in solidified lava. Water, vapour, carbon dioxide, nitrogen\n gas, and sulphurous acid. Permanent gases and hydrogen. The\n poisonous character of the original air. Its purification.\n The importance of plant life and necessity of a solid crust\n in this process. Supply of carbonic dioxide and production\n of oxygen. The work of Koene. Silica. Cooling of the Earth\n and changing surface temperature. The ice-periods. Centres\n of collapse and lines of fissure in the crust. General\n survey of the gradual change of the air.\n\n\n CHAPTER VI\n\n THE PLANET MARS 180\n\n The controversy about the habitableness of Mars. Humidity on\n Mars. Early observations. The spectra of Mars and of the\n Moon compared. Investigations by Campbell and Marchand. The\n work of Lowell. Measurements by Slipher. Calculations by\n Very. The temperature on Mars according to these sources.\n Campbell\u2019s expedition to Mount Whitney in California.\n Oxygen on Mars. The cold on Mars detrimental to anything\n but the lowest forms of life. Cause of different results\n by Slipher and Campbell. Very\u2019s answer to Campbell\u2019s\n criticism. New measurements by Slipher. Campbell\u2019s new\n method of measurement of 1910. Christiansen calculates\n the temperature on Mars from intensity of the Sun\u2019s\n radiation. The sun-constant. Average temperature of Mars\n about forty degrees Centigrade. Possibly low plant life\n around the poles during summer. The canals on Mars are\n probably fissures in the crust. The length of the canals\n compared with that of the fissures in Earth\u2019s crust.\n The double canals on Mars compared with the parallel\n fissures in Calabria. Emanations along the fissures. The\n canals as affected by increasing cold or heat. The polar\n snow. Thawing of the canals. Travel of the water vapour\n independent of the topography. The desert sand on Mars.\n Clouds and mists. Highlands and mountains on Mars. Sand\n filling of the canals. The seas on Mars. The straightness\n and uniform breadth of the canals an illusion. Light and\n dark spots. \u201cNew\u201d canals. The fancies of Lowell.\n\n\n CHAPTER VII\n\n MERCURY, THE MOON, AND VENUS 228\n\n Fissures on Mercury. Lowell\u2019s drawing. Centres of collapse.\n Absence of atmosphere. The climate on the Moon. W.\n Pickering\u2019s belief in frost formations on the Moon. The\n mountains on the Moon. Volcanoes. Circular elevated rings.\n \u201cSeas\u201d on the Moon. The Crater \u201cLinn\u00e9.\u201d \u201cSinuses\u201d and\n \u201cStreaks\u201d on the Moon. The light matter of the streaks\n probably lava-scum. The colour of the Moon and of the\n Earth. Comparison between the Moon and Mars. Changes on\n the Moon. \u201cSnow\u201d and \u201cVegetation\u201d on the Moon according to\n W. Pickering. The fate of Mars and of the Earth. Falling\n meteoric dust. The climate on Venus. Swamps like those of\n the carboniferous age. Abundant vegetation. Low organisms.\n \u201cCulture\u201d on Venus will proceed from the poles. The future\n of Venus. The claims of astrology in modern light. Tycho\n Brahe. The dreams of Giordano Bruno probably true.\n\n\n\n\nILLUSTRATIONS\n\n\n PAGE\n FIG. 1.--THE MILKY WAY 46\n Photo by Easton.\n\n FIG. 2.--PLANETARY NEBULA NO. 7009, NEW GENERAL CATALOGUE 52\n\n FIG. 3.--NEBULA NO. 4594, NEW GENERAL CATALOGUE 66\n\n FIG. 4.--NEBULA NO. 101 IN MESSIER\u2019S CATALOGUE 70\n\n FIG. 5.--NEBULA NO. 51 IN MESSIER\u2019S CATALOGUE 71\n\n FIG. 6.--MILKY WAY BETWEEN CASSIOPEIA AND SWAN 76\n According to Wolf.\n\n FIG. 7.--MILKY WAY IN EAGLE AND SAGITTARIUS 76\n According to Wolf.\n\n FIG. 8.--THE \u201cTRIFID\u201d HOLE IN EAGLE 77\n According to Wolf.\n\n FIG. 9.--TARIM RIVER WITH LAKES AND BAYIRS 96\n According to Sven Hedin.\n\n FIG. 10.--THE FORMER LAKE BONNEVILLE IN UTAH 106\n\n FIG. 11.--JUPITER, 1909 122\n According to F. le Coultre.\n\n FIG. 12.--SATURN, 1909 123\n According to F. le Coultre.\n\n FIG. 13.--SPECTRA OF THE MAJOR PLANETS 124\n According to V.\u00a0M. Slipher.\n\n FIG. 14.--VENUS OBSERVED BY LANGLEY IN 1882 136\n\n FIG. 15.--ROCK FISSURE AT HANGO, SWEDEN 204\n Photo by I.\u00a0I. Sederholm.\n\n FIG. 16.--EARTHQUAKE CENTERS IN CALABRIA 205\n According to I.\u00a0I. Sederholm.\n\n FIG. 17.--MAPS OF MARS BY SCHIAPARELLI AND ANTONIADI _At the end_\n\n FIG. 17a.--MAPS OF MARS BY SCHIAPARELLI AND ANTONIADI _At the end_\n\n FIG. 18.--PHOTO OF MARS BY LAMPLAND 210\n\n FIG. 19.--MARS ON APRIL 8, 1909 210\n According to Quenisset.\n\n FIG. 20.--THE SOUTH POLE SPOT ON MARS, 1909 210\n According to Jarry Desloges.\n\n FIG. 21.--SANDSTORM ON MARS, 1909 210\n According to Antoniadi.\n\n FIG. 22.--CLOUD ON EDGE OF MARS, THE 7TH OF MARCH, 1901 216\n According to Molesworth.\n\n FIG. 23.--MARS, JULY 11, 1907 216\n According to Lowell.\n\n FIG. 24.--MARS, OCTOBER 6, 1909 216\n According to Antoniadi.\n\n FIG. 25.--MERCURY 230\n According to Lowell.\n\n FIG. 26.--THE MOON NEAR THE CRATER TYCHO 230\n Photo from Yerkes Observatory.\n\n FIG. 27.--MARE SERENITATIS AND MARE TRANQUILLITATIS 231\n Photo from Yerkes Observatory.\n\n FIG. 28.--THE MOON NEAR ITS SOUTH POLE 240\n Photo from Yerkes Observatory.\n\n FIG. 29.--THE LUNAR CRATER COPERNICUS AND VICINITY 242\n Photo from Yerkes Observatory.\n\n\n\n\nThe Destinies of the Stars\n\n\n\n\nCHAPTER I\n\nTHE ORIGIN OF STAR-WORSHIP\n\n\nAstronomy occupies a rather unique position among the natural\nsciences. While physics, chemistry, and the biological sciences form\nthe foundation of the extraordinary material development of our day,\nastronomy, in the eyes of most people, is of little practical value.\nWhat benefit could we derive from knowing whether a star lies a hundred\nor a thousand billion miles from the Sun, or from understanding how the\nstellar bodies have evolved in the course of billions of years? And yet\nastronomy has not been as futile as is commonly imagined, neither is\nit useless at the present time. This science is still of the greatest\nimportance to common life by fixing our standards of time and, before\nthe introduction of the compass, was invaluable also to navigation,\nwhich art, moreover, depends now upon astronomy for determination\nof geographical position on the open sea. Observations for these\npurposes, however, are of such a simple nature, that they hardly fall\nunder the astronomical science proper, but rather under the applied\nsciences. They have entered into daily life much as, in commerce, the\ndetermination of the weight of a body is not considered as belonging to\nthe science of physics, although it depends on the use of a physical\ninstrument, the scale.\n\nBut we must not forget that what we now consider so commonplace that\nit entirely has lost the grand aspect of science, once was the goal of\ngroping scientific endeavour. All natural science has grown out of the\nneeds of practical life.\n\nGeometry is probably even older than astronomy. The name means: to\nmeasure land, and the oldest geometry was, accordingly, devoted to the\nmeasurement of distances on the Earth and later to the determination\nof the area of land-holdings. This extremely important practical\napplication of geometry is of such a simple nature that it is not\nmentioned in modern mathematical science, to which geometry belongs.\nIn this manner, the original theses of all our natural sciences have\nbecome the possession of the public to such a degree that they are\nlooked upon as self-evident. This is the case also with those parts of\nastronomy which, because of their practical importance at the outset,\ngave rise to the science itself.\n\nThe growing knowledge about the stars, like all higher insight, became\namong primitive peoples the private possession of their leaders, was by\nthese kept a secret and made a part of the venerable realm of religion.\nWe find that a majority of these old peoples rendered worship to the\nstars, believing them to govern the fates of human beings. This may\nindeed seem highly remarkable, as our everyday experience is that the\nstellar bodies, with the exception of the Sun, exert no perceptible\ninfluence on organic nature, and such conclusion is emphatically\nconfirmed by the systematic collection of all our experiences which we\ncall modern science. The Sun, as stated, is the exception as it reigns\nover the entire nature, the living as well as the lifeless, by virtue\nof the heat and light which abundantly flow from this autocrat of our\nplanetary system. Perhaps the Moon also plays some small active part as\nit seems somewhat to affect the barometric pressure, the magnetic and\nparticularly the electric conditions of the atmosphere, which, in turn,\nappear to influence several life processes. On the other hand we cannot\npoint to any influence upon nature traceable to the other stellar\nbodies.\n\nObviously, primitive man devoted his thoughts only to such conditions\nas affected his interests in a beneficial or detrimental way. On\nthe assumption that these conditions were governed by spirits who\nresembled man and who in particular were endowed with will, our\nancestors endeavoured by sacrifice and exorcism to move the spirits\nthey feared to discontinue their harmful activity. Some such spirits\ndwelt in beasts of prey and in other noxious animals, such as poisonous\nsnakes; others caused earthquakes, volcanic eruptions, snowstorms,\nlightning ravages, fires, floods, heat, drought, etc. Against these\ncalamities religious exercises formed a protection. Religion sprang\nmainly from fear of spirits. Later on thank offerings and hymns were\nbestowed upon benevolent objects and phenomena in nature.\n\nIt is evident that this primitive, simple religion is of far greater\nage than star-worship. The latter presupposes a comparatively high\ndegree of culture. The stars were of no benefit to man until it became\nnecessary to measure time intervals comprising a greater number of\ndays than might be counted on one\u2019s fingers. How this growth in\nall probability took place we shall endeavour to explain in the\nfollowing. Fairly certain it is that star-worship did not grow out\nof man\u2019s admiration for the sublime drama which at dawn of morning\ncommences at the eastern horizon, and proceeds in the course of a day\nover the firmament in order to close before night just beyond the\nwestern expanses, neither was it founded on man\u2019s gratitude toward the\ntorch-bearers of night for their incessant battle against gloomy clouds\nand all the other spirits of darkness.\n\nEven tribes on a rather low stage have no doubt noticed the most\nconspicuous among the stellar bodies. The attitude of the Australian\naborigines is significant in this connection. According to Spencer and\nGillen they possess legends about the Moon, which is male, about the\nSun and Venus, about the pernicious Magellanic clouds, and about the\nPleiades, who, like the Sun and Venus, are considered female. Eclipses\nhave, as is natural, attracted the greatest attention. While these\nprimitive men indulge in an incredible number of religious ceremonies\npertaining to conditions of their daily life, none of these exercises\nare devoted to the stars, if we except stone throwing against the Sun\nduring eclipses. Even this treatment is left with considerable serenity\nof mind for the medicine-men to perform. It is very significant that\nall stellar bodies are of earthly origin, that the Moon is of male\ngender while the Sun, Venus, and the Pleiades are female, which\nindicates that the Moon is considered of greatest distinction. They\ncount time according to \u201csleeps,\u201d _i.\u00a0e._ the number of times they have\nslept, or according to moons; longer periods according to seasons; they\nhave names for summer and winter. They can count to five, or perhaps\nrather to four, as the term five also means \u201cmany.\u201d Ideas of power\ncentred in the stellar bodies are evidently absent and therefore also\nreligious ceremonies pertaining thereto. A few tales exist relating to\nthe stars as to other objects within their observation. Thus conditions\nwould undoubtedly have remained but for the high value which the want\nof a chronometry gave to the regularly changing light of the stellar\nbodies.\n\nThe difference between day and night is of such a deeply fundamental\nimportance that it has left its stamp on the whole organic nature on\nthe surface of the Earth. Plants entirely change their life processes\nin the course of twenty-four hours; during the day they add to their\ngrowth under the stimulus of light; during the night they partly\nexpend the strength gathered in daytime. This cycle is so regular\nthat it functions automatically. The prominent botanist, Pfeffer, has\nexperimented with a Mimosa, which, as is well known, unfolds its leaves\nduring the day but curls them during the night. If left in a dark room\nany arbitrary day, it nevertheless uncurls its leaves. By means of\nelectric light Pfeffer changed night into day for the plant kept in the\ndark room. It took considerable time before the plant adjusted itself\nto the new conditions so that it unfolded its leaves to the influence\nof the electric light. Animals behave similarly. The night and day\nperiod is instilled in their blood. In a certain sense they possess an\ninstinctive chronometry.\n\nIt is often stated that the assurance of the return of sunlight after\nthe darkness of night enabled humanity with greater equanimity to\nacquiesce in the loss of light during one half of its existence and\nthat worship was rendered to the Sun in gratitude therefor. \u201cA new\noutlook upon life,\u201d says Troels Lund, \u201cawakens the moment the great\ndiscovery is made that the night of sleep and the night of fear are\nequally long and always followed by morning and subsequent day.\u201d This\ndiscovery, however, our predecessors made long before they reached the\nhuman stage. Sun-worship by no means derived its origin therefrom.\n\nRather it is traceable to evidence of the Sun\u2019s connection with\nthe changing seasons, although this change also is of domineering\ninfluence in the vegetable world inasmuch as the plants store reserve\nnourishment in the autumn, particularly, and on a large scale, during\nfructification. Also, lower and higher animals, for example, bees and\nsquirrels, gather winter-stores. It is therefore small wonder if men on\na comparatively low stage lay in provisions for the recurring periods\nof scant food supply.\n\nBut a true chronometry beyond five days is foreign to the Australian\nnegro as long as he can only count to four or five. He is aware that\nMoon-phases reappear and that summer and winter return, but he has no\nconception of the duration of the time passed between the recurrences\nof these phenomena. Further progress was made by the people who took\nthe bold step to count the fingers, not on one hand alone, but on both\nhands, and thus reached the number ten. This was utilized in reckoning\ntime so that the larger unit became a decade, _i.\u00a0e._ ten days and\nnights. This unit was original with the Indo-Europeans, Semites,\nHindus, Egyptians, and the islanders in the Pacific Ocean. Another\nadvance yet was made in Mexico where the number twenty was introduced\ncorresponding to the sum of all fingers and toes, and thus a unit of\ntime was obtained comprising twenty days and nights. But to rise from\nthese units to one of 365 days was a step exceedingly difficult for the\nprimitive peoples to take.\n\nThousands of years elapsed before the most intelligent among the\nraces established the length of the solar year. Those who lived in\nregions where the Sun\u2019s altitude notably changes, _i.\u00a0e._ far from\nthe equator, undoubtedly reckoned time in years, without knowing its\nlength expressed in days. Imagine a nomadic tribe like the Lapps in\nthe north of Sweden. In the autumn their reindeer wander down toward\nthe coast in search of food and the Lapps go with them. In spring the\nreindeer lead their masters back again to the mountains. It cannot very\nwell escape the observation of these nomads that the Sun shines almost\ncontinuously during their stay in the uplands while dreary night reigns\nnearly without interruption during their sojourn in the lowlands. They\nare obviously forced to co-ordinate the beautiful summer with the\nduration of sunlight. To them, therefore, the Sun\u2019s extraordinary great\nimportance to life is unquestionable. The same holds true about all\npeople who live sufficiently far from the equator. As a consequence,\nthey become Sun-worshippers. It is not difficult to find examples of\npeoples who have worshipped the Sun; only a few of the more important\nones will be mentioned here.\n\nThe people of the bronze age here in the North were zealous\nSun-worshippers thousands of years ago, as the many relics from this\nperiod, and particularly the rock-carvings, bear witness. The Celts of\nWestern Europe have frequently symbolized the Sun as a cross, while the\nworship of Moon and stars seems to have been foreign to them as well\nas to the bronze-age people of the North. The Jewish Samson (Simson)\nwas a Sun-hero, the name being related to the Babylonian Shamash, the\nSun-god. In Hesiodos\u2019 cosmogony the Sun (Helios) is mentioned before\nthe Moon (Selene). The old Germans worshipped both Sun and Moon,\nparticularly the former. The Slavs possessed a Sun-god Dazbogu, but no\ndeity identified with the Moon. Similar conditions obtained among the\nFinnish forefathers. The Chinese Tao-priests light fires during the\nvernal equinox as we do at Walpurgis and midsummer, and they sacrifice\nrice and salt to the flames. \u201cThis is a remnant of the Sun-cult,\u201d\nsays Solomon Reinach, from whom these data in regard to Sun-worship\nprincipally are taken. In Japan, the Moon is of male sex, the Sun of\nfemale sex, which indicates that there, as with the Australian negroes,\nthe Moon was originally considered more important than the Sun.\nNevertheless the Japanese are now Sun-worshippers; the Sun is placed\nas emblem of the most high in their flag and the Mikado is known to\ntrace his lineage from the Sun. They have, therefore, long ago passed\nfrom Moon-cult to Sun-cult. It is probable that this step was taken\neven earlier in China, where the Sun furthermore is of male sex.\nWith growing civilization all people learn to understand, as have the\nJapanese, the superior importance of the Sun. The Incas of Peru, who\nreached a very high grade of culture, were sun-worshippers and called\nthemselves children of the Sun, although they lived near the equator\nwhere the Moon-cult, as we presently shall see, owns its most faithful\nadherents.\n\nIn the neighbourhood of the equator, winter and summer differ very\nslightly with respect to temperature and altitude of the Sun. Rather,\nit is the alternation of humid and dry seasons that is of deciding\nimportance. No sheet of snow covers the ground in winter-time, kills\nthe vegetation, or decimates the supply of nourishment for animals\nand men. Indeed, contrary to our experience, a suppression of growth\noften accompanies a high altitude of the Sun due to the drought\nwhich simultaneously occurs. The altitude and luminosity of the Sun\nchange altogether too slightly in the course of the year to attract\nthe attention of primitive man. The light of the Moon, on the other\nhand, varies from full intensity to nothing and this takes place in\nperiods so short that memory has no time to forget the cycle. Even\nthe low-standing Australian negroes utilize the phases of the Moon to\ndenote remote times. Chronometry in any true sense they do not possess,\nunable as they are to state the number of days in a month. How much\nmore fortunate the peoples who could count to ten or better yet to\ntwenty and thus were able to use the single or the double decade as a\nmeasure of time. For them it was easy to determine the time between two\nsuccessive phases of the Moon, seven and a half days apart.\n\nThe truth once grasped that four phases separate two new Moons the\nimportant bridge could be established between the short measure, a day,\nand the longer measure, a month. The latter was then found to be nearly\nthirty times longer than the former. On a higher stage of culture, it\nwas discovered that this ratio was not exact and the discrepancy must\ngreatly have puzzled the people. The correct ratio is 29.53. At all\nevents the periodic return of full Moon and new Moon proved the most\nreliable measure of time within their experience. This was something\nentirely different from the irregular occurrences of earthquakes,\nstorms, lightning, and floods, not to mention the ravages of beasts and\nfoes. Spaces of time that hitherto appeared boundless could be surveyed\nand computed. The idea of eternity dawned for the first time on\nhumanity. The Moon was the great master, measurer of all. In Sanskrit\nthe Moon\u2019s name is _M\u00e2s_, _i.\u00a0e._ measurer, and \u201c_mensis_\u201d (Lat. month)\nis closely related to \u201c_mensura_\u201d (Lat. measure).\n\nWith peoples who did not live too far from the equator, the Moon,\ntherefore, took precedence of the Sun. Among the Mexicans existed,\nlong ago, a peculiar unit for measuring long periods of time, called\n\u201c_tonalamatl_,\u201d comprising 260 days. It was undoubtedly intended to\ncontain nine synodical months (reckoned from new Moon to new Moon).\nBut such a period would consist of 265.58 days and so could not be\nmade to agree with the double decade and was therefore shortened to\n260 days, as we round off the solar year, in reality 365.24 days, to\nan even 365 days. Elaborate studies have been made in order to explain\nwhy the Mexicans chose nine synodical months instead of twelve, as\nmost other peoples, but the question has not been solved. This much is\ncertain, that \u201c_tonalamatl_\u201d has nothing to do with the solar year,\nbut only with the month. The high age of \u201c_tonalamatl_\u201d is proved by\nthe fact that the priests adhered to it in magic and horoscope casting\nlong after the solar year came into public use. A learned Mexican, de\nJonghe, has pointed out that \u201c_tonalamatl_\u201d was used by all the tribes\nbelonging to the Nahua-group, which tribes separated very long ago.\nThis unit of time, therefore, bears all the evidence of a very high\nage, but is obviously younger than the synodical month.\n\nOur information in regard to Moon-worship among the peoples of\nMesopotamia is even more explicit. The Moon (Sin) was rendered homage\nfar earlier than the Sun (Shamash). The following translation of a hymn\nin cuneiform letters I quote from L. Bergstr\u00f6m, who published a study\non \u201cSemitic Moon-Worship\u201d in _Nordisk Tidskrift_, 1909:\n\n Oh, Sin, thou who alone givest light,\n Thou, who bringest light to men,\n Thou, who showest favour to the dark-tressed ones,\n Thy light shines on the firmament,\n Thy torch illuminates like fire,\n Thy radiance fills the wide earth.\n Oh, heavenly Anu, whose insight and wisdom no one comprehends,\n Thy light is splendid as Shamash, thy firstborn,\n Before thee prostrate the great gods themselves in the dust\n For on thee rests the fate of the world.\n\nAnu was god of the heaven and seems here to stand for god in general.\nSin was father to the daughter Shamash, who in this hymn already is\nconsidered almost comparable to the father. Later on during the\nHammurabi-dynasty (about 2000 B.C.) the Sun, Shamash, was accepted as\nsupreme god, but the Moon remained the regulator of time for religious\npurposes. For astrological forecasts the priests preferred to use the\nMoon, and the \u201csigns\u201d in the Moon were the most important. This is true\nof astrological prophecies also at the time of Tycho Brahe. \u201cOh, Sin,\nthou tellest the oracles to the gods who pray them of thee,\u201d reads an\nincantation. From Babylon, the heart of civilization, Moon-worship\nspread to Arabs and other Semites, and with the Hebrews, as Bergstr\u00f6m\nremarks, the Moon originally played a far greater part than the\nSun, although at the time of Christ the condition was reversed.\nNevertheless, the Moon has still retained its position as chronographer\nin the Church Calendar. In Psalms 104:19 we read: \u201cHe appointed the\nMoon for seasons.\u201d\n\nIn general, we have built on the belief that the stellar bodies made\nan impression on men by virtue of the light they radiate and it has\ntherefore been difficult to explain why the Moon ranked above the Sun.\nIt is frequently said that the Sun (in Babylonia) was considered an\nenemy of mankind as its heat destroyed the vegetation. (It is true that\na period of severe drought occurs there in the height of the summer.)\nAs opposed to this, the moonlit nights would be considered refreshing\nand salutary. Another explanation is essayed by Bergstr\u00f6m, who says\nthat the luminous Moon with its ever-changing shape appealed to the\nimagination of primitive people in a far higher degree than the fairly\nconstantly brilliant Sun. He is partly correct; the enormous variation\nin luminosity from full to new Moon enables the observer to notice\nthe difference from night to night. The change by about one hour in\neach twenty-four hours of the time for the rising and setting of the\nMoon as compared to the disappearance and reappearance of sunlight,\nand more important yet the short periods of the Moon phases which\nleave the observations from each receding phase fresh in memory,--both\nthese phenomena contribute toward the high value of the Moon\u2019s synodic\nrevolution as a measure of protracted time duration. The purely\npractical need dominates, not, probably, any desire to visualize the\nchanges in legends. The Australian negroes use four different names\nfor the Moon according to its four quarters, showing that they, in all\nprobability, believe themselves confronted with four different stellar\nbodies, just as the Greeks at the time of Homer considered the morning-\nand the evening-star, _i.\u00a0e._ Venus, as two separate planets.\n\nOn the other hand, no ground worth mentioning supports the theory that\nthe scorching heat of the Sun diminished the peoples\u2019 inclination\nfor its worship. On the contrary, homage was generally rendered to\nphenomena one feared. It is further not true that the Babylonians\nthemselves considered the Sun, Shamash, hostile, the Moon, Sin,\nfriendly. The Sun-god, Shamash, by virtue of his light, was believed\nto give life and health. The scorching quality of the Sun was\nattributed to another god, Nergal, prince of the underworld, demon of\nwar and slaughter, source of fever, and, pre-eminently, of plague. No\nreason existed, therefore, why Shamash should take second rank after\nSin, who is said \u201cto carry water and fire,\u201d meaning, according to\nSchrader, that he brought fits of ague and fever. When the Sun after\nthe oppressive day sinks behind the horizon, it is well known that\na sharp fall of temperature occurs, particularly in arid zones, but\nalso in humid regions within the tropics where this very phenomenon\nis utilized for the production of ice. He who exposes himself to the\nsudden cold of the night falls an easy prey to illness. Particularly\nis this true under a clear sky--primitive people say \u201cwhen the Moon\nshines\u201d--because of the strong radiation. Those who sleep in moonlight\nare struck by delirium and madness according to primitive thought, an\nopinion by no means dead among civilized nations--it is common with\nseafaring men--and is no doubt the origin of the expression: moonstruck\n(German: _mondsuchtig_, Ital.: _lunatico_, French: _lunatique_, Swedish:\n_m\u00e5nadsrasande_, etc.). To this belief has probably contributed\nthe fact that epileptic fits frequently possess a period nearly\ncorresponding to the synodical month, which, as I have shown elsewhere,\nmost likely depends on a periodic change in the atmospheric electricity.\n\nIn this connection it might also be stated that the third among the\ngreat star-deities, Ishtar, the queen of heaven (Astarte, Venus),\nwas the mild but potent, all-merciful sister in every affliction,\nwho delivered from sorcery and illness and gave pardon for sin and\nguilt. This radiant goddess, who corresponds to the attractive figure\nof the Catholics\u2019 Virgin Mary, was, in spite of her solicitude for\nthe afflictions of men, placed third in the illustrious triad, Sin,\nShamash, and Ishtar.\n\nThe traveller in the desert is certainly often tortured by the severe\ndrought and a consequent insufferable thirst. This, however, was\njustly ascribed to the scarcity of water and not to the Sun. The\nEgyptians, therefore, wished that their departed ones on the journey to\ntheir new dwelling-places would meet with refreshing springs where they\nmight quench their thirst and northerly winds that might cool the air.\nIt is well known that the Mohammedans have formed similar conceptions\nof a paradise in life to come.\n\nEntirely new conditions arose when the population grew until\nagriculture became a necessity for the production of sufficient food.\nThe influence of the Sun now became so dominating that it must be given\nthe first place among the powers that affect the fates of men. The\nplants have a decided annual period and so have the overflows of the\nrivers which were of the utmost importance in those countries where\nthe cradle of civilization stood. The rainfalls themselves were of\nannual recurrence as were also the intervening droughts. In Egypt the\ngreat importance of the floods caused the introduction of the solar\nyear at a very early stage and its length was fixed at 12 months of 30\ndays, or 360 days, so that the beginning of the year occasionally had\nto be adjusted. This was accomplished by resorting to observations of\nthe rising and setting of the Dog Star or Sirius. Thus we realize how\ndifficult it was to determine the exact length of the solar year from\neveryday phenomena. The great reformer Amenhotep IV. endeavoured about\n1400 B.C. to have the Sun-god recognized as sole master of all the\nworld. He met, however, with such great obstacles on the part of the\nconservative priesthood, which as they largely were serving different\ngods would have lost part of their power if the reform had prevailed,\nthat his successor was obliged to yield to the solid opposition.\n\nIn Babylon the local god Marduk, once representative of the planet\nJupiter, and among the star-gods ranking next to the three Super-gods,\nbecame about 2000 B.C. elevated to the highest position among the gods\nand assumed at the same time the dignity of Sun-god. It may here be\nmentioned that Marduk also played a great part as healer of illness.\nThe evolution in ancient Rome followed the same course although at a\nfar later time. Emperor Aurelianus (270\u2013275 A.D.) under the influence\nof oriental Mithras-cult elevated the Sun-god to supreme god of the\nwhole Roman Empire, which then comprised almost the entire known world.\n\nEspecially significant is the fact that Venus with the Mexicans played\nas important a part as did the Moon and the Sun. The luminosity of\nVenus, unlike that of planets outside of the earth\u2019s orbit, but like\nthat of the Moon, changes from a maximum, intense enough in the\ntropics to throw a shadow, down to a minimum which approaches complete\ndarkness. Its period is closely 1.6 years. It falls short of this\nfigure by about two hours and the Mexicans therefore introduced a\ncorrection similar to the bissextile day in our leap year, of one day\nin every twelve years, which day, however, had to be deducted instead\nof added. Observations of the changing luminosity of Venus and of its\nposition relative to the Sun obviously lent themselves admirably to\nmeasurements of long periods of time and particularly to determination\nof the length of the important solar year as five Venus-periods very\nnearly equal eight solar years. The Mexican priests established the\nfact that 104 solar years correspond to 65 Venus-periods or 146\n\u201c_Tonalamatl_.\u201d\n\nStar-cult was as strongly developed in Mexico as in Babylon. Its\nmain doctrine is stated by Alfredo Chavero thus: \u201cThe Father-Creator\nwas Heaven, Xiuhtecutli, or the Azure-blue master. The mother was\nOmecihuatl, the Milky Way, or the dual mistress.\u201d It is well known that\na large part of the Milky Way, from the \u201cSwan\u201d to the neighbourhood of\nthe Southern Cross, is divided in two parallel branches, which fact\nprobably is responsible for the title, the \u201cDual Mistress.\u201d \u201cHeaven\ninfluenced the Milky Way through fire; from its cosmic matter the stars\nwere set free, the most prominent of which were Tonatiuh, the Sun;\nTezcatlipoca, the Moon; and Quetzalcoatl, Venus. These were made the\nsupreme gods. For the purpose of worship, they were symbolized in human\nshape. Myriads of images, representing these star-gods, were modelled\nin clay, wood, or stone.\u201d\n\nAccording to this remarkable picture the Mexicans should have\narrived at a far better solution of the world-riddle than even the\nBabylonians did. While most other peoples assumed heaven and earth as\nthe original principles, they gave the high position of progenitress\nof all to the Milky Way. From her the innumerable stars, with the\nSun in the lead, issued. This agrees to a considerable extent with\nthe present conception which we have arrived at during this very\nlast decade, principally thanks to the work of American astronomers.\nTheir investigations have shown how the stars are segregated from\nthe nebulous primeval matter of the Milky Way; how they add distance\nbetween themselves and their matrix with age, while simultaneously\nthey develop an increasing individuality.\n\nWe have seen that Venus-Ishtar was honoured with membership in\nthe august triad of star-gods, also among the Babylonians. Their\nsuccessors, the Assyrians, retained the inherited traditions. Thus\ntheir kings in the ninth century before Christ symbolized their divine\nlineage by wearing a necklace with a moon-crescent in the middle, a\ncross in a ring, emblem of the Sun, on one side, and on the other a\nstar, emblem of Venus (compare Montelius, _Nordisk Tidskrift_, 1904, p.\n13, fig. 30). The Jewish synagogues are generally decorated with the\nstar-emblem.\n\nThe Mohammedans, like the Jews, utilize the position of the Moon for\ndetermination of the Church calendar, and we employ the same means for\nfixing Easter time. The Mohammedans reckon with a year of 12 synodical\nmonths. Twelve such months contain only 354.4 days while a solar year\ncomprises 365.24 days, and as a rule, therefore, the synodical month\nwas rounded to 30 days instead of 29.53 and the solar year to 360 days.\nSuch was the arrangement in Egypt and originally also in Babylon.\nPrimitive men comprehend fractions only with extreme difficulty. In\norder to correct the discrepancies, odd months were introduced about\nevery sixth year.\n\nFrom this time we may trace the high reputation of the number twelve.\nThe Zodiac was divided into twelve houses in each of which the Sun\nwas to dwell a month at a time. Day and night were each divided into\ntwelve hours. The circle was divided into 360 degrees corresponding\nto the number of days of the year, so that the position of the Sun\nat noon should proceed one degree of the heaven from day to day. As\nthe Moon dominated chronometry, a complication which must have caused\nconsiderable confusion was in many places introduced. We have seen\nthat the Australian negroes gave four different names to the Moon in\nits four different phases. The great change in appearance of the Moon\nfrom quarter to quarter makes such a division natural. The synodical\nmonth was therefore made to consist of four parts, called weeks. As the\nlength of a month is 29.53 days, the nearest number evenly divisible by\nfour, namely 28, was substituted, and so seven days were allotted to\neach week, thus introducing an error of not less than 5.5%.\n\nTo the establishment of this week the assumption of seven wandering\nstars has no doubt largely contributed. The priests had discovered\nthat besides Sun, Moon, and Venus, four other stars shift their\nposition on the firmament with reference to the fixed stars, which\nlatter appear always to maintain their relative distances. These four\nwandering stars were Mercury, Mars, Jupiter, and Saturn. Each day in\nthe week was dedicated to one of the seven wandering stars and received\nits name. These names have been maintained to the present day, for\ninstance, Sunday, the Sun\u2019s day, Monday, the Moon\u2019s day, etc. The lunar\ncalendar, established through religious considerations, supplanted\nthe more rational one, which latter, however, survived in Egypt, and\nwas reinstated in the Occident during the French revolution, although\nunfortunately only for a short time (1793\u20131805). As a result, the\nsynodical month, in order to suit the calendar, has been changed not\nonly with half a day to thirty days, but also with one and a half days\nto twenty-eight days. If decades had been adhered to we would have had\nmonths of even thirty days and either five leap months of thirty-one\ndays each (during leap year six) or half a decade interpolated at new\nyear.\n\nBesides the seven wandering stars known to antiquity (at present\nover eight hundred planets have been observed), several other stars\nand constellations played an important part. The Magellanic clouds,\nconsidered of evil nature, and the Pleiades appealed already to the\nAustralian negroes. In the northern hemisphere, where the opportunity\nof observing the Magellanic clouds is small, situated as they are near\nthe South Pole, the Pleiades have attracted the greater attention\nand the Ph\u0153nicians especially appear to have taken interest in this\nconstellation. From them, reverence for the Pleiades spread to a large\npart of Africa, where we now to our surprise find this star cluster\nreproduced along with symbols of Sun, Moon, and Venus. Homer also\nmentions the Pleiades and a few other constellations, namely, the\nHyades, Orion, the Great Bear, and the stars Sirius and Arcturus. At\nall events, the Pleiades have frequently occupied a unique position in\nthe old world. Sirius, the brightest star in the heavens, and Canopus,\nthe second in brightness, also belonging to the southern hemisphere\nbut only half as far removed from the South Pole as Sirius, have both\nevoked the attention and the worship of the primitive people, in this\ncase the South Africans.\n\nAt length, the nations, particularly the Babylonians and the Mexicans,\nacquired a wider knowledge of the different stars. As the most\nimportant ones, Sun, Moon, and Venus, guided the seasons and hence\nall natural phenomena, a certain mundane significance was naturally\nascribed also to the younger ones. Not only seasons, months, days, and\nhours were each ruled by its star, but so was everything in nature;\ndifferent winds, provinces, trades, bodily organs, animals, persons,\neach possessed its star and celestial protector. Comprehensive studies\nof these correspondences and connections were made and the conclusions\nwere drawn from immaterial semblances and often wholly arbitrarily,--as\nregards persons from the configuration of the stars at the time of\nbirth. Thus grew an enormously extensive collection of correspondence-\nand sympathy-doctrines accompanied by a detailed symbolism, an entire\nquasi-science, which must never be questioned as it originated with\nthe infallible priests. With the Babylonians, religion and science\ncompletely melted together and even art was entirely subservient to\nthe same interests. Occasionally the loss of this blissful state draws\nforth a sigh. Fortunately it is gone never to return.\n\nThe oriental wisdom was brought over to Greece and was there\namalgamated with the Platonic-Aristotelian philosophy. In this form\nthe Babylonian heritage held sway over the thought of mankind up to\nless than 200 years ago. The most important branches of this fanciful,\nso-called science were astrology and alchemy. Tycho Brahe himself made\nit the object of his life to strengthen astrology by contributing new\nmaterial to it. Kepler is said not to have believed in astrology but he\nnevertheless cast horoscopes not only for princes and persons of high\nposition in order to improve his economy, but also for his own family.\nProbably traces of the old superstition clung to him, and presumably he\nthought: \u201cIf it does no good, neither does it do any harm.\u201d\n\nIn the same manner, alchemy was carried on by faithful adepts, but more\noften by impostors, seldom averse to \u201coccult\u201d sciences. Astrologers and\nalchemists exist even yet among the numerous devotees to occultism; at\nhigh price many of them make their predictions or sell their secrets.\nI have heard a Swedish engineer of very high standing state that their\nprognostications agreed with events. Among the few alchemists in\nEurope, most of whom seem to be religious visionaries, Strindberg is of\na certain interest to us. Correspondence-theory has played a very large\npart in the speculations of the learned up to comparatively recent\ntime. It is utilized extensively in the later fantastic writings of\nSwedenborg. Numerous traces are to be found also in the weakest works\nof Strindberg.\n\nThe renowned French chemist, Berthelot, has given a valuable analysis\nof the alchemist\u2019s method of treating chemical phenomena. His general\nconclusion is that the false principles which led the alchemists astray\nrevert back to Plato\u2019s and Aristotle\u2019s philosophical theories regarding\nthe composition of matter. Something similar can be said of astrology.\nIt plays with ideas of its own fabrication with hardly any foundation\nin reality. The result is almost wholly without value.\n\nThe greatest astronomer in Babylon, Kidinnu (about 200 B.C.),\nconstructed tables of great accuracy giving the position of the stars.\nIn this work he utilized observations gathered over thousands of years.\nThese ephemerides were also intended as scripture source for reading\nthe fate of men and for determination of the auspicious moment for\nthe commencement of an undertaking. At all events, they placed great\nrevenue and power over souls in the hands of the ruling priesthood. It\ndoes not appear that these priests were able to rise to an attempt of a\nphysical explanation as to the nature of the stellar bodies. That was\nprobably also considered dangerous. The stars were deities composed\nof purer and more refined matter than found on Earth. It were not\nimprobable that the gods would inflict vengeance on the presumptuous\none who dared to intrude upon their secrets and pass judgment on their\npeculiarities.\n\nFortunately, there existed in Greece another tendency in philosophy\nbesides the scholastic and the Platonic-Aristotelian. But this was\nmainly represented in southern Italy, Sicily, and later in Alexandria.\nAlready the followers of Pythagoras had made important progress toward\na solution of the stellar problems. The crowning point was reached by\nAristarchos from Samos, who lived in Alexandria about 2100 years ago.\nHe established 1700 years before Copernicus the heliocentric system.\nIt is often said that his work was of little value, as Copernicus\nnevertheless must do it over again. It is then forgotten that\nCopernicus himself cites the philosophers of antiquity who expressed\ntheories in agreement with the heliocentric system and expressly states\nthat he was bold enough to advance his hypotheses because so many\nprominent authorities could be mentioned who favoured them. Copernicus\ndid not dare entirely to break away from the Ptolemaic system, and was\ninconsistent enough partly to use it in his calculations of the motions\nof the stars.\n\nWe have lately advanced farther along the road of Pythagoras and\nAristarchos, of Copernicus and Galileo, and we have perfected their\nmethods to a high degree. Progress in astronomy and kindred sciences\nis nowadays made at a dizzying speed if measured with the standard\nof antiquity. Occasionally we hear a warning voice asking us to\nshow more deference to a philosophy directly descending from the\nPlatonic-Aristotelian. He who is at all familiar with the history of\nnatural science will understand us when we answer: \u201cWe have had more\nthan enough thereof.\u201d\n\nThat non-naturalists sometimes have a peculiar conception of the\npresent status of astronomy is well illustrated by the statement of one\nof our foremost theologians in a review of a popular astronomical work\nwhere he remarked that the astronomer of today had not advanced much\nbeyond those of ancient time who also could forecast eclipses of the\nSun. The predictions were then founded on the recurrences of eclipses\nafter regular intervals much as the new Moons were foretold, with the\ndifference only that the latter occur much more frequently.\n\nOur knowledge of the stellar bodies at present and fifty or sixty\nyears ago are a world apart and the same is true of the latter and\nthat of antiquity. But we must not therefore forget that our brilliant\nstar-science today is derived from men\u2019s desire to measure time, and\nparticularly from their need to foresee the food supply in coming days.\n\n\n\n\nCHAPTER II\n\nTHE RIDDLE OF THE MILKY WAY\n\n\nDuring dark but starlit nights, the gorgeous firmament is decorated\nwith an irregular band of light that describes a winding path across\nthe heavens. It continues also in the quarters hidden from our sight so\nthat it may be said to surround the firmament like a girdle. This band,\nwhich is most luminous in the Northern Hemisphere, is called \u201cThe Milky\nWay.\u201d[1] It forms an angle with the equator of about 60\u00b0 and divides\nthe firmament in two nearly equal parts--the northern, however, is\nslightly larger.\n\n [1] The literal translation of the Swedish name is \u201cThe Wintry\n Way.\u201d\n\nThe Milky Way, no less than other stellar phenomena, attracted the\nearly attention of the people. The Dieri Tribe in Central Australia\nsays that the Milky Way is the stream of heaven and the Mexicans\nconsider it the source of all that is. Tradition endeavoured to explain\nits origin. Its milky appearance caused the Romans to call it \u201c_Via\nLactea_,\u201d a name that is retained in translated form in most modern\nlanguages. This name is coupled with the legend of the Hercules-child,\nwho sucked the breast of Juno and when it was pushed away by the\nincensed goddess, the milk was spread across the sky.\n\nNevertheless, the human race, until about two hundred years ago, had\nlittle conception of the extraordinary importance of the Milky Way.\nAnaxagoras and Democritos surmised, however, that it consists of a\ncollection of exceedingly minute and densely clustered stars each of\nwhich has the nature of our Sun. Ptolemy described, nearly two thousand\nyears ago, its position on the firmament and his observations are\nvalid today as far as determinations with the naked eye suffice. When\nGalileo introduced the telescope, the conception of the Milky Way as\nmade up of innumerable stars was verified. Not quite two hundred years\nago Swedenborg, in his cosmological speculations, considered our solar\nsystem as a part of the Galaxy. Wright, Kant, and Lambert further\namplified these theories.\n\nThe first important forward step was taken by the great William\nHerschel in his statistical researches. He demonstrated that the\nstars lie closer to each other the nearer the Milky Way they are\nlocated. This is mainly true about the small stars invisible to the\nnaked eye while the more luminous ones are more evenly distributed\nover the heavens. In certain parts of the Milky Way the stars are\nover one hundred times more crowded than at its poles--that is, the\npoints farthest removed from the Galaxy. Herschel\u2019s investigations\nwere continued and elaborated by Struve, and later by numerous other\nscientists.\n\nThrough these researches, it has been determined that the Milky Way\nis, so to speak, the foundation upon which the star system, visible\nto us, is built. All kinds of stellar bodies have been studied and\ntheir distribution has proved to be symmetrical with reference to the\nplane of the Galaxy. The majority is greatly concentrated around the\nMilky Way. To these belong the new stars which occasionally blaze into\nexistence, as the well-known new star in Perseus, 1901, and nearly all\nof which have appeared in the Milky Way or in its immediate vicinity.\nWe also find there the irregular nebul\u00e6, enormous, vastly diffused\nvolumes of gas, among which the best known is the Orion nebula, and\nwhich seem to constitute the primeval matter out of which the stars are\nborn. We might further mention the star-clusters, dense, ball-shaped\nagglomerations of stars, and the so-called planetary nebul\u00e6, which--at\nleast in their visible outer shell--also consist of gas accumulations\nwith a spherical or ellipsoid conformation. The numerous spiral nebul\u00e6\non the other hand, those strange stellar bodies to which we later\nshall have occasion to return, are beyond comparison more frequent in\nthe regions surrounding the poles of the Galaxy than in the rest of the\nheavens.\n\nMany astronomers have considered the Milky Way itself a nebula. The\nmost common theory doubtless is that it closely conforms to a spiral\nnebula--an opinion that has found a particularly warm advocate in\nthe Dutch astronomer, Easton (see Figure 1). A few years ago Prof.\nBohlin expressed the view that it is most akin to a planetary nebula,\nor more precisely to a ring nebula which is supposed to grow out of\na planetary ellipsoid nebula by the gaseous matter being driven from\nits poles toward its equator. It is of a certain interest that this\ntheory lends itself to the support of Swedenborg\u2019s--nevertheless\nimprobable--hypothesis about the origin of the planets in the solar\nsystem. As we later shall see the Easton conception has the better\nreasons in its favour.\n\nIf classified according to age the stars are again distributed with the\nMilky Way as a reference point. Thus, let us consider their evolution,\nwhich for various reasons is assumed to take the following course.\nWe may commence when the star-matter existed on the nebula stage. It\nthen radiated the light characteristic of certain incandescent gases,\nprincipally the lightest two, hydrogen and helium, and further of an\notherwise unknown gas called nebulium (nebula-substance). These gases\nwere later condensed and dark spectral lines commenced to appear\nbeside the bright lines of the aforesaid gases. Stars on this stage,\nnamed after their discoverer Wolf-Rayet stars, occur only in the\nimmediate vicinity of the Milky Way. A later stage in their evolution\nis represented by the so-called helium stars in whose spectrum the dark\nhelium lines preponderate. They are considerably concentrated around\nour Galaxy. Somewhat more evenly distributed and yet of decidedly\ngreater frequence in the neighbourhood of the Milky Way, the hydrogen\nstars appear, characterized by strongly developed hydrogen lines and\nsomewhat retreating helium lines. These stars are more developed than\nthe helium stars and form with them the group of white stars so named\nafter the colour of their light. Next in evolution follow the yellow\nstars, to which our Sun belongs. Dark metal lines appear in their\nspectrum. They are more evenly distributed than the groups mentioned\nbefore. Still further is this true about the red stars whose spectra\ncontain the characteristic bands of chemical compounds and therefore\nbetray comparatively advanced cooling. They are fairly uniformly spread\nover the heavens but are still somewhat more numerous in the vicinity\nof the Milky Way than further therefrom.\n\n[Illustration: Fig. 1. The Milky Way, pictured as a spiral nebula by\nEaston]\n\nThese facts are demonstrated in the statistics by E.\u00a0C. Pickering,\nDirector of the Harvard Observatory, who divided the firmament in\nfour equal zones, the first of which is nearest to the Milky Way (and\nincludes it) and the last of which contains the Galactic poles. His\ntable shows the percentages of different stars in each of the four\nzones.\n\n | | | _White | |\n _Galactic | _Helium | _Hydrogen | Yellow | _Yellow | _Red\n Latitude_ | Stars_ | Stars_ | Stars_ | Stars_ | Stars_\n ---------------+---------+-----------+--------+---------+-------\n \u00b18.1\u00b0 | 51.2 | 37.4 | 29.7 | 29.4 | 26.7\n \u00b121.6 | 31.7 | 28.6 | 27.9 | 26.7 | 27.6\n \u00b139.8 | 11.9 | 18.3 | 21.1 | 21.9 | 23.6\n \u00b162.3 | 5.2 | 15.7 | 21.3 | 22.0 | 22.1\n Number of | | | | |\n stars observed | 716 | 1885 | 1329 | 1719 | 457\n\nThe difference is most pronounced in the two first groups; in the\nthree last it is small but unmistakable. An even distribution would\ncorrespond to 25 per cent. in all four divisions of the heavens.\n\nThese comprehensive statistics, embracing 6106 stars, seem to indicate\nthat the stars in their first stage were within the Milky Way but\nsubsequently drifted away with increasing age. This leads us to the\nthought that they originated from the irregular, nebulous accumulations\nwhich occur in the Milky Way and in its vicinity, or more correctly\nfrom similar formations which formerly existed in these regions but\nwhich now have clustered into stars. This agrees very well with\nanother observation. With the help of the spectroscope the motion\nof different stars has been determined with reference to the point\nwhere the sun now is. The velocities have been found greater the\nolder the stars are as shown in the table below taken mainly from the\ninvestigations of the renowned astronomer, Campbell.\n\n _Mean velocity of_:\n\n Irregular nebul\u00e6 0 Km. ( 0 Miles) per sec.\n Wolf-Rayet stars 4.5 \u201d ( 2.8 \u201d ) \u201d \u201d\n Helium stars 6.5 \u201d ( 4.0 \u201d ) \u201d \u201d\n Hydrogen stars 11 \u201d ( 6.8 \u201d ) \u201d \u201d\n Yellow stars 15 \u201d ( 9.3 \u201d ) \u201d \u201d\n Red stars 17 \u201d (11.5 \u201d ) \u201d \u201d\n Planetary nebul\u00e6 25 \u201d (15.5 \u201d ) \u201d \u201d\n\nTo these figures a few remarks founded on recent observations might be\nmade. The average distance between us and the stars in each group is\ndifferent and the yellow stars, to which indeed our Sun belongs, are\nthose nearest to us in space. They are therefore easier to observe than\nstars in the other groups. Campbell\u2019s statistics include also for this\nreason a smaller number of stars in this class than in the others. It\nis conceivable and by the astronomer Halm held to be true that the mean\nvelocity of the smaller stars is greater than that of the larger ones.\nThis is the condition existing in a mixture of different gas molecules,\nwith which the brilliant French scientist, Henri Poincar\u00e9, compared\nthe throng of stars, inasmuch as the heavier molecules possess the\nslower motion. To confirm this W.\u00a0S. Adams of the Carnegie Observatory\non Mount Wilson compared stars of equal velocity in their own orbits.\nSuch stars are considered to be on the average equally far removed\nfrom us. He found the theory of Halm confirmed. The mean velocity of\nthe hydrogen stars was reduced from 11 km. (6.8 miles) to 7.5 km. (4.7\nmiles), that of the yellow stars from 15 km. (9.3 miles) to 9.2 km.\n(5.8 miles), and that of the red stars from 17 km. (11.5 miles) to 14\nkm. (8.7 miles), while that of the helium stars remained unchanged. The\nsequence of the stars arranged according to velocity in the line of\nsight is evidently not modified by this new calculation.\n\nIn regard to the motion of the planetary nebul\u00e6 it should be mentioned\nthat Campbell in this connection has carried out a great number of new\ndeterminations according to which the mean observed velocity of these\nlarge bodies in the line of sight must be increased to not less than 42\nkm. (26 miles) per second.\n\nCampbell and Moore contribute the following interesting data in regard\nto Nebula N.\u00a0G.\u00a0C. 7009 (Fig. 2):\n\n\u201cMeasures of the rotational velocity of the nebula enable us to draw\nsome interesting conclusions concerning its mass. On the most plausible\nassumption as to the location of the axis of rotation the orbital speed\nof the nebular materials lying at a distance of 9 seconds of arc from\nthe centre is about 6 km. (3.7 miles) per second. If we provisionally\nassume the mass of the central nucleus to equal that of the Sun,\nKepler\u2019s law connecting the periodic time with the distance from the\nnucleus tells us definitely that the nebula is distant from us only 8.9\nlight years. This must be regarded as an improbably small value, in\nview of other evidence bearing on the question. For assumed distances\nof 100 and 1000 light years, which we have reason to believe are more\nprobable orders of nebular distance, the masses of the nebula would be\nrespectively 11.3 and 113 times that of the Sun, and the corresponding\nperiods of rotation 1371 and 13,710 years. From these considerations\nit seems certain that the mass of the planetary nebula N.\u00a0G.\u00a0C. 7009\nis several times that of the Sun. The nebula is therefore competent,\nfrom the point of view of its mass, to develop into a system more\npretentious than is our solar system.\n\n\u201cA few speculations concerning this nebula may not be without interest\nand value.\n\n\u201cThe faint extensions to the east and to the west of the elliptical\nfigure suggest an encircling ring of materials whose principal plane,\npassing through the nucleus, passes also near our (the observers\u2019)\nposition in space. These extensions terminate in condensed nuclei at\nequal distances from the nucleus and on exactly opposite sides of the\nnucleus. The faint extensions and condensations may be and probably are\nlargely the effect of the edgewise projection of such a ring, as in the\ncase of Saturn\u2019s rings when the observer is in the plane of the rings.\nThe forms of the two terminating condensations, and especially the wing\nextending up and out from the east condensation, suggest that we are\nnot precisely in the plane of the assumed ring.\n\n\u201cThe form of the main nebula appears to be ellipsoidal and not chiefly\nelliptical.\n\n\u201cThe space immediately surrounding the central nucleus appears to be\nrelatively vacuous. Aside from the nucleus, the principal mass of\nvisible nebulosity exists in the brilliant ring, roughly elliptical\nas to its inner and outer boundaries, which occupies the region about\nmidway between the nucleus and the outer edge of the nebular structure.\nThe brilliant ring is probably in reality an ellipsoidal shell; the\nprojection of such a shell upon a plane at right angles to the line\nof sight would naturally show a relatively dark central area, but the\nprojection principle may not be the only one involved.\n\n\u201cIf this nebula is in process of development into a solar system, the\nindications are for a system having certain resemblances to our solar\nsystem. Our four outer planets have a combined mass 225 times as great\nas that of the four inner planets. Similarly in N.\u00a0G.\u00a0C. 7009, there\nis apparently a paucity of material to form planets near the nucleus\nand an abundance of material for planets at greater distances from the\nnucleus.\u201d\n\n[Illustration:\n\n Fig. 2. Planetary nebula N.G.C. 7009 (composite drawing, from\n Curtis\u2019s photographs of the nebula made with the Crossley\n reflecting telescope. The scale is in seconds of arc).\n\nFrom _Proceedings of the National Academy of Sciences of U.\u00a0S.\u00a0A._]\n\nInteresting observations have been presented recently also with\nreference to the largest among the irregular nebul\u00e6, namely the Orion\nnebula. Three astronomers in Marseilles, Bourget, Fabry, and Buisson,\nfound that parts of this nebula, in the neighbourhood of the so-called\ntrapeze and very close to each other, moved with different velocities\nand that this difference might amount to 10 km. (6.2 miles) per\nsecond. The south-easterly part approaches us while the north-easterly\nrecedes from us. Consequently a violent whirl-motion undoubtedly\ntakes place in this region. This observation has been verified by\nthe well-known Chicago astronomer, Frost, who employed a different\nmethod of investigation than his predecessors. He noted differences in\nvelocity amounting to 11 km. (6.8 miles) per second between points not\nover two seconds of arc distant from the trapeze.\n\nIf therefore we say that the irregular nebul\u00e6 on the average possess\nno motion, this statement does not preclude important local deviations\nfrom the rule within the nebul\u00e6, intimating a transformation which\nprobably leads to the concentration of the nebulous matter toward the\ncentre of the whirl.\n\nLeaving out, to begin with, the planetary nebul\u00e6, it appears that the\noriginal matter of the stars stands still in space, that their average\nvelocity increases with increasing age and approaches a mean value\nof about 18 km. per second or roughly 1000 times the speed of the\nordinary passenger train. Our Sun, in particular, moves with a velocity\nof 20 km. (12.4 miles) per second toward a point in the constellation\nHercules 30 degrees north of the equator.\n\nWhat force then shall we say it is that causes the motion of the stars?\nAs far as we know none but gravitation. It appears therefore as if\nthe gaseous primeval substance of the stars were not governed by this\nforce. It might prove hazardous, however, to make this assumption\nas gases also possess weight and even the most rarefied strata of\nthe Earth\u2019s atmosphere exert barometric pressure by virtue of their\nattraction to the mass of the earth. Rather the immobility of the\nnebul\u00e6 is due to the frequent collisions between the molecules in any\nquantity of gas even if it be attenuated to such a high degree as in\nthe nebul\u00e6. Thus, the molecules strike a balance, as it were, against\neach other so that the different parts of the gas accumulations\nshortly are brought to rest relative to each other. The irregular\ngas mists around the Milky Way form therefore a continuous whole. A\ndifferent condition obtains in regard to condensed stellar bodies such\nas the stars. They may in the densest throng move during billions of\nyears before they collide; but they might on the other hand enter\nnebulous masses and thereby suffer gradual retardation. We now refer\nto stars moving outside of the vapour clouds. They are therefore\nunrestricted and the longer they have obeyed gravitation without\nimpeding encounters with nebulous matter, in other words the longer\nthe time elapsed since they emerged from the gas accumulations which\ngave them birth, the swifter is their motion. Their (average) velocity\ncan of course not exceed a certain limit which in our parts of the\nuniverse appears to be about 18 km. (11.2 miles) per second. Campbell\u2019s\nmeasurements show that for the youngest stars (all except the red) the\nvelocity is greatest in the plane of the Milky Way, a natural enough\ncondition as the attracting matter here is most abundant.\n\nThe planetary nebul\u00e6 possess a greater velocity although they, as\nconsisting of mist vapours, are in the first stage of evolution. Faster\nyet do the spiral nebul\u00e6 move according to measurements by Wolf of\nHeidelberg. This shows that they are of a different nature from the\nirregular nebul\u00e6, which form the matrix of the Milky Way. A closer\nexamination of the few--thirteen in all--planetary nebul\u00e6, determined\nby the American astronomer Keeler, convinced me that they approach the\nGalaxy from its poles with a moderate speed, and subsequently under\nthe influence of its attraction curve their orbit, rapidly gain in\nvelocity, and finally rush into the nearest part of the Milky Way with\na very high speed.\n\nA great number of them are no doubt caught in the mists or star-throngs\nof the Milky Way after exposure to numerous collisions and sweeping\naway all matter in their course. Such clean-swept traces are very\ncommon in the area of the Milky Way. One of the most beautiful examples\nis the so-called Cocoon nebula in the constellation Cygnus (the\nSwan). It has left in its wake a dark rift, in whose bottom, however,\nexceedingly small and evidently very remote stars are visible according\nto the German astronomer Wolf (see _Worlds in the Making_, page 172,\nFig. 55).\n\nThe great mean velocity of the planetary nebul\u00e6 indicates that they\noriginally did not belong to the Galactic system, a conclusion also\nreached by Bohlin, but for other reasons. They are nevertheless more\nabundant in the neighbourhood of the Milky Way than in other parts\nof the heavens. This fact, if viewed superficially, might lead to\nthe belief that they are indigenous to the Galactic system, but is\nexplained by their concentration in obedience to gravitation toward the\nMilky Way.\n\nQuite recently (1917) Van Maanen determined the distance of one of\nthese highly interesting celestial bodies, tabulated in the New\nGeneral Catalogue as No. 7662. Its distance was found to be only about\n140 light years. This is about sixteen times the distance of Sirius and\nthe mean distance of a star of the fifth magnitude. This circumstance\nagrees very well with the idea that this nebula is captured by the\nGalactic system to which it has approached from very distant parts of\nthe space outside of the Galactic system.\n\nOne of the most remarkable astronomical discoveries in recent years\nwas made by Kapteyn, who thereby as well as by other achievements has\ngained perhaps the highest rank among astronomers of today. He has\nshown that the stars rushing forth in the neighbourhood of the Sun\nbelong to two great groups, one coming from the constellation Orion,\nand the other at nearly a right angle (100\u00b0) from the constellation\nScorpio. In the former, we find nearly all the helium stars hitherto\nstudied. We have previously seen that these stars stand almost still\nwith reference to the Galaxy while the irregular nebul\u00e6 possess no\nmotion at all relative to the same reference point--and the Galaxy is\nthe natural datum-line for all astronomical measurements--so that the\nmotion of the first-mentioned star-group toward the Sun is principally\ndue to the Sun\u2019s own motion. This group, according to Kapteyn, obeys\nthe law of relative star velocities even better than the combined world\nof all stars; thus with reference to the Sun, the helium stars are the\nslowest, the yellow stars the fastest, while the hydrogen stars occupy\na middle position, all a self-evident consequence of their own velocity\nwith reference to the Galaxy which increases from helium stars to\nyellow stars.\n\nKapteyn has shown another regularity in this group which is easily\nexplained. We have previously mentioned that the yellow stars are most,\nthe helium stars least removed from their place of birth in the Milky\nWay. The result is that the yellow stars appear (on the average) to\ncome from a point farther from the Galaxy than the apparent origin of\nthe hydrogen stars and more remote yet than that of the helium stars.\nOn account of the relatively high velocity of the yellow stars in\ndifferent directions, their stream appears to be more divergent than\nthe stream of hydrogen stars, and helium stars move in almost parallel\npaths (nearly directly opposed to the Sun\u2019s true motion with reference\nto the Galaxy).\n\nSimilar regularities have been found by Kapteyn in the second\nstar-drift which would lead us to think, as indeed Kapteyn assumes,\nthat these stars also developed from an original nebulous mist, which\narrived in our neighbourhood from the unknown distant, but is now used\nup in the formation of corresponding stars. Here again the yellow stars\nshould have departed farther from their matrix than the white hydrogen\nstars. Helium stars are very rare in this drift, so that no reliable\nstatistics have as yet been made for them.\n\nIt has been one of the most difficult problems of cosmogony to form\na theory to account for the origin of the Galactic system. We may,\nalmost yearly, witness how new stars blaze into existence only to fade\nrapidly and in a few years return to their old insignificance--that is,\nthey become invisible to the naked eye although through powerful lenses\nwe may frequently discover an exceedingly faint star in their position.\nAs a rule, a nebula of the planetary type is formed in the course of a\nfew months. Somewhat later the nebula is transformed into a Wolf-Rayet\nstar. It is interesting to note that Wright found the central bodies in\ncertain planetary nebul\u00e6 to be Wolf-Rayet stars. We have good reasons\nto assume this blazing forth into light to signify the collision of two\nfaintly luminous or possibly extinct stars. The new lights appear also\nin stellar regions where the star density is very great, particularly\nin the Milky Way or its vicinity.\n\nWe see therefore repeatedly how mists with enclosed central stars\noriginate. They remind us to a certain extent of the Galaxy with its\nclouds and stars and along the road thus suggested trials have been\nmade to reach the solution of the riddle. The difficulty lies in the\nfact that the orbs whose collision create \u201cnew stars\u201d are small,\nprobably smaller than our Sun, while the mass gathered in the Milky\nWay most likely is trillions[2] of times greater than that of the Sun.\nIt is true that we know a few unique stars, such as Arcturus, which\nexceed our Sun in size several tens of thousand times, but not even two\nsuch stars would account for the mass of the Galaxy, and furthermore\nthe probability that two stellar bodies of such rare dimensions would\ncollide is so very small that it must be left out of account.\n\n [2] American and French numeration; billions acc. to Swedish\n and English usage.\n\nKapteyn\u2019s star-drifts, containing many thousands or probably millions\nof stars, appear to furnish the bridge that leads to the solution\nof the riddle of the Milky Way. These drifts were once enormous\ngas-clouds, in mass probably several million times greater than that\nof the Sun. They also had an extension equal to trillions of stars.\nThe probability for the meeting of two such gas-drifts is comparatively\nlarge and should not be much smaller than for the entrance of a\nstar-drift into the Milky Way, an occurrence which actually has\nhappened as shown by Kapteyn.\n\nWhen two such enormous gas-clouds meet, each with a cosmic velocity of\nabout 20 km. per second, a long time would not elapse before the gas\nmolecules in the region of interpenetration would be retarded in their\noriginal motions. An extraordinarily strong concentration and heating\nwould occur in this territory, which is surrounded by the comparatively\ncold and heavy masses which remain unaffected because outside of the\nimpact-area. A certain degree of equalization would naturally take\nplace in the layers adjoining the boundary between active and inactive\nparts and the former would, furthermore, be set into a rapid spin\naround an axis perpendicular to the plane containing the two original\nmotions. On account of the great viscosity of gases, particularly\nat high temperature, the central part would rotate as a coherent\nunit. Thus it would form a disk of gaseous matter. This disk would be\nthickest in the middle and would become thinner toward the edge where\ncentrifugal force acts most powerfully.\n\n[Illustration: Fig. 3. N.G.C. 4594. Exposure = 2 hours. 1mm = 6\u201d7.\n\nFrom _Proceedings of the National Academy of Sciences of U.\u00a0S.\u00a0A._]\n\nSuch a discous nebula has been investigated by the astronomer F.\u00a0G.\nPease of the Carnegie Observatory on Mount Wilson. By means of the\nspectroscope he has studied the motion of Nebula No. 4594 in the New\nGeneral Catalogue (see Fig. 3). This body is believed to be a spiral\nnebula like those in Figs. 4 and 5 but viewed from the side so that\nthe spirals appear as a band. As the picture shows, this band is\ncoursed through by a thick dark line, owing, it is believed, to a cold\nnon-luminous dust-cloud outside of the spiral. The bright band is\nbroadest in the centre. The curvature of the dark middle line in the\nshape of an arc, whose apex points downward, combined with the fact\nthat the major portion of light falls above this arc, indicates\nthat we do not view the nebula exactly on edge but from the upper\n(north) side of a plane through the arms of the nebula. The nucleus\nspeeds away from us at the dizzying rate of 1180 km. (730 miles) per\nsecond. The east edge, _i.\u00a0e._ the left on the picture, departs with\nthe still higher velocity of 1630 km. (1100 miles) per second, while\nthe west (right) edge retreats at the rate of only 800 km. (495 miles)\nper second. According to Pease, the nebula rotates as a solid disk so\nthat the difference between the velocity of any point and that of the\ncentre increases in the same proportion as the distance of the point in\nquestion from the centre. It is probable that we have been prevented\nfrom observing the outer parts, corresponding to the spiral arms\nproper, by the ring of dust which encircles the nebula. The visible\nportion occupies an arc of 2\u00bc minutes on each side of the centre. Its\nspectrum corresponds to that of star-group F-5 among the yellow stars\nin the Harvard classification. Therefore, it is not the light of the\ncoherent gas-cloud which preponderates but rather that of the stars\nconsolidated within the cloud, and corresponding to the stars in the\nMilky Way. This star-light is so bright that it entirely suppresses the\nradiation from the gas-cloud itself.\n\nSuch parts of the gas-aggregation as are most removed from the place of\ncollision continue in their course through space little affected by the\nattraction of the central mass because of the great distance involved.\nThe portions nearer the point of impact receive orbits curved by this\nsame attraction and the curvature becomes the sharper the nearer the\naxis of rotation. One result of the mutual gravitation between the\ncentral mass and the particles in the outer sections of the nebula is\nalso that the velocity in the spiral arms becomes smaller the farther\nthe section in question is located from the centre, just as comets in\nthe solar system move slower the farther they are removed from the Sun.\nBut in all portions outside the central region the attraction is too\nweak to give circular orbits to the gaseous matter. All substance in\nthese localities, therefore, departs ever more from the centre. As the\nspiral arms stretch out into straight lines such matter finally leaves\nthe central disk altogether. It is possible that only the disk itself\nremains in the nebula computed by Pease.\n\nAnother astronomer on Mount Wilson, A. Van Maanen, has investigated\na nebula, No. 101 in Messier\u2019s catalogue (Fig. 4). This nebula lies\nnearly at a right angle to the line of vision which consequently almost\ncoincides with the axis of rotation. The motion of the different parts\nof this nebula has been calculated with the help of photographs taken\nin the years 1899, 1908, and 1914, whereby its changed position with\nreference to surrounding fixed stars has been recorded. Out of 87\npoints in the spirals only 9 moved in the direction of the hands on a\nclock while the other 78 moved in the opposite sense. The mean angular\nvelocity is 0.022 seconds of arc per year, corresponding to 85,000\nyears for one complete revolution at 5 minutes\u2019 distance from the\ncentre. The absolute velocity 2 minutes of arc from the centre is 1.5\ntimes as great as at 7.5 minutes\u2019 distance.\n\nFig. 4 is reproduced from Van Maanen\u2019s original. It shows clearly the\ngeneral regularity in the motion of the component parts as well as\nthe numerous exceptions to the rule. Such exceptions may be caused by\nperturbations due to invading masses, which impart their own motion to\nthe entangling matter. These foreign bodies have probably condensed\nsurrounding vapours and this created the bright knots which stud the\nnebular spirals. The upward motion amounts on the average to 0.007\nseconds per year. While the points of condensation describe half a\nrevolution around the centre they depart therefrom to about twice their\noriginal distance. More than a million years is therefore likely to\nelapse before the outer portions of the nebula are so far removed from\nthe nucleus that the spiral form of the nebula is no more apparent.\n\n[Illustration:\n\n Fig. 4. Internal motions in Messier 101. The arrows indicate the\n direction and magnitude of the mean annual motions. Their\n scale (0\u201d1) is indicated on the plate. The scale of the\n nebula is 1mm = 10\u201d5. The comparison stars are enclosed in\n circles.\n\nFrom _Proceedings of the National Academy of Sciences of U.\u00a0S.\u00a0A._]\n\n[Illustration:\n\n Fig. 5. Spiral nebula No. 51 in Messier\u2019s Catalogue; situated in\n Canes Venatici, and photographed February 7 and 8, 1910,\n from Mount Wilson Observatory in California. Scale: 1\n millimeter = 5 sec. arc.\n\n Lyran Herkules\n Ormb\u00e4raren \u00d6rnen Sk\u00f6lden\n Svanen R\u00e4ven\n Pilen\n\n Ormb\u00e4raren Skytten\n Skorpionen\n S\u00f6dra Kronan Kols\u00e4ck\n Syd-Korset\n Skeppet Argo K\u00f6len\n\n Skeppet Argo Styre Segel\n N\n Enh\u00f6rningen\n\n Enh\u00f6rningen\n Kusken\n Cepheus\n Perseus\n Kassiopeja\n Svanen\n]\n\nIt is clear that the Milky Way may have been formed through the\ncollision of two immense nebulous gas-aggregations in the manner just\ndescribed. Subsequently and by virtue of the magnitude of the Galaxy\ngreat quantities of wandering cosmic matter and minor stellar bodies\nhave been gathered in occasionally accompanied by larger clusterings\nsuch as the planetary nebul\u00e6 referred to.\n\nHow well justified we are in looking upon the Milky Way as a spiral\nnebula is apparent from the picture (Fig. 5) reproducing a photograph\nof the familiar regular nebula in the Dogs (Canes Venatici). It shows\na wealth of detail hitherto not surmised. The feat was accomplished in\nthe Carnegie Observatory on Mount Wilson in Southern California with\nthe help of optical resources vastly superior to all earlier means.\nThe Milky Way has previously been compared to this nebula, but due to\ndeficient enlargement their striking similarity has not been fully\nrecognized until now.\n\nAssume the Sun located in the point marked \u201cS\u201d in Fig. 5 and some\ndistance above the plane of the picture, then the nebula if viewed\nfrom this point would appear somewhat as the Milky Way appears to\nus. In the middle we behold the substantial nucleus and on its left\nside a cleft between the two branches of the inner spiral. Farther\nto the left, we see only the outer spiral, first broadening toward\nthe left where it approaches \u201cS,\u201d then narrowing only to spread again\non account of the great clustering in the lower right part of the\nspiral. The axis of the nebula corresponds to the densest parts of\nthe Galaxy in Cygnus (the Swan), the loop in the inner spiral again\nto the empty space between Cepheus and Cassiopeia, the narrow part\nof the outer spiral branch resembles the constriction at Algenib,\nthe following diffusion corresponds to the broad section in Auriga\n(Charioteer) and Monoceros (Unicorn). At the subsequent narrow place\nwe see the outer nebula-clump corresponding in certain respects to the\nMagellanic clouds on our firmament although these are farther removed,\nand apparently not indigenous to the Milky Way. There follows in the\nnebula a massive section in our system represented by the well known,\nfar less compact, yet brightly luminous tract containing the Southern\nCross. Here, from the star Alpha in Centaurus--the nearest bright fixed\nstar[3] to our Sun, \u201conly\u201d 4.5 light years or about 25 trillion[4]\nmiles distant--commences a bi-section of the spiral and strangely\nenough the nebula is similarly forked. Now the outer spiral stretching\nin a faint line upward from the \u201cclump\u201d begins to show as a weak band,\nwhile the inner spiral stands forth powerfully above \u201cS\u201d corresponding\nto the brilliant section of the Galaxy in Scutum (Shield) and Aquila\n(Eagle). The partition in the nebula between these two branches is\nthe counterpart of the 110\u00b0 long \u201cprong\u201d in the Milky Way between the\nconstellations Norma and Lyra. Numerous faint bridges join the two\nbranches in the nebula as well as in the Galaxy, according to Wolf.\n\n [3] Up to a short time ago Alpha Centauri was considered the\n fixed star nearest to the Sun. By comparing old photographs\n of the firmament with such of recent date the renowned\n astronomer Barnard found that a very small fixed star--of\n the magnitude 10.5 and therefore far from visible to the\n naked eye--in the constellation Ophiuchus (Right ascension\n 17 h. 58 m. 44 s., North declination 4\u00b0 27\u00b4.4 January 1,\n 1917) possesses a very large proper motion. It traverses in\n a year 10.3 seconds on the firmament. The distance to this\n star, which has the largest proper motion so far known,\n was later determined to be 3.3 light years or 3/4 of the\n distance from Alpha Centauri to our Sun. Hence its velocity\n at right angle to the line of vision is computed to be\n 49 km. (32 miles) per second. Spectroscopic measurements\n show that it approaches us with a velocity of 91 km. (56.5\n miles) per second along the line of vision. The combined\n velocity, therefore, is 103 km. (63 miles) per second, an\n unusually high value. The value of 3.3 light years used in\n this calculation was determined by the French astronomer\n Gonnessiat, who found it by the study of old photographs\n from Algeria. He also calculated the parallax of this star\n to be 1 second. According to later measurements, given in\n the Harvard Bulletins 616 and 617, its parallax is only\n 0.7 seconds and consequently its distance 4.6 light years\n and its speed perpendicularly to the line of vision 70 km.\n (43.5 miles) per second. Campbell, in the Lick Observatory,\n had determined its radial velocity and found that it\n approaches the Sun at the rate of 128 km. (79 miles) per\n second. Its total velocity is, according to these two last\n determinations, 146 km. (91 miles) per second.\n\n It is by no means improbable that similar discoveries will\n be made in the future, so that the Sun will be found to have\n more stars in its \u201cimmediate\u201d vicinity than previously\n assumed.\n\n [4] American and French numeration; the Swedish and English\n usage is billion.\n\nThe correspondence is indeed surprisingly good. Proportions are, of\ncourse, somewhat different--in particular is the central part of the\nGalaxy not so predominating, which fact has been troublesome to the\nadherents of the nebula theory. Probably it was originally denser but\nhas become attenuated through star-formation, explaining, for instance,\nthe great gap between the constellations Lyra and Vulpecula.\n\nTo give a better idea of the structure of the Milky Way, two\nphotographs are here reproduced as taken by Wolf, the German astronomer\nin Heidelberg, who has done particularly meritorious work in this\ndepartment. One (Fig. 6) shows a section of the Galaxy in Cygnus\n(the Swan) with the star Deneb in the centre and to the left the\n\u201cNorthamerican-nebula\u201d so named from its shape. Above Deneb is the dark\n\u201chole\u201d in Cygnus and below another chasm not quite so black. Left of\nthe \u201chole\u201d is the winding canal enclosing the so-called Cocoon nebula.\n(See _Worlds in the Making_, page 172.)\n\nThe following picture (Fig. 7) contains, in the upper left, the bright\nstar Altair in Aquila (the Eagle) located close to the powerful arm of\nthe Galaxy in this constellation. Farther to the right is the fainter\narm in Ophiuchus (the Serpent-holder). The lower half contains the\nmost brilliant part of the Milky Way in the constellations Scutum (the\nShield) and Sagittarius (the Archer). Bright stars are infrequent but\nthe fainter ones are innumerable: \u201cThey are crowded into dense clusters\nand between them the most delicate star dust is scattered.\u201d--\u201cWe behold\nhow the star-ribbon dissolves into detached tufts which intertwine into\nthe strangest patterns. These clouds of stars reach their greatest\nsplendour in the lower part of the map.\u201d\n\n[Illustration:\n\n Fig. 6. The Milky Way between constellations Cassiopeia and Swan\n from photo by M. Wolf of Heidelberg. A little to the left\n of the middle the beautiful nebula America appears.\n]\n\n[Illustration:\n\n Fig. 7. The Milky Way in constellations Eagle (upper half) and\n Archer (lower half). In the upper left the bright star\n Altair appears. Photo from M. Wolf of Heidelberg.\n]\n\nWe also reproduce (Fig. 8) from M. Wolf a photograph in larger scale\nfrom the region of Gamma (lower part of Fig. 7) in the Eagle\nwith its \u201ctrident-hole,\u201d so called from its peculiar shape, and in\nwhose vicinity mists and star-clouds abound. This picture is a more\ncomplicated counterpart of the flatter photograph by Wolf of the\n\u201cCocoon nebula.\u201d It appears as if three or four stellar bodies here\nhad stepped in from without, swept away the stars in their way, and\nleft clean \u201cstreets\u201d behind. Probably other \u201cempty\u201d spots in the\nneighbourhood have been formed in a similar manner. Another theory is\nthat such dark places are caused by opaque mist-formations which shield\nthe light of the stars behind from our sight.\n\n[Illustration: Fig. 8. The trisected hole (Trifid-hole) in Eagle. Photo\nfrom M. Wolf of Heidelberg.]\n\nThrough these pictures we gain a conception of the manner in which the\npresent stars in the Milky Way have clustered out of the original misty\nchaos. We cannot avoid the idea of great exterior similarity between\nthe lumps formed in curdling or souring milk and those which we observe\nin the Milky Way. The renowned French scientist Duclaux says in his\nmicro-biology: \u201cIn milk, commencing to sour, but yet entirely liquid,\nwe observe under the microscope a precipitation of tiny particles.\nTo begin with they are seen with difficulty and are discovered only\nby slightly displacing the plane of vision. Later they develop into\ndistinct grains, characterized by Brownian movements, just like small\nparticles of clay.... Still later the phenomenon appears as a steady\nmolecular agglomeration. The grains have the tendency of the clay\nparticles to lump and precipitate.\u201d\n\nThe first condensation-nuclei in the mist-clouds are no doubt cosmic\ndust entering from without and perhaps also larger clusterings such as\nmeteorites and comets. At the existing low temperature, surrounding\ngases condense into fluid state on the dust particles which by\nvirtue of these moist shells are cemented into aggregations of such\nsize that gravitation overcomes the repelling radiation pressure.\nGravitation assisted by the retarding vapours further mass these\naggregates together. This process of coalescence is accompanied by\nheat production. Finally, small stars are formed, then groups of such\nstars, while the spaces between, now comparatively devoid of matter,\nappear dark much as the whey between flocks of curd. As yet, the small\nstellar bodies are surrounded by quantities of dust and gas, which,\nhowever, with continued condensation become ever more rarefied. Even\nyet the big stars in Pleiades, belonging to the helium group, appear on\nthe photographic plates interspaced with great patches of dust-clouds.\nThese are now, however, so unsubstantial that they offer little\nimpediment to the procession of the mighty stars. The condensation\nprocess may be greatly accelerated through the invasion of voluminous\ngas nebul\u00e6 similar to the Cocoon nebula. At last all gases in the new\nstar condense, that is to say the shell of tenuous vapours and dust\ncontracts to such an insignificant thickness that it cannot be seen\nexcept possibly from the immediate vicinity. Small bodies ingathered\nthrough friction against the remnants of the original extended\nwrapping wander as planets around the new sun, sweeping away the last\ntraces of unattached matter. The condensation on the new orb leaves a\n\u201chole\u201d in the nebulosity which in this way is transformed into stars\nand their satellites which emerge from the mist and scatter on the\nfirmament.\n\nThe Milky Way appears to be in a rather advanced stage of this\nevolution.\n\nThe \u201cinfinitely small\u201d presents occasionally surprising likeness to the\n\u201cinfinitely large.\u201d\n\nIn this manner we can form a conception of the growth of the wonderful\nstructure which has brought forth the majority of the stellar bodies\nthat we discern. The spiral nebul\u00e6 visible at the Galactic poles are\nsimilar formations but probably of far more modest dimensions. They may\ncompare to the Milky Way as the smaller planets to the Sun. According\nto recent investigations the spiral nebul\u00e6 seem also to possess an\nenormous velocity and they have probably invaded the Milky Way from\nwithout.\n\nAs previously stated, an exceedingly remarkable conception of the\nMilky Way exists among the Mexicans. To them it is the Matrix of all\nand gave birth to the stars, the most important of which are the Sun,\nthe Moon, and Venus. This idea evidently agrees very well with the\nresults of investigations in the last few years.\n\nFinally, a few words about the extent of the Milky Way. So far we have\nnot been able to measure it; only rather uncertain approximations are\npossible. Wolf estimates the diameter, that is the distance between\nthe two spirals at the point where the Sun now is, to be about 10,000\ntimes the distance from the Sun to the nearest fixed star, Alpha in\nCentaurus, which distance on the other hand is about 10,000 times the\ndistance from the Sun to the remotest known planet, Neptune, or 300,000\ntimes that from Sun to Earth. Expressed in the usual units, we arrive\nat 40,000 light years or 400,000 trillion kilometres (240,000 trillion\nmiles). Lord Kelvin makes another estimate of 6000 light years, that is\nseven times smaller. The mean diameter of the nebula proper might be\nabout five times larger, in round figures one hundred thousand light\nyears, or one billion billion kilometres (600 million billion miles).\n\nLike a monstrous octopus, the Milky Way swims in the fathomless\nether-sea. Its dimensions are about as many times larger than those\nof the earth as that globe is larger than an atom. This has caused\nthe gifted Irish physicist Fournier D\u2019Albe to consider the celestial\nglobes as atoms, out of which systems of the order of the Milky Way\nare constructed in the same manner as the earth and other stellar\nbodies are upbuilt with atoms, invisible to us and yet measured with an\nincredible degree of accuracy.\n\nFournier D\u2019Albe goes further still. In poetic flight he does not\nhesitate to endow the Milky Way organism with life. Its evolution\ncannot be denied a certain similarity to the processes of life. The\ngreat nebula owes its origin to the union of two individuals, two\nnebulosities, who met in their course through boundless space. There\nfloated the newborn extending its tentacles in the cool ether-waves\nand gained substance and strength through the smaller beings which\nthe surging billows brought within its reach. It has now attained\nthe zenith of its evolution, and is breaking up into molecules, or\nsolar systems, which again are composed of stellar bodies, or atoms\nwithin the molecule. In violent exuberance of youth these rush through\nspace in fulfilment of their individual life. Many will in due time\nundoubtedly become dust again and then serve to nourish a new youthful\nnebula. Others succumb to a freezing-death but will be restored to life\nin collision with a nebulosity or some other stellar body and give\nform to \u201cnew stars\u201d or planetary clouds. Again and again shall the\nstarry mists go through the cycle of existence and after a lifetime,\nwhose duration stands in proportion to their dimensions, _i.\u00a0e._ may be\nestimated to billions of billions of years, give rise to new celestial\nbeings. Thus shall it for ever continue in an eternal rhythm.\n\n\n\n\nCHAPTER III\n\nTHE CLIMATIC IMPORTANCE OF WATER VAPOUR\n\n\nWhen Aristotle, for two thousand years our leading savant in\ncosmography, about twenty-three centuries ago stated the foundation of\nhis natural science, he laid down as the important principles: moisture\nand heat and their opposites; because the four elements out of which\neverything was made, were: earth, characterized by dryness and cold;\nwater, which was moist and cold; air, which combined moisture with\nheat; and lastly fire, which stood for dryness and heat. Undoubtedly\nhe was considering the requisites of life, which may be designated as\nhumidity and heat. We have seemingly agreed that all life originates\nin the sea, so that moisture can be considered the first requirement\nfor its appearance on the earth. As to heat, life is destroyed by\nfrost and favoured by increased warmth, at least to a certain point,\nabout 35\u00b0 to 40\u00b0\u00a0C. (95\u00b0 to 104\u00b0 Fahrenheit), which temperature is\nmost propitious to the development of life, while a further increase\nis detrimental, so that already below the boiling point of water life\nsuffers more harm than at temperatures below freezing. In fact, the\ngeologists have found that the different epochs in earth\u2019s evolution\nare best characterized by their humidity or dryness. To arrive at a\nclear conception in these matters we shall briefly survey our present\nknowledge of the importance for the evolution of life on earth that we\nshould attach to the humid and to the dry periods or localities.\n\nWe are all familiar with the heavy, moisture-laden warmth which meets\nus when we enter a hothouse. It is particularly favourable to the\ngrowth of plants and to the prosperity of the lower animals. To the\nhigher animals and to man, the humid heat is not so beneficial. In the\nopen such hothouse air exists only in the tropics. Particularly the\nCongo region and the parts of Brazil adjoining the Amazon River are\nremarkable for their humid heat and for their fabulously luxuriant\nvegetation. From our greatest living climatologist, Julius Hann, I have\nborrowed the following description of such a clime:\n\n\u201cThe changes of temperature between the coldest and the hottest month\nare very small in the Congo, from .5\u00b0 to 5\u00b0\u00a0C. (.9\u00b0 to 9\u00b0 Fahrenheit),\nwith an average of about 3.5\u00b0\u00a0C. (6.3\u00b0\u00a0F.). The difference between day\nand night reaches nearly thrice this value, or 9.5\u00b0\u00a0C. (17.1\u00b0\u00a0F.).\nThe dry season becomes shorter the more we approach the equator\nand in Equatorville and Bangala it shrinks to nothing. During the\nrainless months, a dense humid fog settles morning and evening over\nthe savannahs. Low hanging clouds of uniform thickness frequently hide\nthe Sun for weeks at a time. It is during the rainy season alone that\nwe see a clear sky between the showers. This season opens and closes\nwith magnificent thunderstorms coming from the east. In Luluaburg,\nlightning occurs during not less than 106 days in the year. In the\ndry season the wind carries with it clouds of dust which falls to the\nground. The cloudiness is enormous in the Congo basin, so that there\nare veritably no months with a clear sky in this part of the world. In\nVivi, the number of overcast days averages 74 per cent., fluctuating\nbetween 63 per cent. in August and 83 per cent. in November. The\nhumidity is very high, varying in Vivi from 70 to 79 per cent., with a\nmean value of 75 per cent., and in Bolebo the mean itself reaches 79\nper cent. During the rainy season, the heat is sometimes unbearably\noppressive; suffocating fumes rise from vegetable matter which rapidly\ndecays in the excessive humidity. The annual precipitation does not\nreach very startling figures; it varies between 120 and 180 cm. (47 to\n71 inches). In Gabun, close by, the sky is almost continuously covered\nwith clouds during the dry season.\n\n\u201cCorresponding regions in South America are in parts characterized by\nan even higher humidity. In Iquitos by the Amazon River, it reaches not\nless than 83 per cent. of saturation. The annual change of temperature\nis only about 5\u00b0\u00a0C. (9\u00b0\u00a0F.); in Para (1.08\u00b0 south latitude on the\ncoast) it shrinks to 1\u00b0 or 1.5\u00b0\u00a0C. (1.8\u00b0 to 2.7\u00b0\u00a0F.). In the course\nof twenty-four hours the variation is considerably larger. The sky\nis remarkably clear between showers during the rainy season. In the\ninterior of Guiana, the rains continue from the end of April well into\nJuly or even into August. Abundant dew is common during the rainless\npart of the year, thus maintaining the humidity. Sun and Moon are\nrarely visible, and gigantic lightning storms announce the arrival of\nthe rainy period.\u201d\n\nSimilar conditions apparently prevailed during the carboniferous\nperiod, which was characterized by a luxuriant vegetation. The mighty\ntree-trunks of that time fell into the water-covered marshes out of\nwhich they had grown and their decay was thereby prevented. Instead\nthey turned into coal like the peat in the mosses of today. This\nwas for some time thought to indicate that the temperature was not\nparticularly high--Frech estimated about 12\u00b0\u00a0C. (53.6\u00b0\u00a0F.) (1910). But\nsince the discovery and subsequent description by Keilhack (1914) of\npeat-beds on Ceylon, where the average yearly temperature is 26\u00b0\u00a0C.\n(78.8\u00b0\u00a0F.), a return is to be expected to the older conception,\nwhich held that the vegetation during the carboniferous period is\nevidence of a very warm climate. Judging by the appearance of fossil\nplants, the temperature should have been nearly the same all over\nthe globe. Carthaus remarks that the air was stirred by only feeble\nwinds because the trees of that age with their great dimensions but\nfrail root-systems could not have withstood a fresh breeze. The sky\nwas hidden behind a continuous thick cover of clouds which only let a\nfaint light sift through to the ground. The motionless air was almost\nsaturated with moisture. The luxuriance of the vegetation, transcending\nanything existing today, indicates a favourable high percentage of\ncarbonic acid in the air. This combined with the humidity and the dense\nclouds caused the heat radiation from the Sun to be almost entirely\nabsorbed by the upper strata of the atmosphere in which thereby a\nstrong circulation was maintained. As a result, the heat was nearly\nequalized between the poles and the equator and under the cloud cover\nan almost constant temperature reigned day and night, summer and\nwinter. The damp air stood wellnigh still and was filled with dense fog\nat the smallest changes in temperature. Lack of light prevented the\ndevelopment of flowers, and the thriving plants belonged mainly to the\nferns and to the horsetails. Pine and fir trees were yet comparatively\nfew. The conditions in the swampy regions where plant life flourished\nwere nearly identical with those in a hothouse if we were to draw a\ndense veil in front of the windows in walls and ceiling so that a\ncontinuous twilight would prevail.\n\nIn this uniform climate, plant life developed enormously faster than\nanimal life. The dense clouds could store considerable quantities of\nheat in the equatorial belt through evaporation in their upper layers\nand the violent wind storms above the clouds would carry the aqueous\nvapours to colder regions where the heat would be liberated through\nnew cloud formations. Currents in the oceans now largely attend to\nthis heat transportation and give for instance to the coast of Norway,\nand indeed to the whole of Western Europe, its remarkably mild, and to\nlife and civilization, propitious climate, but in the carboniferous age\nhumid air currents fulfilled the same task. They moved considerably\nfaster and more evenly than the ocean currents, were not checked\nor deflected by coasts or islands, and could therefore produce the\nextraordinarily uniform temperature and the marine climate all over\nthe globe. Such a heat distribution takes place also in our days at a\nheight of about 10,000 m. (6.2 miles) in the so-called \u201cstratosphere,\u201d\nbut the temperature here is very low, about -60\u00b0\u00a0C. (-76\u00b0\u00a0F.), so that\nthe vapour suspended is hardly worth mentioning, and cannot give rise\nto cloud formations. The quantities of heat carried in these higher\nstrata of the atmosphere are too insignificant to influence the masses\nof air below, whose temperature, therefore, is almost entirely governed\nby that of the sun-heated surface of the earth, except where the\nocean currents equalize matters, as for instance in the almost wholly\nwater-covered latitudes south of the 30th parallel on the Southern\nHemisphere. Even during the carboniferous period at its height, there\nexisted, of course, a temperature difference between pole and equator,\nbut it was very small, some 10\u00b0\u00a0C. (18\u00b0\u00a0F.) perhaps. Undoubtedly, the\nformation of coal beds was mainly confined to those regions where the\nclimate was most uniform all the year around.\n\nThe opposite extremity, the dry desert climate, is far more pronounced\nin the present time. This condition is well known in all continents\nexcept Europe, where we hardly can claim a desert but instead have\nsteppes, with a vegetation abundant after the spring rains but fast\ndisappearing with the arrival of the burning summer heat. A particular\ntype of plant life has adapted itself to this periodic change from rain\nto drought, from bitter cold during the winter to parching sun during\nthe summer. Perennial plants, and particularly trees, can rarely endure\nthe rigors of such climatic upheavals. Animal life on the other hand\nhas proved fairly adaptable and displays considerable wealth.\n\nThis steppe climate is only an intermediate stage towards the desert\nclimate proper, which is hostile to all life. Its temperature is\nsubject to enormous changes in the course of the day and the year.\nThe annual variation is less pronounced near the equator and the\ndaily variation less on the approach to the poles, on account of the\nsmall changes in the sun\u2019s radiation during corresponding periods.\nThe difference between day and night in Sahara is frequently 30\u00b0\nto 40\u00b0\u00a0C. (50\u00b0 to 70\u00b0\u00a0F.). The lowest temperature observed by\nFoureau-Lamy, 1898\u20131899, was -20\u00b0\u00a0C. (-4\u00b0\u00a0F.) or nearly the same as on\nthe Scandinavian coasts. The highest amounted to 48\u00b0\u00a0C. (118.4\u00b0\u00a0F.) or\na total variation of nearly 70\u00b0\u00a0C. (126\u00b0\u00a0F.). In Upper Egypt (21.9\u00b0\nN. Lat.) the mean temperature changed from 16.3\u00b0\u00a0C. (61.3\u00b0\u00a0F.) in\nJanuary to 34.1\u00b0\u00a0C. (93.2\u00b0\u00a0F.) in July, and nearer the equator in\nCentral Africa (8.1\u00b0 N. Lat., 23.6\u00b0 E. Long.) the difference amounted\nto only 6.9\u00b0\u00a0C. (44.6\u00b0\u00a0F.), 22.7\u00b0\u00a0C. (72.5\u00b0\u00a0F.) in December, 29.6\u00b0\u00a0C.\n(85.1\u00b0\u00a0F.) in April, while in Kiachta (50.4\u00b0 N. Lat., 106.5\u00b0 E. Long.)\nin Siberia, the yearly change reaches 45\u00b0\u00a0C. (81\u00b0\u00a0F.), -26.6\u00b0 C.\n(-15.7\u00b0\u00a0F.) in January, 19.1\u00b0\u00a0C. (66.2\u00b0\u00a0F.) in July. The average daily\nvariation at continental stations is about 12\u00b0\u00a0C. (21.6\u00b0\u00a0F.). All this\nrefers to the temperature of the air, while the surface temperature in\nthe course of twenty-four hours may change 50\u00b0\u00a0C. (90\u00b0\u00a0F.) and in the\ndesert even more. Frost occurs in the Sahara as late as May when the\nmaximum temperature may reach 50\u00b0\u00a0C. (122\u00b0\u00a0F.). While in Scandinavia\nthe diurnal difference between highest and lowest temperature averages\nonly 6\u00b0 to 7\u00b0\u00a0C. (11\u00b0 to 13\u00b0\u00a0F.), a maximum in July of 10.4\u00b0\u00a0C.\n(18.7\u00b0\u00a0F.) and a minimum in November of 4\u00b0\u00a0C. (7.2\u00b0\u00a0F.), Hedin on his\njourney in Tibet, 1899\u20131902, observed a daily variation of 19\u00b0\u00a0C.\n(34.2\u00b0\u00a0F.) and no appreciable difference with change in altitude.\n\nThe result of such a violent temperature change in the course of a day\nis a breaking up of the rocks which subsequently and gradually are\nground to fine dust by unobstructed winds wherever vegetation does not\nbind the soil. In this manner the sand deserts are formed. The arid\nwastes of Asia have lately been vividly described by Sven Hedin. The\nmountains eroded by the sandstorms resemble dilapidated ruins, standing\nas monuments of an ancient highland. The sand in East Turkestan is\nreduced to such a fine powder that it can float in the air for several\ndays after a storm, revealing itself in gorgeous sunsets. Winds sweep\nthe sand into long dunes, which shift in the direction of the blast.\nIt is ferruginous and therefore red or if powderized reddish-yellow.\nWhen moistened it assumes a brown to black shade. After rain, the water\ndescends toward the valley, carrying with it the sand in the form of\nsilt. This, through evaporation, is transformed into a plastic black\ndough, slides like a glacier slowly down the hillsides, and finally\ncomes to rest in some broad hollow which it gradually fills. Such a\nsilt aggregation is called in Persia a \u201cKevir.\u201d Its surface dries,\nbut the interior remains moist. As evaporation continues it becomes\nricher in salt so that white crusts of this substance are formed during\ndry periods. In other districts, as in the basin of the Tarim River,\nthe water occasionally appears in the lowest parts, the so-called\n\u201cBayirs\u201d (see Fig. 9), formations similar to the Kevirs, or in salt\nlakes between the sand dunes. Sand carried by the winds quickly fills\nthese lakes so that they too move in the direction of prevailing\nwinds. They lie with their longest dimensions parallel to each other\nand at right angle to the course of the Tarim River. The sketch map\ntaken from Hedin\u2019s work shows the Bayirs strung out in line with the\nlakes somewhat like panels in a tapestry pattern. This reticulation\nof the landscape is the result of the dune formations. The main dunes\nwith steep western slopes run in the direction N.N.E.-S.S.W. They\nstand at right angle to the prevailing winds. Nearly perpendicular to\ntheir crest lines dunes of smaller height are thrown up by winds in\nanother common direction but less frequent than those which raised the\nfundamental dunes. This system brings to mind the cloud formations\ncalled mackerel sky, clouds rippled in two directions frequently almost\nat right angle to each other. They owe their peculiarity to two series\nof wave motions propelled by winds from two different directions in\nthe upper strata of the atmosphere. The cloud patches correspond to\nthe wavecrests on a surging sea. The map of the Bayirs suggests a\nchessboard with squares somewhat elongated and irregular.\n\n[Illustration: Fig. 9. Tarim river with adjacent lakes and Bayirs,\ndrawn by Sven Hedin.\n\n (solid arrow) Predominating direction of winds.\n\n (dashed arrow) Direction in which the river is shifting.\n\n (hollow box) Vegetation.\n\n (dotted box) Sand.\n\n (horizontal lines in box) Lakes.\n\n (vertical lines in box) Bayirs.\n]\n\nWe may now return to a closer study of the largest of these\nformations, the great Kevir in Persia. This mud-lake, with a dry\nsurface, measures 500 km. (310 miles) in length and 200 km. (124\nmiles) in width over its largest dimensions. Hedin estimates its area\nat 55,000 sq. km. (21,142 sq. miles) or the same as that of the great\nLake Michigan on the boundary between the United States and Canada.\nDue to the continuous growth of the salt proportion through the inflow\nof Kevirs and through superficial evaporation a salt crust of varying\nthickness is formed near the surface of the lake. Hedin caused a hole\nto be cut with an iron bar. He first encountered a 10 cm. (3.9 in.)\ndeep covering of clayey paste, and then the salt crust about 7 cm. (2.8\nin.) thick resting on a semi-dry layer of clay with a depth of 15 cm.\n(5.9 in.). Farther below, softer strata of clay followed, becoming more\nwatery the deeper he went. The iron bar carelessly wielded would have\ndisappeared in the mire. Another investigator, Buhse, examined a piece\nof the crust, which when dry is fairly solid and of a yellowish-grey\ncolour. One half consisted of sand (probably quartz-sand), one sixth of\nlimestone, 6.1 per cent. oxide of iron (causing the yellow colour), 5.3\nper cent. common salt, 2.5 per cent. sulphate of sodium, and 2.1 per\ncent. clay. Rain converts this surface layer into a plastic mass, which\npersistently sticks to the clothes of the traveller or to the bodies of\nthe camels if they should slip and fall into the mud. Not the slightest\ntrace of vegetation or of any life exists. On the shore of the mud-lake\nsmall flat elevations and depressions may be found; otherwise, the\nsurface is as level as that of an ordinary lake.\n\nThe Kevir battles with the drifting sand as does the water in East\nTurkestan. The sand appears to gain in the contest. After storms, vast\nportions of the Kevir are covered with yellow desert sand. \u201cIf the\nclimatic change in Persia continues in the present direction,\u201d says\nHedin, who, however, is dealing with large spans of time inasmuch\nas in his opinion no appreciable alterations have taken place since\nthe invasions of Alexander the Great, \u201cthen it may be taken for\ngranted that the slough of the Kevir will lose in moisture and afflux\nof water and in time will become more solid and that the drift sand\nwith greater ease will gain foothold and territory. The final outcome\nof the physico-geographical transformation now in progress will no\ndoubt be to convert the entire Kevir into a sand desert of the kind\npredominating in East Turkestan. And conversely we may infer that\nEast Turkestan, once a part of the central Asiatic Mediterranean sea,\nin the course of time was filled with the finely divided products of\ndisintegration, such as we now find in the Kevir, and further that its\nexpanse of watery mud and clay finally dried and hardened to such an\nextent that it could support the load of the encroaching sand. That the\nextension of the sand formerly was smaller, is also borne out by the\narch\u00e6ological discoveries in East Turkestan which several travellers\nbesides myself have made. The hardpan laid bare in the \u2018Bayirs\u2019 of the\nCherchen desert strongly reminds of the Kevir-ground. In both cases\nthe same dark, fine powder forming a nearly plane surface. In both\ncases this material when mixed with water is transformed into a slough\nin which one hopelessly sinks, but in East Turkestan the water has\nreceded to a greater depth and as rains are extremely rare travel all\nover the smooth \u2018Bayir\u2019-ground may be undertaken with impunity.\u201d\n\nThese formations are of the greatest interest because they picture\nthe changes taking place on a slowly desiccating planet. In 1858 the\nGeographical Society in Petrograd despatched an expedition under\nthe command of Khanikoff to visit these regions. From Hedin\u2019s work,\n_Overland to India_, from which the preceding quotation is taken, we\nborrow the following vivid description by Khanikoff: \u201cAt last, in\nthe morning of April fourth, and during the most oppressive heat, we\nreached Bala-haus. At this place remnants of a ruined reservoir, long\nsince bereft of its water, could be seen. The desert had here assumed\nthe perfect character of the \u2018the accursed land,\u2019 which name it bears\namong the natives. Not the smallest tuft of grass, not a sign of animal\nlife gladdened the eye, not a sound interrupted the deathlike, awful\nsilence but that of the marching caravan.\n\n\u201cBecause of the slow procession of the camels and the delay suffered\nwhen we lost our way, we only covered 25 km. (15.5 miles) in the night\nstage. After four hours\u2019 rest we resumed our march and directed our\nsteps toward the hills, called Kellehper and situated 20 km. (12.5\nmiles) from Bala-haus; they were plainly visible but positively seemed\nto take flight on our approach. I was somewhat ahead of the caravan and\nsat down at the foot of this sand-elevation; and never can I describe\nthe feeling of weariness and of depression that I was unable to ward\noff as I looked into the ghastly solitude that engulfed me. Scattered\nclouds intercepted the rays of the sun, but the air was hot and heavy;\nthe diffused light lent a monotonous and disconsolating hue to the\ngreyish, burning surface of the desert; hardly a single variation\nof colour gave relief to the immense expanses that the vision\nembraced. The absolute immobility of every point in this mournful\nlandscape, combined with the complete absence of any sound, produced\nan overwhelming depression of the spirit; one felt as set upon a place\nthat had been struck inanimate for ever, a place to which organic life\nwould never return safe through some terrible catastrophe of nature.\nOne witnessed the beginning, so to speak, of the death-agony of our\nplanet.\u201d\n\nIf a drying out has taken place in these regions,--which seems probable\nfrom Hedin\u2019s observation that the water in a Tibet lake, Lakker-tso,\nformerly reached a 133 m. (435 ft.) higher level than at present,--such\na process is nevertheless not so obvious here as in the salt inland\nlakes, for instance the Great Salt Lake in Utah, the Dead Sea, and\nthe Caspian Sea, where the saltness has greatly increased due to\nevaporation. Concerning the Great Salt Lake we know that even at a\ncomparatively late time it had a much wider extension than now. Its\nwater contains 22 per cent. common salt besides other compounds. The\nDead Sea holds 25 per cent. salt. A very variable percentage is to be\nfound in the Caspian Sea. Near the mouth of the Volga it is of course\nlow, only 0.15, and increases southward to 1.32 at the peninsula\nApsheron and to 5.63 in the bay of Kaidak. In the gulf of Karaboghaz on\nthe Asiatic side it reaches 28.5 per cent. It has been computed that\nthis gulf receives annually from the inrushing waters of the Caspian\nSea 350,000 tons of salt which is partly deposited on its shores and\nbottom.\n\nThis desiccation, however, is a mere trifle when contrasted with the\nprocess by which the mighty salt deposits in Germany were formed. It\ntook place, we believe, in a shallow bay extending southward from the\nArctic Sea. As the salts, first gypsum, then common salt, and lastly\nmore soluble potassium and magnesium compounds, crystallized by degrees\nnew water masses entered from the sea. At the same time, the bottom of\nthe gulf slowly receded, giving room for fresh evaporating floods. The\nsalt layers deposited in this manner sometimes reach a depth of more\nthan 1000 m. (about one half a mile). We can thus gain a conception\nof the immense quantities of water evaporated and the enormous time\nrequired therefor. The deposits would long ago have been carried away\nfrom their original place were it not for the fact that they finally\nwere covered with a layer of slime nearly impervious to water. The most\nsoluble salts, such as chloride of magnesium, have nevertheless been\nextracted to a great extent.\n\nThe extremes of aridity or humidity have of course not occurred\nduring the brief time known to history. Of a special interest is the\nquestion in what direction the climate at present is tending. In this\nconnection, Huntington has aroused great attention by propounding the\ntheory that the earth is now in a period of rapid desiccation.\n\nJudging by the testimony of geology, it seems beyond doubt that an age\nof humidity prevailed simultaneously with the ice-period in northern\nEurope, over several parts of the globe, in fact everywhere as far as\nwe know except in Australia. This is clearly borne out by the higher\nlevels of the lakes and their consequent greater extension in earlier\ndays. So far as Tibet and Central Asia are concerned we have already\nmentioned this fact. But in America and Africa the humid period was\neven more patent. The Great Salt Lake has covered an area many times\ngreater than at present as testify the picturesque terraces in its\nsurroundings (compare Fig. 10). According to the researches by Passage,\nthis period was also strongly pronounced in Africa. A large fresh-water\nbody occupied the Congo basin, the Tsad lake had a far greater\nexpansion than now, and mighty rivers traversed Sahara.\n\n[Illustration: Fig. 10. Extension of the great Lake Bonneville in Utah,\nof which the Great Salt Lake is a remnant.]\n\nIt is often assumed that the climate of Africa has been more humid\neven in historic times. The geographer Leo Berg in Petrograd, however,\nis emphatically opposed to this theory. He points out that the\nwriters of antiquity, Diodoros, Polybios, and Pausanias, have given\ndescriptions of the rivers on the North African coast which nearly\nagree with conditions today. The location of two ancient cities on\nthe shores of Lake Chott-el-Djerid in Tunis (Lacus Tritonis of old),\nwhich lake, it is claimed, reached a level very much higher than now\n500 years B.C., plainly demonstrates that the shore-line then ran very\nclose to its present position. Students of ancient Egypt are unable to\nfind evidence of any distinct difference in the climate of that country\nfrom the earliest times to our days. It is true that marshes in the\nNile delta have changed into splendid meadows--but this is the work of\nman. The humid period must have ended long before history commenced.\nA few of the old writers, such as Herodotos, Aristophanes, and Philo,\nassert that rain never falls in Egypt, but this must be classed as an\nexaggeration when contrasted with references to rain, snow, and hail\nin this section made by other ancient authors, for instance Plutarch,\nPliny, and \u00c6lianus. At any rate it seems as if precipitation was as\nrare an occurrence in the land of the Pharaohs as in the land of the\nNile of today.\n\nAgainst the statement by Huntington that the climate of Palestine\nhas become very much more torrid during historic times, stands the\nassertion by Hilderscheid, who has made a thorough study of these\nquestions, that no reason whatever exists for such a conclusion.\n\nOf greatest interest to us in this connection are perhaps Italy and\nGreece. Huntington believes that the river Alpheios, which flooded\nOlympia and covered it with a 4 m. to 5 m. (4 or 5 yards) thick\nsediment, carried a far greater volume of water formerly than today.\nThis flood, however, was caused by an earthquake accompanied by a\nfall of rocks whereby the river was dammed. There is no necessity for\nassuming a greater abundance of the waterflow. According to Strabo,\nthe streams Kefissos and Ilissos, between which Athens is situated,\ndried out during the summer then as they do now. If we are to believe\nPausanias, the brooks which traversed the Argive plain behaved\nsimilarly, and so they behave today. From all we can judge, the climate\nof Greece has not changed perceptibly since the days of Homer.\n\nIn regard to Sicily, it is stated that several of its rivers were\nnavigable in the Middle Age, while such is not the case now. But this\nis explained by the devastation of the forests which formerly equalized\nthe flow of these rivers, and perhaps also by the size of the vessels\nof that time. Cultivation in these regions has sharply declined since\nantiquity. As a consequence, the loose soil, which formerly was\nplanted, has been washed away and the dams and retaining walls, built\nto prevent a too rapid drain of the water, have disappeared. Thus\nthe country has grown increasingly arid. Large cities, as Palmyra,\nexisted in desert regions where lack of water now prevents habitation.\nBut water was brought to the metropolitan cities of old through long\nmagnificent aqueducts, the ruins of which partly remain today. We\nhave all reasons to believe that the marked decrease in cultivation\nand population, laid to changes in conditions of humidity, depended\naltogether on man\u2019s interference with nature. On certain rocks in\nMorocco, carvings have been found portraying in a simple way large\nmammals such as elephants, rhinoceroses, and giraffes, which do not\nexist in these regions now because of lack of nourishment. But these\nrough works of art, resembling those of the bushmen of today, date\nfrom prehistoric time, the so-called paleolithic era, when the climate\nadmittedly was more humid in these regions than it is now.\n\nSimilar conditions obtain, according to Hedin, in Central Asia and in\nPersia. The climate there has without doubt been more humid but not in\nhistoric times. The march of Alexander toward India took place under\nas adverse conditions as now are found in these regions (Baluchistan).\nTheir cities, now in ruins, received their water supply through\nconduits from rivers some of which were then adjacent to the cities,\nalthough they later have changed their course as pointed out by Leo\nBerg.\n\nIn Western and Central Europe numerous marshes and morasses have\nindeed been drained and rendered available for cultivation, but this\ndoes not prove that the climate is become more dry. On the contrary\nall observations, for instance those made by Tycho Brahe on the\nisland Hven, indicate that the difference between summer and winter\ntemperature has decreased during historic time; that is the climate is\nbecome less continental, or more humid, than formerly. Furthermore,\nmany circumstances, such as the occurrence of hazel and of water\nchestnut in far more northerly latitudes and the higher altitude of\nthe timber line in earlier time, prove that the summer in prehistoric\nages was warmer than now. Simultaneously it was dryer. A study of the\nlacustrine pile dwellings in Switzerland shows that the levels of the\nlakes then were not higher than now but very nearly the same, which\ndemonstrates that the precipitation has not changed perceptibly in\nSwitzerland since these buildings were made; the period in question\noccurred, we believe, about 7000 years ago.\n\nWhile great climatic changes have taken place since man\u2019s first\nappearance on earth, presumably before the end of the ice period,\nhistoric time is too short to record any distinct modifications.\nLocal ones may be in evidence such as West Europe\u2019s transition to a\nless continental climate. A variation of this nature has been found\nnot longer back than since thermometrical observations commenced.\nThus the winters in Berlin during the period 1746\u20131847 were colder\nand the summers warmer than during 1848\u20131907. The difference for\nJanuary amounted to -1.5\u00b0 C. (-2.7\u00b0\u00a0F.) and for May to +0.6\u00b0\u00a0C.\n(+1.08\u00b0\u00a0F.). The tabulation below, quoted from Ekholm, shows the mean\ntemperature in Stockholm, Lund, London, and Paris, during winter\n(December-February), spring (March-May), summer (June-August), and\nautumn (September-November) and for the following periods:\n\n -------+-------------------+------------------\n | _Stockholm_ | _Lund_\n |-------------------+------------------\n | _1799\u2013 | _1849\u2013 | _1753\u2013 | _1799\u2013\n | 1848_ | 1898_ | 1798_ | 1898_\n -------+---------+---------+---------+--------\n Winter |+25.5\u00b0\u00a0F.|+26.8\u00b0\u00a0F.|+30.2\u00b0\u00a0F.|30.9\u00b0\u00a0F.\n | -3.6\u00b0\u00a0C.| -2.9\u00b0\u00a0C.| -1.0\u00b0\u00a0C.|-0.6\u00b0\u00a0C.\n -------+---------+---------+---------+--------\n Spring | 37.9\u00b0\u00a0F.| 37.9\u00b0\u00a0F.| 41.2\u00b0\u00a0F.|41.5\u00b0\u00a0F.\n | 3.3\u00b0\u00a0C.| 3.3\u00b0\u00a0C.| 5.1\u00b0\u00a0C.| 5.3\u00b0\u00a0C.\n -------+---------+---------+---------+--------\n Summer | 60\u00b0\u00a0F.| 60\u00b0\u00a0F.| 61\u00b0\u00a0F.|60.2\u00b0\u00a0F.\n | 15.6\u00b0\u00a0C.| 15.6\u00b0\u00a0C.| 16.1\u00b0\u00a0C.|15.7\u00b0\u00a0C.\n -------+---------+---------+---------+--------\n Autumn | 43.9\u00b0\u00a0F.| 43.5\u00b0\u00a0F.| 45.9\u00b0\u00a0F.|45.9\u00b0\u00a0F.\n | 6.6\u00b0\u00a0C.| 6.4\u00b0\u00a0C.| 7.7\u00b0\u00a0C.| 7.7\u00b0\u00a0C.\n -------+---------+---------+---------+--------\n Year | 41.9\u00b0\u00a0F.| 42.1\u00b0\u00a0F.| 44.6\u00b0\u00a0F.|44.6\u00b0\u00a0F.\n | 5.5\u00b0\u00a0C.| 5.6\u00b0\u00a0C.| 7.0\u00b0\u00a0C.| 7.0\u00b0\u00a0C.\n -------+---------+---------+---------+--------\n\n -------+-----------------+-----------------\n | _London_ | _Paris_\n |-----------------+-----------------\n | _1799\u2013 | _1849\u2013 | _1806\u2013 | _1849-\n | 1848_ | 1898_ | 1848_ | 1898_\n -------+--------+--------+--------+--------\n Winter |38.5\u00b0\u00a0F.|39.2\u00b0\u00a0F.|37.9\u00b0\u00a0F.|37.9\u00b0\u00a0F.\n | 3.6\u00b0\u00a0C.| 4.0\u00b0\u00a0C.| 3.3\u00b0\u00a0C.| 3.3\u00b0\u00a0C.\n -------+--------+--------+--------+--------\n Spring |48.2\u00b0\u00a0F.| 48\u00b0\u00a0F.|50.5\u00b0\u00a0F.|50.3\u00b0\u00a0F.\n | 9.0\u00b0\u00a0C.| 8.9\u00b0\u00a0C.|10.3\u00b0\u00a0C.|10.2\u00b0\u00a0C.\n -------+--------+--------+--------+--------\n Summer |61.9\u00b0\u00a0F.|62.2\u00b0\u00a0F.|64.6\u00b0\u00a0F.|64.8\u00b0\u00a0F.\n |16.6\u00b0\u00a0C.|16.8\u00b0\u00a0C.|18.1\u00b0\u00a0C.|18.2\u00b0\u00a0C.\n -------+--------+--------+--------+--------\n Autumn |50.7\u00b0\u00a0F.|50.5\u00b0\u00a0F.|54.2\u00b0\u00a0F.|51.8\u00b0\u00a0F.\n |10.4\u00b0\u00a0C.|10.3\u00b0\u00a0C.|11.3\u00b0\u00a0C.|11.0\u00b0\u00a0C.\n -------+--------+--------+--------+--------\n Year | 9.8\u00b0\u00a0F.| 50\u00b0\u00a0F.|51.3\u00b0\u00a0F.|51.3\u00b0\u00a0F.\n | 9.9\u00b0\u00a0C.|10.0\u00b0\u00a0C.|10.7\u00b0\u00a0C.|10.7\u00b0\u00a0C.\n -------+--------+--------+--------+--------\n\nThe difference is not great. For Stockholm the winter has grown warmer,\nthe autumn colder, for London the winter warmer and so slightly also\nthe summer, but spring and autumn a trifle colder, and for Paris the\nsummer a little warmer while the autumn is considerably colder. Lund\nshows the least variation. The winter has grown 0.4\u00b0\u00a0C. (0.72\u00b0\u00a0F.)\nwarmer and the summer colder by the same amount. The annual mean\nremains nearly constant, only slightly increased, but the climate is\nbecome more marine. (This is hardly apparent from the figures cited as\nfar as Paris is concerned.)\n\nFrom Tycho Brahe\u2019s observations of the number of days when snow or rain\nfell in the place where his observatory was situated on the island\nHven in \u00d6resund not far from Copenhagen, Ekholm has calculated that\nthe temperature there during the time 1582\u20131597 was 1.4\u00b0\u00a0C. (2.5\u00b0\u00a0F.)\nlower in February and 1\u00b0\u00a0C. (1.8\u00b0\u00a0F.) lower in March than in later\nyears (1881\u20131896). On the other hand the first autumn frost occurred at\nthe same time as now and the same was the case with the last frost in\nspring, so that the temperatures on these dates in autumn and spring\nwere nearly identical at the end of the sixteenth century and now.\nEkholm drew the conclusion that the climate is become more marine.\n\nHildebrandson makes the objection that Tycho Brahe\u2019s observations\nwere confined to an abnormally cold period judging by the tables\nSpeerschneider has prepared showing the ice formation in Danish\nnavigable waters. Nine out of the sixteen years in which Tycho Brahe\ngathered his data were notable for abnormally cold winters, while only\nnineteen out of the hundred years composing the sixteenth century were\ncharacterized by equally severe winters.\n\nThus, the conclusion is not warranted that the winters of the sixteenth\ncentury as a whole averaged colder than those of the nineteenth. Later\ninvestigations (in 1917) in regard to the dates when the ice would\nbreak up in Lake M\u00e4lar at Vester\u00e5s, in Neva River at Petrograd, and\nin Dwina River at Riga, have led Ekholm to believe that he has found\na periodicity in winter temperatures of not less than 212 years, a\nconclusion which would agree with Speerschneider\u2019s statistics. If\nso, we are at present living in a period remarkable for its mild\nwinters while a series of extremely severe winter seasons occurred at\nthe time of Tycho Brahe. This law would also have a bearing on the\npreceding table of temperatures in Stockholm, Lund, London, and Paris\nas a succession of severe winters came around in the beginning of the\nnineteenth century while the reverse is true towards its end. On the\nwhole climatic variations during historic time have been insignificant,\nif present at all, provided we extend our comparisons over two or more\ncenturies. Such is also the opinion of Hildebrandson.\n\nThe idea of a slow deterioration of the climate due to increasing\ndesiccation is of old lineage and is most likely related to the\nvenerable conception of a bygone golden age. Aristotle even at that\nearly date believed that a gradual arefaction of the Earth took\nplace. In recent times this faith has been particularly fostered by\nHuntington in a number of treatises where he endeavours to prove that\nAsia, represented for instance by Palestine, Syria, and Persia, and\nfurther Africa and North America are subject to a rapid exsiccation\nclearly traceable through historic time. The contrary, however, is true\nabout Western Europe. It was often said that Southern Russia in recent\ntimes suffered a slow arefaction manifesting itself in the formation of\nsteppes. This led to careful investigations showing the assertion to\nbe erroneous and culminating in the work of Leo Berg. Rather, a slight\nshifting in the opposite direction is detectable as the forest region\nhas expanded at the expense of the steppes in conformity with the\ndevelopment toward the end of prehistoric time. The renowned American\nastronomer, the late Dr. Lowell, embraced the idea of increasing\naridity which he observed himself in Arizona where his observatory\nis located. The drying out of Arizona undoubtedly took place in\nlong bygone prehistoric time. The disappearance of a high culture in\nSyria and Mesopotamia was the result of hostile devastation of their\nwaterworks; a compensation is now offered in the reclamation of the\ndeserts along the Nile, in California and Arizona, and in numerous\nother places.\n\n\n\n\nCHAPTER IV\n\nATMOSPHERE AND PHYSICS OF THE STELLAR BODIES\n\n\nIn a certain sense, we are justified in speaking of an atmosphere of\nsuns and stars. These bodies consist mainly of a comparatively dense\nmass surrounded by a layer of very attenuated gas. The density of our\nSun is about 1.4 times that of water. In other stars it is considerably\nlower, in some cases only a few hundredths of the density of water.\nThis applies particularly to those stars of variable magnitude, the\nCepheid type, named after their longest and best known representative,\nthe mysterious star Delta in the constellation Cepheus, and in general\nto young stars. In any case the stars are gaseous throughout on account\nof their high temperature. An exception must be made for the clouds\nof matter precipitated by easily condensed vapours, such as gaseous\ncarbon, which clouds float in the outer strata, and are responsible for\nthe bright astral light.\n\nThe stars just mentioned belong to the comparatively young stellar\nbodies, while the Sun in common with other yellow stars is considerably\nolder. Correlated with their age is undoubtedly the greater mean\ndensity of the yellow stars. Around many of the young stars, for\ninstance around the brilliant Altair, the principal member of the\nconstellation Aquila, a gas shell of great expansion has been observed,\nusually consisting of hydrogen but frequently also of helium. These\nextensive gas appendages may be considered as a kind of atmosphere\nsurrounding the stars in question. Their density is no doubt\nexceedingly small. Our own central orb, the Sun, is also endowed with\nrarefied gases outside of the luminous clouds. By their absorption of\nlight they cause the dark lines in the Sun\u2019s spectrum, after their\ndiscoverer named Fraunhofer lines. The greatest height from the\nsurface of the Sun is reached by hydrogen, mixed with a small quantity\nof helium and with a gas, unknown on Earth, which we call coronium\nbecause it has been observed in the Sun\u2019s corona. These gases may be\nlooked upon as the atmosphere of the Sun.\n\nSimilar conditions obtain no doubt on the major planets, which possess\na density not essentially different from that of the Sun. They have,\nmoreover, practically the same period of revolution around their own\naxis, Jupiter 9.9 hours, Saturn 10.3, and Uranus (probably) 10.8 hours.\nJudging by their density, they are, in all probability, like the Sun,\ngaseous throughout except for the heavy cloud formations which appear\nto constitute the outer limit of these stellar bodies. Their interior,\nlike that of the Sun, may contain comparatively sluggish gas-masses,\nas certain peculiar patches appear on their exterior, similar to the\nsunspots and persisting for long intervals, sometimes over a year. The\nbest known example of the kind is the so-called red spot on Jupiter,\nwhich has remained since 1878, although it is not so pronounced now as\nduring its early days (see Fig. 11). Characteristic for these planets\nare certain bands of a marked delineation and running parallel with the\nequator (see Figs. 11 and 12). They are caused by the rapid peripheral\nmotion of these planets, with Jupiter 28 and with Saturn 24 times that\nof the Earth.\n\n[Illustration:\n\n Fig. 11. The planet Jupiter in 1909 in Mercator\u2019s projection by\n F. le Coultre of Geneva. The \u201cred spot\u201d over which the\n clouds are dispersed, is found at 355\u00b0 Long. and 20\u00b0 S.\n Lat. in the outcurving of the dark band. South direction\n is upward, as on all pictures obtained with astronomical\n tubes.\n]\n\nWhich gases should we expect to find in the atmosphere of these\nplanets? According to the Kant-Laplace hypothesis, a theory generally\ncredited with a sound kernel, the planets were segregated from the\nSun\u2019s substance at a time when the latter was expanded so as to include\nthe orbits of these planets and beyond. Naturally, therefore, their\natmospheres would originally be composed of the very gases that formed\nthe outmost part of the Sun\u2019s atmosphere, notably hydrogen. Slipher,\nwho has photographed the spectra here reproduced of the outer planets,\nbelieves that certain strong absorption bands in the spectra of\nNeptune and Uranus correspond to the distinctive F and C lines of\nhydrogen, using Fraunhofer\u2019s denotation (see Fig. 13). But because\nthe bands in question, as shown on the figure, are very broad it is\ndifficult to identify them with certainty. Also other gases of unknown\norigin enter into the vapour envelopes outside of the clouds and cause,\nas apparent from their spectra, a strong absorption of the sunlight\nreflected from the clouds below. The absorption increases with the\nplanet\u2019s distance from the Sun; thus, it is most pronounced on Neptune\nand least on Jupiter.\n\n[Illustration: Fig. 12. The appearance of Saturn September 30, 1909,\naccording to F. le Coultre of Geneva.]\n\nAt any rate, the gas appendages of the heavenly bodies just considered\ndiffer in one essential respect from the atmospheres of the inner\nplanets: Mars, Earth, Venus, and Mercury. On the Sun and on the outer\nplanets the atmosphere gradually merges into the interior gas-masses so\nthat no distinct boundary can be found between the rarer and the denser\nlayers. Widely different conditions obtain on the Earth. Here the range\nof air is sharply defined below by the Earth\u2019s solid crust or by the\noceans. In such case alone may we speak of an atmosphere proper, of\nthe kind that enters into our commonplace conceptions. Similar are the\nconditions on all stellar bodies with a solid or a liquid surface.\n\n[Illustration:\n\n Fig. 13. Spectra of the major planets, compared with that of\n the moon. The latter corresponds to the spectrum\n of sunlight reflected from a planet which lacks a\n light-absorbing atmosphere. Photos by V.\u00a0M. Slipher of the\n Lowell Observatory.\n]\n\nBut it is not certain in every case that all such planets possess an\natmosphere. Observations of the Moon when passing some star show that\nthe air envelope, if present, is unable to deflect the light beam from\nthe star, or in other words it has no perceptible power of refraction.\nFrom this we also infer that its density is very small, corresponding\nat most to one or two mm. (.04 to .08 inches) barometric pressure. But\nwe have good reasons to believe that the Moon has been detached from\nthe Earth, carrying away parts of its lightest substance, which theory\nis supported by the fact that the Moon\u2019s mean density (3.3) is only\nsix-tenths of the Earth\u2019s (which again is 5.53 times that of water),\nand we might therefore have expected that the Moon in parting\nshould have shared in the very lightest constituents of the Earth,\nnamely its air-covering. Such was unquestionably the actual procedure,\nbut in the course of time the Moon has lost its originally no doubt\nconsiderable atmosphere. The reason is that the molecules in a gas are\nin a continuous rapid motion, which is the swifter the lighter the gas\nand the higher its temperature. In hydrogen, the lightest gas known,\nthe velocity amounts to 1.84 km. (1.15 miles) per second at 0\u00b0\u00a0C.\n(32\u00b0\u00a0F.). The parts of the Moon exposed to the strongest sunlight are\nheated to about 150\u00b0\u00a0C. (300\u00b0\u00a0F.). At that temperature, the average\nvelocity of hydrogen molecules is 2.29 km. (1.43 miles) per second.\nBut a body departing from the surface of the Moon at a rate of 2 km.\n(1.24 miles) per second, or more, cannot be retained by the attraction\nof that globe and therefore never retraces its path but speeds away\nfor ever. In the same manner a bullet ejected from a cannon with an\ninitial velocity of 11.2 km. (7 miles)--a velocity not even approached\nby present artillery--would fly away from Earth barring the resistance\nof the air. Thus we see that we as yet are far from the realization of\nthe dreams of Jules Verne in his _A Voyage to the Moon_. At any rate,\ngravity on the Moon is too weak to retain hydrogen over the hottest\npoint of the surface. This part of the gas flies away, new supplies\nrush in from the sides, and in a short time all traces of hydrogen have\ndisappeared from the Moon. Probably it was mainly gathered in by the\nSun, where a velocity of 613 km. (380 miles) per second is necessary if\nthe molecules are to overcome the Sun\u2019s attraction, while their actual\nvelocity there amounts to only about 8 km. (5 miles) per second.\n\nIn a similar manner we find that the second lightest gas, helium, at\na temperature of 150\u00b0\u00a0C. (300\u00b0\u00a0F.), possesses a molecular velocity of\n1.62 km. (1.1 miles) per second. This is less than the 2 km. (1.24\nmiles) per second necessary to leave the Moon\u2019s sphere of attraction.\nBut all helium molecules do not move at the same speed; some are\nfaster and some slower than the average. Those moving at a higher rate\nthan 2 km. (1.24 miles) per second constitute a considerable fraction\nof the total. This fraction disappears. Equilibrium is soon restored\nso that in less than a second the same fraction of helium molecules is\nready to depart. In this manner the Moon lost its helium atmosphere\nspeedily, although not quite as rapidly as its hydrogen.\n\nMore slowly yet vanished the gases which are most abundant in our\natmosphere, nitrogen and oxygen, but these too were not fettered\nfor ever by the limited gravity on the Moon. The same fate befell\naqueous vapour, which is nearly twice as light as oxygen. The loss of\nwater, however, was long delayed, as we later shall learn, because\nnew vapour masses were discharged from the lunar volcanoes. In these\nconsiderations, we should also bear in mind that the Moon no doubt was\na fluid molten mass when separating from the Earth and its substance\nresembled the lava from our volcanoes. In this condition it remained\nuntil its exterior temperature had fallen to about 1200\u00b0\u00a0C. (2200\u00b0\u00a0F.).\nAt that point, the average velocity of oxygen molecules is about 1 km.\n(.62 mile) per second, with variations in both directions, so that a\nfew per cent. of them reach a sufficient velocity to leave the Moon for\never. Such gas molecules of medium weight return probably to the Earth\nwhich, as experience tells us, is ponderous enough to hold them in\nbonds.\n\nAll gases, that constitute any considerable fraction of the Earth\u2019s\natmosphere, and which, therefore, most likely were divided with the\nMoon in its parting from us, have again left that globe. The same\nunquestionably holds true for other stellar bodies of equal or smaller\nsize, such as all the minor planets and for the great majority of the\nsatellites to the major ones. Only the very largest of Jupiter\u2019s moons,\nand possibly Neptune\u2019s lonely companion, whose size is not known with\ncertainty, might possibly surpass our Moon in ability to retain gases.\nOur reasoning with respect to the Moon applies also to Mercury. It is\ntrue that the molecules there must possess a velocity one and a half\ntimes as high as on the Moon if they are to leave the planet. But at\nthe same time the temperature on Mercury\u2019s hottest point, always turned\ntoward the Sun, is far higher, about 400\u00b0\u00a0C. (750\u00b0\u00a0F.), so that the\nmolecules there move 1.26 times as fast as similar molecules over the\nMoon\u2019s hottest point. Mercury is consequently better able than the Moon\nto retain gases, but the difference is slight. Direct observations (see\nbelow) also lead us to believe that Mercury is very similar to the\nMoon in these respects. We might possibly imagine that certain gases,\nwhich on the Moon would condense into fluids or solids, on Mercury\nmight remain volatilized on account of the high temperature and thus\nform an atmosphere. Such assumption, however, would be erroneous. The\ninvestigations by Schiaparelli and by all his successors show that\nMercury in turning around its axis always presents the selfsame side\nto the Sun. The opposite side, never reached by a ray of sunlight,\nmust assume an extremely low temperature, very close to the absolute\nzero (-273.7\u00b0\u00a0C. or -460.6\u00b0\u00a0F.) and far below any cold existing on the\nMoon. To this side, all bodies with an appreciable vapour pressure\nmust distil and freeze to solid lumps or frost-coverings without\nperceptible vapour pressure. For these reasons, Mercury cannot possess\nany atmosphere to speak of. There remain in the whole series of planets\nand satellites in our solar system only two bodies besides the Earth\nwhich are endowed with an atmosphere in the original sense of the\nword--namely, Mars and Venus.\n\nWe reach the same conclusion when investigating the ability of the\nplanets to reflect the sunlight falling upon them. The bodies which\npossess an atmosphere hold also suspended therein clouds of water or\nice, and also of dust, whirled up from below. These floating particles\nreflect light far more efficiently than the solid or fluid surface of\na planet. The Moon can now reflect 7.3 per cent. of the sunlight and\nMercury 6.9 per cent. (H.\u00a0N. Russell, _Proceedings Nat. Acad._, 1916).\nThese numbers lie so close that they may be considered practically the\nsame within errors of observation.\n\nIt is therefore probable that Mercury is as devoid of an atmosphere as\nthe Moon. The opposite extreme is represented by Venus, which reflects\nnot less than 59 per cent. of the sunlight received, according to\nH.\u00a0N. Russell. Terrestrial clouds were found by Abbot to return 65\nper cent. We believe from astronomical observations that the entire\nsurface of Venus is hidden behind a thick opaque cloud-covering.\nThe slight difference between O.65 and O.59 may be due to errors of\nobservation, but also to a small absorption of light in those parts of\nVenus\u2019s atmosphere which are outside of the clouds. Saturn and Jupiter\nare very similar to Venus in this regard with 63 and 56 per cent.\nrespectively. The gases above the clouds on these planets extinguish\nto a considerable extent the sunlight reflected from the clouds, as\napparent from their spectra. (Compare Fig. 13.) Hence the value 0.63\ngiven by Russell for Saturn is probably too high. Concerning Jupiter\nit has been observed that its red light becomes deeper when the\nsunspots are few, but whiter when the spots are numerous. The sunspots\nhave been found to favour the formation of high clouds, such as cirrus,\nand this would seem to apply also to Jupiter; when spots are plenty,\nthe clouds are high, and consequently the absorbing layers above, which\ncause the red colour, are thinner, so that Jupiter will then shine with\na whiter--less red--lustre than when the sunspots are rare.\n\nThe two outmost planets, Uranus and Neptune, return, according to\nRussell, 63 and 73 per cent. respectively of the sunlight received.\nThese figures are probably too high. They do not agree well with\nSlipher\u2019s records of their spectra (Fig. 12).\n\nThere now remains Mars. This planet approaches the Moon inasmuch as\nit reflects only 15.4 per cent. of the sunlight arriving to the orb.\nEverything points to the conclusion that the atmosphere of Mars is very\nthin. Lowell estimates, on somewhat meagre grounds, however, that on\neach square metre of the planet rests only 22 per cent. of the mass of\nair supported by each square metre of the Earth\u2019s surface.\n\nIt would naturally be very interesting to ascertain the amount of\nsunlight our Earth throws back into space. This we cannot measure, as\nwe cannot place our instruments outside of the Earth\u2019s cloud-mists\nnor can we read them there. Not less than 52 per cent. of the Earth\nis covered with clouds, whose whiteness (Latin: _Albedo_) is 65. Thus\nthe clouds alone return 0.52 \u00d7 0.65 = 0.338 parts of the sunlight. Of\nthis portion a fraction amounting to about 4 per cent. is extinguished\nin the air above. The remainder is 0.325. Atmosphere and suspended\ndust reduce the sunlight over the cloud-free part, _i.\u00a0e._ 48 per\ncent. of the Earth, by 60 per cent, half of which returns to space,\nwhile the other half reaches the ground in the form of light from the\nsky, and of this fraction again about 4 per cent. is reflected into\nspace; these two items added give 0.15. Finally, the 40 per cent.\nsunlight directly received by the Earth\u2019s surface is reflected to the\nextent of 6 per cent. by the oceans and by the generally moist ground;\ndeserts and bare rocks reflect about twice as much, but their total\narea is comparatively small; of this 6 per cent. reflected light, 70\nper cent. reaches outside space; thus we obtain 0.48 \u00d7 0.40 \u00d7 0.06 \u00d7\n0.70 = 0.008. In all, therefore, the amount of reflected sunlight is\n0.338 + 0.15 + 0.008 = 49.6 per cent. If the air were free from clouds,\nthe reflexion-number or Albedo would be 33 per cent., or considerably\nhigher than that of Mars. When now half or a little more (52%) of the\nEarth\u2019s surface is overcast with clouds and this portion therefore has\nthe whiteness of Venus, the figure 49.6 (Russell calculates the figure\n45) for the entire Earth naturally falls closer--almost 3.6 times--to\n59, the figure of Venus, than to 15.4, the figure for Mars. We may\nalso compare the value 33 per cent., which applies to the cloud-free\nportion of the Earth, with the value 15.4 per cent. for Mars, which is\nalmost without clouds, and with the value 7.3 per cent. for the Moon,\nwhich has neither clouds nor dust, because it lacks an atmosphere. We\ncan then conclude that the atmosphere of our Earth holds almost three\ntimes as much dust suspended over each square metre as does Mars, and\nthis in spite of the smaller gravitational force on Mars, which is\nabout 37.5 per cent. of that on Earth. Taking proper account of the\nlow temperature on Mars we may easily compute, by means of a formula\ngiven by Stokes, that a particle of dust should sink 2.3 times slower\non Mars than on Earth. When, nevertheless and in spite of frequent\nbut thin mists, so few particles of dust float in the atmosphere of\nMars, the conception inevitably comes to our mind that the air on\nthat planet must be extremely rarefied so that the wind-puffs have\nlittle power to raise the dust from the ground. Lowell estimated the\nbarometric pressure at the surface of Mars to be about 64 mm. (2.52\ninches), and Proctor gives about twice this figure. There appears to\nbe ground for considering already the former value too high; both are\nvery uncertain. If we accept that of Lowell, we find that each square\nmetre of the surface of Mars supports a column of air, whose mass is\nonly about one-fifth of the mass resting on each square metre of ocean\nsurface on Earth.\n\n[Illustration:\n\n Fig. 14. The planet Venus, with sunlit atmosphere (to the\n left), as observed by Langley at the Venus passage\n December 6, 1882.\n]\n\nThe dense clouds which float above Venus have long ago led to the\nassumption that the atmosphere of that planet must be far deeper than\nthat of the Earth. Its strong refractory power has also contributed\nto this belief. When Venus is close to the sun-disc the dark body\nstands forth surrounded by a ring of light (see Fig. 14). It is,\nhowever, recognized that this phenomenon requires no greater air\ndensity than that on Earth for its appearance. In this connection we\nshould remember that the inside limit of the vapour shell which we\nin this manner observe, is the cloud-wall, not the ground. And these\nclouds, we have every reason to believe, float on account of the heat\nprevailing at a great height in the atmosphere, so high in fact that\nthey form an impenetrable wall already where the cirrus clouds\nappear in our sky. If these suppositions are correct, the light-ring\nmentioned is caused by a quarter only of the air-masses on Venus, and\nits total air-covering must be far deeper than that of the Earth.\nThe latter occupies probably in this respect as well as in reference\nto position in space a middle ground between Mars with its extremely\nthin and Venus with its comparatively dense atmosphere. If so, we\nmight expect the atmosphere on Mercury to be denser yet, while we\nalready have seen that it is almost wholly lacking on that planet.\nThe explanation is that Mercury has lost its spin around its own axis\nand therefore always presents the same side to the Sun--just as the\nMoon and probably all other satellites turn one side only toward their\nrespective central bodies--hence the opposite side becomes so cold\nthat all gases are there condensed to fluids or solids except the two\nmost volatile ones, hydrogen and helium, which on the other hand leave\nthe planet on its hot side. If Venus, therefore, as held by several\nastronomers from Schiaparelli to Lowell, always turned one side only\ntoward the Sun, this planet also would be without any perceptible\nair-covering. According to investigations by Bjelopolsky of Venus\u2019s\nspectrum, which investigations, however, are in complete disagreement\nwith corresponding measurements by Slipher, that planet has a period\nof rotation on its own axis of about 29 hours. This figure is very\nuncertain and a new determination is therefore highly desirable.\n\nIn order to understand the atmospheres of the planets, it is of great\ninterest to ascertain the composition of the air that surrounds the\nEarth. Our knowledge in these matters has grown considerably of late.\nWe shall in the main follow the presentation by Dr. Wegener of Marburg.\n\nWe know at present with considerable accuracy which gases enter into\nthe air. Besides the previously well-known nitrogen and oxygen which\ncontribute the bulk, 78.1 and 20.9 per cent. respectively, of the total\nvolume at the earth\u2019s surface, we find water vapour in proportions\nchanging with localities and times, and it is for this reason left\nout when fixing the various percentages; further, carbon dioxide 0.03\nvolume per cent. and the rare gases discovered by Rayleigh and Ramsay,\nargon, 0.932 per cent., neon 0.0012 per cent., helium 0.0004 per cent.,\nkrypton 0.000005 per cent., and xenon 0.0000006 per cent. Each one of\nthese constituents diminishes in quantity with height in accordance\nwith the so-called barometer-formula and the rate is the more rapid\nthe heavier the gas. Krypton and xenon, therefore, which are two and\none half and four times heavier than oxygen, occur mainly in the lower\nstrata. The percentage of helium on the other hand, a gas eight times\nlighter than oxygen, should increase rapidly with height. If the air\nconsisted of a mixture of oxygen and helium at 0\u00b0\u00a0C. (32\u00b0\u00a0F.) the\nformer would decrease to one half at an elevation of 5 km. (3.1 miles)\nbut the latter not before we had ascended 40 km. (25 miles) (eight\ntimes higher than for oxygen, as the weights are in the ratio of 1 to\n8). At that altitude, oxygen would have decreased in the proportion\n1:2^8 = 1:256. When, as actually is the case, there is 50,000 times\nmore oxygen than helium at the surface this ratio should decrease\nin the proportion 128:1 at a height of 40 km. (25 miles). Ninety\nkilometers (56 miles) above the surface helium should overbalance\noxygen and thereafter rapidly gain in preponderance. This holds true\nprovided no agitation takes place in the form of vertical currents of\nair.\n\nSimilar laws apply to all light gases which do not turn into fluids or\nsolids at low temperatures. Aqueous vapour, on the other hand, which\nwhen cooled condenses to clouds, diminishes much faster than the nearly\ntwice as heavy oxygen, because the temperature rapidly decreases as we\nmove upward or at a rate of about 5\u00b0\u00a0C. per km. (14.5\u00b0\u00a0F. per mile)\nup to 2.5 km. (1.5 miles) and of 8\u00b0\u00a0C. per km. (23\u00b0\u00a0F. per mile) at a\nheight of 8.5 km. (5.3 miles). The quantity of water vapour shrinks to\none half at 1.9 km. (slightly more than a mile) above ground. Carbon\ndioxide again follows the barometer-formula applicable to other gases\nbecause it occurs in such minute quantity that it never condenses to\nclouds. In fact, it is water vapour alone which must be treated as an\nexception. Carbon dioxide is nearly one and one half times heavier than\nthe other gases of the atmosphere on an average. It should therefore\ndiminish in the proportion 1:2^{1.5} = 1:2.8 in a vertical distance of\n5 km. (3.1 miles) while the density of the air decreases only in the\nratio 1:2. Several determinations of the presence of carbon dioxide\nin the atmosphere as high up as 3.8 km. (2.33 miles) have been made,\nby S.\u00a0A. Andree among others, but the percentage of this gas remains\nconstant within the errors of observation. The same holds true to a\nheight of 7 km. (4.35 miles) for the proportion between oxygen and\nnitrogen, although we might have expected a perceptible change as\noxygen is 14 per cent. heavier than nitrogen. How shall we explain this\nfact which seemingly contradicts the theory just advanced?\n\nThe explanation is quite simple. The preceding statements hold true for\na mass of air at perfect rest. But, if the air is violently agitated,\nthe composition becomes homogeneous all through. We know that in the\nbarometric cyclones and anticyclones strong rising and descending air\ncurrents flow. The composition of the atmosphere, therefore, becomes\nthe same as far up as this mixing action prevails. These currents\nproduce another effect, namely, a fall of temperature with rising\nheight. Because when a gas is transported upward the surrounding\npressure decreases, resulting in expansion and consequent cooling. It\nis well known that a gas is heated when (rapidly) compressed, a quality\nformerly made use of in the pneumatic fire-tool to ignite tinder. It is\nevident that conversely a gas must cool off when expanding. If now the\nmixing of the air were extremely rapid the thermometer would fall very\nclose to 10\u00b0\u00a0C. (18\u00b0\u00a0F.) with each km. (.62 miles) rise in elevation.\nIf, on the other hand, the air stood perfectly still in a vertical\ndirection, the temperature would remain constant at all heights\nover the same point. Between these two extremes, we find the actual\ncondition, inasmuch as the temperature of the atmosphere decreases\nupward 5\u00b0 to 8\u00b0\u00a0C. per km. (14.5\u00b0 to 23\u00b0\u00a0F. per mile) as observed\nduring balloon ascensions.\n\nThis applies to the so-called \u201ctroposphere\u201d--mixing-zone. One of the\nmost remarkable discoveries in recent times, made by Teisserenc de Bort\nand Assman, is the fact that the decrease of temperature with height\ndoes not continue indefinitely but only up to a certain elevation,--in\nmiddle Europe about 11 km. (7 miles), in Lapland about 7 km. (4.5\nmiles), and at the equator about 15 km. (10.5 miles)--and above this\npoint the temperature remains constant. We now meet the peculiar\ncondition that the temperature of this upper layer, which is called\nstratosphere--\u201cfilm-zone\u201d--is lowest over the equator, because it\ncommences at a great height there, and lowest over the polar regions,\nwhere it extends farther down. The stratosphere has received its\nname from the fact that it consists so to speak of lamell\u00e6 almost\nparallel to the earth\u2019s surface and moving in a horizontal direction\nwhile vertical motions are absent. The winds in these strata have a\nmarked westerly direction (_i.\u00a0e._ they are east winds) and they become\nstronger the higher the stratum--at an altitude of 83 km. (52.5 miles)\ntheir velocity is about 100 m. (330 ft.) per second. In the troposphere\non the other hand west winds predominate. The wind direction in the\nstratosphere was observed on the so-called luminous night-clouds which\nwere found as high as 80 km. (50 miles) above the Earth. These strata\nconsequently revolve slower around the earth\u2019s axis than the solid\nbody of the planet itself. At an elevation of 80 km. (50 miles) the\nrotational speed has decreased to 65 per cent. of the angular velocity\nof the earth\u2019s surface. We have reason to believe that the very highest\nstrata stand still, that is do not take part in the earth\u2019s rotation on\nits axis. This would follow if outside space were not entirely devoid\nof vapour so that our atmosphere would merge imperceptibly into the\nexceedingly attenuated gas masses of interplanetary space.\n\nAs high as the mixing-zone extends, so high also is the composition of\nthe air constant and like that at the surface of the earth. But above\nthis limit--in Scandinavia, we might say above an elevation of 10 km.\n(6.2 miles)--commences a rapid tapering of the heavy gases, while the\npercentage of the light ones correspondingly rises. Foremost among the\nlatter is hydrogen, with only half the weight of helium. The presence\nof hydrogen in the atmosphere has been shown by Boussingault, and\nthe proportion in which it occurs has later been measured by Armand\nGautier. It is about one three hundredth part of one per cent. It\nincreases extremely rapidly with height in the stratosphere so that 80\nkm. (50 miles) above the earth and upward hydrogen is more abundant\nthan all other known gases of the atmosphere at the same altitudes.\n\nWe reproduce below a somewhat revised table by Dr. Wegener of Marburg,\nwho has made the most recent computation of the percentages of the\nvarious constituents of air at different heights. Consideration has\nbeen given to the fact that the composition of the air does not change\nexcept as regards the percentage of moisture within the troposphere,\nwhich is assumed to reach a height of 10 km. (6.2 miles). As usual in\nsimilar cases the percentages refer to volume.\n\n -------------+-----------------+----------+--------+----------\n _Height_ | _Pressure_ | | |\n -----+-------+--------+--------+ | |\n _in | _in | _in | _in |_Hydrogen |_Helium |_Nitrogen\n km._| miles_| mm._ | inches_| 2_ | 4_ | 28_\n -----+-------+--------+--------+----------+--------+----------\n 0 | 0 |760 |29.9 | 0.0033 | 0.0005 | 78.1\n -----+-------+--------+--------+----------+--------+----------\n 10 | 6.2 |197 | 7.75 | 0.0033 | 0.0005 | 78.1\n -----+-------+--------+--------+----------+--------+----------\n 30 | 18.6 | 8.95 | .352 | ---- | ---- | 85\n -----+-------+--------+--------+----------+--------+----------\n 50 | 31.0 | 0.45 | .0177 | 1 | ---- | 88\n -----+-------+--------+--------+----------+--------+----------\n 70 | 43.5 | 0.045 | .00177| 13 | 1 | 80\n -----+-------+--------+--------+----------+--------+----------\n 90 | 55.8 | 0.0157| .00062| 68 | 5 | 26\n -----+-------+--------+--------+----------+--------+----------\n 110 | 68.2 | 0.0116| .00046| 94 | 5 | 1\n -----+-------+--------+--------+----------+--------+----------\n 130 | 80.6 | 0.0097| .00038| 96 | 4 | 0\n -----+-------+--------+--------+----------+--------+----------\n 210 | 130.2 | 0.0055| .00022| 99 | 1 | ----\n -----+-------+--------+--------+----------+--------+----------\n 310 | 192.6 | 0.0032| .00013| 100 | ---- | ----\n -----+-------+--------+--------+----------+--------+----------\n 410 | 254.2 | 0.0021| .00008| 100 | ---- | ----\n -----+-------+--------+--------+----------+--------+----------\n 510 | 316.2 | 0.0016| .00006| 100 | ---- | ----\n -----+-------+--------+--------+----------+--------+----------\n\n -------------+-----------------+--------+-------+---------+-------\n _Height_ | _Pressure_ | | | |\n -----+-------+--------+--------+ | |_Carbon |\n _in | _in | _in | _in |_Oxygen |_Argon | Dioxide |_Water\n km._| miles_| mm._ | inches_| 32_ | 39.9_ | 44_ | 18_\n -----+-------+--------+--------+--------+-------+---------+-------\n 0 | 0 |760 |29.9 | 20.9 | 0.937 | 0.03 | 1.41\n -----+-------+--------+--------+--------+-------+---------+-------\n 10 | 6.2 |197 | 7.75 | 20.9 | 0.937 | 0.03 | 0.14\n -----+-------+--------+--------+--------+-------+---------+-------\n 30 | 18.6 | 8.95 | .352 | 15 | 0.29 | 0.0064 | 0.5\n -----+-------+--------+--------+--------+-------+---------+-------\n 50 | 31.0 | 0.45 | .0177 | 10 | 0.10 | 0.0014 | 1.7\n -----+-------+--------+--------+--------+-------+---------+-------\n 70 | 43.5 | 0.045 | .00177| 6 | 0.05 | 0.0005 | ----\n -----+-------+--------+--------+--------+-------+---------+-------\n 90 | 55.8 | 0.0157| .00062| 1 | ---- | ---- | ----\n -----+-------+--------+--------+--------+-------+---------+-------\n 110 | 68.2 | 0.0116| .00046| 0 | ---- | ---- | ----\n -----+-------+--------+--------+--------+-------+---------+-------\n 130 | 80.6 | 0.0097| .00038| ---- | ---- | ---- | ----\n -----+-------+--------+--------+--------+-------+---------+-------\n 210 | 130.2 | 0.0055| .00022| ---- | ---- | ---- | ----\n -----+-------+--------+--------+--------+-------+---------+-------\n 310 | 192.6 | 0.0032| .00013| ---- | ---- | ---- | ----\n -----+-------+--------+--------+--------+-------+---------+-------\n 410 | 254.2 | 0.0021| .00008| ---- | ---- | ---- | ----\n -----+-------+--------+--------+--------+-------+---------+-------\n 510 | 316.2 | 0.0016| .00006| ---- | ---- | ---- | ----\n -----+-------+--------+--------+--------+-------+---------+-------\n\nUnder the name of each gas its molecular weight is given as a measure\nof corresponding specific weight. The quantity of water vapour was\nnot included when the percentages of the other gases were calculated,\nbecause it changes considerably with locality and time. The number\ngiven in the table for water is the mean for the entire globe--it\ncorresponds to 11.4 grammes per cubic metre (.31 oz. per cu. yd.)--or\nthe amount present in air saturated with moisture at 16.5\u00b0\u00a0C.\n(61.7\u00b0\u00a0F.). The bulk of the water vapour forms a layer strongly\nconcentrated toward the surface of the earth. Carbon dioxide also\ntapers rapidly with increasing height because its density is 1.5\ntimes greater than that of air. This is apparent from the molecular\nweight 44 stated under carbon dioxide, while the average molecular\nweight of air is 29. Faster yet do krypton, with a molecular weight of\n83, and xenon, with a molecular weight of 131, decrease as we ascend\nin the atmosphere. These gases, like neon, whose percentage first\nincreases slightly with height, and argon, which decreases upward as\nshown in the table, do not perceptibly influence the processes of\nnature. The reverse is true about water vapour and carbon dioxide,\nwhich nourish the plants and also protect the Earth against a too\nrapid heat radiation into space. We well remember how abruptly the\ntemperature changes in the course of the day in the dry desert\nclimate, while corresponding variation is comparatively slight in\nhumid climates (compare page 86). This is the result of the ability of\nwater vapour to arrest the radiation from the Earth. Carbon dioxide is\nabout evenly distributed over the globe--although somewhat sparser\nover highlands--and its heat-conserving and equalizing influence is,\ntherefore, not so manifest as that of moisture. Only by the most\naccurate investigations has this influence been demonstrated.\n\nIn Wegener\u2019s table a gas is included, called Geocoronium, whose\nexistence in the air has not been directly proved. Conspicuous is,\nhowever, the green light displayed at great altitude by the Northern\nLight arches, a green color which does not, as far as we are aware,\nbelong to any known constituent of the air. It is true that the\ncorresponding spectral line (557 \u00b5\u00b5) lies very close to a line\nbelonging to krypton, but the latter is a heavy gas which cannot occur\nto any traceable extent in the high strata, more than 300 km. (186\nmiles) above the earth, where occasionally the Northern Light arches\nappear--their favoured height according to measurements by St\u00f6rmer\nis about 120 km. (75 miles). Wegener assumes, therefore, that this\ngreen line belongs to an hitherto unknown substance, Geocoronium,\nwhich should be five times lighter than hydrogen. Recent researches\npresent great difficulties to the acceptance of this assumption, and\nfor this reason further discussion of the problem will be omitted.\nAbove a height of 210 km. (130 miles), this gas, according to Wegener,\nwould preponderate. If such postulated gas does not exist, hydrogen\ncompletely dominates in these regions and down to 85 km. (53 miles)\nabove the Earth. Because hydrogen is so light, the density of the\nair in the range of a barometric pressure below 0.02 mm. (.0008\ninches) increases but slowly as we descend toward the Earth. This\nuppermost part of the atmosphere may appropriately be designated as\nthe hydrogen-zone. Even within this range, the \u201cshooting stars\u201d meet\nsufficient resistance to flame into light at a height of about 120\nkm. (75 miles) and dissolve into dust which turns dark about 85 km.\n(53 miles) above the Earth. E.\u00a0C. Pickering recognized the spectrum\nof hydrogen in the light of meteors passing at great height, but\ndecomposed water vapour might possibly be its source. Meteors crossing\nlower strata show the spectrum of nitrogen. Nitrogen becomes important\nfrom a height of about 85 km. (53 miles) downward and from 75 km. (46.5\nmiles) to the surface of the Earth it predominates. As a consequence\nthe pressure increases rapidly as we approach the ground. In these\nregions or up to 80 km. (50 miles) floated the highest luminous night\nclouds, observed by Jesse, indicating that here commenced a new range,\nthe nitrogen-zone. Only the heavy meteorites are able to penetrate\ninto the nitrogen sphere, which checks their speed and causes them to\nexplode, and thereafter the remnants fall with a velocity compatible\nwith the air resistance they meet. To these parts descend also the\nlowest rays of the Northern Lights, the so-called draperies--St\u00f6rmer\nobserved them once at a height of 37 km. (23 miles). Finally, water\nvapour presents itself in appreciable quantities at an elevation of\nabout 10 km. (6.2 miles), where the troposphere commences. We now meet\nthe highest clouds, cirrus (with the exception of the \u201cluminous night\nclouds\u201d observed only in the years 1883\u20131892 after the eruption on\nKrakatoa). To these heights, reach the vertical air currents which are\nessential to cloud formations. Only light clouds, however, float at\nthese altitudes; the heavy clouds (alto-cumulus) do not rise above 4\nto 5 km. (2.5 to 3.1 miles) and the rain clouds proper (cumuli) occur\nonly below a height of 2 km. (1.25 miles). This is the result of the\ndownward concentration of water vapour within the troposphere.\n\nIf gravity decreased in intensity, the effect would be the same as if\nthe gases were lighter. On Venus, the intensity of gravity is eight\ntenths of that on Earth. The difference is slight. If everything else\nwere similar the various air-zones would reach 25 per cent. higher on\nVenus than they do on our globe. But one essential condition is varied\nby the far higher temperature on our neighbour. The proportion of\nmoisture in the air is thereby vastly increased. The dense clouds rise\nto much greater heights than on Earth. If there be ten times as much\nwater in the air on Venus as there is in the air on Earth--which might\nfairly represent the actual condition--the heavy rainclouds would there\nrise to a height of more than 10 km. (6.2 miles), and their smaller\nweight on Venus would also contribute to their buoyancy. The light\ncirrus clouds should appear as high as about 30 km. (18.5 miles) above\nthe ground. Under such circumstances, we cannot expect but that the\nplanet must be entirely hidden from our sight as well as from the rays\nof the Sun.\n\nOn Mars, the intensity of gravity is 2.68 times smaller than on Earth.\nIn consequence barometric pressure falls 2.68 times slower with\nincreasing height there than here. The same ratio holds for decrease in\ntemperature and for shrinkage of proportion of moisture when comparing\nconditions on the two planets. The strong cold precludes anything but\ninsignificant quantities of water vapour. The air on Mars is similar\nto the atmosphere on Earth in and above the cirrus-region. The clouds\nexisting there are not only extremely thin and transparent--it is well\nknown that cirrus clouds throw no shadows--but they are confined to\nsmall fractions of the planet\u2019s sky. They are replaced by light mists.\n\nWe shall later return to the consequences of these peculiarities.\n\nWith help of the spectroscope we have ascertained that the gases on\nthe Sun are, in the main, also arranged according to specific weights,\nso that the lightest reach the greatest heights. Somewhat similar\nconditions obtain in the gas-appendages of the stars (compare page\n119).\n\n\n\n\nCHAPTER V\n\nTHE CHEMISTRY OF THE ATMOSPHERE\n\n\nOf a very particular interest is the question of the atmosphere of\nthe planets. The great problem of habitability of the latter is most\nintimately connected therewith. Primitive fancy, very early, populated\nthe stellar bodies, especially the stars and the Sun, with beings\nsimilar to those on Earth. Gradually, however, the insight awoke that\nthese bodies are incandescent and therefore unfit to shelter life of\nthe kind with which we are familiar. Attention then turned to the\nplanets, as they and the Earth belonged to the same order of heavenly\nbodies. Perhaps they furnished abodes for our kin. And the stars, suns\nlike our Sun, should not they be surrounded each with its throng of\nplanets, gravitating around their central source of light and heat?\nThis beautiful thought vied with the conception of Earth as the centre\nof the universe and as wholly set apart from the other stellar bodies,\nwhose prime object it were merely to furnish light and to indicate time\nfor the inhabitants of the Earth. Much to be regretted, it was the\nlatter far less attractive theory which gained firm hold on the Church,\nalthough a few of its unbiased men, like the renowned Cardinal Nicolaus\nCusanus (1401\u20131464), declared in favour of the contrary opinion, and\ndid so unmolested. But times grew harder, ironclad orthodoxy triumphed,\nand Giordano Bruno, whose defence was that he simply accepted the\ntheory of the great Cusanus, was burned at the stake to expiate his\nfearless assertion that other worlds, no less than ours, might be\nblessed with the presence of living beings.\n\nUndoubtedly, other planets are upbuilt of the same material which\nenters into the composition of the Earth--as held already by Leonardo\nda Vinci. Spectral analysis teaches us that the same constituents\nform all the suns, including our own. If we agree that the suns have\nfurnished the original substance of the planets revolving around them\nit is a natural conclusion that this matter should combine into similar\nchemical compounds on planets equally advanced in their evolutionary,\nthat is cooling, process. And we know, indeed, that the same elements\ncompose the Sun and the Earth, and that the samples brought to us from\nother worlds, _i.\u00a0e._ the meteors, are of a composition which strongly\nreminds us of the rocks in the interior of the Earth. We seek in vain\nonly for indications of the action of water, which substance has left\nsuch obvious traces on the surface of our globe and in the immediate\nstrata below. But it should be remembered that the water, in the form\nof vapour, as previously set forth, has left all the minor stellar\nbodies, and the meteorites manifestly belong to the small or smallest\namong the wanderers of the heavens.\n\nThere is then no reason to doubt that the material of which the\nplanets are built essentially is the same throughout the universe.\nTheir interior should, like that of our Earth, consist of the heavy\nmetals, principally iron,--strongly prevalent also in the Sun and in\nthe meteors,--and this metallic nucleus should be clothed with the\nsilicates, oxides, carbonates, sulphides, and hydrates of all metals,\nparticularly aluminum, and among the metals we may also count hydrogen.\nThe melting points of these exterior and lighter substances lies above\n1000\u00b0 C (1800\u00b0\u00a0F.). No life could exist in such a molten mass, so\nthat not until a solid crust had been formed through cooling was the\npossibility of life at hand.\n\nLife is, at least on Earth, tied to certain so-called compounds, in\nwhich carbon is the essential common element, while hydrogen, nitrogen,\nand oxygen together with sulphur, phosphorus, iron, magnesium, and a\nfew other less important elements also enter therein. No substance but\ncarbon possesses this quality of being a prerequisite of life. Silica\nis a close kin to carbon and a substitute in certain organic compounds,\nbut protoplasm, the main constituent of the living cell, cannot be\nbuilt without carbon. In the inorganic world, however, silica by\nvirtue of its affinity, which is kindred to that of carbon, plays a\nr\u00f4le somewhat similar to the latter in the almost infinitely variably\nsilicates. Protoplasm cannot endure in a temperature above 60\u00b0\u00a0C.\n(140\u00b0\u00a0F.) or thereabout--certain alg\u00e6, it is sometimes stated, thrive\nin hot springs up to 80\u00b0 to 90\u00b0\u00a0C. (176\u00b0 to 194\u00b0\u00a0F.) but certainly not\nover 100\u00b0\u00a0C. (212\u00b0\u00a0F.). At these temperatures--strictly speaking at\nall temperatures between O\u00b0\u00a0C. (32\u00b0\u00a0F.) and 365\u00b0\u00a0C. (689\u00b0\u00a0F.)--water\ncan exist in fluid state and this too is a prerequisite of life. We\nmay say therefore that life is confined to a small temperature range\nbetween the freezing and boiling points of water. But wherever water\noccurs, except in a vessel which it completely fills, there exists also\nin the adjacent space, if unoccupied by fluids or solids, water vapour\nof at least 4.6 mm. (.18 inches) pressure. There is, therefore, always\nan atmosphere of aqueous vapour on any planet whose surface is partly\ncovered by water.\n\nThe pal\u00e6ontologists have agreed that all life commenced in the water.\nThe manifold living beings which now inhabit the solid crust of the\nEarth all descend from ancestors which floated in the waves of the\nocean, the cradle of all organisms. It is not absolutely certain\nthat oxygen is necessary to all living beings but many biologists\nhold that opinion. Certain bacteria are able to draw the oxygen they\nrequire for their development from compounds in which oxygen is bound\nsometimes in a very intimate manner, as in sulphates. But these\nbacteria are considered degenerate plants, and free oxygen is certainly\nindispensable to the existence of the animals and probably also to the\nplants with the exception just mentioned. As we shall see later, free\noxygen cannot be present on the planets until a solid crust has been\nformed. We may therefore state that the conditions for the existence of\nlife on a planet are fulfilled when a true atmosphere containing oxygen\nand water surround its body.\n\nIf we are to understand these conditions, we must study the processes\nwhereby oxygen is supplied to the atmosphere. As the planets are\nsegregations from the Sun, they should originally have the composition\nof the Sun, particularly that of its outer layers. Here metals occur in\ngreatest abundance, but there are also a few oxides, especially those\nof titanium and magnesium (according to Fowler), hydrogen in great\nquantities, oxygen, carbon, cyanogen, and carbon monoxide. It may seem\nstrange that free oxygen exists side by side with a surplus of hydrogen\nand sodium, strong so-called reducing substances which bind oxygen.\nBut at the high temperatures prevailing on the Sun compounds of oxygen\nand the reducing substances, for instance hydrogen, _i.\u00a0e._ water, are\nlargely dissociated into their constituents. But, if the temperature\nshould drop to about 1200\u00b0\u00a0C. (2200\u00b0\u00a0F.), at which point crust building\ndoes not yet take place, the oxygen would be entirely absorbed in the\nformation of the compounds mentioned. The compound substances of the\nEarth, like those of the Sun, are also strongly reducing, so that we\nmust infer that free oxygen did not enter into the gas covering of\nthe Earth at the time when its solid crust was formed. We may gain\na conception of the gases which then existed in the outmost layers\nof the Earth by studying the gases on the Sun and on other stellar\nbodies, particularly the comets, and also by investigating the gases\nabsorbed by the molten interior of the Earth. Previous to the crust\nformation, the entire mass of the Earth except the gases in its outmost\nlayers were of the same character as possessed by its molten interior\nnow. This molten mass, or magma, when in contact with the surrounding\ngases partly imbibed them through the process called absorption. An\ninvestigation of the gases present in the magma will therefore give\nus an idea of those existing in the original vapours surrounding the\nEarth. The magma occasionally comes into view in volcanic eruptions,\nand the confined gases are then partly given up into the air, but they\nare also partly retained in the solidifying lava, or volcanic rocks,\nwhence they may be driven off by high temperature and subsequently\nanalyzed. The direct gas emanations from the craters may also be\ngathered and analyzed. Such investigations have been carried out on\na large scale by Albert Brun, Frenchman, Arthur Day, American, and\nhis co-labourers Shepherd and Perret. Brun reached the surprising\nconclusion that water vapour, hitherto considered the most important of\nthe volcanic gases, in reality was not one of them but originated in\nthe crust of the earth. This theory, however, was completely refuted\nthrough the investigations by Day and his associates. As an example,\nwe give the analysis (the mean of several determinations) of volcanic\ngases from the crater Halemaumau on the volcano Kilauea in Hawaii:\n\n _May, 1912_\n _Per cent. of Volume_\n\n Carbon dioxide 55.4\n Carbon monoxide 4.3\n Hydrogen 7.7\n Nitrogen 29.6\n Sulphurous acid 2.9\n\n _December, 1912_\n _Per cent. of Weight_\n\n Carbon dioxide 42.9\n Nitrogen 25.8\n Water 27.5\n Sulphurous acid 3.7\n\nIn the latter case, it has been shown that air had gained entrance to\nthe volcanic gases, which air might have carried a quantity of water.\nBut this quantity could not have been large judging by the amount of\nnitrogen present which corresponds to not quite 3 per cent. water by\nweight. In the former case water was not included in the analysis. At\nany event, a high percentage of water has frequently been observed in\nvolcanic gases.\n\nWhen the gases were left in contact with water a considerable part was\nabsorbed thereby, particularly compounds of chlorine and fluorine and\nalso ammonia and sulphurous acid. An analysis of such water showed 10\nper cent. more fluorine than sulphurous acid and two fifths as much\nchlorine as fluorine. The ammonia amounted only to half of one per\ncent. of the chlorine. None of the rare air gases were present, which\nindicates that the nitrogen originated entirely from the magma and not\nfrom the air.\n\nBrun has analyzed lavas from different volcanoes. The gases extracted\ntherefrom naturally do not give as reliable information about the\noriginal atmosphere of the Earth as do the gases directly emanating\nfrom the volcanoes. As examples we quote the composition of the vapours\nin lavas ejected March 4, 1901, from Stromboli, and from Vesuvius in\nthe well-known eruption of 1906. They show in percentages of volume:\n\n _Stromboli_ _Vesuvius_\n Free chlorine 12.8 0\n Hydrate of chlorine 2.0 6.6\n Sulphurous acid 4.5 12.0\n Carbon dioxide 60.2 73.8\n Carbon monoxide 11.5 traces\n Hydrogen 0.5 7.6\n Nitrogen 6.9 traces\n Marsh-gas 1.6 0\n ----- ------\n 100.0 100.0\n\nIt will be noticed that the composition varies considerably. Free\nchlorine cannot very well be primigenial as it, like oxygen, combines\nwith reducing substances. Chlorine may be produced by heating chloride\nof calcium with silica and ferro-silicates which are present in the\nmagma. At all events, carbon dioxide constitutes the bulk. Next\nin importance are sulphurous acid and hydrate of chlorine. Carbon\nmonoxide, hydrogen, and nitrogen may occur in quite considerable\nquantities but are sometimes almost wholly absent.\n\nDay and Shepherd reached the conclusion that the gases emitted by the\nhot lava in the Halemaumau crater are nitrogen, water, carbon dioxide,\ncarbon monoxide, sulphurous acid, hydrogen, sulphur vapour, also\nsmall quantities of chlorides, fluorides, and possibly ammonia. Such,\nat least approximately, should also the original composition of the\nEarth\u2019s atmosphere have been when the crust was newly formed. Nitrogen,\nwater, and carbon dioxide were the most important ingredients; in\nthe high strata hydrogen was present. Oxygen was totally lacking and\nreducing gases such as hydrogen, sulphurous acid, and carbon monoxide\nabounded instead. If we further note the composition of comets and\nmeteorites we find that cyanogen, carbohydrates, and carbon monoxide\nalso are present in the former, argon and helium in the latter. It\nis therefore probable that these substances, although absent in the\nemanations from Kilauea, yet belonged to the primary atmospheres of the\nplanets. The rare gases of the air especially should originally have\ncome from the exterior parts of the sun, as did the nitrogen.\n\nAn atmosphere of such a composition would be utterly unendurable to\nliving beings. It must, if organisms are going to thrive therein,\nbe purified from such poisons as carbon dioxide, gaseous sulphur,\ncyanogen, and sulphurous acid. We know that such a process has taken\nplace and that the sunlight has been the great chemist who produced\noxygen and carbon from the carbon dioxide. The just mentioned poisonous\ngases were subsequently oxidized through electrical discharges. We\nall know that the plants up-build their framework under the influence\nof sunlight, consuming in the meantime carbon dioxide, water, and a\nlittle ammonia. In the process, oxygen is formed, as are also starch,\ncellulose, sugars, and albuminous substances with the aid of the\ngreen colouring matter in plants, chlorophyll, which considerably\naccelerates the action. Subsequently these new substances, which all\n(except the albuminous ones) belong to the carbohydrate group, are\nconverted into principally carbon and water. The final result is that\ncarbon dioxide through the agency of sunlight is split into its two\nconstituents, carbon and oxygen. This process, which is comparatively\nrapid in the presence of chlorophyll, should also, although more\nslowly, take place without that medium; and in recent trials the\nchemists--particularly Daniel Berthelot--have, indeed succeeded in\nimitating without chlorophyll this important function of the plants\nthrough the application of light of a short wave length. In the course\nof the many millions of years which geology has proved necessary\nfor the evolution of our planet, the carbon dioxide in the air was\ngradually converted into oxygen and carbon. As long as reducing gases,\nsuch as the poisonous ones mentioned, or any considerable quantities\nof carbohydrates and hydrogen yet remained in the atmosphere, the\noxygen was consumed in their combustion. If a solid crust had not\nexisted to prevent the oxygen from entering into the interior molten\nmass, it would also have found its way there and would have oxidized\nthe reducing substances in the magma. The separation of the interior\nfrom the surrounding gas shell is therefore a necessary requisite for\nthe existence of free oxygen in the air. Another condition is that the\ncombustible gases escaping from the volcanoes must be added to the air\nat a sufficiently slow rate not to consume all of the simultaneously\nformed oxygen. A third requirement is that the liberated carbon should\nnot in a renewed process of oxidation bind the oxygen just recovered.\nAs long as the air still was reducing, this last condition was no doubt\nfulfilled for that very reason. At all events, the crust once formed\nand the original violent volcanic activity somewhat abated, the time\nfinally arrived when free oxygen existed in the air. The previously\npresent reducing gases were, except for small fractions, burned into\nwater, carbon dioxide, and sulphuric acid and the nitrogen compounds\nhad no doubt yielded free nitrogen to the stores of that gas already\na part of the atmosphere. The time was now ripe for the first plants,\nprobably low forms of alg\u00e6, which, in the oceans, commenced life on our\nplanet. The carbon dioxide and hydrochloric acid of the air as well as\nthe newly formed sulphuric acid were absorbed by the running water and\ncaused a rapid disintegration producing silica and acid silicates. As\nplant life developed and extended the formation of oxygen increased.\nFalling vegetable matter was imbedded in slime which prevented the\naccess of oxygen during decay and in this manner the fossil fuels were\ndeposited. Koene of Brussels first pointed out that the carbon and the\nsulphuric compounds accumulated in the Earth would suffice to bind the\noxygen of the air. Later investigations lead to the conclusion that the\ncarbon alone is sufficient for the purpose. It would therefore appear\nthat all the oxygen of the air is derived from carbon dioxide belonging\nto the original atmosphere or contributed thereto by the volcanoes.\n\nThe reason why carbon dioxide and water continuously are liberated from\nthe magma is undoubtedly that the acid silicates are lighter than the\nbasic and therefore accumulate in the exterior parts of the magma. A\ngreat surplus of silica exists there. Compounds containing water and\ncarbon dioxide, _i.\u00a0e._ hydrates and carbonates, are also light and\nshould therefore congregate to the same strata where silica abounds,\nthere partly to be dissolved by the free silica and thus setting\nwater and carbonic acid free. The latter are, in contrast to silica,\nvolatile and evaporate therefore into the air leaving the silica\nbehind. This process is yet in evidence wherever the magma emerges as\nthrough the volcanoes. But also a few other acids in the magma are\nhighly volatile, as sulphurous, thiosulphuric, and hydrochloric acids.\nThese also belong to the volcanic gases, are dissolved by the water,\nand partake in the processes of disintegration. The carbon dioxide\nand hydrochloric acid form carbonates and chlorides. The former are\nextracted from the sea water by crustacea, sometimes also by plants,\nand form part of our sedimentary strata; the latter are soluble and\nremain in the water, chiefly as sodium chloride or common salt. The\nthiosulphuric acid, probably a product of ferrous sulphide and acids in\nthe magma, has entered into numerous insoluble metallic sulphides found\nin the Earth. Partly, it has also been oxidized, like the sulphurous\nacid, into sulphuric acid and has then assisted in the processes\nof disintegration, forming gypsum which has been deposited in the\nsedimentary rocks.\n\nThe geologists believed formerly that the Earth gradually and\ncontinuously has grown cooler. This theory, however, struggled with\nthe difficulty that certain cold time intervals, ice periods, were\nsucceeded by warmer epochs. To begin with efforts were made to\nsurmount this obstacle by assuming that an ice period on the north\nhemisphere was counterbalanced by a warm period on the south hemisphere\nand vice versa. In this manner, the mean temperature for the entire\nsurface of the globe might possibly have been continuously decreasing\nalthough fluctuations had occurred on the two hemispheres. But this\nview has proved untenable, because the ice period has left traces also\nwithin the tropics, near the equator, as on Kilimanjaro, in New Guinea,\nand so on. It is now practically agreed that the last great ice period\nwas characterized by a temperature between 4\u00b0 to 5\u00b0\u00a0C. (7\u00b0 to 9\u00b0\u00a0F.)\nbelow the present all over the surface of the Earth. This determination\nhas been accomplished by measuring the difference in height between the\nterminals of the glaciers at present and the lowest points where their\ngrinding action has left obvious traces. The ice coverings of North\nEurope, North-East America, South America, along the coast of Chile\nand in Argentina, as well as on the southern island of New Zealand,\nall appear to have existed simultaneously. Also during earlier eras,\nfor instance during the Algonkian and the Permian epochs, ice periods\nhave occurred. The latter, which was felt in Australia, India, and\nSouth Africa, is called the Gondwana-time. This period was formerly\nsupposed not to have caused any temperature drop except in the tracts\nmentioned. Later investigations lead us to believe, as asserted by\nHolland in his presidential address to the geological section of the\nBritish Association at its 1914 meeting, that also this ice period\nsimultaneously embraced the entire globe.\n\nAs the Algonkian time belongs to the oldest epochs of geological\nhistory it appears that the temperature on the Earth as long as life\nhas existed on our planet on the whole has been nearly constant,\nwith important alternations, however, of warm and cold periods. For\nan explanation of these fluctuations, our well-nigh only recourse is\nthe assumption that the heat-conserving quality of the atmosphere has\nchanged by virtue of a varying composition. Warm periods occurred when\ncarbon dioxide was abundant in the atmosphere due to volcanic activity,\ncold periods again accompanied a paucity of carbon dioxide. With rising\ntemperature, the percentage of water vapour in the air also increased,\naffording further protection against radiation loss of heat.\n\nThus, it would seem as if the mean temperature of the Earth\u2019s surface\nhardly had changed to any extent worth mentioning during immense spans\nof time estimated to about 500 million years. Nevertheless, a slow\nprocess of cooling proceeding toward the centre of the planet probably\ntakes place. Ever growing quantities of matter are transported from the\ninterior of the earth through volcanic action. Sedimentary deposits\nincrease continuously while the interior becomes hollow. As a result\nthe crust must gradually settle, causing large cracks in the process.\nFor these weakened places the volcanic products show a special liking\nand the craters are strung out in lines along such fissures. In other\nplaces, where volcanic action is less pronounced, hot springs appear\ninstead, generally emitting carbon dioxide in abundance, occasionally\nalso sulphurous acid and sulphuretted hydrogen. The dislocations in the\ncrust also take place along these cracks accompanied by earthquakes.\nThe study of these various phenomena has enabled us to map out the\nfissures, which generally radiate in nearly straight lines from one\npoint, the so-called centre of collapse, as the cracks in a pane of\nglass issue from the point of breakage caused by a swift blow. We shall\nlater see that such breakage lines and centres of collapse are common\non all stellar bodies which possess a solid crust and are observable\nfrom the Earth.\n\nWe may now easily form an idea of the general trend in the development\nof the atmosphere. The gases originally present were all, except the\nhydrogen, the nitrogen, and the rare gases, strongly absorbent of light\nand in particular of heat. It is, therefore, natural that the planets\nwhich have not formed a solid crust possess a strongly absorbing\nvapour-shell, as indeed is the case with the large planets (compare\nFig. 13). The crust once formed and the air gradually purged of these\ngases, thanks to the sunlight, so that mainly nitrogen and oxygen,\nsmall quantities of the rare gases, and carbon dioxide besides water\nremained, the temperature fell rather rapidly. Carbon dioxide formed\nthe last effective heat-conserving ingredient. As the crust grew\nthicker, the supply of this gas diminished and was further used up\nin the processes of disintegration. As a consequence the temperature\nslowly decreased, although decided fluctuations occurred with the\nchanging volcanic activity during different periods. Supply and\nconsumption of carbon dioxide fairly balanced as disintegration ran\nparallel with the proportion of this gas in the air. But evolution on\nthe whole can only proceed in one direction toward a final cooling of\nthe Earth. This must occur if for no other reason because the store of\nenergy in the Sun and therefore its radiation must slowly decrease.\nWith deepening crust and disappearing carbon dioxide vegetation must\nebb, and with it the production of oxygen. This gas also partakes in\nthe general disintegration through oxidation of iron protoxides in the\nmineral rocks. The oxygen portion of the air must therefore finally\nreach its maximum and start on the decline. Calculations point to the\nconclusion that the carbon dioxide of the air would be consumed in a\nfew tens of thousand years if new supplies were not furnished from the\ninterior. Water is also absorbed in the processes of decay as hydrated\ncompounds are formed, increasing in quantity with falling temperature.\nAs the amount of water in the ocean is immensely larger (about 50,000\ntimes) than the stores of carbon dioxide in the air and in the seas\nthe lack of the latter will undoubtedly first become serious. But a\nslow desiccation of the planet must subsequently take place, and will\nproceed at an accelerated rate with the continued cooling of the Earth.\nThen the vapour in the air and consequently precipitation will wane.\nThen, as during the ice periods, mighty ice caps will cover the poles\nand impound a large portion of the water in the ocean. Finally, the\nentire planet, perhaps after having harboured life during trillions\nof years, becomes an ice waste with a few cracks in its hard crust\nthrough which warm and acid vapours rise and create small melted areas\ncharacterized by a darker colour than the desert and ice-landscape in\ngeneral. Organic life lacks the conditions for existence and ceases\ntherefore to cheer the planet with its interesting variations. The\nplanet is dead but continues in obedience to gravitation to describe\nits orbit in space.\n\n\n\n\nCHAPTER VI\n\nTHE PLANET MARS\n\n\nThrough the works of Schiaparelli, Flammarion, and Lowell the vivid\ninterest of the general public has been directed toward our neighbour\nplanet Mars. Several investigators, Flammarion and Lowell among them,\nassert with full confidence that Mars has intelligent inhabitants, who\nhave built and maintain the curious \u201ccanals,\u201d which, it is stated,\ncould not have been created except by intelligent beings far superior\nto man.\n\nAir, water, and sunshine exist there, says Flammarion in his well-known\ngreat work, _La Plan\u00e8te Mars_ (1902, page 515). \u201cIt appears incongruous\nto us to condemn a world like Mars, where all the conditions for life\nexist, to such a fate\u201d (to be a dry desert). No doubt sentiment and the\ndesired result play a part in all such deductions, as indeed the words\nchosen by Flammarion would indicate.\n\nAs contrasted to the Earth, Mars is, on the other hand, considerably\nfurther removed from the Sun, whose radiation therefore on Mars\npossesses only 43 per cent. of its intensity on Earth. Judging by this\nfact, the mean temperature of Mars should fall far below that of the\nEarth and considerably below the freezing point of water and under such\nconditions it is hard to imagine a vegetation near the poles of Mars\nas Lowell does in his volume, _Mars as the Abode of Life_ (1909), or\neven in the neighbourhood of the canals anywhere on the surface of the\nplanet as assumed by Flammarion.\n\nWith such ideas in vogue we can well understand that the astronomers\nwould point their lately extremely sharpened instruments toward our\nruby-coloured neighbour in the sky when, in 1909, it passed very close\nto the earth under conditions particularly favourable to accurate\nobservations, more so in fact than they had been during the seventeen\npreceding years.\n\nNumerous astro-physicists, among them the world\u2019s foremost\nrepresentatives of their discipline, have repeatedly turned their\nspectroscopes toward Mars in order to ascertain whether water vapour\nwas present there or not. In the spectrum of the Sun we find several\nso-called \u201crain-bands\u201d due to the fact that the light before it reaches\nthe apparatus has passed through the moisture of the air. The more\nhumid the air the more strongly developed these rain-bands are. If we\ndirect the instrument first on the Moon, which lacks an atmosphere\nand therefore also moisture, and then on Mars, which for the sake of\nsimplicity we assume standing close to the Moon-disk, a difference\nshould appear in the spectra of these two bodies, provided moisture\nis present in the atmosphere of Mars. The rain-bands ought to be more\npronounced in sunlight that has passed the atmosphere of Mars (passed\nit twice as the light is reflected by the surface of the planet) than\nin light reflected from the naked Moon. The bands appear of course\nin both spectra as the light on its final stage to the spectroscope\npasses the atmosphere of the Earth, which never is free from moisture.\nIn this manner Huggins and Janssen, scientists of world-wide fame,\nbelieved that they had demonstrated the presence of water vapour on\nMars. Campbell, on the other hand, the prominent director of the\nLick Observatory, made similar investigations of the planet in 1894,\nand so did a French astronomer, Marchand, in 1896 and 1898, both\nunder unusually favourable circumstances as the former installed\nhis instrument 1283 m. (5200 ft.) and the latter 2860 m. (9370 ft.)\nabove sea level, but neither found any indication of moisture in the\natmosphere of Mars.\n\nIt is evident that the observations would be far more accurate if we\ncould eliminate the moisture from the atmosphere of the Earth, in which\ncase no rain-bands would appear in the spectrum of the Moon. It would\nthen be unnecessary to compare the two spectra; we would only have to\ndetermine whether rain-bands were present in the spectrum of Mars or\nnot. We can never entirely avoid the water vapour of the air, but its\ninfluence may be greatly reduced by making our observations from high\nmountains or in desert climates where the air is comparatively dry,\nthat is free from water vapour. Investigations undertaken where the\nair is dry deserve therefore more confidence than those handicapped by\ngreater humidity. The observations by Campbell and Marchand fall in the\nformer category, and it would, therefore, appear that the presence of\nwater vapour on Mars to any extent worth mentioning is highly doubtful.\n\nIn later trials, Campbell and Keeler have employed an improved method,\nusing photographs of the spectra on sensitive plates, but neither has\nsucceeded in discovering any water vapour in the atmosphere of Mars.\n\nObviously photography offers a great advantage over direct ocular\nobservation. The two pictures may be placed side by side and very\naccurate measurements may be made at leisure. We may also choose the\nmoments for exposure when the two stellar bodies stand equally high\nover the horizon so that the sunlight reflected from them traverses\nequal distances in the humid atmosphere of the earth.\n\nIt now devolved upon Lowell to test his theories by means of the\nmagnificent resources at his disposal in Flagstaff observatory in the\ndesert of Arizona 2200 m. (7200 ft.) above sea level. In the months of\nJanuary and February the dew-point there is about -7\u00b0\u00a0C. (+19.4\u00b0\u00a0F.)\n_i.\u00a0e._, each cubic meter (1.3 cu. yds.) of air contains 2.8 grammes\n(43.25 grains) of water vapour while saturated air at zero temperature\n(32\u00b0\u00a0F.) holds nearly twice this amount or 4.8 grammes (74 grains)\nper cubic meter (1.3 cu. yds.). Slipher, working in this observatory,\npushed the sensitiveness of his plates to the utmost then obtainable,\nand photographed the spectrum of Mars in January and February, 1908.\nHe found that the most important rain-band always was more prominent\nin the spectrum of Mars than in the spectrum of the Moon photographed\nlater during the same night. Peculiarly enough, it was only the\nrain-band designated \u201cA,\u201d and located in the red spectral field, that\nwas of a marked difference in the two spectra. Other bands gave no\nindication of the presence of water vapour on Mars. This result did not\ndirectly contradict the conclusions reached by Campbell and Keeler,\nalso by means of photography; they had investigated other bands than\n\u201cA.\u201d The \u201cA\u201d-line might therefore possibly be more sensitive to water\nvapour than the others.\n\nSlipher\u2019s discovery was considered so valuable that it must be employed\nto the limit. The well-known physicist Very was therefore called in\nconsultation; he made careful measurements of the intensity of the\n\u201cA\u201d-lines on the various plates and calculated that the atmosphere of\nMars contained 1.75 times as much water vapour as that of the Earth at\nthe point of observation. If we desire to determine the proportion\nof water vapour in the air at the surface of Mars from this statement\nwe may figure in the following manner. The amount of water vapour in\na vertical column of air one square meter (1.2 sq. yds.) in section\nis, according to Hann, 2500 times the amount in a cubic meter (1.3 cu.\nyds.) at the surface of the earth. At the time of the observation, the\nlatter amount was 2.29 grammes (35.4 grains); on each square meter (1.2\nsq. yds.) of the ground rested therefore 5725 grammes (12 lbs. 11 oz.)\nof water vapour. That the quantity of water is not larger, although\nthe depth of the atmosphere far exceeds 2500 m. (1.5 miles), is due\nto the fact that the temperature rapidly decreases with distance from\nthe ground. On Mars, the temperature ought not to fall so quickly with\nchange in height because the intensity of gravity there is 2.68 times\nsmaller than on the Earth. The temperature drops there 2.68 times\nslower with ascent in the atmosphere, and a column of air on Mars one\nsquare meter (1.2 sq. yds.) in section should therefore contain 6680\ntimes as much water vapour as a cubic meter (1.3 cu. yds.) at its\nsurface. As Mars did not stand in zenith, the distance traversed by the\nlight-ray in the atmosphere was greater--in fact 1.43 times greater\nthan if such had been the case. A column of air in the direction of\nthe light-ray, one square meter (1.2 sq. yds.) in section contained\ntherefore 8175 grammes (18 lbs. 3 oz.) water vapour. In the atmosphere\nof Mars which the light passed in a vertical direction there was, if\nwe are to believe Very, 1.75 times as much, or 14,300 grammes (31\nlbs. 8 oz.) and in a cubic meter (1.3 cu. yds.) at the surface of the\nplanet, consequently 6680 times less, or 2.14 grammes (33.1 grains).\nThe corresponding dew-point is then, according to this determination,\n-10.3\u00b0\u00a0C. (+13.5\u00b0 F.). It is agreed upon that a desert climate\nprevails on Mars. It might at the time of the observation conform to\nthe extremely dry climate at Salt Lake City in the height of summer\nwhen the humidity there is only 31 per cent. of saturation. Under\nsuch conditions saturated air at noon in the equatorial belt on Mars\nshould contain 7 grammes (108 grains) per cubic meter (1.3 cu. yds.)\ncorresponding to a temperature of 5.3\u00b0\u00a0C. (41.5\u00b0\u00a0F.).\n\nIt must be admitted that this was not very encouraging to Lowell. If\nthe temperature in the middle of the day, when the sunlight falls\nperpendicularly on the surface of the planet, rises only to about 5\u00b0\u00a0C.\n(41\u00b0\u00a0F.), the mean temperature for twenty-four hours, even in the midst\nof the summer, must in this entirely clear, light air be far below\nfreezing and vegetation on Mars is therefore not very well conceivable.\nIn spite of this, Lowell saw in Slipher\u2019s measurements a confirmation\nof his theory that Mars is the abode of an intelligent race that\nutilizes, in their wrestle with existence, a verdant vegetation pushed\neven into the polar regions.\n\nCampbell, however, went one step further than Slipher. In August and\nSeptember, 1909, Mars occupied a position in the sky particularly\nfavourable to observations. Campbell decided to benefit thereby.\nWith the support of a rich patron of science, a Mr. Crocker, who\non several occasions has made magnificent contributions toward\nastronomical research, Campbell equipped an expedition to Mount Whitney\nin California, 4425 m. (14,502 ft.) high and the loftiest peak in the\nUnited States. He was accompanied by an able scientific staff, the most\nprominent of which were Dr. Abbot, head of the observatory belonging\nto the Smithsonian Institution, and a well-known German astronomer,\nAlbrecht. The members of the expedition were affected by mountain\nsickness and suffered many severe hardships when the wind was high,\nreaching about 25 m. per sec. (56 miles per hour), and at the same time\ncold, falling below zero (freezing) during the night. The barometric\npressure was only 447 mm. (17.6 inches). During the nights, when the\nobservations were made, the water content of the air fell to between\n0.5 and 0.9 grammes (7.7 grains to 13.9 grains) per cubic meter (1.3\ncu. yd.) or 2.5 to 4 times less than Slipher had to contend with. The\nspectra of the Moon and of Mars were photographed in close succession,\ntwo exposures being made in each case. The band \u201cA\u201d was plainly visible\non several plates. No indication of greater prominence of this band\nin the spectrum of Mars could be found. Other rain-bands were also\ninvestigated with the same result. Neither were the characteristic\nbands of oxygen stronger in the spectrum of Mars, than in that of the\nMoon. Slipher believed that he had discerned a difference, although of\na hair\u2019s breadth, which would indicate the presence of oxygen in the\natmosphere of Mars. The conclusion itself is not improbable, but the\namount of oxygen there is in any case considerably smaller than in the\nEarth\u2019s atmosphere.\n\nSeveral statements by Campbell, as well as Slipher\u2019s observations,\nindicate that a difference ought to have appeared between the spectrum\nof Mars and that of the Moon if the water content in Mars\u2019 atmosphere\nhad been the same as in the Earth\u2019s at the time of the observation.\nThis content, as stated before, was about 3 times smaller on Mount\nWhitney than at Flagstaff. At the latter place, the measurements gave\n1.75 as the ratio of water vapour on Mars to that on the Earth. The\namount of water vapour with the Sun in zenith on Mars should therefore,\naccording to Campbell\u2019s observations, only reach 0.4 gramme (6.1\ngrains) per cubic meter (1.3 cu. yds.) corresponding to a dew-point of\n-28\u00b0\u00a0C. (-18.4\u00b0\u00a0F.) or to an actual temperature of -17\u00b0\u00a0C. (+1.4\u00b0\u00a0F.)\nallowing also for a desert climate with only 31 per cent. saturation.\nThis temperature is probably higher than the mean for a summer day as\nthe observations were made at noon on Mars.\n\nIt must now be evident that we should consider Mars as unfit to\nharbour living beings. There is possibly a slight amount of oxygen in\nthe thin air but the extremely low temperature and the scant supply\nof water vapour form insurmountable obstacles to the subsistence of\neven the simplest forms of life in the equatorial regions on Mars.\nThe temperature difference between day and night must be enormous on\naccount of the desert climate. Even if life could develop during the\nday, which has nearly the same duration as with us--Lowell fixed it at\n24 hours, 37 minutes, 22.6 seconds--and during which the temperature\npossibly might rise above the freezing point, it would nevertheless be\ndestroyed without mercy by the bitter frost at night.\n\nCampbell has offered an explanation of the indications of water vapour\non Mars, apparent on Slipher\u2019s photographs. An analysis of the latter\u2019s\nobservations shows that the Moon was photographed about four hours\nlater in the night than was Mars. On all occasions except one, clouds\nappeared in the sky. This indicates the presence of moisture in the\nair, so that the humidity should change with the temperature which\nlatter rapidly falls in the course of the night. Campbell, himself,\nfound during the clear nights, when he made his observations, that\nthe humidity in the hours of the night up to midnight falls to a\nfraction--a half or a third--of its original value an hour or so after\nsunset. This rapid temperature drop is probably confined to the strata\nimmediately above the observation point but the moisture is strongly\nconcentrated downward so that this change in humidity undoubtedly\nshould have been taken into account. Or better, observations should\nbe avoided in the beginning of the night and the Moon and Mars\nphotographed as soon after each other as possible, precautions taken\nby Campbell but not by Slipher. That the latter found less traces of\nwater on the lunar photos than on the martian ones is, therefore,\nprobably due to the fact that the former were taken about midnight but\nthe latter not long after sunset, when the atmosphere contained much\nmore water vapour. Thus, we learn how a small slip, more obvious to the\nmeteorologist than to the astronomer, may spoil a labour otherwise done\nwith extraordinary care.\n\nTo Campbell\u2019s critique Very answered by the suggestion that the\nmeteorological conditions during the Mount Whitney observations should\nhave been exceptionally unfavourable. The entire south-west of the\nUnited States and the north of Mexico were visited at that time by\ncloudy weather and heavy downpours. Very contends that this humidity\nshould partly have extended to the high strata above Mount Whitney and\ntherefore rendered the calculation of the moisture content of the air\nentirely unreliable.\n\nSimultaneously (August, 1910) new measurements were published of\nSlipher\u2019s photo-plates from February, 1908, which Very had examined.\nThe result was now that the rain-band \u201cA\u201d was 2.5 times more pronounced\nin the spectrum of Mars than in that of the Moon. Furthermore, the\noxygen absorption-band \u201cB\u201d was 1.5 times stronger for Mars than for the\nMoon. Great quantities of water vapour and oxygen should, therefore,\nundoubtedly exist in the atmosphere of Mars.\n\nIn the meantime Campbell had not been idle. The difficulty with the\nolder measurements consisted in the fact that the absorption line\nof water vapour in the atmosphere of Mars occupies the identical\nplace of the line due to vapour in the Earth\u2019s atmosphere. There\nexists, however, a method, as already pointed out by Campbell in 1896,\nof separating the two, which method is available when Mars either\napproaches or departs from the Earth with sufficient velocity. The\nlatter could be determined both from the known motions of the two\nplanets and from the displacement of certain spectral lines of the Sun.\nThese two determinations were in almost perfect agreement; for instance\nJanuary 26\u201327, 1910, astronomical calculations gave a relative velocity\nof 19.1 km. (11.86 miles) per second and spectroscopical measurements\n19.2 km. (11.93 miles) per second, while on February 3\u20134 the relative\nvelocity was 18.1 km. (11.24 miles) a difference of 1 km. (.62 miles)\nper second. This trial shows the accuracy of the method. Among the\nabsorption lines of water vapour and of oxygen there was, however, none\ndue to the atmosphere of Mars. Campbell assumes that such lines would\ncertainly have been visible if they had been only one-fifth as strong\nas the so-called tellurian lines. The advantage of this method is\nevidently that the \u201cmartian\u201d and the \u201ctellurian\u201d lines lie close beside\neach other on the same plate so that differences in sensitiveness,\nexposure, and atmospheric conditions are entirely eliminated.\n\nFrom these and the following data we may calculate water content and\ntemperature of the atmosphere on Mars anew: water vapour at the point\nof observation was 1.9 grammes (29.3 grains) per cubic meter (1.3 cu.\nyds.), zenith-distance of Mars 55\u00b0 and incident as well as reflected\nsun-rays formed an angle of 70\u00b0 with the surface of Mars; hence, the\namount of moisture at the surface was only 0.12 gramme (1.85 grains)\nper cubic meter (1.3 cu. yds.), corresponding to -38\u00b0\u00a0C. (-36.4\u00b0\nF.) for saturated air and to -27\u00b0\u00a0C. (-16.6\u00b0 F.) for air of 31 per\ncent. saturation. Oxygen content per cubic meter (1.3 cu. yds.) at\nthe surface of Mars would be only a sixteenth part of corresponding\nnumerical value on the Earth. This determination is more accurate\nthan any of the previous ones and reduces the temperature another\n10\u00b0\u00a0C. (18\u00b0\u00a0F.) below the lowest value derived earlier in this chapter.\nWe should remember, however, that, during the trial of September,\n1909, the sun stood practically in zenith on Mars, while in January\nand February, 1910, we are concerned with a point where sunrise had\noccurred about four and a half hours previously. The latter observation\nshould give a value close to, but slightly above, the mean diurnal\ntemperature on Mars.\n\nNo determination comparable in precision with this one by Campbell\nappears to have been made. We must therefore recognize it as conclusive.\n\nWe may easily calculate the surface temperature of a planet from the\nintensity of the solar radiation received, or insolation, provided\nthe surrounding vapour shell contains no heat retarding gas. The most\nimportant gases of this kind are water vapour, which, as we just have\nseen, is very sparse in the atmosphere of Mars, and carbon dioxide,\nof which there probably also, for reasons stated below, is only a\nscant supply in the martian gas shell. Such calculations were first\nperformed by Christiansen of Copenhagen, who assumed 2.5 calories as\nthe solar constant on Earth, _i.\u00a0e._, the amount of energy received\nthrough insolation per minute by each square centimeter (.15 sq. in.)\nof the Earth\u2019s surface when at right angle to the radiation and on\nmean distance from the Sun. On Mars, the radiating energy received\nunder similar conditions is only about 1.1 calories. The surface of\nthe planet is heated until it radiates as much energy into space as it\nreceives from the Sun. In this way we obtain an average temperature\nof -37\u00b0\u00a0C. (-34.6\u00b0\u00a0F.) for the entire surface of Mars. The regions,\nexposed to the Sun in zenith at noon, might, if heat were not conveyed\ntherefrom, possibly reach a daily mean temperature of +8\u00b0\u00a0C. (46.4\u00b0\u00a0F.)\nand perhaps slightly more at noon. Probably not even the freezing\npoint is reached, as the heat is rapidly carried away by the freely\ncirculating air. The above-mentioned mean temperature of -37\u00b0\u00a0C.\n(-34.6\u00b0\u00a0F.) seems on the whole to agree well with the observations by\nCampbell on Mount Whitney.\n\nRecent accurate determinations of the intensity of the solar radiation\nby Abbot, K. \u00c5ngstr\u00f6m and others, indicate that it has been estimated\nabout 20 per cent. too high. If we take the solar constant to an even\n2.0 calories, which is a trifle high, we reach the conclusion that the\nmean temperature on Mars would fall about 50 degrees below freezing.\nEquatorial regions might then reach an average of -8\u00b0\u00a0C. (+17.6\u00b0\u00a0F.)\nand at noon the temperature might possibly rise slightly above zero\n(32\u00b0\u00a0F.). A higher temperature yet might be attained at the pole where\nthe Sun during the summer remains for months above the horizon or a\nhigh mark of +8\u00b0\u00a0C. (46.4\u00b0\u00a0F.) provided no heat were carried away by\nair currents. Such losses naturally must occur, and the temperature\nprobably hovers around freezing. At the martian poles we might possibly\nimagine the existence of some low forms of vegetation (snow-alg\u00e6,\netc.) during the height of the short summer.\n\nWhen we hitherto on the authority of Lowell, Very, and others, have\nassumed an average temperature of +10\u00b0\u00a0C. (50\u00b0\u00a0F.) on Mars, we have\ndone so on the supposition that the atmosphere of the planet contained\ngreat quantities of heat-conserving gases. This assumption appears\nto be no more tenable than the belief in the high temperature on\nMars. After all, the temperature is probably about 10\u00b0\u00a0C. (18\u00b0\u00a0F.)\nhigher than our last calculation would indicate--or about -40\u00b0\u00a0C.\n(-40\u00b0\u00a0F.)--because the air on Mars is very clear and admits, therefore,\nall sun-rays, retaining also a fraction by virtue of what little water\nvapour, carbon dioxide, and other heat-conserving gases there may be\npresent in the atmosphere. The mean summer temperature at the martian\nequator (-27\u00b0\u00a0C. or -16.6\u00b0\u00a0F. acc. to Campbell\u2019s data) would then lie\nabout 13\u00b0\u00a0C. (23.4\u00b0\u00a0F.) above the mean for the planet. This agrees\nclosely with conditions on the Earth where the highest mean in July\nat the equator is 27\u00b0\u00a0C. (80.6\u00b0\u00a0F.) and the mean for the earth 16\u00b0\u00a0C.\n(60.8\u00b0\u00a0F.).\n\nWe are consequently obliged to revise in their entirety our ideas about\nMars. The belief that organic life (green vegetation) causes the colour\nof the so-called seas on Mars, as assumed by Lowell, or that the red\ntints belong to the gorgeous dress in which autumn arrays the plants\nbefore their leaves are shed under the attacks of frost, as intimated\nby Flammarion, must nowadays take its place in the shadowy realm of\ndreams.\n\nThose who do not believe that the so-called canals are real\nwaterways, devoted to freight carrying and irrigation, or illusions,\nwhich conception the photographs contradict (for example Fig. 18),\ngenerally consider that they signify cracks or fissures. As in the\ncrust of the Earth, they generally run in nearly straight lines or\nin regularly bent curves (Fig. 17 and 17a). Flammarion mentions that\nthe renowned physicist Fizeau looked upon the \u201ccanals\u201d as cracks in\nthe ice-coverings of the oceans on Mars. Penard, in 1888, expressed\nthe more likely opinion that they correspond to the fissures in the\ncrust of the Earth. Flammarion contends that such fissures do not have\nthe rectilinear configuration of the \u201ccanals.\u201d This is completely in\nerror, as shown on the map here reproduced (Fig. 16). It is also stated\nthat they are so inexplicably long, for instance the canal Phison is\n2250 English miles (Lowell) or 3620 km. in length. The longest known\nearthquake crack along the entire length of which a dislocation has\ntaken place _at one time_ is 600 km. (373 miles) in extension; the\nviolent earthquake in California, 1906, originated from this crack.\nThere is no doubt, moreover, that a great fissure in the Earth follows\nthe coast of Chile from Arica to the Strait of Magellan in a nearly\nnorth and south direction for a distance of about 32 parallels or 3560\nkm. (2210 miles). This fissure is almost as long as Phison on Mars.\nSuch cracks exist along the entire coast of the Pacific Ocean. As yet,\nwe do not know their position in much detail, because long stretches\nrun below the sea or through territories not yet occupied by civilized\npeople. As an example of a small fissure, a picture taken by Sederholm\nfrom Segelsk\u00e4r, east of Hang\u00f6 in the Baltic, may serve (see Fig. 15).\nAs the studies of earthquakes are prosecuted with increasing interest\nin later years, fissures of all dimensions will undoubtedly soon be\ndiscovered. The solid crust on Mars is, furthermore, somewhat thicker\nthan that of the Earth as the cooling of that planet has progressed\nfurther. The sections broken off at the bursting of the Martian crust\nought therefore to be much larger both in breadth and in length.\nNo doubt, the facts that the intensity of gravity on Mars is only\nthree-eights of its intensity on the Earth and that the curvature of\nthe Martian surface is twice as sharp as the Earth\u2019s contribute to\nthis result. Imagine two vaults, one built with higher and broader\nwedge-shaped stones than the other and with half the radius and\nfurthermore loaded only one-third as heavily as the other, and it\nwill become evident that we can permit a much larger span in the former\nthan in the latter case without fear of collapse. In other words, it\nrequires a much more extensive caving or shrinkage of the molten mass\nbeneath the crust of Mars to cause a rupture than under the terrestrial\ncrust.\n\n[Illustration:\n\n Fig. 15. Narrow bay on the left side of Segelskar, east of\n Hango in Finland. The bay owes its existence to the fact\n that the ice has laid bare a territory coursed through by\n fissures. Photo by I.\u00a0I. Sederholm.\n]\n\n[Illustration:\n\n Fig. 16. Earthquake centres in Calabria and in Sicily. On the\n larger map the damaged localities are indicated, on the\n smaller the most prominent tremor lines. Drawn by I.\u00a0I.\n Sederholm.\n]\n\nAs a consequence, the fissures on Mars ought to be longer than the\ncorresponding formations on the Earth. A thorough study of the large\nfissure in Calabria shows that it consists of a veritable network of\nsmaller straight cracks (as is apparent on Figure 16, which is taken\nfrom a work by the well-known Finnish geologist Sederholm). On this\nmap the radial cracks (see _Worlds in the Making_, Fig. 16), charted\nby Suess, are also shown, and their direction under the sea designated\nby dotted lines. The sketch in the upper left corner of Fig. 16 is in\nstriking similarity to a picture drawn by Schiaparelli in Mercator\u2019s\nprojection of the planet Mars (see map at the end of book). We notice\non both, the numerous equidistant lines corresponding to parallel\ncracks and duplex canals. Not every fissure has its parallel and not\nevery canal its mate--generally only one of the latter is visible and\nsometimes both disappear.\n\nAs the radial cracks in the drawing by Suess if extended meet in the\nLipari Islands, so also several canals on Mars run together in a\nso-called lake (Lowell called them \u201cgroves\u201d or \u201coases\u201d) which evidently\nis a centre of collapse (many appear on Fig. 17). It is plain that all\ncrossings of the \u201ccanals\u201d are not necessarily such centres of collapse.\n(See maps Figs. 17 and 17a at end of book).\n\nWe shall consequently assume that the canals on Mars correspond to the\ngeological dislocation fissures on the Earth. Along these fissures\nemerge the gases liberated in the cooling process on both planets;\nwhich are similar gases to those which escape through the volcanoes.\nThese vapours are primarily water, next carbon dioxide and, in\nconsiderably smaller quantities, sulphuretted gases and hydrochloric\nacid. They discharge through cracks in regions which, geologically\nspeaking, not so long ago were the scene of volcanic activity. In the\ndislocation-grooves, lakes, and water courses are often formed, as we\nmay observe in several places in Sweden, for instance near Stockholm.\n\nAssume now a gradual cooling of our earth. Most territories are covered\nby stratified, comparatively light rocks. To the dislocation fissures\nwater gathers from the surrounding strata and occasionally from the\ninterior, partly washes away the loose material and transforms the\nfissures into furrows, generally with flat bottoms. Dissolved salts\nare carried to the sea. As cooling proceeds, the ocean commences to\nfreeze. Each summer the surface melts to a certain extent, as is the\ncase now in our polar regions. Finally, the entire ocean freezes to the\nbottom, the ice is now to be considered as a kind of rock, flexures and\ndislocations cease and the ice assumes a smooth surface. In the strong\nsunlight during the summer this surface thaws, as do the water-courses\non the mainland, and these continue to carry their salts to the open\nsurface water. At the approach of winter the latter solidifies again\nbut not as the water in our inland lakes from the top but from the\nbottom, as ordinary sea-water possesses its greatest density below\nthe freezing point while the opposite is true of fresh water. The\nconsequence is that the ice foundation grows upward and as the surface\nwater becomes increasingly shallow it is turned into a concentrated\nsalt solution. With a further drop in temperature the ice formation is\naccompanied by crystallization of the salts.\n\nSomething similar takes place on the Martian mainland in its flat river\nbasins, which correspond to the salt lakes in our deserts. On account\nof the bitter cold and the consumption of the water in the process of\ndisintegration (the carbon dioxide has been largely used up in the\nsame manner), precipitation has almost ceased on Mars and most of the\nwater in circulation emerges from the interior of the planet along\nthe fissures. As it contains hydrochloric acid and carbon dioxide it\nextracts from the soil salts, such as the chlorides of sodium (common\nsalt), of calcium and of magnesium, all present in common sea-water\nto which it was brought by the rivers. The compounds of calcium and\nmagnesium are not precipitated as carbonated salts through the medium\nof crustacea as is the case on earth. The strong solar radiation during\nthe summer partly evaporates the water into the thin air, leaving the\nsalts behind. On account of the low temperature, this vaporization on\nMars is probably slower than on the Earth. Along the cracks in the\ncrust, a kind of dry salt-lakes are formed similar to the generally\nshallow and occasionally dry lakes common in the deserts of Central\nAsia as described by Hedin. We know that Mars possesses a pronounced\ndesert climate. There finally remains in the lowest sections of the\nwater courses a concentrated salt solution, which parts with its water\nmore and more reluctantly, so that the salts which most strongly hold\nthe water crystallize at the deepest points. If the winter\u2019s cold is\nsufficiently severe (below -55\u00b0\u00a0C. or -67\u00b0\u00a0F.) ice is extracted even\nfrom the most concentrated solutions, which mainly contain chloride of\ncalcium. In spite of such extreme temperatures, evaporation into the\nrare atmosphere is not negligible and the ice crystals partly vanish,\nto reappear in the coldest regions of the planet, that is, around the\npole which at the time is turned away from the sun. On the ocean, now\nfrozen solid throughout, a polar-cap of snow and hoar-frost is formed\nwhich finally reaches as far as the 38th parallel on the southern\nhemisphere (see Figs. 18 and 19), where winter occurs when Mars is most\nremoved from the sun, and to the 58th parallel (see Fig. 19) on the\nnorthern hemisphere where winter reigns while Mars is nearest to the\nSun and consequently not quite so cold. Similar conditions obtain on\nthe Earth although not to such a marked degree.\n\n[Illustration:\n\n Fig. 18. Photograph of Mars, enlarged and retouched; taken by\n Lampland\n]\n\n[Illustration:\n\n Fig. 19. Appearance of Mars April 8, 1907, as observed by\n Qu\u00e9nisset. Below one pole a dark line is plainly visible.\n\n]\n\n[Illustration:\n\n Fig. 20. The south pole spot on Mars observed by Jarry-Desloges\n July 10, 1909.\n]\n\n[Illustration:\n\n Fig. 21. The appearance of Mars during an observation by\n Antoniadi in 1909. The whole disk is somewhat hazy; below,\n the details are hidden by clouds of sand.\n]\n\nIn the vicinity of the snow-white polar cap, whether there be continent\nor sea, bodies of water occur with solidly frozen surface covered by\ncrystals of very hygroscopic salts, such as the chlorides of calcium,\nmagnesium, and sodium. When the summer warmth returns and the polar\ncap is heated, the hoar-frost evaporates, and the now comparatively\nhumid air spreads over the surrounding territory. We observe also\nfrequent mist-formations in these places. The ground near the edge\nof the polar snow assumes then often a dark hue on account of the\nmoisture (Fig. 19). Occasionally canals and lakes appear in the polar\ncap (see Fig. 20). This is evidently due to hot emanations along the\ncracks. The moist air sweeps over the salts, which then absorb water\nand dissolve into concentrated solutions. New quantities of water\nvapour are supplied from the pole as they distill over toward the\nother pole, where winter now exists, and push on toward the equator\nwhich they finally pass. In their course they dissolve the salts\nin the depressions along the fissures and particularly at the deep\ncrossings where the centres of collapse or the so-called \u201coases\u201d are\nlocated. Lowell has observed that the \u201ccanals\u201d in this manner gradually\n\u201cliquify\u201d from 78\u00b0 N. Lat. to the equator in fifty-two days.\n\nThe canal theory presents great difficulties to the explanation of this\ncurious phenomenon. In order to make the water flow it must be assumed\nthat the surface of Mars is entirely smooth or at least very nearly so\nand that the inhabitants convey the water melted at the poles through\npumping stations. The canals vary in width; according to Lowell, their\nmean is 16 km. (10 miles), according to Flammarion between 300 and 60\nkm. (185 and 37 miles) which latter estimate probably is too high. The\nsame canal differs widely in breadth in successive years and sometime\ndisappears altogether. When the supply of water vapour is scant, only\nthe most hygroscopic salts are dissolved, _i.\u00a0e._, those deposited in\nthe deepest furrow of the canal, but when the moisture sweeping over\nthe canal is more abundant the broader portions absorb water, darken\nand thus become visible. The same holds true in regard to the inland\nlakes (\u201coases\u201d). As the water vapour diffuses in the air, the canal\nbecomes liquid along its entire length independent of the altitude of\nits various parts.\n\nAll agree upon the desert climate of the mainland on Mars. Like most\ndeserts on the Earth, it is, therefore, probably a table-land, where\none plateau mounts above the other, each one nearly level. By the\naction of the wind, the upper layers have been transformed into fine\nsand. On the dead planet no further sediments are deposited by the\nsea. The only accretions to the planet are meteorites and cosmic dust\nwhich slowly rains down. It contains among other substances iron,\npartly metallic and partly in the form of protoxides (which have a\nlight green colour).[5] The oxygen in the atmosphere of Mars transforms\nthese compounds to ferro-oxide which has different colours according\nto its coarseness, but generally is ochre. The surface of Mars is also\ndescribed as possessing this colour. Dross has, therefore, assumed\nthat the Martian soil is mingled with ferro-oxide. The finest dust,\nhowever, is yellow while larger crystals tend toward violet. We often\nobserve on Mars that the details are covered by a yellow veil. This is\nof course finely powdered ferro-oxide probably mixed with less coloured\nsand which the desert wind whirls up over large portions of Mars. Vast\nsections of the planet bore such wrappings in the autumn of 1909, as\nobserved and described by Antoniadi in Paris (see Fig. 21). Similar\nobservations have previously been made by W.\u00a0H. Pickering and others.\n\n [5] In the deepest portions of the oceans on the Earth where\n no sediments from the coasts are deposited, large\n accumulations containing iron compounds have been found\n and the presence of certain minerals therein points to\n their meteoric origin.\n\nAs a rule, only the central and the polar regions of the surface of\nMars can be seen. Territories near the equator more than 40 to 50\ndegrees removed from the point in line with the Sun and the centre of\nthe planet are generally hidden behind a thin, white veil of mist. As\nsoon as the Sun leaves the zenith and reaches half-way to the horizon\nthe moisture of the air is precipitated near the ground. This shows\nthat the planet does not possess any quantities of heat-conserving\nvapours in its gas shell. The mist does not extend to the poles, whose\nwhite caps always appear distinctly, because the Sun cannot greatly\naffect the evaporation in regions where the Sun\u2019s altitude is neither\nvery high nor very variable. The same holds true for other snow-covered\ntracts, even if they are not located in the immediate vicinity of the\npole.\n\nWhen the supply of water vapour is scant, only the most salient canals\ncome into view. As a rule they do not then appear double, as one of the\nmates is always less prominent. Lowell showed, he believed, that it\nalways is the same canal out of a pair which first comes to sight and\nthat its position always remains unchanged in contrast to Schiaparelli\nwho has reached the opposite conclusion. This, of course, is quite\nnatural.\n\nOn account of the small amount of water vapour in the atmosphere of\nMars true clouds are rare. Figure 22 shows such a cloud at the edge\nof the planet. The aforementioned mists are often called clouds, for\ninstance by Pickering.\n\n[Illustration:\n\n Fig. 22. Cloud at the upper right edge of Mars observed by\n Molesworth, March 7, 1901\n]\n\n[Illustration:\n\n Fig. 23. Mars as observed by Lowell, July 11, 1907. Even the\n dark portions appear coursed through by \u201ccanals.\u201d\n]\n\n[Illustration:\n\n Fig. 24. Mars, as observed by E.\u00a0M. Antoniadi, October 6, 1909.\n]\n\nThat elevations really may be found on Mars is evident from the fact\nthat snow or hoar-frost often remains in patches near the pole and\noccasionally quite far therefrom, for instance on the large island\nHellas (40\u00b0 S. Lat.), while it disappears from the surroundings and\nsometimes from the pole itself (the south pole). Such a highland\ncovered by ice exists near the south pole, and is shown near the\nupper edge of Fig. 24. In places where snow always remains, a feeble\nglacier formation may occur. Most investigators assume that mountains\nand plateaus exist on Mars, although of modest altitude (Campbell\nbelieves that he has observed peaks 3000 m. (9800 ft.) high). Lowell\nwho diligently has looked for mountains at the edge of the illuminated\npart of Mars, has reached the conclusion that they, if present,\ncannot rise more than 600 to 900 m. (2000 to 3000 ft.) above the\nsurrounding plains. It were indeed improbable that all inequalities\nof the Martian surface should have been removed in the process of\ndisintegration, which although at work for enormous extensions of time,\nhas long been extremely feeble and is unassisted by torrents of rain\nwhich might rapidly wash the products into the valleys. At present, it\nis mainly the sand carried by the desert wind that slowly reduces the\nroughnesses and in this process extensive highlands are hardly touched.\nBut, without the assumption, in itself very unlikely, of a nearly level\nsurface on Mars it becomes difficult to comprehend how the canals, if\nfilled with pure water, can proceed in straight lines without reference\nto existing differences in altitude. Like the rivers on the Earth they\nought to bend according to the topography, even if constructed by\nengineers.\n\nWhen the canals freeze at the approach of winter, they invariably\nhave been observed to disappear in company with the lakes or oases\nat their crossings. They are then all covered by the reddish-yellow\ndust carried by wind from the surroundings. When a canal is about to\nreappear it frequently first comes to sight as a dark streak evidently\nthe result of moistened ferro-oxide. Occasionally a mist formation\nprecedes the appearance of the canal. It is plain that the cold, misty\nair settles in the valleys, there as here, and gives up its moisture to\nthe salts on their bottom and the canal is thus brought out as a dark\nline. Sometimes the vicinity also assumes a darker shade indicating\nthe absorption of some moisture. On the sides of the canals the less\nhygroscopic salts are deposited. Possibly the green colour of the\ncanals is partly a contrast-effect due to the red surrounding, possibly\nalso the result of finely divided matter in the liquid. It is also\nconceivable that the cause is the reducing influence on the ferro-oxide\nof the sulphuric gases emerging from the fissures; an exceedingly\nsmall quantity accomplishes in this case large results. F. le Coultre\ndescribes the colour as being sometimes a dead black.\n\nSomething similar applies to the seas. When these freeze, especially in\nshallow places, yellowish-red dust from the continent settles on their\nsurface and lends it hues between the original dark green and the light\nyellowish-red. When the ice subsequently melts this dust sinks in the\nwater which latter resumes its dark green colour.\n\nChloride solutions, if concentrated, freeze at the following\ntemperatures; that of calcium at -55\u00b0\u00a0C. (-67\u00b0\u00a0F.) that of magnesium\nat -44\u00b0\u00a0C. (-48.2\u00b0\u00a0F.) and that of sodium at -22\u00b0\u00a0C. (-7.6\u00b0\u00a0F.). If\nnow, as we previously have seen, the mean temperature of Mars as\na whole is about -40\u00b0\u00a0C. (-40\u00b0\u00a0F.), of the equatorial belt about\n-10\u00b0\u00a0C. (+14\u00b0\u00a0F.), and of the pole in the height of summer about 0\u00b0\u00a0C.\n(32\u00b0\u00a0F.), it is evident that a liquefaction of the ocean surface and of\nthe canals, particularly where salts are deposited, very readily may\ntake place. We should in this connection remember that the ice on Mars\nis stationary while on Earth it is in motion. The consequence is that\nsand and dust in the course of thousands of years have accumulated on\nthe bottom of the shallow basins in the polar ice. These seas appear\ntherefore dark in spite of their exceedingly small depth and the white\nsalt and ice-crystals remaining undissolved are unable to display\ntheir light colour. Even in the \u201cocean,\u201d Lowell was persuaded that he\nhad observed canals (see Fig. 23), and it may be possible that cracks\nare in evidence there, particularly in the most shallow sections, as\nis the case in the Tyrrhenian sea north of Sicily. It is significant\nthat Flammarion has reached the conclusion, which at first appears\nhighly hazardous, that the freezing point of water is lower on Mars\nthan on Earth. This is entirely correct, if we let water stand for salt\nsolutions.\n\nIt is customary to point to the strictly uniform breadth and the\nrectilinear appearance of the canals as clear evidence of their being\nartificial, _i.\u00a0e._, the work of engineers. The Italian astronomer\nCerulli strongly objected to this conception. \u201cIn the exceedingly\nrare cases when both sides of the canal plainly may be seen,\u201d states\nSchiaparelli, \u201cI have observed curves and notches in the borders.\u201d\nThis occurred with the canals Euphrates and Triton in 1879, and with\nthe Ganges in 1888. And it would seem obvious that watercourses\nproduced in old furrows would not, as a rule, be of uniform breadth.\nAntoniadi, by his observations in the autumn of 1909 (see Fig. 17a and\n24), has confirmed this opinion, as has le Coultre, who found twice\nas many irregular canals as rectilinear ones. Antoniadi remarks that\nsome canals appear to be collections of lakes strung out in a certain\ndirection while others are narrow lines which bend and twist. \u201cThe\ncomplicated network of straight lines is probably illusory.\u201d The spots\non Mars, he continues, are very irregular, and \u201cpresent by no means\nany geometrical form\u201d (on which the belief largely is founded that\nthey are the product of intelligent beings). \u201cThe appearance of the\nplanet reminds one of that of the Moon (except that the latter is dead,\n_i.\u00a0e._, unchangeable) or of a terrestrial landscape viewed from a\nballoon.\u201d--\u201cIn a word, the \u2018geometry\u2019 of Mars is revealed as a pure\nillusion.\u201d Exceedingly instructive is a comparison between the two maps\nof Mars drawn by Schiaparelli (1886) and by Antoniadi (1909) reproduced\nhere and found at the end of the volume. While Schiaparelli as a rule\nrepresents the canals as narrow, straight, or slightly curved bands\nof uniform width, these formations on the Antoniadi chart frequently\ndissolve into a series of dark spots joined by less obscure sections\n(see for example the canals Nectar and Oeroe at the Sunlake). The\nsame is true about several of the so-called \u201cseas,\u201d particularly the\nTyrrhenian (Mare Tyrrhenum), and the Sunlake (Lacus Solis); also about\nthe \u201cOcean-bays\u201d such as the well-known Syrtis major which with the\nSunlake form the most conspicuous objects on the surface of Mars. These\nmaps are, moreover, of great interest because several canals and other\nfeatures present on one are absent on the other and vice versa. In this\nway, we obtain a vivid conception of the remarkable changeableness of\nthe Martian surface as contrasted with the exterior of the Earth. The\nlatter, if viewed from Mars, would not have presented any noticeable\nchange in historical time except for the seasonal variation of the snow\nfields. This peculiarity of Mars is only explained by the fact that the\ngeographical features of that planet as a rule are surface formations\nof a slight depth and therefore subject to rapid transformations.\n\nFrequently, large white spots suddenly appear, especially near the\nlakes, such as the spot at Lake Ph\u0153nix near the centre of Fig. 24 which\nrepresents Mars on October 6, 1909, according to Antoniadi. These\nwhite spots disappear as suddenly as they show forth. The white colour\nis probably due to a very thin snow or hoar-frost, which is easily\ncondensed in the vicinity of the lakes but which as readily vanishes at\nthe approach of a warm draft or of sunshine.\n\nOccasionally, dark spots on Mars are described as dissolving under\nstrong enlargement into dark and light squares giving the appearance\nof a chessboard. This reminds one of the bayirs in Turkestan (see Fig.\n9).\n\nThe collections of lakes along the cracks on Mars which appear to\nus as \u201ccanals\u201d are repeatedly filled up by sand and dried out. They\nare revived through new depressions along the dislocation fissures,\ncorresponding to our earthquakes, when vapours of water and other\ngases pour forth and condense to lakes in the deepest pockets of the\nfissures. Canals are therefore created rather rapidly, sometimes over\nnight, and vanish occasionally as suddenly. The most remarkable case of\n\u201cnew\u201d canals was made known through a communication by Lowell. Two new\ncanals, at the time the most conspicuous on the surface of Mars, were\nobserved east of \u201cSyrtis magna\u201d on September 30, 1909, from Flagstaff\nobservatory, when they also were photographed, which precludes an\nillusion. (On the other hand there was no sign of the great canal\nAmenthes, shown on the map Fig. 17, a short distance to the left,\n_i.\u00a0e._, east of Syrtis in the very section where the new canals were\nobserved.) Also two new oases through which the new slightly curved\ncanals passed were observed for the first time, as were also a few\nminor canals in the neighbourhood.\n\nIn 1913, the double canal \u00c6thiops (see map at Long. 240\u00b0; the canal is\nthere single) was rediscovered from the Lowell observatory after an\nabsence of fifteen years.\n\nThese data make it evident that one or possibly several rather strong\nearthquakes took place east of Syrtis major just prior to September\n30, 1909 with the two oases as centres of collapse. The fissures now\nmade visible have probably existed before but filled with sand and have\nnow reappeared as a result of the condensation of water vapour when it\nemerged into the cold Martian air.\n\nThis fact, that the most prominent canals in such manner now suddenly\nappear and now as rapidly vanish, ought to convince us beyond doubt\nthat they are not magnificent products of engineering skill, for the\nconstruction of which we should require centuries on the Earth.\n\nThe theory that intelligent men exist on Mars is very popular. With\nits help everything may be explained, particularly if we attribute an\nintelligence vastly superior to our own to these beings, so that we\nnot always are able to fathom the wisdom with which their canals are\nconstructed. The crossings of the latter are said to be cities (Lowell)\nfifty times greater than London. The trouble with these \u201cexplanations\u201d\nis that they explain anything, and therefore in fact nothing. If we\nwould endeavour to understand the phenomena on Mars, we must in the\nfirst place avoid the formerly so popular principle of \u201cpurposiveness\u201d\nwhich led even the most prominent scientists into so many amusing\nerrors. Neither may we base our conceptions, as does Flammarion, on the\nassumption of natural forces unknown to us, no matter how much such a\ncourse may appeal to mystics. Only forces with which we are familiar\ncan be resorted to, if we really are to understand nature. It seems to\nme that such method of research might with good results be applied also\nto the planet Mars.\n\n\n\n\nCHAPTER VII\n\nMERCURY, THE MOON, AND VENUS\n\n\nThe planet Mercury probably resembles Mars in many respects, but\ndiffers particularly in lacking an atmosphere. The fissures in the\ncrust of the Earth or of Mars are as a rule rapidly filled and their\ncontours largely hidden from sight by alluvium or sand carried by\nwindstorms, so that they reveal themselves only through tremors and\nvarious emanations along their course. The fissures on Mercury on\nthe other hand must remain as yawning chasms. It is probable that\nreducing gases stream out of these cracks as on Earth, and colour\nthe environment in a darker shade than the other visible part of\nthe planet\u2019s surface, that is the hemisphere turned toward the Sun.\nNot very volatile gases, such as sal-ammoniac, other chlorides and\nsulphur, which on the Earth are deposited inside the fissures, may\nhere spread over large areas and discolour surrounding territory,\nparticularly where iron compounds are present, and, under the attack of\nsulphur, turn black. Lowell has made drawings of the dark spots visible\non Mercury, one of which is reproduced as Fig. 25. These spots lie, as\non Antoniadi\u2019s drawing of the surface of Mars (Fig. 17a), arranged in\nlines which are almost straight or of a slight curvature only. This\nseems to indicate that the spots belong to areas immediately adjoining\nenormous fissures. According to Lowell\u2019s drawing, these cracks are\nfar more regularly distributed on Mercury than on Mars. Very close to\nthe centre of the ever-sunny side we see a dark spot, a \u201clake.\u201d It is\nevident that this spot is located in by far the hottest point on the\nsurface of Mercury. This gives rise to the following conception. The\nhottest part of Mercury was naturally the last to solidify. Mercury\nevidently ceased to rotate around its own axis, leaving one side\ncontinually exposed to the Sun, while its surface yet consisted of\nlava that was fluid, at least where the sunshine was most intense. The\nweakest point on the planet was therefore the one just opposite the\nSun. When later collapses occurred the cracks commenced at this weak\npoint. We see on the figure how not less than six fissures radiate\nfrom this centre. Others were formed where the crust broke off from\nadjacent solid portions. These latter fissures have a less rectilinear\nappearance than those diverging from the centre of collapse. Along\nthese faults, reducing gases no doubt issue from the interior of the\nplanet and give a dark tone to the surface layers, which probably\nconsist of ferruginous dust falling from space. In the neighbourhood\nof the Sun, such dust ought to be more plentiful, concentrated as it\nwere by the gravitation of the Sun. Mercury lies five times nearer\nthe Sun than the Earth does, and twelve times nearer than Mars. There\nprobably also exist on Mercury, as on the Moon, large mountains which\nare not subject to the wear of running water and blowing sand. We\ncannot, however, observe them from the Earth. Possibly they correspond\nto the widely extended spots, which several investigators as Schroeter,\nVogel, and others, have noticed, formations resembling the \u201cseas\u201d on\nthe Moon. Vogel believed that he had found traces of water vapour in\nthe atmosphere of Mercury as in that of Mars, a belief in both cases\nundoubtedly founded on erroneous observations.\n\n[Illustration:\n\n Fig. 25. Drawing by Lowell, representing the planet Mercury\n with \u201ccanals.\u201d\n]\n\n[Illustration:\n\n Fig. 26. A part of the moon near its south pole. The big crater\n above, in the interior and on the walls of which a large\n number of smaller craters appear, is Clavius. A little\n below and to the right is Longomontanus just at the edge\n of the shadow; almost in the middle of the picture appears\n Tycho with its central cone. The moon diameter corresponds\n to 43.4 cm. Photo by Yerkes Observatory.\n]\n\n[Illustration:\n\n Fig. 27. Mare Serenitatis (below), Mare Tranquillitatis (upper\n left) and vicinity. To the left of Mare Serenitatis the\n great crater Posidonius; 2.8 cm. from the right edge a\n small white spot may be seen. This is the remarkable\n crater Linn\u00e9, said to have undergone changes. The\n moon diameter corresponds to 35.7 cm. Photo by Yerkes\n Observatory.\n]\n\nThe part of Mercury which is turned from the Sun must be characterized\nby a tremendous cold due to radiation into space. The temperature\nstays probably about 200\u00b0\u00a0C. (360\u00b0\u00a0F.) below the freezing point of\nwater (328\u00b0 below zero F.). Even the most concentrated solutions we\nknow of freeze to ice precipitating the salt considerably above this\ntemperature. Moisture in fluid state can, therefore, not very well\nexist on this side. On the sunny hemisphere it must be lacking as well,\ndue to evaporation over to the cold side. As a result, the desolation\non Mercury must be far greater than that on Mars and surface changes\ncaused by variations in temperature are almost precluded. On account\nof the so-called libration, certain dark portions near the boundary of\nthe illuminated hemisphere occasionally enter the sunlight. But, during\nthis interval, all traces of moisture are undoubtedly driven away from\nthese parts, also never to return.\n\nThe Earth\u2019s moon is not entirely as stagnant as Mercury, although on\nthe whole it closely resembles this planet. The Moon always turns the\nsame side to the Earth--a small libration exists here also--so that\neach part of its surface is illumined by the Sun during one half of the\nsynodical month (29.53 days). This time, however, is so long that the\nmoon\u2019s surface in the meantime almost assumes the temperatures due to\ncontinuous sunlight and continuous night.\n\nSome investigators, as W.\u00a0H. Pickering, are persuaded that portions\nof the moon just emerged from the shadow show a lighter colour than\nafter a short time of illumination. These observations, however, have\nnot been accepted as correct. According to Pickering, the light colour\nshould result from a slight formation of snow or hoar-frost during the\nlong night of 355 hours. If an appreciable trace of vapour existed on\nthe Moon, it ought to evaporate and form white caps over the poles\nwhere the Sun\u2019s heat is not sufficiently strong to melt them. As no\nsuch signs have ever been observed, the faith in snow on the Moon is\nnot likely to find many defenders.\n\nThe lunar mountains are not attacked by water or sandstorms, nor do\nthey peel off due to rapid heating by the Sun. They rise, therefore, to\nfull stature over their surroundings. Their height can be measured by\nthe length of their shadows. M\u00e4dler, in this manner, computed one of\nthe peaks of the Mountain Newton to rise 7300 m. (24,000 ft.) above the\nterritory on which its shadow falls. Six peaks reach between 6000 and\n7000 m. (19,500 and 24,000 ft.), 21 between 5000 and 6000 m. (16,500\nand 19,500 ft.), 82 between 4000 and 5000 m. (13,000 and 16,500 ft.),\nand 582 reach 2000 m. (6500 ft.) and more. These figures show the\nextraordinary mountainous character of the Moon\u2019s surface compared to\nthat of the Earth which is thirteen times larger.\n\nIn Fig. 26, we see a picture of the portion of the Moon most rich in\nvolcanoes, with the crater Tycho in the centre and Clavius above.\n\nThe numerous volcanoes are particularly characteristic of the Moon.\nThey vary in magnitude from a diameter of over 200 km. (125 miles),\nfor example the colossal Clavius with its companion craters, down to\ndimensions just visible with the aid of a telescope. The largest exceed\nour biggest many times in width and differ essentially from them,\ninasmuch as their bottoms are flat, occasionally provided with smaller\nvolcanic cones--see the crater Longomontanus to the right of Tycho on\nFig. 26--and surrounded by a high (inwardly often very steep, outwardly\nmore sloping) wall as on Clavius, Longomontanus, and Tycho. The\nlargest, as for example Clavius, may be compared to a province such as\nBohemia, surrounded as it is on all sides by mountains. The elevated\nring, as well as the interior of Clavius, is adorned with numerous\nlarge and small craters. The smallest of these resemble hemispherical\nexcavations in the crust of the Moon, or they may be small volcanic\ncones which break through the walls. Sometimes they are strung out like\npearls along rents in the ground.\n\nAll these volcanoes have undoubtedly given passage from the interior\nto the surface of the Moon for enormous volumes of gases previously\nenclosed in the lunar magma. Nor is it less certain that these gases\nhave consisted largely of water vapour. If this had been condensed to\nwater, oceans and rivers would have been formed, and on the bottom\nof the seas would have been deposited sediments carried down from\nthe mountains. Such, however, is not the case. The so-called \u201cseas\u201d\non the Moon are indeed on a lower level than their surroundings, but\ntheir surface is even (see Fig. 27 with Mare Serenitatis below and\nMare Tranquillitatis above to the left; see also Fig. 29 with Mare\nImbrium below; it is bounded on the right by the \u201cCarpathians\u201d). The\n\u201cseas\u201d consist of volcanic rocks, and are not at all covered with loose\nsediments which if present ought to reflect light better than the\nvolcanic vitreous rocks. But the lunar \u201cseas\u201d are much darker than the\nenvironments. This shows that seas proper, or bodies of water, have\nprobably never existed on the Moon. Even before the surface had changed\nfrom its molten condition the water vapour had departed from the\natmosphere, and the new quantities which the volcanoes emitted from the\ndepths below disappeared so rapidly that lakes were never formed. The\nhistory of other atmospheric gases on the Moon was no doubt similar.\nAll evidence, therefore, points to the conclusion that life never\ninhabited its rough surface. Fig. 27 shows that the \u201csea-bottoms\u201d are\nnot free from volcanoes. They also abound in folds, corresponding to\nmountain-chains on the Earth. These folds indicate old breaks in the\ncrust while it was yet very thin. To the right, in Mare Serenitatis,\nappear a few white spots which W.\u00a0H. Pickering ascribed to snow. The\nlargest is the much discussed \u201ccrater\u201d (?) Linn\u00e9. Mare Serenitatis is\nsurrounded by a ring of volcanoes.\n\nA noted astronomer, Cerulli, observed, when he directed a glass of\nmoderate power, such as opera glasses, toward the Moon that the spots\nseemingly arranged themselves in rows forming intersecting lines\nsimilar to the canal-system on Mars. As the regularity disappeared\nwith greater enlargement, Cerulli believed that the canal-system on\nMars also would dissolve into small spots if a sufficiently powerful\ntelescope were used. His idea, which partly has been verified, was more\nrecently adopted by the Englishman, Maunder, who denies the existence\nof canals on Mars. Photography, however, has proved their reality (Fig.\n18).\n\nIf we disregard the illusory reticulation, there are nevertheless\non the surface of the Moon numerous designs of a nearly rectilinear\noutline. There are to begin with the sinuses, extended trenches,\noften dotted along their sides with minor volcanoes. Fig. 27 shows,\nin the upper right corner, two such sinuses, the right one with a\nsmall volcano, Hyginus, in the middle. There are, further, five\nsuch volcanoes in its left arm, not visible on the photograph, and\ntwo in the right arm. The second, \u201cSinus Ariadaeus,\u201d commences to\nthe left with the Volcano Ariadaeus, not visible on the figure. The\nexplanation of the origin of these sinuses is probably to be found in\nthe different contraction of the Moon\u2019s surface layer and of the hotter\nsubstrata immediately after the solid crust was formed. In a way, they\ncorrespond therefore to cracks in the glazing on porcelain. Like the\ntwo sinuses just mentioned they frequently commence and end with small\ncraters which formed weak spots in the crust that facilitated the\noriginal break. Later on, volcanoes broke through along the sinuses\nthemselves. In several regions of the Moon, and particularly in the\nequatorial belt, observers have claimed discoveries of new sinuses\nand occasionally of minor craters, \u201cwhich could not possibly have\nescaped notice if they had existed before.\u201d At present, the almost\nunanimous verdict is that such changes are very improbable, and that\nthe visibility of the \u201cnew\u201d objects largely depends on favourable\nsidelight, so that they might well have been overlooked if the\nregion in question previously was examined under less advantageous\nillumination.\n\nThe most peculiar formations on the Moon are the so-called \u201cbright\nstreaks\u201d which as a rule issue in almost straight lines from some of\nthe larger craters, particularly Tycho and Copernicus. Those around\nTycho (see Fig. 28) do not seem to be either raised above nor depressed\nbelow the surroundings to any degree worth mentioning. For this reason\nthey are not visible under oblique illumination as in Fig. 25. They\nproceed in straight lines independent of elevations. This quality\nis in striking conformity with the characteristics of fissures on\nearth as for instance those that traverse the Tyrrhenian Sea and the\nCalabrian mountains. They also resemble the canals on Mars in this\nrespect. Nasmyth and Carpenter caused a glass ball, containing water\nunder pressure, to break at one point and obtained a system of beams\nradiating from this point and vividly reminding of the streaks around\nthe lunar craters. The same effect appears if a homogeneous plate, of\nglass for instance, is broken by a blow in one point. No doubt these\nstreak centres were once centres of collapse although they sometimes\nnow are found at a considerable elevation, like Tycho. This may be\nthe result of a later secular lifting of the rocky substrata like the\nslow rise of the Scandinavian peninsula. The streaks around Copernicus\n(see Fig. 29) are very different from those around Tycho. They are not\nrectilinear and consist next to the crater of distinct mountain chains\nplainly visible under oblique illumination. They penetrate into Mare\nImbrium (Fig. 29 below) crossing the mighty \u201cCarpathian\u201d mountains.\nFrequently, they are provided with minor volcanoes, as in the streak\ndirected almost straight downward on the figure, _i.\u00a0e._, to the north.\nThey are obviously volcanic fissures like those on the Earth.\n\n[Illustration:\n\n Fig. 28. Tycho in full illumination with surrounding magnificent\n system of streaks. In the lower right corner Copernicus\n with a less regular system appears. Between them Mare\n Nubium, in the upper right Mare Humonum, with the\n great crater Gassendi below. The moon diameter\n corresponds to 16.7 cm. Photo by Yerkes Observatory.\n Compare Figs. 25 and 28, showing parts of the same\n territory under side light.\n]\n\nThe streaks, in many cases, would not be visible at all were it not\nfor their different colour, which is considerably lighter than that\nof the surroundings. The only explanation offered for this fact is\nthe assumption that the original cracks were filled by some light\nmatter forced out from the interior of the Moon, that is by the\nlunar magma. This magma was not very viscous, as it has spread out\nconsiderably beyond the edges of the cracks proper. These presumably,\nlike those on Earth, were of a rather moderate width, not enough to\nbe distinguishable at the Moon\u2019s distance. Similar light-flowing\nemanations from long fissures are known also on our planet, for\ninstance, from the Laki eruption on Iceland in 1783. The colour\nmay be light simply by comparison with the previously solidified\ncrust, which, optically, as regards reflexion of light, has proved\nvery similar to obsidian or, even more like another volcanic mineral\nproduct, vitrophyre. It is also possible, however, that gas bubbles\nwere liberated as the lava solidified and gave the surface a milkwhite\nappearance--gravity on the Moon is only one sixth of that on the Earth\nso that the bubbles would rise and evaporate extremely slowly from\nthe magma. Due to the very low atmospheric pressure on the Moon, the\nbubbles would also occupy a larger volume than in a corresponding case\non Earth and become more conspicuous in proportion. They probably\npartly remained on the surface of the outpoured lava as a thin scum,\nwhich hardened in that state. Since then, it has suffered no more\nchange than all other formations on the Moon, while on the Earth it\nwould soon have been scoured away by sand and water.\n\n[Illustration:\n\n Fig. 29. The great lunar crater Copernicus surrounded with streaks.\n Below the Carpathian mountain range and at bottom part of\n Mare Imbrium. The moon diameter corresponds to 55 cm.\n Photo by Yerkes Observatory.\n]\n\nBefore we leave the Moon it may be well to say a few words about its\ncolour. M\u00e4dler states in agreement with several other observers that\nMare Serenitatis, a \u201csea\u201d on the Moon\u2019s north side (25\u00b0 latitude) just\nto the right of the centre meridian (see Fig. 27) is remarkable for\nits beautiful pure green colour, while Mare Crisium about 16\u00b0 Lat. N.\nnear the right edge of the Moon is of a dark grey-green hue. In Mare\nHumorum (about 22\u00b0 Lat. S., not far from the edge of the Moon, see Fig.\n28) grey and dark green shades alternate and in Mare Frigoris, just\ninside the lunar north pole, the colour is a dingy yellowish-green.\nIn other words, the characteristic colour of the great lava seas is\napparently green. This agrees closely with conditions on the Earth\nwhere similar formations are coloured green by silicates of ferrous\nprotoxides, certain species of which are called green-stones. Franz,\nhowever, questions the observations of M\u00e4dler and professes the belief\nthat very light craters appear bluish and assumes this to be a contrast\neffect to the general yellow hue of the Moon. Langley investigated the\nlunar radiation with the spectroscope and found that the ratio of\nblue to yellow was smaller in the moonlight than in the sunlight, for\nwhich reason the general colour of the moon resembles that of yellow\nsandstone.\n\nA very interesting observation was made at the Lowell observatory when\ninvestigating the spectrum of the sparse light reflected from the Earth\nto the portions of the Moon not exposed to the sunlight. It proved to\nbe of a far more blue tinge than sunlight reflected from the Moon.\nOur conclusion must be that the Earth shines with a blue lustre. This\nis perfectly natural, as the diffused light which reaches us after\nhaving been scattered by particles suspended in the air (and by gas\nmolecules as well) is a deep blue and there exists no reason why that\npart of the light which is thrown outward into space should be of a\ndifferent colour. The Earth, therefore, is blue in contradistinction\nto Mars which is red, on account of its desert surface, and Venus\nwhich is bright white. The cloudy portions around the equator and the\npoles should appear light blue from without and should be separated\nby dark blue bands over the so-called horse latitudes, under which the\ncloudless desert regions are located on either side of the equator.\n(Compare the title page illustration.)\n\nCompared to Mars the Moon offers a scene of far greater desolation.\nOn Mars, we observe at least some considerable changes such as the\ndisappearance of the white pole-caps at midsummer when at the same time\na dark ring appears to surround them; then the \u201clakes\u201d and the \u201ccanals\u201d\ncome into view, beginning close to the ring mentioned, later on\nnearer the equator, and finally on its other side, while the opposite\npole-cap puts on its winter hue. Again, we have the sudden appearance,\nand equally hasty disappearance, of white spots, particularly in the\nneighbourhood of the lakes, and the sand storms which hide the surface\nof Mars and often fill its canals. The abruptness of the changes\nindicate that they are confined to a very thin surface layer. The\nformation, on the other hand, of canals, for many years unobserved,\nmust be ascribed to a volcanic activity which, while feeble, yet must\nbe seated in the deeper portions of the planet. In addition, a stunted\nvegetation of low forms is not unthinkable in the polar regions.\n\nAs against this, the Moon is undoubtedly a stellar body entirely\ninsusceptible of surface change. Near its centre, it is probably not\ncompletely solidified and an extremely slow growth of the firm crust\nis therefore likely. Gases are no doubt set free during this process,\nbut they are unable to penetrate the enclosing thick armour and remain\ntherefore as bubbles in the hardening magma.\n\nAs a matter of fact, no changes have, with certainty, been detected on\nthe Moon\u2019s surface. It is true that the great Wm. Herschel, known as\nan excellent observer, believed that he discovered, in 1873, mountains\nwhich had not existed before that time, and Schr\u00f6ter, who diligently\nstudied the lunar surface, was of the opinion that he too had discerned\nnumerous changes. These discoveries, however, were doubted by careful\ncritics, and after the publication of M\u00e4dler\u2019s great work about the\nMoon (1837) the complete stagnation on that body was taken for granted.\nNevertheless, there are several astronomers, such as Schmidt in Athens\n(1866) and lately W.\u00a0H. Pickering in Cambridge, Mass., who think that\nthey have discerned considerable modifications. The former held that\nthe crater Linn\u00e9 (Fig. 27) had vanished since the publication of\nM\u00e4dler\u2019s work. In 1867, M\u00e4dler, himself, proclaimed that it had the\nsame appearance as before. Pickering, again, reports periodic changes\nof \u201csnow\u201d and \u201cvegetation.\u201d (Compare Fig. 27 taken from Pickering\u2019s\nMoon-atlas.) Closer analysis, however, indicates that the phenomena\nare probably only apparent and depend on the angle of illumination at\neach particular time of observation. For some time, rather more than\na quarter of a century, photography has been pressed into the service\nof lunar investigation with far more objective results than would be\npossible through direct ocular inspection alone. During this period,\nwhich, it must be admitted, is not very long, no distinct signs of\nchanges have been recorded by the photographic plates.\n\nThe great difference between Mars and the Moon depends upon the\nexistence of a real atmosphere on the former. The oxygen will probably\nvanish from Mars also, being used up in the course of disintegration.\nBut nitrogen, argon, and the other permanent gases will always remain,\nas will the water vapour from the bodies of water ever present,\nparticularly around the south pole. It is true that this water vapour\nalso will diminish with sinking temperature and when the latter finally\nhas reached the freezing point of the salt solutions on Mars, the\ncanals and the lakes will cease to thaw out or liquify under the vapour\ndistilled over from the warm to the cold pole. But sand storms and thin\nmist formations will always appear and cause colour changes on the\ndesolate planet.\n\nIf we wish to picture to us the future fate of our Earth when it\ngradually enters the reign of darkness and cold in consequence of the\nenfeebling of the Sun, we must seek our illustration on Mars and not\non the Moon. Slowly are the oceans going to freeze, finally down to\ntheir bottom, the abundance of the rainfalls will diminish, only light\nsnow will now and then bring change to a surface evermore transformed\ninto a sand desert as far as the continents reach. Rents in the rocky\nsubstrata of the latter will appear as dark lines, caused by the gases\nrising from the interior. When the temperature at the equator has\nfallen below the freezing point, the polar regions will remain the only\nparts where a light covering of frost will melt in the height of the\nsummer season and where the last feeble organisms will eke out their\nhard existence, resorting to a prolonged winter\u2019s sleep of their seeds\nand spores. Finally, the last remnant of life will also disappear and\nsandstorms alone, save for the gasps of gas emanation from fissures\nin the rocky ground, will bring relief to the monotonous desolation.\nFalling meteoric dust, which now exists in original state only on\nthe bottom of the oceans, will gradually cover the entire surface of\nthe Earth with a mantle coloured brick-red through the influence of\natmospheric oxygen. When the oxygen itself is used up, the meteoric\ndust will retain its original greyish-green hue and lend it to the\nfuneral pall of the Earth.\n\nVery different conditions obtain on our neighbour planet, which is\ncloser both to the Sun and to ourselves, the radiant Venus, an object\nof interested human attention already in ancient times. The average\ntemperature there is calculated to about 47\u00b0\u00a0C. (116.6\u00b0\u00a0F.) assuming\nthe sun constant to two calories per cubic centimeter (.061 cu. in.)\nper minute. The humidity is probably about six times the average of\nthat on the Earth, or three times that in Congo where the average\ntemperature is 26\u00b0\u00a0C. (78.8\u00b0 F). The atmosphere of Venus holds about\nas much water vapour 5 km. (3.1 miles) _above_ the surface as does the\natmosphere of the Earth _at_ the surface. We must therefore conclude\nthat everything on Venus is dripping wet. The rainstorms on the other\nhand do not necessarily bring greater precipitation than with us. The\ncloud-formation is enormous and dense rainclouds travel as high up as\n10 km. (6.2 miles). The heat from the Sun does not attack the ground\nbut the dense clouds, causing a powerful external circulation of air\nwhich carries the vapour to higher strata where it condenses into\nnew clouds. Thus, an effective barrier is formed against horizontal\nair currents in the great expanses below. At the surface of Venus,\ntherefore, there exists a complete absence of wind both vertically, as\nthe Sun\u2019s radiation is absorbed by the ever present clouds above, and\nhorizontally due to friction. Disintegration takes place with enormous\nrapidity, probably about eight times as fast as on the Earth, and the\nviolent rains carry the products speedily downhill where they fill the\nvalleys and the oceans in front of all river mouths.\n\nA very great part of the surface of Venus is no doubt covered with\nswamps, corresponding to those on the Earth in which the coal deposits\nwere formed, except that they are about 30\u00b0\u00a0C. (54\u00b0\u00a0F.) warmer. No\ndust is lifted high into the air to lend it a distinct colour; Only\nthe dazzling white reflex from the clouds reaches the outside space\nand gives the planet its remarkable, brilliantly white, lustre. The\npowerful air currents in the highest strata of the atmosphere equalize\nthe temperature difference between poles and equator almost completely\nso that a uniform climate exists all over the planet analogous to\nconditions on the Earth during its hottest periods.\n\nThe temperature on Venus is not so high as to prevent a luxuriant\nvegetation. The constantly uniform climatic conditions which exist\neverywhere result in an entire absence of adaptation to changing\nexterior conditions. Only low forms of life are therefore represented,\nmostly no doubt belonging to the vegetable kingdom; and the organisms\nare nearly of the same kind all over the planet. The vegetative\nprocesses are greatly accelerated by the high temperature. Therefore,\nthe lifetime of the organisms is probably short. Their dead bodies,\ndecaying rapidly, if lying in the open air, fill it with stifling\ngases; if embedded in the slime carried down by the rivers, they\nspeedily turn into small lumps of coal, which, later, under the\npressure of new layers combined with high temperature, become particles\nof graphite. Fossils proper are not formed as was also the case in the\nearly periods of the Earth.\n\nThe temperature at the poles of Venus is probably somewhat lower,\nperhaps about 10\u00b0\u00a0C. (18\u00b0\u00a0F.) than the average temperature on the\nplanet. The organisms there should have developed into higher forms\nthan elsewhere, and progress and culture, if we may so express it,\nwill gradually spread from the poles toward the equator. Later, the\ntemperature will sink, the dense clouds and the gloom disperse, and\nsome time, perhaps not before life on the Earth has reverted to its\nsimpler forms or has even become extinct, a flora and a fauna will\nappear, similar in kind to those that now delight our human eye, and\nVenus will then indeed be the \u201cHeavenly Queen\u201d of Babylonian fame, not\nbecause of her radiant lustre alone, but as the dwelling place of the\nhighest beings in our solar system.\n\nThe ancients believed that the fates of men could be read in the\nstars and this faith persisted with the power of a religion until\na few centuries ago. It was shared by the foremost astronomers,\npre-eminently by Tycho Brahe, who endeavoured to support it through\nhis investigations. Traces are yet to be found in popular conceptions.\nThese ideas have been verified today in a certain sense although with a\nwholly different meaning than held by our forefathers. The planets do\ntell us the conditions that existed on the Earth at the first dawn of\nlife and we can also draw from them a prediction of the fate that once,\nafter milliards of years perhaps, will befall the latter descendants of\npresent generations.\n\nIn one respect the dreams of our ancestors have not proved true,\nnamely, with reference to the habitability of the other globes in our\nsolar system. According to the great Kant, conditions on the wandering\nstars outside of the Earth\u2019s orbit were so favourable to life that\ntheir inhabitants ought to have reached a far higher development than\nbeings on the Earth. The last remnant of this conception lives in the\nspeculations about the marvellously proficient engineers who built the\nmagnificent system of giant canals on Mars. A thorough critique has\ndemonstrated that any other planet in our solar system hardly can offer\nan abode for higher beings, except this very Earth, which therefore\njustly may be called \u201cthe best of worlds\u201d among those that we know. And\nyet, it was undoubtedly a great truth that Giordano Bruno gave his life\nfor, because it is highly probable, nay almost certain, that around\nthe countless suns which dot the firmament spin dark bodies, although\nunfortunately our most powerful lenses do not reveal them. A number\nof these unseen stellar bodies shelter living beings, which even might\nhave climbed to a higher point on the ladder of evolution than have the\ninhabitants of the Earth.\n\n[Illustration:\n\n Fig. 17. Map of the planet Mars in Mercator\u2019s projection\n according to drawing by Schiaparelli. A comparison\n with the drawing by Antoniadi (Fig. 17a) suggests that\n Schiaparelli has made a somewhat diagrammatic picture,\n which sets forth a very great number of strictly straight\n \u201ccanals.\u201d\n]\n\n[Illustration: Fig. 17a. Map of the planet Mars in Mercator\u2019s\nprojection, drawn in 1909 by E.\u00a0M. Antoniadi.\n\n Explanations: Meredies = south; Oriens = east; Occidens = west;\n Septentrio = north; Nix = snow.\n Abbreviations: M = Mare, sea; S = Sinus, bay; Fr = Fretum, channel;\n L = Lacus, lake; Fl = Flumen, river;\n R = Regio, region; I = Insula, island;\n Pr = Promontorium, cape.\n]\n\n\n\n\n _A Selection from the\n Catalogue of_\n\n G.\u00a0P. PUTNAM\u2019S SONS\n\n \u2767\n\n Complete Catalogue sent\n on application\n\n\nThe Essence of Astronomy\n\nThings Every One Should Know About the Sun, Moon and Stars\n\nBy Edward W. Price\n\n _12mo. Fully Illustrated. Price $1.50. By mail, $1.65_\n\nHere is a volume quite different from the usual \u201cpopular book on\nastronomy.\u201d\n\nIt answers in untechnical language the every-day questions of every-day\npeople, the material being so arranged that it is readily available for\nquick reference use, as well as for interesting consecutive reading.\n\nAn individual chapter is devoted to each member of the Solar System.\nSpecial space is given to \u201cFreaks and Oddities of the Skies.\u201d\n\nThe illustrations are from photographs taken at the great\nobservatories. The drawings of Mars are the most recent published,\nbeing made by Professor Lowell in January of this year.\n\nThe chronological table and annotated bibliography are of real value.\n\n\nSun Lore of All Ages\n\nA Collection of Myths and Legends Concerning the Sun and its Worship\n\nBy William Tyler Olcott\n\nAuthor of \u201cStar Lore of All Ages,\u201d \u201cA Field Book of the Stars,\u201d etc.\n\n _8^o. With 30 Illustrations. $2.50 net. By mail, $2.70_\n\nA companion volume to _Star Lore of All Ages_ by the same author. It\ncomprises a compilation of the myths, legends, and facts concerning the\nsun, of equal interest to the lay-reader or to the student.\n\nThe literature of the subject is teeming with interest, linked as it\nis with the life story of mankind from the cradle of the race to the\npresent day, for the solar myth lies at the very foundation of all\nmythology, and as such must forever claim pre-eminence.\n\n G.\u00a0P. Putnam\u2019s Sons\n\n New York London\n\n\nA Beginner\u2019s Star-Book\n\nAn Easy Guide to the Stars and to the Astronomical Uses of the\nOpera-Glass, the Field-Glass, and the Telescope\n\nBy Kelvin McKready\n\n _Square 8vo. Including 70 Illustrations._\n _$2.75 net. Postage Additional_\n\nThis volume, peculiarly definite and helpful in method, is especially\nadapted to the practical needs of those who wish a well illustrated\nand clearly written handbook,--accurate in its scientific information\nand yet popular enough to meet the wishes of the average man or woman.\nThe book is distinguished from other volumes on popular astronomy by\na novel system of mapping, and by an unusually full discussion of the\nuses of the simpler astronomical instruments. Special care has been\ngiven to reproductions of recent astronomical photographs.\n\n\u201c_Mr. McKready\u2019s book is the finest thing for the beginner that I have\never seen. It is a pleasure to read a book so excellent in so many\ndifferent ways. I have never seen photographs reproduced better. I have\nnever seen maps of the heavens so intelligible to the beginner, and\nI have never read explanations so concise and yet so complete as in\nthis book._\u201d--Prof. S.\u00a0A. Mitchell, Department of Astronomy, Columbia\nUniversity, New York City.\n\n New York G.\u00a0P. Putnam\u2019s Sons London\n\n\nA Revised Edition of a Standard Work\n\nA Field Book of the Stars\n\nBy William Tyler Olcott\n\nAuthor of \u201cStar Lore of All Ages,\u201d etc.\n\n _Second Edition, Revised. With Additional Material. 16^o._\n _With Fifty Diagrams. $1.00 net. By mail, $1.10_\n\nIn the new edition of this standard work the author has given full\ninformation, together with diagrams representing the result of the\nlatest investigations. All matters of a technical or theoretical nature\nhave been omitted. Only what the reader can observe with the naked eye\nor with an opera-glass have been included in it.\n\nExcellently arranged and copiously illustrated, this manual is a real\nfield-book and will prove valuable for all who wish to become familiar\nwith the stars.\n\n New York G.\u00a0P. Putnam\u2019s Sons London\n\n\nStar Lore of All Ages\n\nA Collection of Myths, Legends, and Facts, Concerning the\nConstellations of the Northern Hemisphere\n\nBy William Tyler Olcott\n\nAuthor of \u201cA Field Book of the Stars,\u201d etc.\n\n _8^o. With 164 Illustrations and Diagrams_\n _$3.50 net. By mail, $3.75_\n\n\u201cA sumptuous treasure-house in which the lover of ancient myth and\nmodern miracle may wander for enchanted hours. Its red and gold\ndoors open upon a gallery of masterpieces in art, all being inspired\nconceptions connected in some way with star lore. The pictures and\nthe legends of all ages have been ransacked to make this gallery\nirresistible to art and nature lovers, and not in vain. Withal the most\nintense facts of astronomical knowledge and discovery are given beside\nthe tapestried romance which earlier peoples wove with star-stuff as\nthe medium of their art. It is a book delightful to the eye, scholarly\nin conception and treatment, and charming to the inner sense.\u201d--From\n_Scientific American._\n\n\u201cHere all the myths, legends, and facts relating to all our northern\nconstellations are set forth fully as well as with scientific\nexactness, are illustrated with clear maps and diagrams, and are\nbrought into close association with their classic origins by\nbeautifully reproduced photographs of works of art and architecture.\u201d\n\n _The Outlook._\n\n New York G.\u00a0P. Putnam\u2019s Sons London\n\n\n\n\nTranscriber\u2019s Notes\n\n\nPunctuation and spelling were made consistent when a predominant\npreference was found in this book; otherwise they were not changed.\n\nSimple typographical errors were corrected; occasional unbalanced\nquotation marks retained.\n\nThe spelling and accent marks of non-English words have not been\nchanged.\n\nAmbiguous hyphens at the ends of lines were retained; occurrences of\ninconsistent hyphenation have not been changed.\n\nIllustrations have been moved, when necessary, to fall between\nparagraphs and outside of quoted text. In some cases, this places them\non different pages than the ones given in the Table of Illustrations.\nIn versions of this eBook that support \u201clinks\u201d, the page numbers in\nthat table link to the correct illustrations.\n\nWide tables on pages 113 and 146 have been split to fit within\nrecommended width limits. The left-hand identifier columns have been\nduplicated in both halves of the split tables.","title":"The Destinies of the Stars","tradition":"scripture-revelation","translated_text":null,"word_count":47486}