{"collection":"philosophy-ethics","full_text_available":true,"graph_url":"https://unchartedknowledge.5gfusion.net/v2/api/page/gutenberg_64537/graph","html_url":"https://unchartedknowledge.5gfusion.net/v2/page/gutenberg_64537","id":"gutenberg_64537","license":"Public Domain (US)","rights_basis":"gutenberg_metadata_copyright_false","source":"gutenberg","source_url":"https://www.gutenberg.org/ebooks/64537","summary":null,"tags":["Category: History - Other","Category: Philosophy & Ethics","Category: Science - Physics","Cosmogony"],"text":"MODERN COSMOGONIES\n\n\n\n\nBy the Same Author\n\n\nA POPULAR HISTORY OF ASTRONOMY DURING THE NINETEENTH CENTURY\n\n FOURTH EDITION.\n DEMY 8VO., CLOTH, ILLUSTRATED\n PRICE 15s. NET\n\n\nPROBLEMS IN ASTROPHYSICS\n\n DEMY 8VO., CLOTH, ILLUSTRATED\n PRICE 20s. NET\n\n\nTHE SYSTEM OF THE STARS\n\n SECOND EDITION\n DEMY 8VO., CLOTH, ILLUSTRATED\n PRICE 20s. NET\n\n\nA. & C. Black \u00b7 Soho Square \u00b7 London, W.\n\n\n\n\n '_The world's a prophecy of worlds to come._'--Young\n\n MODERN\n COSMOGONIES\n\n BY\n\n AGNES M. CLERKE\n\n HON. MEM. R.A.S.\n\n AUTHOR OF\n\n 'A POPULAR HISTORY OF ASTRONOMY DURING THE NINETEENTH CENTURY,'\n 'THE SYSTEM OF THE STARS,' 'PROBLEMS IN ASTROPHYSICS,'\n AND OTHER WORKS\n\n LONDON\n\n ADAM AND CHARLES BLACK\n\n 1905\n\n\n\n\nPREFACE\n\n\nOf the sixteen chapters constituting this little work, thirteen have\nbeen published as a series, begun in _Knowledge_ and continued in\n_Knowledge and Illustrated Scientific News_, and to the proprietors of\nthose journals, for their courteous permission to reprint them, I offer\nmy sincere thanks. Three additional chapters, equivalent to, though\nnot identical with, those that now appear, formed an integral part\nof the original plan of the book, now presented to the public in the\nhope that it will enable general readers to follow, with the profound\ninterest it should inspire, the course of modern inquiries regarding\nthe origin of the world. Their advance is by no means smooth or facile.\nMany difficulties and perplexities are encountered in the attempt to\nget back towards the beginning of things. Some of the old tracks, too,\nhave been torn up by the pioneers of twentieth century science, and\nthe process of constructing new ones, which shall lead further into\nthe unknown fore-time, is slow and laborious. But the rail-head in the\ndesert is a peculiarly suggestive place of pilgrimage, and several such\noutlying posts and temporary halting-places are more or less vaguely\nlocalized in the following pages.\n\n London, _November, 16, 1905_.\n\n\n\n\nCONTENTS\n\n\n CHAPTER                                             PAGE\n\n I. FROM THALES TO KANT                                1\n\n II. THE NEBULAR HYPOTHESIS                           21\n\n III. CRITICISMS OF THE NEBULAR HYPOTHESIS            39\n\n IV. THE NEBULAR HYPOTHESIS VARIED AND IMPROVED       60\n\n V. TIDAL FRICTION AS AN AGENT IN COSMOGONY           83\n\n VI. THE FISSION OF ROTATING GLOBES                  100\n\n VII. WORLD-BUILDING OUT OF METEORITES               118\n\n VIII. COSMOGONY IN THE TWENTIETH CENTURY            135\n\n IX. PROTYLE: WHAT IS IT?                            150\n\n X. UNIVERSAL FORCES                                 166\n\n XI. THE INEVITABLE ETHER                            183\n\n XII. THE FORMS OF NEBUL\u00c6                            199\n\n XIII. THE PROCESSION OF SUNS                        216\n\n XIV. OUR OWN SYSTEM                                 232\n\n XV. REMNANTS AND SURVIVALS                          250\n\n XVI. LIFE AS THE OUTCOME                            265\n\n INDEX                                               283\n\n\n\n\nMODERN COSMOGONIES\n\n\n\n\nCHAPTER I\n\nFROM THALES TO KANT\n\n\nVery few even of the most savage tribes are content to take the world\njust as it is without speculating as to how it came to be. For time\nhas three dimensions--past, present, and future--and we can no more\nrestrict our thoughts within one of them than we can exist corporeally\nin Flatland. We are, indeed, told that the Abipones and Esquimaux\nrefuse to trouble themselves with questions of origin, on the ground\nthat the hard facts of life leave no room for otiose discussions;\nbut even they feel obliged to justify their incuriosity. In easier\ncircumstances they, too, would claim the entirely human privilege of\n'looking before and after,' as their forgotten progenitors may have\ndone. It is, indeed, difficult to think at all about the framework of\nnature without attempting to divine, were it only by a crude surmise,\nthe process of its construction. We are instinctively convinced that\nthere is no such thing as fixity of condition. So far, Heracleitus was\nin the right.\n\nExperience tells us of continual change in ourselves and whatever\nsurrounds us. Reason teaches us that its minute momentary effects, if\npursued backward for an indefinite time, must sum up to a prodigious\ntotal. No limit, that is to say, can be put to the difference\nbetween what is and what was. Yet the machinery of modification\nmust somehow have been set going. An initial state is prescribed by\nlogical necessity. And the start was made on certain terms--it was\n'conditioned.' But the conditioned implies the absolute; ordinances, an\nenactive power. The inevitableness of the connection has been more or\nless obscurely perceived wherever men have tried to establish some kind\nof accord between phenomena and intuition, with results legible in the\nwavering outlines of many primitive cosmogonies. Only, however, in the\nHebrew Scriptures has the idea of Creation been realized in all its\nfulness and freedom; elsewhere the gods invoked to bring the world into\nexistence themselves demanded a birth-history, a theogony being the\nusual and necessary prelude to a cosmogony.\n\nNevertheless 'picture-thoughts' (it has been well said),[1] and nothing\nmore, were represented by these prefatory genealogies. Night and\ndarkness loomed into personal shape, and from the obscurity of their\nunion the creatures of light radiantly sprang, and proceeded, according\nto a predetermined law of order, to sort out the elements of chaos and\ndispose them into cosmical harmony.\n\nThis mythical phase of thought terminated in Greece with the rise\nof the Ionian School of Philosophy. Immemorial legends, discredited\nby the advent of a new wisdom, took out a fresh lease of life under\nthe guise of folk-lore; Orphic fables were left to the poets and the\npeople; and the sage of Miletus set on foot a speculative tradition,\nmaintained by a long succession of metaphysicians down to the very\nthreshold of the recent scientific epoch. All were what we should call\nevolutionists--Thales of Miletus no less than Descartes and Swedenborg;\ntheir main object, in other words, was to find a practicable mode of\nevoking a systematic arrangement of related parts from the monotony\nof undifferentiated confusion. Now, in essaying this enterprise they\nencountered two distinct problems. One was concerned with the nature\nof the primeval world-stuff; the other with the operations to which it\nhad been submitted. Modern theorists have made it their primary object\nto expound the mechanism of cosmic growth--the play of forces involved\nin it, the transformations and progressive redistribution of energy\nattending it. But questions of this kind could only in the scantiest\nmeasure be formulated by early thinkers, who accordingly devoted their\nchief attention to selecting an appropriate material for the exercise\nof their constructive ingenuity.\n\nThales asserted all things to have been derived from water, and\nwater is still among unsophisticated tribes the favourite 'Urstoff.'\nAnaximenes substituted air. Heracleitus gave the preference to the\nmobile and vital element (as he thought it) of fire. Anaximander,\non the other hand, might put forward a colourable claim to priority\nover Sir William Crookes in the invention of 'protyle.' He imagined\nas the matrix of the world a boundless expanse of generalized matter,\ncontaining potentially all the chemical species, which, separating out\nby degrees through the affinity of like for like, formed, by their\ncontrasts and conjunctions, the infinitely varied sum of things.\nThe successors of Anaximander had recourse to spontaneously arising\ncondensations and rarefactions as the mainspring of development; but\nall these vague principles were quickly crowded into oblivion by the\ndefinite and intelligible doctrine of the 'four elements' enunciated\nby Empedocles, which, guaranteed by the imprimatur of Plato, took a\nplace unchallenged for nearly two millenniums among the fundamentals\nof science. Erroneous and misleading though it was, it yet served as\na means of regulating appearances and guiding vagrant ideas--it was a\ntrack to follow in the absence of any better method of orientation.\n\nLeucippus and his more famous disciples, Democritus and Epicurus, were\nthe first who ventured to trace the mechanical history of the cosmos.\nTheir primordial atoms were endowed with weight, and it was weight\nor gravity which ultimately determined their spacial arrangement and\nmutual relations. Rectilinear in the first draft of the scheme, their\nmovements were somewhat arbitrarily deflected by Epicurus; and the\ngyrations thence ensuing eventually became, so to speak, authentic and\nprecise in the Cartesian vortices and in Swedenborg's solar maelstrom.\nKant's _Natural History_ of the universe was another, though an\nentirely separate branch of the atomistic stock. The Democritean atoms,\nhowever, and in a lesser degree the Kantian atoms, differed essentially\nfrom the ultimates of chemical analysis postulated by Dalton. They were\na scratch lot--an incongruous assortment of fragments, rather than of\nelementary portions of matter, indefinitely various in size, shape, and\nmass.\n\nNor was this diversity created as a mere play of fancy. It was\nstrictly necessary to the plan of action adopted. For, apart from\nheterogeneity, there could obviously be no development. Absolute\nuniformity involves absolute permanence. Change can originate only\nthrough inequality. There must be a tilt of level before the current\nwill begin to flow; some cause of predominance is needed to set it\ngoing in a given direction. Here, of a surety, is the initial crux of\nall cosmogonists. They usually surmount it by assuming the occurrence\nof casual condensations, secure against disproof, while incapable of\nverification. The expedient thus begs the question.\n\nTheories of world-history made an integral part of antique philosophy.\nEach founder of a school aimed at establishing a complete system of\nknowledge, co-extensive with phenomena, embracing all things, from\nthe _primum mobile_ overhead to the blade of grass underfoot, and\nrationalizing the past, present, and future of the comprehensive whole.\nModern science is less ambitious. Aspiring to no such vast synthesis,\nit is content to make laborious acquaintance with the facts of nature,\nto ponder their implications, and, if possible, to reconstruct on the\nbasis supplied by them the condition of things in the 'dim backward' of\nunmeasured time. By no such means, it is true, can their beginning in\nany real sense be arrived at; the weapons of induction become blunted\nlong before they strike home to the heart of that mystery; yet the\nrecognition of their inadequacy brings compensation in a fuller mastery\nover their properly adapted use. Science, so called, was, indeed, down\nto the Baconian era, a turbid mixture of physics with metaphysics. The\nsolution, it might be said, was attempted of an insoluble material\nwhich refused to dissolve and was hindered from precipitating.\n\nThe Greek view of nature was essentially pantheistic. The Ionian\nspeculators appear to have presumed without expressly insisting upon\nits self-regulating power. Aristotle alone emphatically rejected the\ndoctrine of cosmic vitality or sub-conscious tendencies. But Plato\naccepted and magnified the Oriental tradition; the conception of a\n'World-Soul' owed to him its vague splendour and perennial fascination.\nThe function of the Platonic vice-creator (for such the World-Soul\nmust be accounted) was that of moulding brute matter into conformity\nwith the archetypal ideas of the Divine mind; this was not, however,\naccomplished once for all, but by a progressive spiritualizing of what\nin its nature was dead and inanimate. The spiritual agent, becoming\nincorporated with the universal frame, lent to it a semblance of life,\nan obscure sensitiveness, and even some kind of latent intelligence;\nand so the _anima mundi_ was shaped into existence, and continued\ncentury by century to be the subject and source of imaginings beyond\nmeasure wild and fantastic.\n\nOne great thought--that of the unity of nature--lay behind them, but\nits significance was lost amid the phantasmagoria of Neo-Platonist\nexaltations. Hence the Bacchic fervours of Giordano Bruno took their\ninspiration; here was the groundwork of Spinoza's pantheism. Shelley's\nDemiorgon, felt as 'a living spirit,' seen as 'a mighty darkness,'\ndescended lineally from that strange essence--formless, inarticulate,\ndevoid of individual self-consciousness--which animated the submerged\nphilosophy of Neo-Pagan times with the barren ardours of mysticism. The\ndoctrine, in its original and more sober version, obtained memorable\nexpression in Virgil's melodious hexameters:\n\n 'Principio c\u0153lum, ac terras, camposque liquentes,\n Lucentemque globum lun\u00e6, Titaniaque astra,\n Spiritus intus alit, totamque infusa per artus\n Mens agitat molem, et magno se corpore miscet.'\n\nIn Conington's rhymed version they run as follows:\n\n 'Know first, the heaven, the earth, the main,\n The moon's pale orb, the starry train,\n                   Are nourished by a soul,\n A bright intelligence, whose flame\n Glows in each member of the frame,\n                   And stirs the mighty whole.'\n\nKepler was no cosmogonist, but he aspired to found a 'physical\nastronomy,' and in his gropings for a mechanical power that might\nsuffice to regulate the movements of the heavenly bodies, he stumbled\nupon a mode of action highly appropriate for the explanation of their\ngrowth. His ignorance of the laws of motion precluded him from the\nconception of velocities persistent in themselves, and merely deflected\nfrom straight into curved paths by a constant central pull. Hence he\nwas driven to the twofold expedient of creating a whirling medium for\nmaintaining the revolutions of the planets, and of supposing the sun\nto exercise a 'magnetic influence,' by which they were drawn into\nclosed orbits. Here, then, central forces made a definitive entry on\nthe astronomical stage, although with scarcely a discernible promise\nof their brilliant future. But it was otherwise with the clumsy\nmachinery they helped to animate. Kepler's simple _modus operandi_,\nadopted, or more probably re-invented by Descartes, was published as\nan epoch-making discovery in his _Principia Philosophica_ (1644), and\nsprang under its new aspect into swift notoriety. The wide acceptance\nof the theory of vortices was at least in part due to the impressive\nlargeness of its framework. Descartes left nothing out. The spacious\nscope of his speculations embraced all that was knowable--nature,\nanimate and inanimate, life and time:\n\n 'Planets and the pale populace of heaven,\n The mind of man, and all that's made to soar.'\n\nA philosophy, a metaphysic, and a cosmogony were linked together in a\nsingle plan. Its author distinguished in matter three gradations of\nfineness. The coarsest kind was that composing the earth and other\nopaque bodies; the more sublimated materials of the sun and stars\ncame next; finally, there was the ethereal substance of the skies, so\ndelicately constituted as to be luminous or luminiferous. This last\nvariety was regarded as of subordinate origin. It represented, in fact,\na kind of celestial detritus. Interstellar space had gradually become\nfilled with intangible dust, the product of molecular attrition among\noriginally angular solar and stellar particles. Ether was thus supposed\nto bear to the subtlest description of ordinary matter very much the\nsame sort of relationship that ions presumably do to atoms.\n\nEnough has been said to show that the Cartesian universe was based on\ncrude atomism. Its mode of construction, moreover, evinced a total\ndisregard of mechanical principles. Yet some acquaintance with the\nlaws of motion was by that time easily within reach. The first of the\nthree, at any rate, had been unmistakably enounced by Galileo in 1632,\nand Descartes himself strongly championed its validity. Yet he thought\nit necessary, in order to keep the planets moving, to immerse them in\none great self-gyrating vortex centred on the sun, each being further\nprovided with a similar subordinate whirlpool for the maintenance\nof its domestic system. Comets were left in a singularly anomalous\nposition. They circulated freely on the whole, their exemption from\nplanetary restrictions being tacitly recognized; nevertheless, they\ntook advantage of every encountered swirl to help themselves on towards\ntheir destination.\n\nAmong the fables of pseudo-science Delambre declared that, had the\nchoice been offered to him, he would have preferred the solid spheres\nof Aristotle to the _tourbillons_ of Descartes. 'The spheres,'\nhe added,[2] 'have proved helpful both for the construction of\nplanetariums representing in a general way the celestial movements, and\nfor their calculation by approximate rules deduced from them; but the\nsystem of vortices has never served any purpose whatsoever, whether\nmechanical or computative.'\n\nIts vogue had, nevertheless, been brilliant and sustained. Advanced\nthinkers in the time of Louis Quatorze piqued themselves upon being\nCartesians. The vortical hypothesis was novel--it seemed daring; and\nthough it might not be true, it had plausibility enough for fashionable\ncurrency. Nor did it deserve the unmitigated contempt with which it\nwas treated by Delambre. A glance at the skies makes us pause before\ncondemning it to scornful oblivion. Just two centuries after its\npromulgation the first spiral nebula was identified in Canes Venatici.\nThat the heavens swarm with analogous objects is certain, and their\nstatus as partially developed systems is visible in every line of their\nconformation. Our own planetary world may, or may not, have traversed\nthe stage they so copiously illustrate; but in any case they prove\nbeyond question that vortices variously conditioned are prevalent\namong the forms assumed by cosmic masses advancing towards an orderly\narrangement.\n\nMystical cosmogonies belong to the period of ethnic infancy. They\nhave not ceased to be current. World-fables must be invented wherever\nthe obscure wonder of savage communities is excited by the mysterious\nspectacle of Nature's apparently designed operations and irresistible\npower. But they were superseded among peoples in the van of progress\nby philosophic cosmogonies at the epoch when Thales began to diffuse\nthroughout Ionia the wisdom of the Egyptians and Chaldeans. Schemes,\nhowever, such as he and his successors elaborated result from the\ndiscourse of reason unfettered by any close attention to facts.\nThey have been mostly wrought out by men who, in Delambre's words,\n'Dissertaient \u00e0 perte de vue, sans jamais rien observer, et sans jamais\nrien calculer.'\n\nThe insubstantial fabrics reared by them were then fatally\ndiscredited by Baconian methods and the Newtonian reign of law; they\nsurvived--forms of thought die slowly--but insecurely, with noticeably\nundermined foundations. Swedenborg was the last eminent reactionary,\nand his restoration in 1734 of the Cartesian gyrating medium as the\nmotive power of the solar machine was a palpable failure. It could not\nbe otherwise, since its inceptive idea had grown superannuated. The\nmodern era of scientific cosmogony was at hand.\n\nIt was preceded by some remarkable attempts at sidereal generalization.\nCosmology is the elder sister of cosmogony. What _is_ must be studied\nbefore what _was_ can be inferred. Precedent states remain visionary\nunless they can be closely linked to actual and observable conditions.\nNow about the middle of the eighteenth century an intelligible plan of\nthe stellar universe, so far as the telescope had then disclosed it,\nbegan to be a desideratum. And the enterprise of supplying the need was\nundertaken independently by two men of obscure origin and imperfect\neducation--one English, the other German.\n\nThomas Wright, of Durham, was the son of a carpenter at Byer's\nGreen, where he was born September 22, 1711. His life was one of\nmany vicissitudes, but ended happily. Having struggled hard for a\nlivelihood--now at sea, then again on shore as a clock and almanac\nmaker, a teacher and lecturer--he finally attained, somewhat\nunaccountably, to distinction and affluence, built himself a handsome\nhouse hard by his native shanty, and prosperously and reputably\ninhabited it during a quarter of a century. He died February 25,\n1786, just one year after Herschel had described to the Royal Society\nthe outcome of his first experiments in 'star gauging.' As the\noriginator of the 'cloven disc' theory of the Milky Way, Wright is\nstill deservedly remembered, for although that majestic structure is\nassuredly otherwise designed, it was no mean achievement to have\ninitiated the science of its architecture.\n\nHeinrich Lambert was a still more adventurous speculator than his\nunknown English rival. His father was a poor tailor at M\u00fchlhausen,\nthen in Swiss territory, and he worked as his apprentice. But his\nirrepressible talents brought him into notice, and he died, in 1777,\nthrough the favour of the second Frederick, a Berlin Academician. His\n_Cosmological Letters_, published in 1761, were entirely original; they\nwere composed in ignorance of what Wright and Kant had already written.\nIn some respects he overtopped them both. He had splendid intuitions,\nand just touched the confines of greatness. And if his performances\nfell short of the very highest, it may have been rather through\nabridgment of opportunity than through lack of capacity. The Milky Way\nmarked, to his apprehension, a sidereal ecliptic, and he coincided with\nWright in regarding it as a disc of aggregated stars, but with breaches\nand gaps indicating a multiplicity of systems circulating, he thought,\nround a common centre. Nor did he doubt the existence of other\nMilky Ways--numberless, remote, unseen--grouped into a combination\nof a higher order; while beyond, and still beyond, stretched further\nhierarchies of systems on an ascending scale of magnitude and grandeur.\n\nOur knowledge of the structural facts of the universe can never be made\nexhaustive; in the middle of the eighteenth century, before Herschel\nhad opened his sidereal campaign, it was barely elementary. Wright\nand Lambert were accordingly on a stint of material--they had to make\nbricks with very little straw. Yet they did their best with what was\nat hand. Both paid profound attention to the stellar heavens; they\nearnestly sought the true interpretation of the appearances presented\nby them, holding it possible, as we, despite accumulating difficulties,\nstill do, to harmonize countless detached phenomena in one vast\nsynthetic plan.\n\nIt was this purpose of fidelity to Nature which gave value to their\nwork, and made it a new thing in cosmological history. This alone\nlent it impulsive force, and caused the meditations of two lonely\nthinkers to become effective in stimulating fresh attempts, favoured\nby improved conditions, to comprehend what actually exists, and to\ninfer thence, with rational confidence, its sources in the vague but\nundeniable past.\n\nFOOTNOTES:\n\n[Footnote 1: Zeller, _History of Greek Philosophy_, translated by S.F.\nAlleyne, vol. i., p. 86.]\n\n[Footnote 2: Quoted by R. Wolf, _Handbuch der Astronomie_, Bd. II., p.\n593.]\n\n\n\n\nCHAPTER II\n\nTHE NEBULAR HYPOTHESIS\n\n\nImmanuel Kant was, in 1751, still in the plastic stage. His period of\n'pure reason' was remote, and might have appeared improbable. Such\nas they were, his distinctions had been won in the field of concrete\nscience, and the world of phenomena invited his speculations more\nseductively than the subtleties of logic. A seed was accordingly thrown\ninto fertile soil by his reading of Thomas Wright's _New Theory of the\nUniverse_, as summarized in a Hamburg journal. It set him thinking,\nand his thoughts proved to be of the dynamic order. Wright regarded\nthe heavens under a merely statical aspect. He laid down the first\ndefinite plan of their construction, showing that the stars were not\nscattered at random, but aggregated by method; and this was much for\none necessitous human being to have accomplished unaided.\n\nBut the young professor of K\u00f6nigsberg could not rest satisfied with\nthe idle contemplation of any subsisting arrangement. His mind was\nincapable of acquiescing in things simply as they presented themselves;\nit craved to know further how they came to stand to each other in just\nsuch mutual relations. He was, moreover, permeated with Epicurean\ndoctrines. Not in any reprehensible sense. He could not be reproached\neither as a hedonist or as an atheist. His pleasures were intellectual,\nhis morals austere, his convictions orthodox. Behind the veil of\nmaterial existence he divined its supreme immaterial Originator, and\nhis perception of the activity in Nature of an ordering First Cause\nremained equally vivid, whether its disclosures were taken to be by\nimmediate creation or through tedious processes of modification and\ngrowth. His large and luminous view embraced besides the ethical\nsignificance which such processes adumbrate. The following sentence\nshows an appreciation of the place of man in Nature truer and more\nprofound than was attained perhaps by any other of his philosophical\ncontemporaries: 'The cosmic evolution of Nature,' he wrote in memorable\nwords, 'is continued in the historic development of humanity, and\ncompleted in the moral perfection of the individual.'[3]\n\nNevertheless, he owned to a community of ideas with Democritus as to\nthe origin of the universe. Lucretius had cast over him the spell\nof his lofty diction, and captured his scientific adhesion by the\nstately imagery of his verse. With reservations, however. Docile\ndiscipleship was not in his line. He availed, then, of the Democritean\natoms, but by no means admitted their concourse to be fortuitous.\nChaos itself, as he conceived it, half concealed, half revealed the\nrough draft of a 'perfect plan.' His postulates were few. He demanded\nonly a limitless waste of primordial matter, animated by no forces\nsave those of gravitation and molecular repulsion, and undertook to\nproduce from it a workable solar system. The attempt was no more than\npartially successful. Retrogressive investigations lead at the best\nto precarious results, and this one, in particular, was vitiated by\na fundamental error of principle. Its author clearly perceived that\nplanetary circulation must be the outcome of a vortical swirl in the\nnebulous matrix; but he failed to see that no interaction of its\nconstituent particles could have set this swirl going.\n\nSystems cannot of themselves add to their 'moment of momentum.' No\nchanges of internal configuration avail to increase or diminish the\nsum of the products obtained by multiplying the mass of each of the\nconnected bodies into its areal velocity projected on a common plane.\nThe sum is of the algebraic kind. Equal and opposite motions cancel\neach other, the total representing only the aggregate excess of speed\nin either direction. A system with all its parts in rapid motion might\nthen conceivably be devoid of moment of momentum. And if this were its\nstate to begin with, it should be its state to the end of time, unless\nexternal force were applied to alter it. But the possibility may be\ndismissed as ideal. The establishment of so nice a balance as it would\nrequire is not practically feasible. In the actual world one side of\nthe velocity account would be sure to exceed the other, albeit very\nslightly, and the smallest predominance would suffice to set on foot an\neventual rotation of the system.\n\nHad Kant been better acquainted with mechanical principles, he\nmight then have safely trusted to the minute beginnings supplied by\naboriginal inequalities of movement and dissymmetry of arrangement for\nthe development in his colossal dust-cloud of the wheeling movement\nnecessary for his purpose; and he would thus have escaped stumbling\nat the threshold of his daring inquiry. Rightly averse to employing\narbitrary expedients, he piqued himself on the simplicity of his\npostulates, and was thus misled into substituting an imaginary for\na real cause. The hypothesis adopted by him was that the particles\nforming the initial inchoate mass fell together by gravity, but were\ndeviated from rectilinear courses through the effects of unequal\nresistance. And he derived from the combination of these multitudinous\nencounters a common axial rotation for the entire agglomeration. The\nfutility of this mode of procedure was adverted to by M. Faye in\n1885.[4] The deviations in question would, in fact, exactly balance one\nanother, there being no reason why movement in one sense should prevail\nover movement in the opposite; consequently a general rotatory movement\ncould not even begin to affect the seething mass, which would condense\nin sterile rigidity. Kant should then, as Laplace did when his turn\ncame, have assumed the gyration indispensable to his purpose. He asked\ntoo little from Nature on one side, and too much on the other, with the\nresult of arresting the machinery he designed to set going.\n\nKant made the germ of the future sun to consist in an aggregation\nof atoms at the core of the nebula, which, growing by successive\ninnumerable accessions, provided the motive power for the machinery\nof planetary construction. For it was, as we have seen, the jostling\nof the particles drawn towards the gradually preponderating centre of\nattraction which set on foot, it was supposed, the whirl eventually\ntransformed into the tangential velocities of the sun's attendant\nbodies. They were formed, like the sun, by the perpetuation and\nincrease of subordinate nuclei sure to arise in the elemental tumult.\nThey were formed, not under the guidance of a definite law, but just\nwhere chance--or what seemed like chance--favoured an accretion.\n\nThe progressive increase of planetary distances noted by Titius\nand Bode could never have arisen in the Kantian system. Nor could\nthe Kantian planets have had a direct rotation.[5] Under the given\nconditions retrograde systems should have originated. This would\nhave necessarily ensued from the incoherence of their materials.\nParticles revolving independently one of the other have smaller\nvelocities the more remote they are from the focus of movement. Should\nthey agglomerate into a globe, the inner flights must, as being\nthe swiftest, determine the direction of its rotation, which will\nconsequently reverse the direction of its orbital revolution. Hence,\nit depends upon the nature of their generating stuff no less than upon\nthe advance of central condensation whether planets, in their domestic\narrangements, contravene or obey the larger law of circulation\nprevailing in the system to which they belong, and Kant's nebula was\nundoubtedly such as to involve its contravention.\n\nYet his scheme, with all its deficiencies, bore the authentic stamp of\ngenius--of genius imperfectly equipped with knowledge, but original,\npenetrative, divinatory. The very entitling of the work, _A Natural\nHistory of the Heavens_ was an audacity implying a radical change of\nconception. It was in this remarkable treatise that 'island universes'\nmade their definitive appearance. Wright, it is true, had, five years\npreviously (in 1750), thrown out the idea that 'cloudy spots' might\nrepresent 'external creations,' but as a mere vagary of the scientific\nimagination. Kant unhesitatingly laid hold of it, classed nebul\u00e6\nas so many separate galaxies, and regarded them as combining with\nour own into a revolving system on a surpassing scale of grandeur.\nKant was also the first to take into account the effects on their\ndevelopment of the plasticity of the heavenly bodies. He published in\n1754, in a K\u00f6nigsberg paper, by way of preliminary to his forthcoming\n_Natural History_, an outline of the workings of tidal friction in the\nearth-moon system. He saw clearly that it had acted in the past to\nreduce our satellite's rotation to its present minimum rate, and that\nit even now, by very slow degrees, tended to retard the spinning of\nthe earth. This brilliant forecast remained unnoticed for well-nigh a\ncentury.\n\nThe assertion, however, that Kant's cosmogony was an anticipatory\n'Meteoritic Hypothesis' lacks foundation. It is only true in the\nsense that his building materials were pulverulent, not 'fluid.'\nLaplace's primitive nebula was a coherent mass. It rotated as a whole;\nit divided only under considerable strain; its separated parts had\nindividual unity--they held together with, so to speak, a purpose of\nconcentration. Kant's elemental matter, on the contrary, was a loose\naggregate of independent particles, each pursuing its way, disturbed,\nindeed, by its neighbours, but essentially isolated from them. They\nwere, in short, genuine Lucretian atoms, intended to stand for the\nirreducible minima of Nature. The chaos that they formed was in nowise\na 'meteoritic plenum,' unless the phrase be emptied of all distinctive\nmeaning. Meteorites, so far from being primordial units, have the\nshow and semblance of advanced cosmical products. They raise special\nquestions in chemistry, mineralogy, geology, and physics, claiming to\nbe dealt with by experts in each branch. Before serving for explanatory\npurposes, in fact, they themselves need to be explained.\n\nLaplace enounced his hypothesis in 1796, and republished it with\nsupplementary details in 1808. Herschel had meanwhile ascertained the\nretrograde movement of the Uranian satellite-system, a circumstance\nhighly damaging to the validity of the adopted line of reasoning; yet\nits author was content to leave it in jeopardy. He must, to be sure,\nhave regretted that Nature had seen fit to mar the admirable symmetry\nindicative of her presumed plan of action, running counter thereby to\nthe plainest teachings of the doctrine of probabilities. But he kept\nhis own counsel on the subject, preferring that it should be discussed,\nas it has been in full detail, by posterity; and posterity has, at\nany rate, learned that the seeming caprices of Nature are often more\ninstructive than her most harmonious regularity, and has derived a\nwarning from her frequent breaches of continuity against the undue\nextension of apparently well-grounded inferences.\n\nNevertheless, the constructive scheme handed on by the eighteenth to\nthe nineteenth century has not, up to the present, been consigned\nto the limbo of vanities. It accorded too profoundly with undoubted\nrealities to be thus summarily disposed of. No one then living had\nstudied the mechanism of the solar system so attentively, or was so\nintimately acquainted with its workings, as Pierre Simon Laplace.\nNone knew better how admirable, yet how far from inevitable, were the\nadjustments by which its stability was secured. Long meditation upon\ntheir poise and plan persuaded him that the subsisting congruities\nof arrangement must have had their source in a community of origin.\nHe thus acquired the settled conviction that the sun engendered his\ncort\u00e8ge, or was together with it engendered from one parent-mass.\nAnd this virtually new truth (for Kant's speculation had attracted a\nnegligible amount of notice) was set forth by him with a directness\nand lucidity which won for it an immediate place among the permanent\nacquisitions of the human intellect. Few, perhaps, any longer believe\nthat planetary formation took the precise course laid down for it in\nthe _Syst\u00e8me du Monde_, but fewer still doubt that the entire ambit of\nthe solar system was once occupied by an inchoate sun, and that its\ncomponent bodies came into being incidentally to that sun's progressive\ncontraction.\n\nIn favour of this view Laplace could allege no clinching argument; it\nrecommended itself to him solely through its inherent probability.\nUnexpected confirmation has, none the less, been afforded to it by the\nmodern theorem of the conservation of energy, applied by Helmholtz with\nwidely illuminative effect to solve the problem of the maintenance of\nsolar heat. Laplace assumed an enormously high initial temperature. It\nwas the only way open to him, and he took it. But a transcendentally\nhot nebula is not easily conceivable; an exalted thermal state seems,\nand probably is, incompatible with a high degree of attenuation.\nThe key to the enigma was given by the demonstration that a diffuse\nmass, although actually cold, might contain vast stores of potential\nheat. There was then no need to postulate a primitive 'fire-mist'; the\nsurrendered energy of position amply sufficed to meet the requirements\nof the case. The temperature of the nebula necessarily rose as it\ncontracted through gravitational stress; shrinkage and heat-evolution\nproceeded together; and they in all likelihood proceed together still.\nOur existence depends in part, or wholly, upon the collapse of the sun.\nIf its particles ceased to descend, their incandescence would become\nless intense, and terrestrial vitality would be seriously compromised.\n\nTheir number, however, being finite, the store of energy they can\nsupply in falling even from an infinite distance is also finite. The\nprocess of solar sustentation is then terminable; it had a beginning,\nand it will assuredly come to an end. Now the _terminus ad quem_\nis of a calculable remoteness: it can be located (unless shifted\nby radio-active processes) within certain limits of time. But the\n_terminus a quo_ depends upon too many conditions to be satisfactorily\ndefined. It is only certain that the sun is to-day slightly more\ncondensed than it was a year ago. It might a few millenniums back have\nbeen measurably larger, had modern micrometrical methods been available\nin the Stone Age; while, looking into the geological past, we discern a\ncontinually more diffuse globe, filling the orbit of Mercury when the\nearth was perhaps still red-hot, then successively ampler spheres, out\nto, and beyond, that of Neptune. And just such a vastly diffused sun\nrealizes the nebula of Laplace. The state of things he imagined can be\nreached accordingly, either by tracing forward the development of a\ntenuous rotating mass, or by pursuing backward the surely indicated,\nunceasing, and inevitable distension of the sun. Hence, no sooner\nwas it acknowledged that energy may be transformed, but cannot be\ndestroyed, than the nebular cosmogony assumed a new and authoritative\naspect.\n\nBut here a _caveat_ has been entered by the latest inquirers--a\n_caveat_ not to be ignored, though based upon modes of action still\nexceedingly obscure. Radio-activity is a fledgling science; its\ncapabilities, though immense, are vaguely outlined. Until they more\nfully approve themselves, it would be unwise to admit conclusions which\nthey may eventually enforce. Subversive ideas are in the air; the\ntheory of atomic dissociation goes to the very root of things, and it\ninsistently claims assent. Its verification, by disclosing the presence\nin the universe of a measureless store of unsuspected energy, would\noverthrow all the calculations of cosmic time heretofore attempted, and\nmight protract indefinitely the radiative span of the sun.\n\nMr. W. E. Wilson pointed out in 1903[6] that its entire thermal output\ncould be supplied by the spontaneous liberation of energy from 3\u00b76\ngrammes of radium in each cubic metre of its volume; and although we\nhave no evidence of the actual existence of radium in the sun, the\npossibility that chromospheric helium represents the decay of solar\nradio-active elements[7] must be taken into consideration. The ground\nhere is undermined with pitfalls. We can only see that although\nHelmholtz's gravitational rationale of the sun's long life-history\nremains true, the results derived from it may be profoundly modified\nby co-ordinate processes, variously efficacious according to\ncircumstances, perhaps knowable, but as yet unknown.\n\nThe scope of the nebular hypothesis had widened prodigiously by the\ntime Helmholtz took it in hand. Five years before its promulgation at\nParis, Herschel gave at Slough the first hint of a corresponding scheme\nof sidereal evolution. The discovery of a nebulous star in Taurus\n(N.G.C. 1514) set him pondering; and he found himself, as the upshot of\nhis meditations, reduced to the dilemma either of concluding nucleus\nand _chevelure_ to be alike stellar, though composed of stars differing\nenormously in real magnitude, or of admitting the possession by the\nstar of a voluminous appendage constituted of a peculiar and unknown\n'shining fluid.' He chose the latter alternative, adding the pregnant\nremark: 'The shining fluid might exist independently of stars,' and\n'seems more fit to produce a star by its condensation than to depend on\nthe star for its existence.'[8]\n\nThus tentatively, and under the compulsion of phenomena rather than\nby the deliberate choice of its inventor, the universal theory of\nthe genesis of stars from nebul\u00e6 took its rise. Herschel shaped it\ndefinitively in 1811 and 1814 into a formal plan for the interpretation\nof celestial appearances, but in a large and general way. He made no\nattempt to realize the particularities of a _modus operandi_ vaguely\nconceived of as involving growth by absorption or assimilation. He and\nLaplace thought out their separate schemes quite irrespectively one\nof the other. There is no evidence of their having exchanged views\npersonally or by correspondence, nor does their mutual influence appear\nto have been appreciable.[9] Yet Laplace needed as the raw material for\nhis solar system precisely the 'shining fluid' elaborated, one might\nsay, by Herschel, partly through the revelations of his telescopes,\npartly as the outcome of his reasonings concerning the _chevelure_ of\nthe star in Taurus. Halley, it is true, had, by a sagacious intuition,\nsurmised the composition of nebul\u00e6 out of a 'lucid medium.' But the\nineffectual phrase remained stranded in the pages of the _Philosophical\nTransactions_, and has only of late been set floating on the stream of\nscientific literature.\n\nDown to the end of the eighteenth century world-building had been a\npurely speculative undertaking. It lacked actuality; it was concerned\nwith operations thought of as belonging exclusively to a past order\nof things, now over and done with, and lying wholly outside the\nrange of experience. Through Herschel's synthesis, however, those\ndimly apprehended operations were brought into view as variously\nprogressing even now in different parts of the cosmos, as incipient\nin some regions, far advanced in others, the rubbish of the workshop\nhere half masking the rising edifice, while elsewhere signs of\ndecay and exhaustion give legible presage of an appointed end. And\nthis stupendous vision of a forming universe has not vanished on\ncritical scrutiny. It is no dream-tissue; it cannot dissolve into\nairy nothingness; it is based upon a firm substratum of reality.\nThe immeasurable purposes of creative wisdom are still only in\npart fulfilled. It has become the strange privilege of humanity to\ncontemplate from its little shoal of time the oceanic flow of their\ndevelopment. Thus, in the swing of the ages, Laplace's thought was\ncaught up and vitalized. He himself was scarcely sensible of their\nmovement. He recognised very imperfectly, if at all, his obligations to\nHerschel's nebulous star. His means were inadequate; his field of view\nnarrow; his knowledge, though co-extensive with that of his time, fell\nshort of what his boundless task demanded. In some respects his mode\nof procedure was faulty; his forecasts have been belied; the behaviour\nimputed by him to a nebula such as he devised is questionable, if\nnot impossible. But with the instinct of consummate intelligence he\nhit off the 'psychological moment,' and, divining the genetic import\nof harmonies of construction obvious to perception, but arduous of\ninterpretation, he laid down with masterly simplicity the ground-plan\nof a structure likely to maintain its substantial integrity despite\ninnumerable additions and rectifications.\n\nFOOTNOTES:\n\n[Footnote 3: Quoted by Dr. Hastie in the preface to his translation of\nKant's _Cosmogony_, Glasgow, 1900.]\n\n[Footnote 4: _Sur l'Origine du Monde_, 3e \u00e9d., p. 136.]\n\n[Footnote 5: This also was pointed out by M. Faye, _loc. cit._, p. 150.]\n\n[Footnote 6: _Nature_, July 9, 1903.]\n\n[Footnote 7: Rutherford, _Radio-activity_, p. 342.]\n\n[Footnote 8: _Philosophical Transactions_, vol. lxxxi., p. 85.]\n\n[Footnote 9: Herschel met Laplace during a visit to Paris in July,\n1801, but what passed between them is unrecorded. In the sixth edition,\nhowever, of the _Exposition du Syst\u00e8me du Monde_, Laplace referred to\nHerschel's observations of nebul\u00e6 as confirmatory of his own genetic\nscheme.]\n\n\n\n\nCHAPTER III\n\nCRITICISMS OF THE NEBULAR HYPOTHESIS\n\n\nLaplace's theory was a perfectly definite conception. In this lay its\ndistinctive merit; in this also its special susceptibility to attack.\nHere was no question of condensation round nuclei arising at discretion\namid the large possibilities of boundless elemental confusion; but of\nan orderly succession of occurrences, rendered inevitable by the steady\noperation of mechanical laws, and harmonizing, in their outcome, with\nthe array of ascertained phenomena visible in the planetary system.\nThese accordingly ceased to be regarded as arbitrary or casual; they\nbecame linked together in the present, and with the past, as joint\nproducts of one grand scheme of development. The mode of origin of\nthe bodies exhibiting them accounted, its inventor claimed to have\nshown, simply and entirely for them all; and at least the fundamental\npropositions laid down by him could not be gainsaid.\n\nClearly, the unanimity of planetary movements is no result of chance;\nit represents quite obviously a survival of the general swirl of an\ninchoate mass, occupying primitively the whole recognised sphere of\nsolar influence. Ambiguities set in only when details come to be\nconsidered. The engendering nebula devised by Laplace was provided\nwith a vast endowment of heat and a slow movement of rotation; hence\ncooling, contraction, and acceleration advanced _pari passu_, the last\nas a consequence of the mechanical law by which the algebraic sum\nof the areas described by any number of bodies round a given axis,\nmultiplied by their several masses and projected upon a single plane,\nremains constant to the end of time. In other words, to repeat what has\nbeen stated a few pages back, the moment of momentum of a congeries\nof particles can neither increase nor diminish through the effects of\ntheir mutual interactions, however varied and prolonged.\n\nThe nebula then quickened its pace until a stage was reached at\nwhich centrifugal speed could no longer be controlled by gravity;\nseparation became inevitable, and an equatorial ring was abandoned,\nwhich thenceforward revolved on its own account in the period conformed\nto by the undivided mass at the epoch of its secession. This was the\nfirst of many subsequent crises of instability, each eventuating in\nthe detachment of a nebulous ring. These rings, however, were regarded\nas merely transitional forms. They survived, just for illustrative\npurposes, in the Saturnian system; elsewhere they broke up into\nfragments, which ultimately coalesced into globes, and the globes were\nembryo planets. There was, indeed, a hitch in the line of argument\nwhich did not escape the acumen of the French geometer. The direction\nof the axial movement imparted to the members of the solar family\ndepended essentially upon the relative velocities of the portions of\nmatter brought together for their construction. If the inner sections\nof the self-shaping mass moved faster than the outer, the resulting\nrotation should have been retrograde; if slower, direct rotation would\nhave ensued. Now, in a ring like that of Saturn, composed of discrete\nparticles, linear speed decreases continuously outward, each of its\nminutest constituents obeying independently Kepler's law of periods and\ndistances. Such a formation, since it would necessarily have yielded\nbackward-spinning planets, would have been unfit for the purpose in\nview, and Laplace accordingly substituted an annulus endowed with a\nconsiderable amount of cohesion, and capable of rotating, like a solid,\nin a single period. It is true that such unanimity of movement was\nincompatible with the other postulated conditions; but the anomaly\nescaped notice for above half a century.\n\nProfessor Darwin has moreover pointed out[10] that a ring of matter\ndistributed with any approach to uniformity must concentrate, if at\nall, round its own centre of gravity. It should accordingly collapse\nupon, and become re-absorbed by, the parent-body. If markedly\nunsymmetrical and ill-balanced, its materials might certainly collect\nat an interior point more or less remote from the centre; but in no\ncase could the focus of condensation be situated in any part of the\nannular circumference, where it was located by Laplace.\n\nWhether workable or not, the genetic plan traced out by him was a\nstrictly regulated one; its steps were marked with characteristic\nprecision. Yet by this very determinateness it gave hostages to the\nfuture. It challenged the application of tests which designs more\nvaguely sketched might have evaded. The primary criterion of its truth\nwas the prevalence of concordant motion throughout the solar domain.\nCounter-currents were formally excluded; their possibility was not\neven contemplated. Hence, the discovery of the retrograde systems of\nUranus and Neptune flatly contravened its pretensions to unconditional\nacceptance. With less evidence, but equal certainty, Laplace's\nhypothesis, strictly interpreted, involves the consequence that each\nplanet circulates in the identical time occupied by the rotation of the\nundivided nebula just before instability toppled over into separation.\nEach of the planetary periods should accordingly bear a certain ratio,\nprescribed by inexorable mechanical law, to the actual period of the\nsun's rotation. In point of fact, however, the periods in question\nare much shorter than comports with the necessity for the conservation\nfrom age to age of the system's moment of momentum. The discrepancy was\nadverted to nearly half a century ago by M. Babinet.[11] He showed in\nMarch, 1861, that the axial movement of the solar mass, when distended\nto fill the sphere of Neptune, should have been, by the law of areas,\nso excessively slow that more than 27,000 centuries would have been\nneeded for the completion of a single rotation; while the period, even\nwhen the shrinking nebula had come to be bounded by the terrestrial\norbit, must still have been protracted to 3,181 years. Under these\ncircumstances, centrifugal force would never have overbalanced central\nattraction; no rings could have separated, and no planets could have\nbeen formed.\n\nQuite recently, Mr. F. R. Moulton, of Chicago,[12] has reconsidered\nthe subject in the course of a careful and candid discussion of the\ndifficulties besetting the nebular cosmogony as viewed from the\nstandpoint of modern science, and he comes to essentially the same\nconclusion. His calculations, though founded on data expressly chosen\nso as to give the classic theory the benefit of every doubt, made it\nperfectly clear that the moment of momentum of the embryo planetary\nsystem should have exceeded its present value no less than 213 times\nif, when it extended to the distance of Neptune, it rotated in what\nis now the period of Neptune. But moment of momentum is a constant.\nThe lapse of millions of years makes no difference to it; it is not,\nlike energy, subject to 'dissipation'; it can neither have gained nor\nlost value since the sky was first flecked with the 'breath-stain'\nappointed to condense into our sun, which, in this respect at least,\nmust at every stage of its subsequent evolution have maintained\nimmutability. On the other hand, this being so, its primeval wheeling\nmotion would have been much too leisurely to permit the occurrence\nof accesses of instability. Gravity would have steadily kept its\nsupremacy over the forces tending to disruption until the nebula had\ncontracted to less than the compass of the Mercurian sphere, and its\noverthrow at that epoch would have been too late for the origination\nof any of the sister orbs of the earth. These results, it is true,\ndepend in part upon the mode of variation in density ascribed to the\nprogressively shrinking nebula; but the law adopted by Mr. Moulton\nhas a consensus of authorities in its favour. Nor could its deviation\nfrom exactitude--if it be inexact--possibly suffice to account for the\nenormous discrepancies which calculations based upon it have brought to\nlight.\n\nThe nebular hypothesis stipulates further that satellites must revolve\nmore slowly than their primaries rotate. The reason is patent. In\nthe periodic time of a body detached by centrifugal acceleration the\nrate of gyration of the original mass is, if the theory be valid,\nperpetuated. Subsequent contraction tends to quicken, and very\ngreatly to quicken, the rotation of the planet, while the period of\nthe satellite survives unaltered as a standing record of what the\njoint period was. This relation may indeed be modified by the effects\nof tidal friction, but it is more than doubtful whether it can ever\nbe reversed. It is, then, a characteristic feature of the mode of\nevolution described by Laplace that no month--so to call it--can be\nshorter than the corresponding day. And the rule is conformed to in\nnearly every part of the solar system. Nevertheless, two flagrant\nviolations of it have lately obtruded themselves upon notice, and\ncan scarcely be explained away by supplementary hypotheses. The\nfirst ascertained anomaly of the kind was met with in the swift\ncirculation of Phobos, the inner satellite of Mars, which completes\nthree revolutions and enters upon a fourth while the planet attended\nby it wheels once on its axis. The fact is most perplexing, and the\nconfident persuasion that solar tidal friction would avail to remove\nthe difficulty has not proved well grounded. Solar tidal friction, it\nmay be remarked, acts as an external force upon subordinate systems\nsubmitted to its influence. Within their precincts moment of momentum\nmay be destroyed by it; it tends, so far, to abrogate the law of\nconservation; and the supposition was hence feasible that the rotation\nof Mars had, in the course of ages, greatly slackened through the\nretarding effect of sun-raised tides. But the agency was demonstrably\ninadequate to the task assigned to it.\n\nThe reduction of the rotational moment of Mars to about one\ntwenty-fifth its primitive amount[13] would have brought other\nconsequences in its train, at least one of which did clearly not ensue.\nAt an early stage of the process Phobos should have been re-engulfed\nin the mass of its primary.[14] For the pull of the small tidal wave\nraised by it on the surface of that body would have been backward from\nthe instant that the balance of periods became inclined, through solar\ncompulsion, in a direction contrary to that it would have naturally\ntaken; and the ensuing loss of velocity must have entailed the descent\nof the little satellite along a spiral path towards an inevitable doom.\nIts continued existence, then, closes this way of escape from the\ndifficulty raised by the shortness of its period. M. Wolf had recourse\nto a different explanatory subterfuge.[15] He believed that Phobos\nmight have owed its origin to one of Roche's 'elliptic sheddings' of\nnebulous matter dropped downward from near the polar regions of the\ndistended Martian spheroid, and rotating, owing to its low rate of\nlinear speed, in the immediate vicinity of the cooling planet. The\nexplanation, though ingenious, is too recondite to be satisfactory. The\nmind takes no grip of it; it evades distinct apprehension.\n\nThe Saturnian system exhibits a case of the same kind, but still more\nperplexing to speculative prepossessions. Saturn's ring-system has\nalways appealed to thinkers as a striking object-lesson in nebular\ndevelopment. It forcibly arrested Kant's attention, and he sketched its\nbirth-history on lines anticipatory of those adopted by Laplace for the\nsolar system in its entirety. Laplace himself regarded the formation\nas the one surviving relic of the annular stage of planet-building--as\na witness from the dim past to a condition of things elsewhere\ntransitory. Yet the witness has turned king's evidence, and betrayed\nthe whole situation. The innermost Saturnian ring has a period far\ntoo short to be compatible with the requirements of theory. For its\nmeteoric constituents, known on spectroscopic testimony to revolve each\non its own account, complete their circuits in between five and six\nhours, while the planet needs just ten hours and a half for its axial\nrotation. Moreover, tidal friction is here far less available than on\nMars; yet no other retarding agency has been invented. The deadlock\nappears final and hopeless.\n\nAn objection quite as formidable, and even more fundamental, was raised\nby Kirkwood in 1869. The nebulous material of the uncondensed sun must\nhave been, at the outset, of the utmost tenuity. Atmospheric air is,\nby comparison, a dense and massive substance. Yet no reasonable person\ncould ascribe to aerial matter the least power of resisting strain.\nWe know perfectly that a rotating globe of air, and, _\u00e0 fortiori_,\na globe of matter thousands of times less compact than air, would\nunintermittently disintegrate at the surface with the progress of\nacceleration. The disturbance and restoration of equilibrium would be\nvirtually simultaneous. There could be no accumulation of internal\nstress, and consequently no definitely separated epochs of instability.\nAt the first solicitation, at the first instant that centrifugal\nvelocity gained the upper hand over gravity, nebulous wisps would\nhave become detached, and their detachment would have gone on without\npause. Space would have been strewn with the d\u00e9bris of the condensing\nnebula, and there should have resulted a vast cloud of cosmic dust, not\na majestic array of revolving spheres.\n\nFurther, the possibility of their emergence from pre-existent annuli\nis by no means assured. Even if the nebulous material had possessed\nthe fabulous cohesion indispensable for its division into voluminous\nrings with wide intervening empty gaps, their ultimate agglomeration\ninto planetary globes would probably never have been effectually\naccomplished. Kirkwood long ago questioned the feasibility of the\nprocess. Mr. Moulton has gone far towards demonstrating that it must\nhave had an abortive outcome. Professor Darwin pronounces its very\ninception, apart from very special conditions, to be impracticable.\n\nAnother grave objection to Laplace's scheme is founded on the\nmarked deviations visible in the solar system, from conformity to a\nfundamental plane of motion. Unless acted on by influences difficult to\nimagine or explain, all the planets should circulate along the level\nof the sun's equator, and rotate on axes perpendicular to it. How far\nthis is from being realized in nature we have only to look around us\nto perceive. We owe the changes of our seasons to the tilted fashion\nof the earth's spinning. Yet it is by no means easy to understand how\nthe pole of its equator comes to be situated in the tail of Ursa Minor,\nwhile the pole of the ecliptic is involved in the folds of Draco. They\nshould have coincided if the simple rules of the nebular prescription\nhad been followed in the making and modelling of the planets. Nor are\nthe terrestrial arrangements exceptional. The Saturnian equator and the\nSaturnian rings have a still higher inclination; while in the systems\nof Uranus and Neptune--if we may thus interpret their retrograde\nrevolutions--the angle exceeds the limit of a quadrant. These and other\nsimilar discrepancies prove the solar mechanism to have originated by\na more complex method than that imagined by Laplace, and an hypothesis\nwhich invokes the aid of a multitude of auxiliary devices for its\nextrication from accumulating embarrassments falls thereby under the\nsuspicion of not being worth the trouble of extricating. It forfeits,\nat any rate, all claim to commendation for directness and simplicity.\n\nThe cosmogony turned out at Paris has thus proved vulnerable on a\nnumber of points; but all the blows aimed at it have not told with such\ndeadly effect as those just referred to. Some have fallen harmlessly,\nor glanced aside. One hostile argument in particular, which for a time\nseemed irresistible, has been completely overthrown by the logic of\nfacts, and deserves mention only as a historical curiosity. Towards the\nmiddle of the nineteenth century the progress of sidereal astronomy\nseemed to take the direction of showing all nebul\u00e6 indiscriminately to\nbe of stellar composition. With Lord Rosse's great reflectors a good\nmany such objects were genuinely, and some besides were deceptively,\nresolved into stars, the illusory effects being confirmed by Bond's\nobservations with the deservedly celebrated 15-inch refractor then\nrecently built by Merz for Harvard College. Hence the rash inference\nwas drawn that resolution was wholly a question of optical power,\nand that no real distinction existed between the stellar and the\nnebular realms. Herschel's 'shining fluid' assumed a mythical air;\n'island-universes' came into popular vogue; and all but a few careful\nthinkers held nebul\u00e6 and clusters to be differentiated merely by\ndegrees of remoteness. But if space contained only full-grown stars\nand no stars in the making--no star-spawn, no star-protoplasm--then\nthe imagined evolutionary history of our system was left in the air,\ndestitute of even the most fragile prop of observed fact.\n\nFrom this precarious position it was rescued, partly by the cogent\nreasonings of Whewell and Herbert Spencer, finally and triumphantly\nby Sir William Huggins's spectroscopic discovery of the cosmic gas\n'nebulium.' Since August, 1864, there has been no possibility of\ndenying that the heavens contain ample stores of just the kind of\nmaterial Laplace wanted, though whether it played just the part he\nassigned to it in the manner that he supposed is a question to be\nanswered with profound and growing reserve.\n\nAn objection of late urged against the nebular theory from the\nstandpoint of the kinetic doctrine of gaseous constitution is of much\nspeculative interest. A gaseous nebula equal in mass to the sun and\nplanets, and distended sufficiently to fill the orbit of Neptune, would\nhave been, supposing the prevalent opinion correct, subject to a rapid\nleakage into space of its lighter ingredients. Of hydrogen and helium,\nwe are told, it should infallibly have become depleted; yet there is no\nlack of either in the sun of the twentieth century. Their retention,\nit must be admitted, is, on the hypothetical conditions, difficult to\naccount for. The 'critical velocity' at the limiting surface of the\nsupposed nebula would have been 4\u00b78 miles a second. This is, in fact,\nat the distance of Neptune, parabolic speed. The planet itself, if it\ncould attain to it, would break the bonds that bind it to the sun,\nand seek its fortunes under some different allegiance. Similarly, any\nparticle of the primitive nebula thus accelerated should have become an\nirreclaimable vagrant.\n\nNow, the velocity of hydrogen molecules at the zero of Centigrade is,\nin the mean, about 1-1/6 miles a second, but attains in the extreme\nto above seven miles. Hydrogen could not then have been permanently\nretained by the solar nebula, and the escape of helium would have\nmore slowly ensued. Yet these results, though seemingly inevitable,\ndid not actually come to pass, either because the generating body\nwas differently constituted from what has been supposed, or because\ncountervailing influences were brought to bear. It is, for instance,\namply possible that the dynamical condition of gases may be essentially\nmodified by rarefaction carried to a degree transcending the range of\nexperimental enquiries. The progress of science affords many warnings\nagainst trusting implicitly to the rule of continuity. Curves of change\nseldom preserve indefinitely a uniform character. Their unexplored\nsections may include quite unlooked-for peculiarities of flexure, and\nthe possibility seriously undermines confidence in inferences depending\nupon 'extrapolation.' The presence of hydrogen and helium in our system\ncannot, then, be ranked among facts incontestably contradictory of the\nnebular hypothesis.\n\nThe concerted advance of mathematical astronomy during the eighteenth\ncentury was effected with the confident serenity of irresistible\npower. One after another the obstacles barring its path went down\nbefore repeated and skilful onslaughts, the unbroken succession of\nwhich lends a certain exultant sameness to the story of the heroic age\nof analysis. The _M\u00e9canique C\u00e9leste_ attested 'victory all along the\nline.' There were no more worlds to conquer that Laplace knew of; the\nreign of gravitational law was firmly established throughout the solar\ndominions; menaced revolts had been appeased; anomalies removed; no\nextant observations any longer impaired the perfect harmony between\nwhat was and what had been foreseen. Nature for the moment submitted\nreadily to the trammels put upon her by human thought; her intricacies\nhad apparently ceased to defy unravelment; her modes of procedure\nlooked straightforward and intelligible. As they were judged to be in\nthe present, so they might be presumed to have been in the past; and\nthe temptation was irresistible to adventure backward speculation,\ninferring initial conditions from the elaborated product laid open to\nscrutiny.\n\nIt was an epoch of peremptory renewals. The formula of equality\npromised to regenerate society; a political panacea had been found\nby the creation of a republic 'one and indivisible'; and the success\nof the guillotine in securing its supremacy was almost outdone by\nthe triumphs of the calculus in vindicating the unimpeded sway of\ngravitation.\n\nHumanity had made a fresh start; science should do likewise. The\nsanguine spirit of a rejuvenated world animated all forms of human\nendeavour. It has long since evaporated. The buoyant hopes of a century\nback have been crushed; the future of civilization looks dim; and its\nuncertainty compromises the future of knowledge. But we, at any rate,\nno longer delude ourselves with the idea that he who runs may read\nthe secrets of the universe. We have learned by convincing experience\nhow much, and how variously, 'the subtlety of nature transcends the\nsubtlety of sense and intellect'; we are vividly aware that there is no\nsingle and simple recipe for the 'cosmification' of chaos.\n\nThat devised by Laplace has ceased to be satisfactory. Its simplicity,\nat first sight so seductive, leaves it at a disadvantage compared with\nthe intricacy of the effects it was designed to elicit. The relations\nclaiming explanation have multiplied with the progress of research.\nThose of the dynamical order were alone attended to by the geometers of\nthe eighteenth century, and even they have grown recalcitrant; while\nthose of a physical and chemical kind have proved wholly unmanageable.\nIt has, indeed, become abundantly clear that the series of operations\ndescribed by Laplace could scarcely, under the most favourable\ncircumstances, have been accomplished, and in a thin nebulous medium\nwould have been entirely impossible. The nebular cosmogony has not,\nthen, stood 'Foursquare to all the winds that blew.'\n\nIts towers and battlements have crumbled before the storms of adverse\ncriticism. It survives only as a wreck, its distinctive features\nobliterated, although with the old flag still flying on the keep. In\nthe next chapter we shall attempt a survey of the works set on foot for\nits reconstruction.\n\nFOOTNOTES:\n\n[Footnote 10: Presidential Address to the British Association,\nJohannesburg, August 30, 1905.]\n\n[Footnote 11: _Comptes Rendus_, tom. lii., p. 481.]\n\n[Footnote 12: _Astrophysical Journal_, vol. xi., p. 103.]\n\n[Footnote 13: Moulton, _Astrophysical Journal_, vol. xi., p. 110.]\n\n[Footnote 14: Nolan, _Nature_, vol. xxxiv., p. 287.]\n\n[Footnote 15: _Bulletin Astronomique_, tom. ii., p. 223.]\n\n\n\n\nCHAPTER IV\n\nTHE NEBULAR HYPOTHESIS VARIED AND IMPROVED\n\n\n'Restorations' often go very far. Things may be improved beyond\nrecognition, nay, out of existence. So it has happened to the nebular\nhypothesis. _Stat nominis umbra._ The name survives, but with\nconnotations indefinitely diversified. The original theme is barely\nrecalled by many of the variations played upon it. Entire license of\ntreatment prevails. The strict and simple lines of evolution laid\ndown by Laplace are obliterated or submerged. Some of the schemes\nproposed by modern cosmogonists are substantially reversions to Kant's\n_Natural History of the Heavens_; the long-discarded and despised\nCartesian vortices reappear, with the \u00e9clat of virtual novelty, in\nothers; nor are there wanting theories or speculations reminiscent\neven of Buffon's cometary impacts. Moreover, the misleading fashion\nhas come into vogue of bracketing Kant with Laplace as co-inventor\nof the majestic and orderly plan of growth commonly designated the\n'nebular hypothesis.' This has been, and is, the source of much hurtful\nconfusion. Save the one fundamental idea--and that by no means their\nexclusive property--of ascribing unity of origin to the planetary\nsystem, Kant's and Laplace's evolutionary methods had little in common.\nTheir postulates were very far from being identical; they employed\nradically different kinds of 'world-stuff'; and the 'world-stuff' was\nsubjected, in each case, to totally dissimilar processes.\n\nYet it is often tacitly assumed that to defend or refurbish one\nscheme is to rehabilitate the other. Under cover of the intellectual\nvagueness thus fostered, a backward drift of thought is, indeed,\ndiscernible towards the view-point of the K\u00f6nigsberg philosopher. It\nis recommended, not so much by the favourable verdict of science as\nby the wide freedom of the prospect which it affords. The imperative\nguidance of Laplace, reassuring at first, led to subsequent revolts.\nBut Kant is highly accommodating; one can deviate widely from, without\nfinally quitting, the track of his conceptions; they are capacious and\nindefinite enough to comport with much novelty both of imagination and\nexperience, and hence lend themselves with facility to the changing\nrequirements of progress.\n\nA noteworthy attempt was made, in 1873, by the late \u00c9douard Roche of\nMontpellier to reconstruct, without subverting, Laplace's hypothesis.\nThis remarkable man lived and died a provincial. Only a few scattered\nstudents have made acquaintance at first hand with his works; his fame,\nalways dim, now already begins to seem remote. Yet a score of years ago\nhe was still lecturing at the Lyc\u00e9e of his native town. The waters of\noblivion have grown, perhaps, more turbid than of yore. Anyhow, Roche\nof Montpellier is only vaguely remembered, and that by a specially\neducated section of the public, as having fixed a limit within which\na satellite cannot revolve intact.[16] Nearer to the ruling planet\nthan 2\u00b744 of its mean radii, it could not--setting aside improbable\nconditions of density--maintain a substantive globular status under the\ndisruptive strain of tidal forces. In point of fact, all the moons so\nfar discovered in the solar system circulate outside 'Roche's limit';\nand Saturn's rings, which lie within it, owe to that circumstance,\nit may plausibly be asserted, their pulverulent condition. Professor\nDarwin accordingly regards knowledge of that condition as dating from\n1848, the year in which Roche published the law involving it as a\ncorollary.[17]\n\nRoche was the precursor of Poincar\u00e9 and Darwin in those profound\ninvestigations of the figures of equilibrium of rotating fluid bodies\nwhich have opened up new paths and disclosed untried possibilities\nin evolutionary astronomy. His researches, moreover, into the origin\nof the solar system[18] constituted a reinforcement of first-rate\nimportance to the strength of Laplace's position. He was perhaps its\nmost effective and timely defender; he came to the rescue just when its\nsafety was seriously compromised, repaired its breaches, and threw up\nskilfully constructed outworks. Adopting the same premisses, he drew\nvirtually the same conclusions as Laplace, ingeniously modifying them,\nhowever, so as to evade certain objections, and temporarily to silence\nthe less obstinate cavillers. His results were, indeed, almost as\ndifficult to disprove as they had been to attain. They were arrived at\nlaboriously, legitimately, by long-drawn analytical operations; and the\nreasonings survive in full credit, even although the initial conditions\nthey started from now wear an aspect of unreality. Thus, the invention\nof _train\u00e9es elliptiques_ not only usefully met an argumentative\nemergency, but still remains as a supplementary adjunct to cosmic\nprocesses. Undeniably, polar annulation may have played a part in\nplanetary formation; the possibility cannot be gainsaid.\n\nThe 'ellipsoidal trains' investigated at Montpellier were huge\nnebulous strata detached from the polar regions of the primitive\nspheroid, which, bringing with them the low rotational velocity proper\nto that situation, tended, some to constitute interior equatorial\nrings, others to become agglomerated with the central mass. But their\nincorporation should have had as its consequence--since the 'law of\nareas' is inviolable--a quickening of angular rotation throughout the\nnebula. The 'law of areas,' it may be explained, is merely a short\ntitle for the 'law of conservation of moment of momentum,' which\nprescribes--as we know--that the sum total of the areas described in a\ngiven time on a given plane by the members or constituent particles of\na rotating system, multiplied by their several masses, remains constant\nunder all conceivable circumstances of re-arrangement or mutual\ndisturbance. Hence, approach towards the centre, because it narrows\nthe circle, must quicken the speed of rotation. A short line having\nto sweep over the same space as one of greater length, its moving end\nmust proportionately hurry its pace. An engulfment, accordingly, by the\nembryo sun of one of Roche's 'elliptic trains' would have occasioned\nan immediate shortening of the period of revolution of both nucleus\nand atmosphere, an accession of centrifugal force producing sudden\ninstability, and, as a consequence, the separation of an equatorial\nring.\n\nBy this subtly devised expedient Roche sought to explain away the\ndifficulty connected with the wide intervals between the planets.\nFor they originated, he conceived, not in the regular course of\ncondensation, but through complications arising abruptly and\nexceptionally. What he called the 'limiting surface' of the nebula\nmight also be described as the atmospheric limit. It corresponds to\nthe widest possible extension of a true atmosphere. Its boundaries\nare fixed at the distance just outside of which a satellite could\nfreely circulate in the axial period of its primary. Now the\nlimiting surface, if contraction had proceeded equably, should have\nretreated continuously, as axial movement quickened, its withdrawal\nbeing attended by the shedding of slender rivulets of superfluous\nmatter. But by the introduction of 'elliptic trains,' stability,\nartificially maintained (so to speak) throughout long spells of time,\nwas overthrown only by catastrophic downrushes from the shoulders of\nthe nebulous spheroid, when, with the prompt abridgment of the axial\nperiod, the limiting surface as promptly shrank inward, and there was\nleft, outstanding and self-subsistent, the tenuous ring destined to\ncoalesce into a planet. A singular and unexplained felicity of Roche's\nanalysis consisted in the symmetry of time-relations established\nby it. The successive births of his planets followed each other at\nequal intervals. A species of translation of Bode's law of distances\n(extended by him to satellite-systems) in terms of the nebular\nhypothesis thus appeared to be rendered feasible.[19]\n\nThat hypothesis, in its original form, as explained in the last\nchapter, produced planets with retrograde rotation--that is, spinning\nin an opposite sense to that of their circulation. For the purpose\nof abolishing the anomaly, Kirkwood, in 1864,[20] had recourse to\nsolar tidal friction, and he was followed, doubtless independently,\nby Roche, and by Roche's interpreter, C. Wolf of Paris. Objections to\nany particular mode of planetary formation, on the ground that its\noutcome must have been inverted axial movement, lost their validity,\nthey remarked, through the consideration that solar tidal friction\nwould have availed to redress the incongruity. For its retarding\naction would have ceased only when synchronism with the revolutionary\nperiod was attained--that is, when the planet wheeled in its orbit,\nas Mercury seems to do, turning always the same face inward; and then\nalready direct rotation would have set in, and, becoming accelerated by\ncontraction, should permanently retain the direction impressed upon it\nby the friction of sun-raised tides. A certain air of plausibility is\ngiven to this view by the fact that the only two retrograde planetary\nsystems are situated entirely beyond the possible range of any such\nmanner of influence, and may accordingly be supposed to have preserved\nunaltered their primitive fashion of gyration.\n\nThe late M. Faye was less loyal to tradition than the savant of\nMontpellier. The appearance in 1884 of his work, _Sur l'Origine du\nMonde_, gave the signal for renewed activity and a larger license in\ncosmological speculation. Conservative opinions on the subject are now\nrarely held; the old groove has been by most definitively quitted;\ninquiry becomes continually more individual and less constrained by\ntradition. Faye's reform, however, was not avowedly of a revolutionary\ncharacter. He did not make a clean sweep of the work of his great\npredecessor, by way of preliminary to setting forth his own more\nperfect plan. Yet his emendations of it went very deep.\n\nLaplace's nebula was of a gaseous consistence, and it stood in a\ngenuine atmospheric relation to the central condensation--that is to\nsay, its strata gravitated one upon the other; they were subject to\nhydrostatic pressure. Faye ruled things otherwise. The nebulous matrix\nwhich he postulated was a vast congeries of independently moving\nparticles, forming a system governed by a single period, in which both\ngravity and velocity increased in the direct ratio of the distance from\nthe centre. Now, globes formed by the method of annulation (admitting\nits practicability) out of materials thus conditioned, should have\npossessed, _ab initio_, a direct rotation; their axial spinning would\nhave been in the same sense as their orbital circulation. And this it\nwas which recommended to Faye the adoption of a meteoric structure for\nthe inchoate solar system. But the simple law of force regulating it at\nfirst would, by degrees, have undergone essential alteration. That of\ninverse squares, familiarized to ourselves by long habits of thought,\nwould have begun to supersede it so soon as a sun, properly so called,\ncould be said to exist. The retrograde planets, Uranus and Neptune,\nmust, however, by Faye's supposition have taken shape under the modern\nregimen; they were formed subsequently to the earth and all the rest\nof her sister orbs. This unexpected inversion of the recognised order\nof planetary age involved the further consequence that the ante-natal\noffspring of the sun--thus paradoxically to designate them--must have\ndrawn closer to him as his attractive power developed, Uranus and\nNeptune alone among the entire cort\u00e8ge preserving the original span of\ntheir orbits.\n\nFaye's scheme, if it did not meet all the arduous requirements of the\nproblem it confronted, served, at any rate, to illustrate very forcibly\nthe devious variety of tracks by which nebular evolution might advance\ntowards its goal. The particular one chosen was certainly not clear\nof impediments. In his preoccupation with the removal from Laplace's\nhypothesis of the flaw relating to planetary rotation, M. Faye had\ndiscarded its cardinal merit of explaining secessions of material by\nthe growth of centrifugal force. He alleged no sufficient reason, and\nnone could be alleged why the remodelled nebula should have separated\ninto rings.[21] The process implies definite and special conditions;\nit testifies to a rhythmically acting cause. Laplace brought such a\ncause into play. Faye abolished it, and his annuli, accordingly, wear\na fictitious aspect. It is, indeed, true that an annular structure\nis commonly visible in nebul\u00e6, but it is begging a most arduous\nquestion to assume that nebular spires have anything in common with\nplanet-forming rings.\n\nThese would probably never have been heard of save for the Saturnian\nexample. A pattern is easily copied; an idea palpably feasible is\ntempting to adopt; a demonstration on the _solvitur ambulando_\nprinciple cannot but prove convincing. But how if the rings cannot be\nmade to coalesce into globes? And the difficulty of the transformation\nbecomes more apparent the more clearly its details are sought to be\nrealized. Reversed in direction, it might better find a place in the\norder of Nature. 'Analysis seems to indicate,' Kirkwood wrote in\n1884,[22] 'that planets and comets have not been formed from rings, but\nrings from planets and comets.' Nor is this mode of procedure merely\npossible according to theory; it is also vividly illustrated by facts.\nMeteoric swarms can be observed, decade by decade, to disperse under\nthe scattering influence of the sun and planets, and unmistakably tend\nto become more or less uniformly distributed along the entire round of\ntheir orbits. Their advance is directed, not towards condensation, but\ntowards disaggregation; and they pursue it with surprising rapidity.\n\nFaye's theory was disfigured by a still more glaring incongruity.\nNothing in the planetary economy seems more evident than that the\nzone of asteroids marks a division between two strongly dissimilar\nstates of the solar nebula. It is a visible halting-place. One series\nof events came to an end, and there was an interlude before the next\nbegan. During that interlude, during the partial suspension of activity\nwhich ensued upon the production of the Ajax among the planets, the\ncrowd of planetoids were launched to fill the blank space. Here, if\nanywhere, Nature changed her hand and tried a fresh method. Faye's\nshifting of the scene of change to trans-Saturnian regions is then, as\nM. Wolf justly perceived, non-natural, and undermines the credit of a\nplan to which the device is essential.\n\nOn the other hand, it had the merit of being elastic enough to include\nthe great cometary family. Kant had also, although in an unsatisfactory\nmanner, made room for them; but Laplace had no choice save to regard\nthem as casual intruders from space, the admission of which as natives\nof his well-ordered domain would have led to the subversion of all\nits harmonious regulations. Modern inquiries, however, prove comets\ndecisively to be no such stray visitors as Laplace supposed, but to\nbe of the same lineage--however remotely traceable--with the planets,\nand to own the same allegiance. Drifting with the sun, they form part\nof its escort on the long, irrevocable voyage it is engaged upon, and\ncannot, save by accidents of perturbation, be driven finally to part\nfrom its company. The problems of planetary and cometary origin are\nthen inseparable; the two classes of body are fellow-citizens of one\nkingdom. Comets become only by compulsion cosmopolitan wanderers from\nstar to star.\n\nThere was yet another motive and semblance of justification for Faye's\nreform of the nebular hypothesis. The discovery of the conservation\nof energy supplemented, as we have seen, very happily the mechanics\nof a condensing nebula by satisfactorily solving the enigma of\nsolar radiation. Helmholtz was thus able, in 1871, to sketch cosmic\ndevelopment as, in its essence, a thermodynamic process on the grandest\nscale. Yet the alliance entered into, fruitful and fortifying though\nit was, had an attendant embarrassment. Time had now to be reckoned\nwith. In the cosmogonies of Kant, Herschel, and Laplace the allowance\nof \u00e6ons was unstinted. Because the rate of change was indeterminate,\nthey might be permitted to elapse _ad libitum_. But it was otherwise\nwhen the driving-power came to be defined. 'Conservation of force'\nimplies the measurableness of force. Equivalence cannot be ascertained\nwhere no limits are determinable. Knowledge, accordingly, regarding the\nsource of the sun's heat brought with it the certainty that the source\nwas by no means inexhaustible. The stock of energy rendered available\nby shrinkage from a primitively diffuse to its present compact state\nwas enormous, but not boundless. The task then became incumbent\nupon cosmogonists of proving its sufficiency, or of eking out its\nshortcomings.\n\nThe problem is both retrospective and prospective. We look back towards\nthe birth of the sun, we look forward to its demise; and each event\nhas, if possible, to be located on our time-scale. Helmholtz assigned\nterms of twenty-two millions of years in the past and seventeen\nmillions in the future for the shining of our luminary with its actual\nintensity. Geologists and biologists, however, claimed a much more\nextended leisure for the succession of phenomena on this globe, and\nefforts on the part of physicists to meet their demands barely availed\nto tone down without removing the discrepancy. M. Faye then came to\nthe rescue. His suggestion that the earth took separate form while the\nsun was still nebulous was designed to conciliate the demands of those\nwho needed all but eternity for the slow accumulation into specific\ndifferences of infinitesimal variations. In this way a start was\ngained upon the sun; the preparations for vitality on our planet were\ngoing forward long before the lavish radiative expenditure designed\nto nurture its development had begun. The earth, in fact, was shaping\nitself for its destiny in advance of the epoch when time began to count\nfor the sun.\n\nThis supposed relation of precedence cannot, indeed, be insisted upon;\nit was imagined to save a difficult situation, and intimates a design\nmore or less academic. Yet the expedient was significant as regards the\neffect of the introduction into modern thought of the principle of the\nconservation of energy. It gave definiteness and a kind of solidity\nto speculation by widening the basis upon which it was made to rest.\nAt the same time it necessitated adjustments between the exigencies\nof the various sciences, and brought into prominent view apparent\nincompatibilities only to be removed by prolonged investigations of\nwide scope and intricate bearings. Modern cosmogony, in short, while\ndisposing of enlarged means, has to meet multiplied requirements. Quite\nlately, nevertheless, some authoritative exponents of geological and\nbiological science manifest a satisfactory disposition to 'hurry up\ntheir phenomena,' quite independently of the inadequate age of the\nsun.[23] On neither side, accordingly, are the irreconcilable claims of\nthe past any longer insisted upon, and a compromise has become easily\npossible.\n\nA theory of planetary evolution marked by some novel features was\nably expounded by M. du Ligond\u00e8s in 1897.[24] Designed to improve, by\nsimplifying, Faye's plan, it reduced postulates to a minimum, and left\nthe freest possible play to 'original indetermination.'[25] The embryo\nworld of M. du Ligond\u00e8s was a tumultuous m\u00eal\u00e9e of particles moving\nanyhow. Their jostlings, however, did not, and could not, exactly\nbalance, and the inequality, small though it might be, sufficed to\nafford a basis for harmonious growth. Motion became regularized by\ncollisions; counter-currents of velocity were gradually eliminated; and\nthe particles pursuing eccentric or retrograde courses, brought sooner\nor later to a stand, fell towards the centre and accumulated into the\nsun, while the remnant that travelled in the prevalent direction along\ncircular paths finally constituted the planets. They were formed, not\nat haphazard, but through the medium of zones of maximum density,\ndue to the variations of gravity within the disc towards which the\nprimitive spheroid finally collapsed; and each, as it took shape,\nbecame a source of perturbative influence on its subsequently developed\nneighbours, by which the inclinations of their orbital planes and of\ntheir axes of rotation were in various ways altered. The planetary\nzones, too, contracted with the advance of condensation, so that the\nmatured planets occupied positions much nearer to the sun than those\nassigned to their inchoate materials. The _modus operandi_ employed, in\nshort, adapted itself with praiseworthy readiness to the diversities of\nnature.\n\nSir Robert Ball is at one with M. du Ligond\u00e8s in regarding the origin\nof the solar system chiefly under its mechanical aspect. Like Helmholtz\nand Faye, he chooses pulverulent materials to work with; his nebula is\na 'white nebula.' But looking still further back, he discerns as its\nparent an irregular 'green' nebula, the confused movements of which\nfalling into a settled order as the result of encounters, it slowly\nflattened down into the 'plane of maximum areas'--the fundamental plane\nconformed to more and more closely as the energy of a system inevitably\nwastes. He dispenses with the troublesome process of annulation, and\nstarts his planets virtually by Kant's method of accidental nuclear\ncondensation.[26] A spiral structure, moreover, would be imparted to\nthe entire nebula by the gradual propagation outward of the central\nacceleration due to contraction.\n\nBut would it have contracted? It had, by supposition, reached the stage\nof approximate unanimity in movement. The great bulk of its constituent\nbodies circulated in the same direction, in nearly the same plane,\nand presumably in orbits not deviating much from circularity. Their\naggregate condition might then be regarded as permanent and stable. The\ncentral mass would, accordingly, no longer be fed by the engulfment\nof particles brought to rest by their mutual impacts; motion being\nunimpeded, heat could not be evolved; and the imagined transformation\nof a disc-like meteoric formation into a sun and planets would fail to\ncome to pass.\n\nWhat, then, we may ask ourselves, is the upshot of these various\nefforts at reconstruction? They establish, certainly, the unassailable\nunity of the solar world; and the solar world must be understood to\nembrace comets and cometary meteors. The arguments favouring this\nunity have gained enormously in cogency through modern discoveries.\nFor those depending upon structural coincidences and harmonies\nof movement have been reinforced by others of a totally different\nnature, furnished by the doctrine of the conservation of energy and\nthe teachings of spectrum analysis. The sun is hot because it was\nanciently expanded; the energy of position formerly belonging to its\nparticles incontestably provided a large part, if not the sum total,\nof its present thermal energy, and this amounts to saying that a\nsphere indefinitely great was once filled by our inchoate system. The\nconclusion that it arose from an undivided whole through the gradual\ndifferentiation of its parts is further ratified by the identity of\nsolar and terrestrial chemistry. The earth is thus strongly averred to\nhave once made an integral part of the substance of the sun, and what\nis true of the earth is no less true of its sister planets.\n\nRegarding the mode and manner of cosmic change there is, nevertheless,\nno consensus of opinion. Faye made a noteworthy effort to elaborate a\nprocess that might endure modern tests of feasibility, yet his theory\nhas been well-nigh torn to pieces by adverse criticism. M. du Ligond\u00e8s\nescapes some, but not all, of the objections which proved fatal to\nhis predecessor. That there was in the beginning a solar nebula, all\nare agreed; but whether it was gaseous or pulverulent, whether it\nshone with interrupted or continuous light, how it became ordered and\norganized, how it collected into spheres, leaving wide interspaces\nclear, the wisest are perplexed to decide.\n\nMr. Moulton concludes, from his careful examination of the subject,\nthat 'the solar nebula was heterogeneous to a degree not heretofore\nconsidered as being probable, and that it may have been in a state'\nresembling that exhibited in recent photographs of spiral nebul\u00e6.[27]\nBut, even if all the facts do not chime in with this tempting analogy,\nthere can be little reason to dissent from his intimated opinion that\n'the Laplacian hypothesis is only partially true, and that we do not\nyet know the precise mode of the development of the solar system.'\n\nFOOTNOTES:\n\n[Footnote 16: _M\u00e9moires de l'Acad\u00e9mie de Montpellier_, tom. i.]\n\n[Footnote 17: _The Tides_, p. 327.]\n\n[Footnote 18: _M\u00e9moires de l'Acad\u00e9mie de Montpellier_, tom. viii.]\n\n[Footnote 19: C. Wolf, _Bulletin Astronomique_, tom. i., p. 596.]\n\n[Footnote 20: _American Journal of Science_, vol. xxxviii., p. 3.]\n\n[Footnote 21: G. H. Darwin, _Nature_, vol. xxxi., p. 506.]\n\n[Footnote 22: _Proceedings of the American Philosophical Society_, vol.\nxxii., p. 109.]\n\n[Footnote 23: De Vries, _Die Mutationstheorie_, Bd. II., p. 714.]\n\n[Footnote 24: _Formation M\u00e9canique du Syst\u00e8me du Monde._ See also _Le\nProbl\u00e8me Solaire_, by the Abb\u00e9 Th. Moreux, p. 63 _et seq._]\n\n[Footnote 25: _Revue des Questions Scientifiques_, January, 1904.]\n\n[Footnote 26: _The Earth's Beginnings_, p. 247.]\n\n[Footnote 27: _Astrophysical Journal_, vol. xi., p. 130.]\n\n\n\n\nCHAPTER V\n\nTIDAL FRICTION AS AN AGENT IN COSMOGONY\n\n\nThe effects of tidal friction are of almost infinite complexity. How it\nwill act in each particular case cannot be predicted offhand; it is a\nmatter for detailed inquiry. Mutually countervailing influences have to\nbe taken into account, nor is the balance easy to strike. The manner of\nits inclination may, indeed, often depend upon qualities and relations\nof the bodies concerned which lie outside the range of what can be\ndistinctly ascertained. All that may be hoped for, then, is to arrive\nat estimates neither misleading by their ostensible precision, nor yet\nso vague as to be wholly uninstructive, of the part played by tidal\nforces in moulding the history of connected globes.\n\nThe assumption that they attract one another as if the mass of each\nwere collected at its centre, is one of those convenient fictions\nwithout which the advancing feet of science would be impeded by tangled\nthickets of illusory refinements and superfluous elaborations. The\nfiction would correspond with fact only if the globes were truly\nspherical, and they could be truly spherical only if they were ideally\nrigid. Cosmic bodies, however--suns and planets alike--are actually\nplastic spheroids; they can, to be sure, be treated without sensible\nerror as attractive points when their distances are very great\nrelatively to their diameters; but upon a closer approach inequality\nof action supervenes. The component parts of the gravitating masses\nrespond, each individually, and in a measure independently, to the\ngraduated pulls exercised upon them, and tidal strains begin variously\nto take effect.\n\nTheir historical significance was in part divined by Kant. His\npenetration of so recondite a secret is truly astonishing. A struggling\nyoung pedagogue in a remote Prussian province, profoundly learned,\nthough no more than half skilled in technical acquirements, saw by\nintuition what escaped the acumen of all the great geometers of the\neighteenth century--namely, that the moon turns one perpetual face\ntowards the earth, because its primitive rotation was stopped by the\nfriction of earth-raised tides. He perceived besides that a reciprocal\naction of the same kind must affect the earth, and will continue to\naffect it until the day coincides in length with the month. Nor did he\nfail to point out that, in a molten state of the globes, the process\nwould advance with comparative rapidity. To one solitary thinker, then,\nit became apparent, already in 1754,[28] that oceanic tides are, in\ncosmogony, of negligible importance compared with bodily tides.\n\nThere is no substance in nature that will not change its shape through\nprolonged stress, and the more readily the nearer it approaches to the\nfluid condition. The heaping-up of the waters on the earth's surface at\nthe bidding of the moon is thus a differential effect. Continents heave\nand subside as well as oceans, though not nearly to the same extent.\nThe measurable rise of water serves to gauge the relative mobilities\nof the solid globe and of its liquid envelope. If the former did not\nyield at all to the pull so readily obeyed by the latter, the tides\nwould, in fact, be greater than they actually are in the proportion of\nabout three to two, the ratio indicating for the earth an effective\nrigidity at least equal to that of steel.[29] Were there no discrepancy\nin rigidity between the various parts of our terraqueous world, tides\nwould fail to be perceptible. The ocean and the bed of the ocean would\nrise and fall together, and to the same extent. In the far past there\n_was_ no discrepancy. The viscous earth took, as a whole, the form\nmomentarily impressed upon it by the unequal attractions of the sun and\nmoon on its variously distant sections, with the upshot of bringing the\nyear, month, and day into relations so familiar as to appear inevitable.\n\nTidal friction does not merely act as a check upon rotational speed.\nOne element of motion in a system cannot be altered without some\ncounter-change in the others. They are coupled up together like a train\nof geared wheels. From the principle of the conservation of moment of\nmomentum, we know with certainty that a loss in one direction must\nbe compensated by a gain in some other. Tidal friction had, then,\nreactive consequences. They were first adverted to by Julius Robert\nMayer in 1848,[30] and were brought prominently into view in the series\nof investigations begun by Professor Darwin in 1879. The rotational\nmomentum removed from the earth by the drag of a circulating wave of\ndeformation must assuredly have reappeared in some other part of the\nsystem. It was restored, all but the percentage wasted as heat, by the\nwidening of the lunar orbit.[31] Concomitantly with the slackening of\nthe earth's axial rate, the moon retreated from its surface, pulled\nforward by the tidal crest continually in advance of its position. This\nredressed the balance by augmenting orbital momentum, while at the same\ntime diminishing the moon's linear velocity. The importance of this\nsecondary frictional effect in the history of the earth-moon system was\nthe virtual discovery of Professor Darwin.\n\nThat system occupies a critical situation in the solar cort\u00e8ge. The\nplanets interior to it have no satellites; the planets exterior to it\n(Neptune making probably only an apparent exception to the rule) have\ntwo or more. The earth alone is truly binary; and the moon is not only\nits solitary companion, but it is by far the largest companion-body,\nrelatively to the mass of its primary, to be found within the precincts\nof the solar domain. These circumstances are certainly not disconnected\none from the other, and they obviously depend upon a single cause.\nSolar tidal friction was here the determining factor. The apportionment\nof satellites to the various planets was, beyond doubt, in great\nmeasure prescribed by the degrees of retarding power exerted on their\naxial movement through the agency of sun-raised tides in their still\nplastic bodies. Hence, the disruptive rate of spinning needed for\nthe separation of satellites was never attained by either Mercury or\nVenus; they remained moonless for all time, and exposed, through the\ncutting down of their rotational velocity, to uncompensated extremes\nof temperature. How the earth was to fare in both respects long hung\nin the balance. Rightly to forecast its destiny would, indeed, have\ndemanded no common perspicuity in an intelligent onlooker from some\nother sphere. Although the solar brake acted upon terrestrial rotation\nwith no more than one-eleventh the power brought to bear upon that\nof Venus, it nevertheless sufficed during uncounted ages to hinder\nacceleration from reaching the pitch involving instability.\n\nOur embryonic planet had long ceased to be nebulous, and had, in fact,\nshrunk by cooling nearly to its present dimensions before the die was\ncast. Then, at last, the hurrying effects of contraction prevailed\nover the slowing down due to tidal resistance, axial speed overbore\nequilibrium, and the spheroid divided. Now globes thus far advanced\nin condensation are apt to split less unequally than globes in a more\nprimitive stage; and the moon, because late-born, was of large size.\nIts mass is 1/81 that of the earth; the masses of Titan and Saturn are\nas 1 to 4,600; while Jupiter's third and greatest satellite contains\nonly 1/11300 part of the matter englobed in the parent-body. Moreover,\nProfessor Darwin has made it clear that the satellites of Jupiter and\nSaturn revolve now in orbits not widely remote from those at first\npursued by them; while the moon, on the contrary, started on its career\nalmost, if not quite, from grazing contact with its primary. Owing to\nthese two exceptional circumstances--its considerable relative mass\nand its close initial vicinity--the moon wielded over the earth tidal\ninfluence incomparably more powerful than that exerted by any of its\ncompeers in the sun's realm.\n\nThe lunar-terrestrial system offers, accordingly, an example unique\namong those in solar subordination of a pair of globes, the mechanical\nrelations of which have been settled on their present basis by the\npredominating agency of bodily tides. It holds forth, too, the one\ncase in which origin by fission was possible. Professor Darwin's\ncommunication to the Royal Society in 1879 occasioned on this point a\nremarkable diversion of ideas. Saturn's rings were at last, through\nthe reasonings contained in it, perceived to be illustrative of only\none among many feasible modes of cosmic growth. It became clear that a\nsingle cut-and-dried method would not answer all the infinitely varied\npurposes of creative design. Annulation might have served its turn,\nbut there were alternatives. A fresh standpoint was virtually attained,\nand the wide prospect commanded by it begins already to spread out\ninvitingly before the gaze of investigators.\n\nBut whether the moon emerged from the earth as a protuberance, or was\nabandoned by it as an irregular equatorial ring, it was revolving,\nwhen our theoretical acquaintance with it begins, in a period of\nnot less than two and not more than four hours, quite close to the\nearth's surface; while the nearly isochronous rotation of the earth\nwas conducted with all but disruptive rapidity. The situation is so\nsuggestive that it needs only a short and tolerably safe leap in the\ndark to reach the conclusion that the two masses had very recently\nbeen one. With their division, at an epoch estimated to have been\nabout sixty million years ago, the process began by which the moon was\npushed back along a widening spiral course to its present position,\nthe vanished rotational momentum of the earth cropping up again in the\naugmented orbital momentum of the moon. And the transformation is, at\nleast in theory, still going on.\n\nTidal friction has further capabilities. The transference of momentum\nfrom one part of a system to another is only the most obvious among\nthe crowd of its results. Scarcely an element of movement escapes its\ninfluence. It increases, as a rule, orbital eccentricity. The smallest\ninitial deviation from circularity develops, through the inequality of\naccelerative action thence ensuing, into pronounced ovalness. That of\nthe moon's path can in this way be accounted for. Moreover, its plane\nwas, in all probability, shifted simultaneously and under compulsion\nof the same power, from its original coincidence with the earth's\nequatorial plane to the level it now occupies. The obliquity of the\necliptic, too, is partially explicable on the same principle. 'The\npresent motion of the two bodies' (to quote Professor Darwin's words),\nare 'completely co-ordinated by the theory that tidal friction was the\nruling power in their evolution.' Holding this clue, we are enabled to\ntrace them back to the start of their dual existence, and to follow\nthe insensible modifications by which their state was moulded to its\nactual form.\n\nIn no other satellite-system is this possible. No moon besides our own\npossesses a stock of orbital momentum large enough to intimate for it\nan analogous history. Planetary attendants elsewhere travel nearly in\ntheir original tracks; the fluid ripples raised by them on the surfaces\nof their primaries lacked power to displace them sensibly. Their own\nrotation, indeed, seems to have been completely destroyed. Destroyed,\nthat is, relatively to the destroying body. There is a certainty that\nsome, there is the strongest likelihood that all, of the Jovian and\nSaturnian satellites turn unchangingly the same face towards their\nprimaries. They rotate in the period of their several revolutions,\njust as our moon does, and as a consequence of the same cause. Tidal\nfriction, however, appears to have been otherwise of subordinate\nimportance in shaping their dynamical relations.\n\nThe agency will not, then, serve in all cases for a _deus ex machin\u00e2_.\nIt is not indiscriminately efficacious. The modes of its action have,\nin each of the systems considered, to be delicately distinguished.\nThe stage of development arrived at by the bodies affected, their\ndegree of viscosity, their comparative mass and bulk, their modes of\nmotion, all avail profoundly, and it may be incalculably, to modify the\noutcome. The facility of error in estimates of the kind is illustrated\nby Professor Darwin's remark that the magnitude of the tide-raising\nforce is only one factor of the product.[32] The other is relative\nmovement. Now, in the case of the moon the former continually augmented\nretrospectively, while the latter fell off. Tidal generative power\nvaries inversely as the cube of the distance; in antique times, then,\nwhen the earth and moon revolved contiguously, the bodily distortions\nthey mutually produced were beyond question on an extremely large\nscale. Yet, because of the near coincidence of the periods of the\nglobes, they must have been almost inoperative for frictional purposes.\nThe travelling of the piled-up matter over their surfaces was too slow\nto lend it much power as a friction-brake. The insignificant waves\nraised by the sun were, we are led to believe, because of their swift\nrelative motion, more influential at that early epoch in checking\nterrestrial rotation than the colossal, but nearly stationary waves due\nto the moon.\n\nNumerical calculations, where they are practicable, afford the only\nsafe guide to this intricate field of inquiry. It does not suffice to\nshow that tidal action would have been of the kind required--would\nhave taken the right direction--for bringing about some apparently\nanomalous result. Proof must, besides, be forthcoming that the action\nwould have been of adequate power. Plausible guesses on the subject\nmay be entirely fallacious. The machine, even if properly constructed\nfor the end in view, may work too feebly for its attainment. We are,\nfor instance, assured that no difficulty connected with the sense of\nplanetary rotation need impede acceptance of the theory of planetary\norigin from separated rings, since even if the embryo globes gyrated\nthe wrong way at the outset, solar tidal friction would promptly have\nreduced them to conformity with the general current of movement. This\nis true in principle, but will it bear quantitative investigation?\nMany promising hypotheses have broken down under the weight of\nfigures; whether this particular one is strong enough to survive their\napplication remains to be seen. We are, indeed, sure of its validity as\nregards Mercury, but the efficacy of tidal friction decreases as the\nsixth power of increasing distance, and the actual rotation of Venus\nfurnishes an enigma sufficiently perplexing to discourage scrutiny of\nits dimly discerned antecedent conditions. As regards the earth and the\nexterior planets, the question could only be answered with the help of\ninformation which is not forthcoming.\n\nThe unexpected circumstance that the newly-discovered ninth Saturnian\nmoon circulates from east to west can thus be no more than tentatively\nexplained by invoking this agency of change. Admitting (as we seem\nbound to do) that satellites are the offspring of the planets they\nattend, there is no evading the conclusion that the small body under\ndiscussion was thrown off from a primary endowed with a rotation\nopposite to that now possessed by it. And the reversal must have been\ncompletely brought to pass before the eighth satellite, Japetus, came\ninto existence. The crux is most arduous; there is no other resource\nfor meeting it but to consider the effects on planetary rotation of\nsolar tides, and this Professor W. H. Pickering, the discoverer of\nPh\u0153be, has done.[33] But a cause may be true without being sufficient;\nand close calculation will be needed to determine, in this instance,\nhow the matter stands.\n\nProfessor Darwin's researches were fruitful just because they were\ndefinite. They demonstrated, once for all, the diverse faculties of\ntidal friction as a cosmogonic agency, and indicated clearly the\ndepartments of cosmogonic change in which its competence lay. They\navailed, moreover, to determine for the earth-moon system the amount of\nwork actually done by tidal friction in these several departments, and\nto prove its large excess over the corresponding output in any other\nsub-system falling within the sphere of observation. This memorable\nresult suggests that our terrestrial home may be singular, not only in\nits evolutionary history, but in the innumerable adjustments fitting it\nto be the abode of life.\n\nThe relations of the earth and moon adumbrate, and scarcely more\nthan adumbrate, the physical influences mutually exerted upon each\nother by numerous twin-globes in stellar space. Tidal friction is of\nmaximum power in systems formed of equal masses; and those of double\nstars are seldom widely disparate. Most, if not all of them, were,\nbesides, primitively very near neighbours, so that their symmetry must\nhave been marred by conspicuous tidal deformations. The results upon\ntheir development have been expounded in detail by Dr. See. One of\nthe most remarkable is the high average eccentricity of their orbits.\nVisual binaries, with few exceptions, travel in considerably elongated\nellipses, while spectroscopic binaries as a rule pursue approximately\ncircular paths. Dr. See's argument that the eccentricity of the more\nspacious systems was acquired under the influence of tidal friction,\nduring the long course of progressive separation, is well-nigh\nirresistible.\n\nTrue, this line of explanation is not wholly clear of obstacles and\nincongruities. Yet they may probably be described as of a complicating,\nrather than of a contradictory kind. The theory of tidal friction\nis not a universal solvent of the difficulties encountered in the\nstudy of double stars. That the mode of action it deals with had a\ncontributory share towards regulating their mechanical arrangements\nmay, nevertheless, be regarded as certain, while the potency and\nperhaps even the manner of its operation varied extensively from system\nto system. What precisely it effected in each lies beyond our range of\ndetermination. For the data available regarding the viscosity, density,\nand axial movements of embryo star-pairs must always be too scanty and\ninsecure to provide a basis for rigorous computations. The mystery of\nthe fore-time can never be entirely dissipated. Enough if we can look\nat it through a glass which darkens, without distorting, the objects\npresented in its field of view.\n\nFOOTNOTES:\n\n[Footnote 28: _S\u00e4mmtliche Werke_, Bd. VI., pp. 5-12, 1839.]\n\n[Footnote 29: G. H. Darwin, _Encyclop\u00e6dia Britannica_, article on\n'Tides.']\n\n[Footnote 30: _Dynamik des Himmels_, p. 49.]\n\n[Footnote 31: Darwin, _Philosophical Transactions_, vol. clxxii., p.\n528.]\n\n[Footnote 32: _Philosophical Transactions_, vol. clxxi., p. 876.]\n\n[Footnote 33: _Harvard Annals_, vol. liii., p. 58.]\n\n\n\n\nCHAPTER VI\n\nTHE FISSION OF ROTATING GLOBES\n\n\nFew people need to be told that a rotating fluid mass is shaped very\nmuch like an orange. It assumes the form of a compressed sphere. And\nthe reason for its compression is obvious. It is that the power of\ngravity, being partially neutralized by the centrifugal tendency due\nto axial speed, decreases progressively from the poles, where that\nspeed has a zero value, to the equator, where it attains a maximum.\nHere, then, the materials of the rotating body are virtually lighter\nthan elsewhere, and consequently retreat furthest from the centre. The\n'figure of equilibrium' thus constituted is a spheroid, a body with\ntwo unequal axes. In other words, its meridional contour--that passing\nthrough the poles--is an ellipse, while its equator is circular.\n\nNow we know familiarly, not only that a spinning sphere becomes a\nspheroid, but that the spheroid grows more oblate the faster it spins.\nThe flattened disc of Jupiter, for instance, compared with the round\nface of Mars, at once suggests a disparity in the rate of gyration.\nBut there must be a limit to the advance of bulging, or the spheroid,\naccelerated _ad infinitum_, would at last cease to exist in three\ndimensions. Clearly this unthinkable outcome must be anticipated; at\nsome given point the process of deformation must be interrupted. A\nbreach of continuity intervenes; the train is shunted on to a branch\nline. Nor is it difficult to divine, in a general way, how this comes\nto pass. Equilibrium, beyond doubt, breaks down when rotation attains a\ncertain critical velocity, varying according to circumstances, and the\nspheroid either alters fundamentally in shape or goes to pieces.\n\nSo much plain common-sense teaches, yet the precise determination of\nthe course of events is one of the most arduous tasks ever grappled\nwith by mathematicians. M. Poincar\u00e9 essayed it in 1885;[34] it was\nindependently undertaken a little later by Professor Darwin;[35]\nand the subject has now been prosecuted for eighteen years, chiefly\nby these two eminent men, with a highly interesting alternation of\nachievement, one picking up the thread dropped by the other, and each\nin turn penetrating somewhat further into the labyrinth. The results,\nnevertheless, are still to some extent inconclusive; they indicate,\nrather than indite, the genetic history of systems. A strong light is,\nindeed, thrown upon it; but in following its guidance, the limitations\nof the inquiry have to be borne in mind. The chief of these are, first,\nthat the assumed spheroid is liquid; secondly, that it is homogeneous.\nNeither of these conditions, however, is really prevalent in nature,\nso that inferences based upon them can only be accepted under reserve.\nThey were adopted, not by choice, but through the necessities of the\ncase. There was no possibility of dealing mathematically with bodies\nin any other than the liquid state. The equilibrium of gaseous globes\ndefies treatment, except under arbitrary restrictions.[36] Nor is\nit possible to cope with the intricacies of calculation introduced\nby variations of interior density. Cosmical masses, as they actually\nexist, are nevertheless strongly heterogeneous, so that at the utmost\nonly an approximation to the genuine course of their evolution can\nbe arrived at by the most skilful analysis. Yet even an approximate\nsolution of such a problem is of profound interest. We can here only\nattempt briefly to specify its nature.\n\nThe course of change by which the equilibrium of a rotating liquid\nspheroid is finally overthrown has, at any rate, been satisfactorily\ntracked. When its spinning quickens to a disruptive pitch, it acquires\nthree unequal axes instead of two. The equator becomes elliptical like\nthe meridians. A 'Jacobian ellipsoid' is constituted. To this new form,\nit would seem, a long spell of stability must be attributed; only its\nmajor axis becomes more and more protracted as cooling progresses,\nand with cooling, contraction, and with contraction the increase of\naxial velocity. Then at last a crisis once more supervenes; there\nis a collapse of equilibrium, and its re-establishment involves the\nsacrifice of the last vestige of symmetry. An 'apioid,' or pear-shaped\nbody, replaces the antecedent ellipsoid; and its apparent incipient\nduality suggested to M. Poincar\u00e9 that the furrow unequally dividing it\nmight deepen, with still accelerated gyration, into a cleft, splitting\nthe primitively single mass into a planet and satellite. But this\neventuality, he was careful to note, had no direct bearing on Laplace's\nhypothesis, which dealt with a nebula condensed towards the centre,\nwhile the fissured apioid was liquid and homogeneous.[37]\n\nProfessor Darwin followed out the conditions of this remarkable\npear-shaped body to a closer degree of approximation than its original\ninvestigator had done, and succeeded in virtually demonstrating its\nconditional stability. But his analysis tended to smooth away the\ncharacteristic peculiarities of its shape, and, so far, to diminish\nthe probability of its ultimate disruption. Mr. Jeans, on the other\nhand, from an elaborate study of a series of cigar-shaped figures\nwhich in theory follow a parallel course of development to that\npursued by ellipsoids, derived, by strict mathematical reasoning, the\nactual separation of a satellite from one end of a parent-cylinder.\nThe representative figures reminded Professor Darwin 'of some such\nphenomenon as the protrusion of a filament of protoplasm from a mass\nof living matter.' 'In this almost life-like process' he saw 'a\ncounterpart to at least one form of the birth of double stars, planets,\nand satellites.'[38]\n\nBut the resemblance, when examined dispassionately, seems shadowy and\nevasive, especially when we confront it with the case of double stars.\nHere, indeed, an entirely different set of conditions comes into play\nfrom that postulated by Poincar\u00e9 and Darwin, since stars are certainly\nnot liquid bodies.[39] They are most likely gaseous to the core,\nthough the indefinite diffusiveness incident to gaseity is restricted\nby their condensed photospheric surfaces. This circumstance intimates\nthe possibility that the results arrived at for liquid globes by\nmathematical analysis may, with qualifications, be extended to stars;\nbut the necessary qualifications, unfortunately, are vague and large;\nfor too little is known regarding the physical condition of stellar\nspheres to warrant assumptions that might provide a secure basis for\nresearch.\n\nThe evolution of binary stars can then only be treated of\ninferentially, not rigorously; and we must, at the outset, discard\nthe idea that it is illustrated by the phenomena of double nebul\u00e6.\nMany such objects thought to supply clinching visual arguments for the\nactual effectiveness of slow cosmic fission proved, on the application\nto them of the late Professor Keeler's searching photographic methods,\nto be knots on spiral formations. Their mutual relations are then\nentirely different from what had been supposed by telescopic observers;\nthey are, in fact, still structurally connected, and the mode of their\norigin, however inviting to conjecture, scarcely comes within the scope\nof definitely conducted inquiries. Their future destiny is no more\naccessible to it than their past history, and only by a daring flight\nof imagination can we see in spiral nebul\u00e6 the prototypes of double\nstars.\n\nQuestions as to the mode of genesis of these latter systems have, in\nrecent years, acquired extraordinary interest. Conclusive answers\ncannot, indeed, at present be given to them, because the terms in which\nthey are couched lack distinctness, owing to our lack of knowledge;\nbut probable answers may legitimately supply their place, at least _ad\ninterim_, above all when their probability is heightened almost to\ncertainty by the accumulation of circumstantial evidence.\n\nObservations and investigations of stellar eclipses have created a\nnew department of astrophysics, and have vastly widened the domain of\ncosmogony. They have brought to notice a number of systems, not merely\nin a primitive, but seemingly in an inchoate stage of development. The\nperiods of occulting stars are nearly all of them less than seven days,\nalthough one extending to thirty-one has lately been recognised; and\nthe comparative length of the intervals of obscuration shows them to\nbe produced by the circulation in narrow orbits of distended globes.\nThese are characteristic symptoms of juvenility, for, as we have seen,\norbits widen and periods lengthen with the efflux of time through the\nfrictional power of bodily tides.\n\nNow the class of stars which obviously and certainly undergo eclipses\nhas some outlying members of a still dubious nature. And their marginal\nposition serves greatly to enhance the present, the prospective, and\nthe retrospective interest attaching to them. These remarkable objects\nvary in light continuously. Their phases are not, like those of Algol,\nmere interruptions to a regular course of steady shining. They progress\nwithout a moment's sensible pause; they are represented graphically by\na smoothly-flowing, symmetrical curve. The eclipses by which they are\noccasioned--if they are so occasioned--must, accordingly, succeed each\nother in a strictly unbroken series. No sooner has one terminated than\nthe next commences. One star passes first behind, then in front of its\ncompanion, and their combined brightness is seen undimmed only during\nthe few moments of actual maximum. This means that they revolve in\ncontact; they are separated by no sensible gap of space.\n\nGoodricke's variable, \u03b2 Lyr\u00e6, is held to be thus constituted. The\npossibility, at least, of employing the 'satellite-theory' to account\nfor its changes was demonstrated some years ago by Mr. G. W. Myers, of\nIndiana.[40] He found the system to be composed of two barely separated\nellipsoids, circulating in the visual plane, and producing, by their\nsuccessive transits, two unequal eclipses in the course of each period\nof 12\u00b791 days. The joint mass of the pair is just thirty times that of\nour sun, but their mean density has the almost incredibly small value\nof 1/1200 that of water. Their real existence is conditional upon the\npossibility that masses much more tenuous than atmospheric air should\nradiate with the intensity of true suns. Spectroscopic observations\nare not wholly unfavourable to Mr. Myers's hypothesis, but their\ninterpretation is hampered by discrepancies so numerous and perplexing\nthat no secure inference can be derived from them. Moreover, the star\nsupposed to be alone presented to view at the principal minimum is\nthat giving the bright-line spectrum; yet it is compulsorily assumed,\nin order to meet the exigencies of the situation, to be much more\nmassive, while much less intrinsically bright, than its companion. This\nis disquieting, but nearly everything connected with \u03b2 Lyr\u00e6 _is_ more\nor less disquieting.\n\nA variable of the same type, but much fainter, was made the subject\nof a similar inquiry by Mr. Myers in 1898.[41] U Pegasi never attains\nninth magnitude; hence, spectroscopic complications equally with\nspectroscopic verification remain at present out of sight. The star,\nnevertheless, excites keen interest, and claims sustained attention.\nIts light-curve has been laid down with exquisite accuracy at Harvard\nCollege, and shows two slightly unequal minima to be comprised within a\nperiod of nine hours, signifying, on the adopted theory, the occurrence\nof alternating eclipses at intervals of four and a half hours. The\ndistance from centre to centre of the occulting stars, the smaller of\nwhich is of about eight-tenths the brightness of the larger, 'does not\nmaterially differ,' Mr. Myers tells us, 'from the sum of their radii,\nsuggesting the probable existence of the \"apioidal\" form of Poincar\u00e9.'\nIf they do not actually coalesce, the component bodies revolve in\ncontact, and rotate synchronously. Thus, it is hard to say whether U\nPegasi should be accounted as a single pear-shaped mass spinning in the\ntime of light-change, or as a close couple circulating freely in that\nidentical period. The mean density of the system appears to lie between\none-third and one-fourth that of the sun.\n\nAnother specimen of the 'dumb-bell' system is possibly met with in R2\nCentauri. The narrow range of its variation makes it a delicate object\nto observe; but Mr. A. W. Roberts, who first noticed its peculiarity\nin 1896, has since accumulated an extensive series of wonderfully\naccurate visual determinations of its fluctuating brightness, and has\nbesides rendered them the basis of an able and exhaustive theoretical\ndiscussion.[42] The double period of R2 Centauri is restricted to\nfourteen hours thirty-two minutes. Within this brief span quadruple\nphases are included--that is to say, two evenly balanced maxima and\ntwo slightly disparate minima. These result, Mr. Roberts concludes,\nfrom the mutual eclipses of interpenetrating ellipsoids, one somewhat\nmore luminous than the other, revolving--if they can properly be said\nto revolve--in an orbit inclined 32\u00b0 to the visual plane. They are of\njust one-third the solar density, and the forms satisfying photometric\nrequirements by the varying areas of luminous surface presented to\nsight in different sections of their path show a surprising agreement\nwith the bi-prolate figure given by Professor Darwin's analysis as the\nshape of a body on the verge of disruption through accelerated rotatory\nmovement. The inference is, then, almost irresistible that R2 Centauri\nreally exemplifies the nascent stage of binary stars. To establish\nthis completely, however, spectroscopic data are needed; and they are\ndifficult to procure for a star below the seventh magnitude.\n\nNo such obstacle impedes the investigation of the analogous, but much\nbrighter object, V Puppis. Detected as a spectroscopic binary by\nProfessor Pickering in 1895, this star traverses so wide an orbit in\nthe short period of thirty-five hours as to imply--if the published\ndetails are correct--that the pair possess no less than 348 times the\ngravitational power of the sun. They are, nevertheless, according\nto Mr. Roberts, fifty times more tenuous, and each globe should have\na diameter of about 16-1/2 million miles; yet nothing of all this is\nincredible. The light-curve of V Puppis, as traced by Mr. Roberts,\nis closely modelled upon that of U Pegasi. And he postulates similar\nconditions of eclipse. It rests with the spectroscope to determine\nwhether those conditions are realized or not.\n\nProbably all short-period variables are binaries, with coincident\norbital- and light-cycles. But all are not occulting binaries. There\nare some--we are still ignorant of their proportionate numbers--which\nundergo a course of light-change, apparently compatible with an\nocculting hypothesis, yet certainly escape eclipse. Professor\nCampbell has made it unmistakably clear that \u03b6 Geminorum is thus\nconstituted.[43] Two stars are present, but their plane of motion\nis inclined at an unknown angle to the line of sight; it does not\napproximate to coincidence with it. Now the possibility is not\nexcluded that V Puppis belongs to the same class. Mr. Roberts's\nassumptions are, indeed, in themselves plausible, and they may at any\nmoment be proved, by a few well-timed spectrograms, to be undeniably\ntrue.\n\nThe one conclusive test of their truth is the cessation of radial\nmovement at epochs of minimum. Evidently, if the diminution in lustre\nbe due to an eclipse, the eclipsing and eclipsed bodies must be\ncrossing the line of sight just when the obscuration is deepest. There\nis no evading this geometrical requirement, and it must be rigorously\ncomplied with in the circular orbits traversed by bodies revolving in\ncontact. Before, then, Mr. Roberts's theory of V Puppis can be accepted\nwith implicit confidence, it has to be ascertained whether a zero of\nradial speed is reached concurrently with the photometric minima. If\nso, these may be unhesitatingly set down as eclipse-phenomena; if,\non the contrary, the decline in brightness prove to be unrelated to\na slackening of speed, then the supposition that it accompanies and\nindicates a transit must be peremptorily discarded. Moreover, the\nspectroscopic verdict as regards V Puppis can safely be applied to\nstars with similar light-curves, especially to R2 Centauri and U\nPegasi, and may serve to clear away some of the intricacies connected\nwith the exceptional system of \u03b2 Lyr\u00e6. The measurement of a single\nspectrographic plate might thus, by deciding the test-case of the\nbinary in the poop of Argo, be made essentially to supply the lack of\ndesirable, but at present unattainable determinations as regards a\nconsiderable number of analogous objects.\n\nThe existence of stellar systems of the 'dumb-bell' type would violate\nno mechanical law. 'Roche's limit' does not apply to globes comparable\nin size. The range of disparity within which it holds good has not,\nindeed, been theoretically established; but it may be said, in general\nterms, to concern the relations of planets and satellites (to use\na purposely vague phrase), not those of double stars. What the law\nasserts is that a subordinate small body cannot revolve intact at\na less distance than 2\u00b744 radii of its primary from that primary's\ncentre, if their mean density be the same. For satellites of slighter\nconsistence the limit should be extended. Our own moon, for instance,\ncould never have circulated, without being rent in pieces by tidal\nstrains, in an orbit less than 22,000 miles in diameter.[44]\n\nBodies of co-ordinate mass are, however, exempted from the prohibitive\nrule against mutual approach. No analytical veto is imposed upon the\norigin by fission of double stars, or upon the subsistence of stellar\nSiamese twins. The inequalities of their mutual attractions avail to\ndistort, not to disrupt, such embryo globes. Their individuality,\ntherefore, once created, is in a manner indestructible. It tends, in\nfact, to become more pronounced as the orbital span gradually widens\nthrough the reactive effects of tidal friction. The 'dumb-bell'\ncondition may then be regarded as in a manner transitory. Nor can we\nbe assured of its actuality otherwise than by the peculiar nature of\nthe eclipses attending upon it, taken in connection with correlated\nspectroscopic observations proving eclipses of the kind veritably to\ntake place. The disclosure, by such means, of systems so strangely\nconditioned promises to afford a deeper insight than would else have\nbeen possible into the cosmical order, and fills a blank page in the\nmarvellous history of sidereal birth and growth.\n\nFOOTNOTES:\n\n[Footnote 34: _Acta Mathematica_, vol. vii., Stockholm, 1885.]\n\n[Footnote 35: _Proceedings Royal Society_, vols. xlii., lxxi.;\n_Philosophical Transactions_, vols. cxcviii., cxcix., Series A.]\n\n[Footnote 36: J. H. Jeans, _Philosophical Transactions_, vol. cxcix.,\nSeries A, p. 1.]\n\n[Footnote 37: _Figures d'\u00c9quilibre d'une Masse Fluide_, p. 172.]\n\n[Footnote 38: _Proceedings Royal Society_, vol. lxxi., p. 183.]\n\n[Footnote 39: J. H. Jeans, _Astrophysical Journ._, vol. xxii., p. 93.]\n\n[Footnote 40: _Astrophysical Journal_, vol. vii., p. 1.]\n\n[Footnote 41: _Astrophysical Journal_, vol. viii., p. 163.]\n\n[Footnote 42: _Monthly Notices_, vol. lxiii., p. 627.]\n\n[Footnote 43: _Astrophysical Journal_, vol. xiii., p. 90; _Science_,\nJuly 27, 1900.]\n\n[Footnote 44: G. H. Darwin, _The Tides_, p. 327.]\n\n\n\n\nCHAPTER VII\n\nWORLD BUILDING OUT OF METEORITES\n\n\nThe idea is seductive that we see in every meteoric fire-streak a\nremnant of the process by which our world, and other worlds like or\nunlike it, were formed. It is not a new idea. Chladni entertained it in\n1794; and it has since from time to time been revived and rehabilitated\nwith the aid of improved theoretical knowledge and a larger array of\nfacts. Survivals are tempting to thought. It costs less effort to\nrealize differences in degree than differences of kind. The enhanced\nactivity of familiar operations is readily imagined, while perplexity\nis apt to shroud the results of modes of working strange to experience.\nHence the presumption in favour of continuity; nor can it be said, even\napart from our own mental inadequacy, that the presumption is other\nthan legitimate. Nature is chary of her plans, lavish of her materials.\nHer aims are characterized by a majestic unity, but she takes little\naccount (that we can see) of surplusage or wreckage. Now, it seems\nlikely that meteorites represent one or the other of these two forms of\nwaste stuff. They are analogous, apparently, either to the chips from\nshaped blocks, or to the dust and rubbish of their destruction. Let us\nconsider what it is that we really know about them.\n\nIt cannot be said that the sources of our information are scanty.\nFully one hundred millions are daily appropriated by the earth as\nshe peacefully spins through the ether. Their absorption leaves her\nunaffected. It produces no perceptible change in her internal economy,\nand makes no sensible addition to her mass. The hundred millions of\nsmall bodies taken up have, nevertheless, in Professor Langley's\nopinion, an aggregate weight of more than one hundred tons.[45] And\nthis increment is always going on. Yet its accumulated effect is\nevanescent by comparison with the enormous mass of our globe. That it\nwas more considerable in past ages than it is at present might be\nplausibly conjectured, but cannot reasonably be maintained. Geological\ndeposits contain--unless by some rare exception--no recognisable\nmeteoric ingredients. There is nothing to show that the earth was\nsubject to a heavier bombardment from space during the Silurian era\nthan in the twentieth century. Nor could the whole of its constituents\nhave been, in any case, thus provided. Out of kiln-dried fragments,\nlike the Mazapil iron or the 'thunder-stones' of Adare, a terraqueous\nplanet could not have been formed. This objection, urged by Mr. O.\nFisher,[46] is seemingly irrefutable.\n\nMeteorites signify their existence to us, in general, only by the\nbale-fires of their ruin; but in a few cases their tangible relics\ncome to hand. Those substantial enough to escape total disintegration\nthrough atmospheric resistance to their swift movements plunge into\nthe sea or bury themselves in the earth, and in a certain proportion\nof cases find their way to museums and laboratories, where they are\nsubjected to the searching investigation demanded by their exotic\norigin. Its results are scarcely what might have been expected.\nAerolites--as these samples from space are distinctively called--are\nnot chemically peculiar; they consist exclusively of the same\nelementary substances composing the crust of the earth; but their\nmineralogy is strongly characteristic. They are extremely complex\nstructures, formed apparently in the absence of water, and with a\nshort supply of oxygen; the further condition of powerful pressure is\nindicated with some probability, nay, with virtual certainty for those\nincluding small diamonds,[47] while prolonged vicissitudes of fracture\nand re-agglomeration are possibly recorded by the brecciated texture of\nmany of these rocky _trouvailles_. Their aspect is thus anything but\nprimitive; each fragment tacitly lays claim to an eventful history;\nthey suggest a cataclysm, of which we behold in them the shattered\noutcome. The nature of such cataclysms is scarcely open to conjecture;\nonly a hint regarding it may be gathered from the circumstance that the\nmost profound terrestrial formations are those which approximate most\nclosely to the mineralogical peculiarities of meteorites.\n\nNevertheless, the only ascertained relationships of meteorites are\nwith comets. In every system of shooting stars the primary body most\nprobably is, or at any rate was, a comet. Each appears to be the\noffspring of a cometary parent, and develops _pari passu_ with its\ndecay. The view has hence been adopted, and not without justification,\nthat comets in their primitive integrity are simply 'meteor-swarms.'\nAssent may be given to it with some qualifications which we need not\nhere stop to discuss. What immediately concerns us is the interesting\nquestion as to the constitution of meteor-swarms. What is the real\nmeaning of the term? What does it convey to our minds? A meteor-swarm\nmay be defined as a rudely globular aggregation of small cosmical\nmasses, revolving under the influence of their mutual attraction,\nround their common centre of gravity. Each must revolve on its\nown account, though all have the same period; and their orbits may\nbe inclined at all possible angles to a given plane, and may be\ntraversed indifferently in either direction. From this tumultuous\nmode of circulation collisions should frequently ensue, but they\nwould be of a mild character. They could not be otherwise in a system\nof insignificant mass and correspondingly sluggish motion. We are\nconsidering, it must be remembered, only cometary swarms, as being\nthe only collections of the sort that come, even remotely, within our\nken; and comets include the minimum of matter. This we are entitled\nto infer from the fact that none of those hitherto observed, whether\nconspicuous or obscure, newly arrived from space, or obviously effete,\nhave occasioned the slightest gravitational disturbance to any member\nof our system.\n\nA cometary swarm, if left to itself, might eventually shape itself into\na reduced model of the 'Saturn' planetary nebula. Colliding particles\nshould, owing to their loss of velocity, subside towards the centre,\nand accrete into a globular mass. A predominant current of movement\nwould, through their elimination, gain more and more completely the\nupper hand; and it would finally, with the inevitable diminution of\nenergy,[48] be restricted almost wholly to the principal plane of a\nsystem, composed essentially of a rotating nucleus encompassed by\na wide zone of independently circulating meteorites. But this mode\nof evolution is not even distantly followed by comets. It would be\npossible only if they were isolated in space, and, in point of fact,\ntheir revolutions round the sun are of overwhelming importance to their\ndestinies. The sun's repulsive energy causes them to waste and diffuse\nwith expansion of splendid plumage. Under the sun's unequal attraction\nat close quarters they are subject to disruption, and the upshot of the\ntidal stresses acting upon them is the dispersal of their constituent\nparticles along the wide ambit of their oval tracks.\n\nWe are, nevertheless, invited to look further afield. Cometary\nmeteor-swarms may be only miniature specimens of the contents of\nspace. Why should not remote sidereal regions be thronged with similar\nassemblages, colossal in their proportions, countless in number?\nAnd may they not supply the long-sought desideratum of a suitable\n'world-stuff' for the construction of suns and planets? From some\nsuch initial considerations as these Sir Norman Lockyer developed,\nin 1887, a universal meteoritic hypothesis, designed on the widest\npossible lines, based on promising evidence, and professing to supply\na key to the baffling enigma of cosmical growth and diversification.\nThe meteoric affinities of comets formed its starting-point; comets\nwere assimilated to nebul\u00e6; and from nebul\u00e6 were derived, by gradual\nprocesses of change, all the species of suns accessible to observation.\nThe view was of far-reaching import and magnificent generality, but its\nvalue avowedly rested on a body of facts of a special kind. In this\nit differed from the crowd of ambitious speculations regarding the\norigin of things by which it had been preceded. In this it attained an\nimmeasurable superiority over them, if only the testimony appealed to\ncould be established as valid. Indeed, it is scarcely too much to say\nthat, whether it were valid or not, the mere circumstance of having\ncalled the spectroscope as a witness in the high court of cosmogony\nconstituted an innovation both meritorious and significant.\n\nThe spectrum of the nebul\u00e6 was a standing puzzle. A theory which set\nout by making its meaning plain secured at once a privileged position.\nThis was seemingly accomplished by Sir Norman Lockyer through the means\nof some simple laboratory experiments on the spectra of meteorites.\nCertain 'low temperature' lines of magnesium given out by the vapours\nof stony aerolitic fragments were shown to fall suspiciously close\nto the chief nebular lines previously classed as 'unknown.' The\ncoincidences, it is true, were determined with low dispersion, and were\npublished for what they were worth, but they looked hopeful. Their\nsubstantiation, had it been feasible, would have marked the beginning\nof a new stadium of progress. Nature, however, proved recalcitrant.\nThe suggested agreements avowed themselves, on closer inquiry, as\napproximate only; magnesium light makes no part of the nebular glow,\nand nebulium, its main source, evades terrestrial recognition. The\nlight of cosmic clouds is _sui generis_--it includes no metallic\nemissions; while the fundamental constituents of meteorites are metals\nvariously assorted and combined.\n\nThe decipherment of the nebular hieroglyphics was the crucial test;\nits failure to meet it left the hypothesis seriously discredited; for\ncoincidences between spectral rays, common to nearly all the heavenly\nbodies, naturally counted for nothing. Yet the investigation had its\nuses. The energy with which it was prosecuted, the ingenuity and\nresource with which it was directed, told for progress. There has been\na clash of arms and a reorganization of forces. Thought was stirred,\nobservation and experiment received a strong stimulus, fresh affluents\nto the great stream of science began to be navigated. Efforts to prove\nwhat had been asserted were fruitful in some directions, and the work\nof refutation had inestimable value in defining what was admissible,\nand establishing unmistakable landmarks in astrophysics.\n\nThe discussion, it must be admitted, threw very little light on\nthe part played by meteorites in cosmogony. Their world-building\nfunction remains largely speculative. Doubts of many kinds qualify\nits possibility, and lend it a fantastic air of unreality. But this\nmay in part be due to a defect of imaginative power with which the\nuniverse was not concerned. Waiving, then, preliminary objections,\nwe find ourselves confronted with the fundamental question: Given a\nmeteor-swarm of the requisite mass and dimensions, is there any chance\nof its condensing into a planetary system? Sir Norman Lockyer set aside\nthis branch of his subject. His hypothesis was, in fact, 'pre-nebular.'\nHe assumed that the small solid bodies with which it started would,\nin course of time, become completely volatilized by the heat of their\nmutual impacts, and that the resulting gaseous mass would thenceforward\ncomport itself after the fashion imagined by Laplace. Professor Darwin\nregarded the matter otherwise. It seemed to him possible to combine\nthe postulates of the meteoric and nebular theories in a system\nplanned on an original principle. For this purpose it was necessary to\nexcogitate a means of rendering the kinetic theory of gases available\nfor a meteor-swarm. 'The very essence,' he wrote,[49] 'of the nebular\nhypothesis is the conception of fluid pressure, since without it the\nidea of a figure of equilibrium becomes inapplicable.'\n\nM. Faye abandoned this idea; he built up his planets out of incoherent\nmaterials, thereby avoiding the incongruities, but forfeiting the\nlogical precision of Laplace's stricter procedure. Professor Darwin\nconsented to forfeit nothing; he stood forward as a syncretist, his\nobject being to 'point out that by a certain interpretation of the\nmeteoric theory we may obtain a reconciliation of these two orders of\nideas, and may hold that the origin of stellar and planetary systems\nis meteoric, whilst retaining the conception of fluid pressure.' For\nthe compassing of this end he adopted a bold expedient. Fluid pressure\nin a gas is 'the average result of the impacts of molecules.' Fluid\npressure in a meteor-swarm might, he conceived, be the net product of\ninnumerable collisions between bodies to be regarded as molecules on an\nenormously magnified scale. The supposition is, indeed, as Kepler said\nof the distances of the fixed stars, 'a big pill to swallow.' Between\nmolecules and meteorites lies a wide unbridged gap. The machinery of\ngaseous impacts is obscure. It can be set in motion only by ascribing\nto the particles concerned properties of a most enigmatical character.\nThese particles are, however, unthinkably minute; and in sub-sensible\nregions of research the responsibilities of reason somehow become\nrelaxed. We are far more critical as to the behaviour of gross,\npalpable matter, because experience can there be consulted, and is not\nunlikely to interpose its veto.\n\nMeteorites are, doubtless, totally dissimilar from molecules, however\nmany million-fold enlarged; and they would infallibly be shattered by\ncollisions which only serve to elicit from molecules their distinctive\nvibrations. Moreover, the advance of the shattering process would\nadmittedly end the prevalence of fluid pressure. So that the desired\ncondition, even if initially attained, would be transitory. There\nis, besides, a radical difference between a group of bodies in\norbital circulation and a congeries of particles moving at haphazard,\nunconstrained by any predominant law of force. A meteoric swarm belongs\nto the first category; it is a community swayed in some degree by a\ncentral power; while the gaseous contents of a retort or a balloon\nobey purely individual impulses. The analogy looked for by Professor\nDarwin can then scarcely be said to exist, and his paper stands out\nas a monument of ingenious mathematical treatment applied to an ideal\nstate of things.\n\nAn aggregation of revolving meteorites has no figure of equilibrium,\nand it is through the consequences necessarily resulting from this\nproperty that mathematicians are enabled to trace the progressive\nchanges of a rotating fluid mass. In the absence of any such direct\nmeans of attack, their position regarding the problem presented by an\nassemblage of flying stones is not much better than that occupied by\nKant, face to face with an evolving universe. It seems, nevertheless,\nclear that a meteor-swarm can be impelled to condense no otherwise\nthan through the effects of collisions among its constituents. When\nthe irregularities of movement upon which their occurrence depends are\ngot rid of, the system must remain _in statu quo_. Order makes for\npermanence; a tumultuary condition is transient. The eventual state of\nthe system can, however, be no more than partially foreseen. Bodies\narrested in their flight should fall inward, hence a central mass\nwould form and grow; but the production of planets would seem to be\nconditional upon the existence of primitive inequalities of density\nin the swarm. These might serve as nuclei of attraction for meteoric\ninfalls, not yet completely exhausted, but plying with harmless fire\none at least of the globes they helped to shape.\n\nThere could, indeed, on this showing, have been no such harmonious\nsuccession of events as constituted the predominant charm of Laplace's\nscheme. The planets should be supposed to have issued pell-mell out of\na chaos; or, rather, the chaos should have contained from the beginning\nthe seeds of a predestined cosmos. Its evolution would have been like\nthat of the oak from the acorn, an unfolding of what was already\nessentially there. And it may be that at this stage of penetration\ninto the past, the unaided human intellect meets its _ne plus ultra_.\nThere is a vital heart of things which we cannot hope to reach. Thought\ninstinctively pauses before the vision of the symbolical brooding dove.\n\nTo resume. Meteoric cosmogony has a rational basis. The modes of\naction it demands are still operative. Enfeebled almost to evanescence\ncompared with the vigour they must have needed to be efficacious in\nworld-building, they continue to make play in our nocturnal skies.\nThey make play, it is true, with a very small quantity of material;\nbut it may even now be distributed elsewhere in relatively enormous\nprofusion, and in the solar system itself it presumably was much more\nabundant formerly than it now is. The earth has been raking up meteoric\ngranules by hundreds of millions daily during untold ages, and her zone\nof space is still very far from being swept clean. The persistence of\nthe supply, however, may be occasioned by the continual arrival of\nreinforcements from interstellar realms.\n\nComets appertain to, and travel with, the sun's cort\u00e8ge, and this is\nalso inevitably true of comet-born meteors. But a multitude besides\ncirculate independently of comets, and with much higher velocities.\nTheir orbits are, then, hyperbolic; they belong to the category of\n'irrevocable travellers,' and by their capture we are privileged to\npossess genuine shreds of sidereal matter. Universal space contains\nprobably a vast stock of them, yet there is nothing to prove their\ncollection into swarms. The spectroscope supplies no assurance to that\neffect; it has given its verdict against the meteoric constitution of\nnebul\u00e6 and temporary stars. And if we admit, through the persuasion\nof mineralogical testimony, that the aerolites so strangely landed\non terrestrial soil are really the d\u00e9bris of ruined worlds, we can\nsee for them no chance of restoration. Solitary they are, even if\nthey occasionally pursue one another along an identical track, and\nsolitary they must remain. Bodies do not of themselves initiate mutual\ncirculation. Planetary or stellar outcasts cannot become re-associated\ninto a gravitational system. Of a cosmic swarm, as of a poet, it may be\nsaid, _Nascitur, non fit_; and their birth-secret is undivulged.\n\nFOOTNOTES:\n\n[Footnote 45: _The New Astronomy_, p. 197.]\n\n[Footnote 46: _American Journal of Science_, vol. xi., p. 421, June,\n1901.]\n\n[Footnote 47: Carbon does not liquefy under ordinary conditions. In the\nproduction of his artificial diamonds M. Moissan employed tremendous\npressure and great heat; and, although the genuineness of his products\nhas been denied (Combes, _Moniteur Scientifique_, November, 1903), his\nmethods at least seem to have approximated to those by which Nature\nfabricates her most authentic crystals.]\n\n[Footnote 48: Sir R. Ball, _The Earth's Beginnings_, p. 243.]\n\n[Footnote 49: _Proceedings of the Royal Society_, vol. xlv., p. 4.]\n\n\n\n\nCHAPTER VIII\n\nCOSMOGONY IN THE TWENTIETH CENTURY\n\n\nProspective and retrospective inquiries into physical conditions stand\nvery much on the same footing. The same degree of uncertainty attaches\nto results of both kinds; the same qualifications need to be applied\nto them; a similar reserve is understood to accompany our admission of\nthem. The reserve grows more marked as science unfolds to our surprised\napprehension the multiplex possibilities of Nature. The time has gone\nby when 'men of light and leading' could draw cheques for unlimited\namounts on the bank of public credulity. Not that the balance has\ndiminished, but that it is reserved for other uses. Most of us in these\ndays, have learnt to 'look before and after' for ourselves, and we\ninstinctively mix the proverbial grain of salt with what is told to\nus, even on the highest authority. Ideas are on the move; dim vistas\nare opening out; much that lies beyond the verge of actual experience\nis seen to be possible, and sedate reasoning may at any moment suffer\noutrage by fantastic discovery. Hence, finality of assertion is out of\ndate.\n\nThe secular parallax affecting men's views of the universe is nowhere\nmore strongly apparent than in the trend taken by speculations as to\nits origin. They have become more subtle, more far-reaching, yet less\nconfident. They have ramified in unexpected directions, but rather\ntentatively, than with the full assurance of attaining absolute truth.\nLaplace considered only the solar system, from which he arbitrarily\nexcluded comets. On the vast sidereal world he bestowed barely casual\nattention. Sir William Herschel, on the other hand, occupied himself\nexclusively with the growth-processes of nebul\u00e6, relegating the details\nof planetary evolution to a position of secondary importance. Later,\nthe spectroscope having become available for discriminating generic\ndifferences among the suns in space, their relative ages, the order\nof their succession, their mutual affinities, claimed predominant\nattention. Just now, however, the flood of speculation is too high to\nbe restrained within separate channels; cosmogonists look far afield;\nthey aim at obtaining a general survey of relations bewildering in\ntheir complexity. To some extent they have succeeded; parts are\nbeginning to find their places in a great whole; links are seen to\nconnect phenomena at first sight seemingly isolated; on all sides\nanalogies are springing into view. The unwearied circling of the moon\nand its imperturbable face remind us how a sun may have been born;\nthe flash of every meteor suggests the mode by which suns die. The\nfilmy traceries of comets intimate the nature of the force acting in\nnebul\u00e6; the great cosmic law of spirality is remotely hinted at by the\nantipodal disturbances of the sun. Thus, one set of facts dovetails\ninto the next; none can be properly considered apart from the rest.\n\nThe limitations of the human mind impose, nevertheless, restrictions\nof treatment. Individual efforts cannot grapple with the whole of\nthe known and the knowable, and the larger part of both is included\nin the scope of modern cosmogony. It deals with all that the skies\nhold, visibly or invisibly; draws unstintingly on time past and time\nto come; concerns itself equally with gradual transformations and\nsudden catastrophes, with the dissipation and concentration of energy,\nwith the subtle interplay of matter and force, with physical and\nultra-physical, chemical and electrical modes of action. But let us\nconsider a little more particularly how things actually stand, so as to\ncollect some definite ideas regarding the lines of advance practicable\nand promising for the immediate future.\n\nTo begin with our domestic circle. The insecure state to which\nLaplace's scheme has been reduced by the assaults of numerous objectors\nhas found compensation in the development of the tidal theory. Much\nlight has thereby been thrown upon planetary pre-history. The relations\nof planets to the sun, and of satellites to planets, have been rendered\ncomparatively intelligible. Noticeable above all is the discovery\nthence ensuing of the earth's suggestive position, just outside the\nboundary of the region where planetary rotation was destroyed by\nsun-raised tides, and with it the prospects of planetary vitality.\n\nMoreover, the dubious state of the inchoate terrestrial spheroid,\nconsequent upon its intermediate situation, accounts for the peculiar\nmode of birth of the moon, and the distinctively binary character\nof the earth-moon system; while the variety perceptible in the\ncircumstances of the different planets precludes the employment\nof any single recipe for their development from a primal vortex.\nThe forces concerned, we can now see, acted in a far more complex\nmanner than could formerly have been supposed, and their balance was\nproportionately more delicate. To which side it would have inclined in\na given case must then often be incalculable, or calculable only with\nthe guidance of the known result. The strict bonds of reasoning have\nthus become somewhat relaxed, and difficulties that looked formidable\nhave, in the long run, proved not to be insuperable. But conviction has\nalso grown faint. The old, imposing fa\u00e7ade of theory remains erect;\nthe building behind it has been, for the most part, pulled to pieces,\nand the architect has yet to be found who can reconstruct it to our\nsatisfaction.\n\nOn one point we have, nevertheless, acquired certainty. It is now known\nthat comets with their dependent trains of meteors are aboriginal in\nthe solar system. They are no unlicensed intruders, but collateral\nrelations of the planetary family. Possibly they represent waste scraps\nof world-stuff which escaped the action of the formative machinery;\nand if so, they exemplify its primitive texture. Not that their\ncomposition need be, on this supposition, identical with that of the\nplanets. A sifting of elements would have been likely to accompany the\nprocesses of cooling and contraction. Comets were, perhaps, made (to\nspeak illustratively) of the white of the nebulous egg, planets of\nits yolk. But in any case we may safely regard the glimmering fabrics\nof acetylene and cyanogen that occasionally illuminate our skies as\nshearings from a wide-spreading, fleecy haze, flung aside before\n'the starry tides' had as yet begun to 'set towards the centre.' In\none respect the quality of these relics is a surprise. They show no\nchemical affinity with nebul\u00e6. Their spectra are radically different\nfrom nebular spectra, gaseous or continuous. They accordingly lend no\ncountenance, although not fatally adverse to the view that the sun was\nonce, in the distinctive sense, a nebulous star.\n\nThe grand topic of sidereal succession is no longer abandoned to\nfruitless surmises. Broad lines have been laid down, along which,\nso far as we can at present see, progress must inevitably have been\nconducted. And one fact of overwhelming significance in this connection\nis entirely of recent discovery. The multitudinous existence of obscure\nbodies in space had, indeed, been foreseen as a logical necessity long\nbefore Bessel founded the 'Astronomy of the Invisible'; but its strong\nsubstantiation is almost wholly due to the use of modern spectrographic\nmethods. Decrepit or dusky suns are assuredly no imaginary product,\nbut a potent reality, though it would be too much to assert that all\nhave sunk to extinction by the same road. Nor is it absolutely certain\nthat their present state is uniformly the outcome of prolonged decay.\nCircumstances connected with many of them suggest rather a congenital\nincapacity for shining.\n\nWe stand, too, on firmer ground than our predecessors in respect to the\nhistory of stellar systems. That its course is mainly prescribed by\nthe influence of tidal friction has been ably demonstrated by Dr. See.\nTelescopic double stars can be led back by the aid of this clue to an\ninitial stage, when they revolved close together, very much like the\nearth and moon in Professor Darwin's theory; and it was owing to their\nvoluminousness and the unequal attractions it engendered that their\norbits became enlarged and elongated to the degree generally observed.\n\nThis theoretical inference has been confirmed with singular aptness by\nthe discovery of spectroscopic binaries. Pairs circling in orbits too\nnarrow for visual discernment are the natural complement of pairs just\ndivisible with the telescope; the first class represent the unseen,\nearly stages of the second. The two together form an unbroken sequence\nof stellar systems, for spectroscopic binaries include couples fully\nseparated, and still separating, as well as others barely divided, and\nrevolving almost in contact. Nay, they include specimens, we are led\nto believe, of globes conjoined into the apioidal figure theoretically\ninvestigated by Darwin and Poincar\u00e9, which may be regarded as\npreparatory to the development by fission of two mutually revolving\nstars from one primitive rotating mass. Some of these supposed\ndumb-bell systems are variable in light; and if the eclipse-rationale\nof their obscurations be confirmed by the spectroscope, there is no\ngainsaying the inference that each flickering object is composed of two\nstars actually contiguous, if not confluent.\n\nNow, compound stars are by no means of exceptional occurrence. Their\nrelative abundance has been found to augment rapidly with every advance\nin our knowledge of the heavens. From the measures of stellar radial\nvelocity lately carried out at the Yerkes Observatory by Professors\nFrost and Adams, it appears that the proportion of binary to single\nstars considerably exceeds Professor Campbell's earlier estimate.\nIf those giving helium-spectra are alone considered, there are most\nprobably as many of one kind as of the other. But why the distinction?\nit may be asked. The answer is not far to seek. Helium stars are the\nmost primitive, and form the closest and most readily apparent systems.\nThe companions of more fully developed stars would be likely to give\nless striking spectroscopic signs of their presence. A physically\ndouble star must always remain such. There is no law of divorce by\nwhich it can put away its companion, although their relations must\nalter with time. But their alteration tends continually to enhance the\ndifficulty of their detection. For as the members of a pair are pushed\nasunder by tidal friction their velocity slackens, and the tell-tale\nswing of their spectral lines diminishes in amplitude, and finally, by\nits minuteness, evades observation.\n\nAnd since the majority of spectroscopic satellite-stars are very\nimperfectly luminous, their eventual telescopic discovery, when far\nenough away from their primaries to be optically separable from them,\nwould rarely ensue. It must then be concluded that half the stars in\nthe heavens (let us say) broke up into two or more bodies as they\ncondensed. What follows? Well, this. Half the stars in the heavens\nwere, from the first, incapacitated from becoming the centres of\nplanetary systems. To our apprehension, at least, it appears obvious\nthat a binary condition must have inhibited the operations of planetary\ngrowth. These innumerable systems are doubtless organized on a totally\ndifferent principle from that regulating the family of the sun. The\nnebular hypothesis, even in its most improved form, has no application\nto them; the meteoritic hypothesis still less. Mathematical theories\nof fluid equilibrium, combined with a long series of changes due to\ntidal friction, afford some degree of insight into the mode of their\norigin and the course of their development. Yet the analogy with the\nearth-moon couple, which irresistibly suggests itself, is imperfect,\nand may be misleading, owing to the wide difference in state between\nplastic globes approaching solidification, and sunlike bodies radiating\nintensely and probably gaseous to the core.[50]\n\nThe world of nebul\u00e6 confronts us with entire cycles of evolutionary\nproblems, which can no longer be treated in the offhand manner perforce\nadopted by Herschel. The objects in question are of bewildering\nvariety; yet we can trace, amid their fantastic irregularities, the\nunderlying uniformity of one constructive thought. Nearly all show,\nmore or less markedly, a spiral conformation, and a spiral conformation\nintimates the action of known or discoverable laws. Their investigation\nmust, indeed, be slow and toilsome; its progress may long be impeded by\nthe interposition of novel questions, both in physics and mechanics;\nnevertheless, the lines prescribed for it seem definite enough to\ngive hope of its leading finally to a clear issue. And when at last\nsomething has been fairly well ascertained regarding the past and\nfuture of nebulous spirals, no contemptible inroad will have been made\non the stupendous enigma of sidereal relationships.\n\nIts aspect, if we venture to look at it in its entirety, is vast\nand formidable. Not now, as in former times, with a mere fragment\nof creation--a single star and its puny client-globes, one of which\nhappens to be the temporary abode of the human race--but with the\nundivided, abysmal cosmos, the science of origin and destiny concerns\nitself. The obscure and immeasurable uncertainties of galactic history\ninvite or compel attention. We know just enough to whet our desire to\nknow a great deal more. The distribution of stars and nebul\u00e6 is easily\nseen to be the outcome of design. By what means, we cannot but ask\nourselves, was the design executed? How were things ordered when those\nmeans began to be employed? How will they be ordered when all is done?\nFor an ultimate condition has, presumably, not yet been reached. And\nif not, agencies must be at work for the perfecting of the supreme\npurpose, which are not, perhaps, too subtle for our apprehension.\nMeanwhile, facts bearing on sidereal construction are being diligently\ncollected and sifted, and we shall do well to suspend speculation until\ntheir larger import is made known.\n\nThe inquisitions of science do not cease here. They strive to penetrate\na deeper mystery than that of the scattering in space of stars and\nnebul\u00e6. What are they made of? is the further question that presents\nitself. What is the nature of the primal world-stuff? Whence did\nit obtain heat? By what means was motion imparted to it? If it be\nurged that such-like topics elude the grasp of finite intelligence\nand belong to the secrets of creative power, we may reply that we are\nnot entitled, nor are we able, to draw an arbitrary line, not to be\ntransgressed by our vagrant thoughts. The world has been, by express\ndecree, thrown wide to their excursions, and it is not for us to\nrestrict their freedom. We need not fear getting too near the heart of\nthe mystery; there is no terminus in the unknown to which we can travel\nby express; in a sense, we are always starting, and never get nearer to\nour destination. But that is because it retreats before us. We do, in\ntruth, advance; and as we advance the mists clear, and we see glimpses\nbeyond of imperishable order, of impenetrable splendour. Our inquiries\nneed not then be abandoned in despair at the far-reaching character\nthey have spontaneously assumed.\n\nFrom the earliest times there has been a tendency to regard varieties\nof matter as derivative. They have been supposed to be procured by\nsupramundane agency, or by the operation of inherent law, from some\nuniversal undifferentiated substance. We moderns call that substance\n'protyle,'[51] and believe ourselves to be in experimental touch\nwith it. The implications of this view we shall consider in the next\nchapter.\n\nFOOTNOTES:\n\n[Footnote 50: _Cf._ Jeans, _Astrophysical Journal_, vol. xxii., p. 93.]\n\n[Footnote 51: A term signifying 'first matter,' constructed from\ncorresponding Greek words by Roger Bacon, and revived by Sir William\nCrookes.]\n\n\n\n\nCHAPTER IX\n\nPROTYLE: WHAT IS IT?\n\n\nThe notion of a primordial form of matter meets us at every stage\nof cosmogonical speculation. It is the outcome of an instinctive\npersuasion that, if we could only 'lift the painted veil' of phenomena,\nthe real business of the universe would be found to be proceeding in\nthe background, 'without haste or rest,' on a settled plan everywhere\nthe same; that uniformity is fundamental, diversity only incidental;\nand that the transformations of the one simplified substance might be\nrepresented by a single formula, the discovery of which would place\nin our hands the master-key to the locked secrets of the universe.\nAmong untutored thinkers some familiar kind of matter, idealized and\ngeneralized, commonly stood for the typical world-stuff. Water was the\nfirst favourite. Thales, the 'wise man' of Miletus, procured his cosmos\nby precipitation from an aqueous solution, and many savage tribes\nhave devised analogous expedients. Anaximenes regarded air as the\nuniversal solvent; Heracleitus replaced it with fire, and set on foot\na scheme of what is now often designated 'elemental evolution.' From\nthe perpetual 'flux of things' he conceived that the four substances\nselected by Empedocles as the bases of nature were not exempt, and a\nfragment of his scheme survived in Francis Bacon's admission of the\nmutual convertibility of air and water. In the main, however, the\nauthor of the 'Novum Organum' adhered to the Paracelsian doctrine of\nan elemental triad,[52] although he regarded the association of salt\nas a fundamental 'principle' with sulphur and mercury as inept and\nunnecessary.[53]\n\nThese twilight fancies faded in the growing light of chemical science;\nyet the mental need that they had temporarily appeased survived,\nand had somehow to be satisfied. An 'Ur-Stoff' was still in demand,\nbut the nineteenth century characteristically attempted to supply it\nby weight and measure. Dalton's combining equivalents afforded the\nwarrant for Prout's hydrogen hypothesis. The problem to be faced was\nto find a unit-atom by the varied combinations of which all the rest\nof the chemical atoms might be formed. The condition indispensable to\nbe fulfilled was that their weights should be exact multiples of that\nof the unit, and it came near to fulfilment by the hydrogen-atom or\nsemi-atom. It was, nevertheless, a case in which approximate agreement\nwas of no avail; the adverse decision of the balance finally became\nunmistakable; and Prout discreetly fell back, in 1831,[54] upon the\nexpedient of deriving hydrogen itself from some body lower in the\nscale. His hypothesis, in short, dissolved into a conjecture. It had\nonly emphasized the stipulation that the 'protyle' of the ancients must\nbe such as would serve not only for the physical unification of the sum\nof things, but likewise as the substratum of all the chemical species.\n\nMeanwhile, the theoretical search for it had been carried on in\nwidely different fields of inquiry. Laplace's speculations, no less\nthan Herschel's observations, had led to the conception of some\nkind of 'fire-mist' as the genuine star-plasm. But its nature and\nproperties remained indefinite, or were assigned at the arbitrary\nchoice of adventurous cosmogonists. So the 'shining fluid' of space was\n'everything by turns and nothing long,' until Sir William Huggins, in\n1864, gave it spectroscopic individuality. The 'recognition-mark' of\nnebulium is a vivid green ray, by the emission of which it is known to\nhave a concrete existence. Yet the little that has besides been learned\nabout it discountenances its identification with the _materia informis_\nof antique philosophy. This we should expect to be the subtlest of all\nsubstances. Professor Campbell, however, has gathered indications that\nnebulium is denser than hydrogen. Its luminosity, at least, which is\ninvariably associated with that of hydrogen, spreads less widely in the\nsame formations; it is confined to a lower level. The nebulium-atom is\nnot, then, the chemical or the cosmical unit.\n\nThis evasive entity, or something that curiously simulates it, has\nproved to be of less recondite origin. Sir William Crookes is amply\njustified in claiming the venerable designation of protyle for the\n'radiant matter' first produced in his vacuum-tubes nearly thirty years\nago. The discovery was astonishing and unsought, and its significance\nhas not yet been measured. Matter assumes the 'fourth state,' in which\nit is neither solid, liquid, nor gaseous,[55] under the compulsion\nof an electric discharge in high vacua. At an exhaustion of about\none-millionth of an atmosphere the manner of its transit abruptly\nalters. Conduction gives way to convection. Luminous effects are\nabolished. The tubes cease to glow with brilliant, parti-coloured\nstri\u00e6; the poles are no longer marked by shimmering halos or\nbrushes; only a green phosphorescence is seen where the glass walls\nof the receptacle are struck by the stream of projected particles.\nThey come, with half the velocity of light, exclusively from the\nnegative pole, the positive pole remaining inert. Hence the name\n'cathode-rays,' bestowed by Goldstein on the carriers of electricity in\nhighly-exhausted bulbs.\n\nThese mysterious, sub-sensible agents possess certain very definite\nproperties. Their paths are deflected in a magnetic field; they can\ntraverse metallic films; and their investigation in the open, thereby\nrendered feasible, has shown them to possess photographic efficacy,\nand the faculty of breaking down electrical insulation; moreover, they\ntransport a negative charge of fixed amount, and have a determinate\nmomentum. They are, then, assuredly no mere pulsations of the ether;\nunless our senses 'both fail and deceive us,' their quality is\nmaterial. Material, yet not quite with the ordinary connotation of the\nterm. The most essential circumstance about the cathode-rays is that\nthey remain unmodified by the chemical diversities of the originating\ngases.[56] A hydrogen tube yields identically the same radiant matter\nas an oxygen or a nitrogen tube. Here, then, at last we have within\nour grasp undifferentiated substance--matter not yet specialized,\nneither molecular nor atomic, matter destitute of affinities, exempt\nfrom the laws of combination--matter in its inchoate, and perhaps\nultimate form; in a word, the far-sought protyle.\n\nAlready, in 1879, Sir William Crookes conjectured the infinitesimal\nmissiles propelled from the cathode to be the 'foundation-stones\nof which atoms are composed.'[57] And in 1886 he pronounced them\nmore decisively to be the raw material of atoms, which, to Sir John\nHerschel's apprehension, bore the unmistakable stamp of a 'manufactured\narticle.' Nor did his recent commentator refrain from attempting\ndistantly to divine the method of their construction, or from laying\nhis finger on the by-products and residues associated with it,[58]\nalthough he felt compelled to relegate the cosmic factory to the edge\nof the world, where inconceivable things may happen. All this, indeed,\nseemed, in the late Victorian era, like mounting the horse of Astolfo\nfor a trip to the moon; and sane common-sense pronounced it fantastic\nenough to 'make Democritus weep and Heracleitus laugh.'[59] But we have\nsince learned from Nature herself some tolerance of audacities.\n\nStep by step the new order of ideas has irresistibly come to the front.\nIt owed its origin to Sir William Crookes's skill in producing high\nvacua, and the consequent development in his tubes of radiant effects.\nThen, in 1879, universal importance was claimed for them, and matter\nin the 'fourth state,' by a revival of the dreams of the ancients,\nexpanded into a kind of visionary protyle. Philipp Lenard made the next\nadvance towards its actualization by slipping it, in 1894, through an\naluminium window, and watching its behaviour towards ordinary matter.\nTwo years later R\u00f6ntgen rays made their entry on the scene; and before\nthe end of 1896 Becquerel, hurrying along the track of novelties, came\nupon the momentous discovery of radio-activity.\n\nA revision of ideas has ensued. Some time-honoured assumptions have had\nto be discarded; so-called laws have been found to need qualification;\nthe old system of physics is consequently out of gear, and much time\nand patient labour must be expended upon the adjustment of the new and\nimproved system destined to replace it. The leading and indisputable\nfact of the actual situation is that a number of hitherto unsuspected\nmodes of energy have been disclosed as widely operative in nature.\nAll are of a 'radiant' character. They travel in straight lines with\nenormous speed; they start from a material base, and produce their\nseveral effects on reaching a material goal. Now, these effects are\nclosely alike, notwithstanding that the rays themselves are radically\ndissimilar. Those of the cathodic kind are corpuscular. They consist\nof streaming particles, each, according to Professor J. J. Thomson,\nof about one-thousandth the mass of the hydrogen atom. Others, the\nnoted 'alpha rays,' are atomic; they are supposed to aggregate into\nhelium. Finally, the R\u00f6ntgen variety are ethereal; they are composed\nof light-vibrations reduced in scale, and augmented correspondingly in\nfrequency.\n\nWhat is most remarkable is that these various forms of activity give\nrise, by different means, to very much the same results. They are, in\nfact, distinguishable only by careful observation. They possess in\ncommon, though not to the same degree, the faculties of penetrating\nopaque matter, of impressing sensitive plates, of evoking fluorescence;\nwhile under the impact of cathode and R\u00f6ntgen rays, as well as of\nultra-violet light, insulated electric charges leak away and evanesce.\nThere is, however, one clear note of separation between cathodic and\nX rays in the sensibility of the former, and the indifference of\nthe latter, to magnetic influence. Thus alone, it would appear, is\nelectrified matter set apart from what we call ether. A magnet acts\nonly upon bodies carrying an electric charge; so that, if flying\ncorpuscles could be obtained in a neutral condition, the only tangible\ndistinction between the various kinds of rays would vanish. But this\nis evidently impracticable. Indeed, advanced physicists abolish the\nmaterial substratum of the corpuscle, and assign its attributes to\nthe associated atom of electricity. It is, at any rate, undeniable\nthat the electrical relations of matter become more intimate as our\nanalysis of its constitution goes deeper. Ether, electricity, matter,\nall seem to merge together in the limit; their differences ultimately\nevade definition. So animal and vegetable life appear to coalesce in\ntheir incipient stages, and strike apart with advance towards a higher\nperfection.\n\nThe various branches of inorganic nature, too, possibly spring from\na common stock. Our powers of discrimination fail to separate them\nas we trace them downward; but that may be because of the inadequacy\nof the guiding principles at our command. A larger synthesis is\ndemanded for the harmonizing of multitudinous facts, at present\ngrouped incongruously, or left in baffling isolation; and it is\nrendered increasingly difficult of attainment by the continual growth\nof specialization. Year by year details accumulate, and the strain of\nkeeping them under mental command becomes heavier; yet what _can_ be\nknown _must_, in its essentials, be known as a preliminary to extending\nthe reign of recognised law in Nature.\n\nSooner or later, nevertheless, the wealth of novel experience recently\nacquired will doubtless be turned to the fullest account. Just now,\nwe can grasp only tentatively its far-reaching import. That it bears\nprofoundly on the hoary problem of the genesis of visible things is\nsufficiently obvious. The questions of what matter is, and of how it\ncame to be, have been cleared of some of the metaphysical cobwebs\ninvolving them _ab antiquo_, and insistently crave definite treatment\nby exact methods. We should, indeed, vainly aspire to reach--or to\ncomprehend, even if we could reach--an absolute beginning. To quote\nClerk Maxwell's words: 'Science,'[60] he wrote, 'is incompetent to\nreason upon the creation of matter itself out of nothing. We have\nreached the utmost limit of our thinking faculties when we have\nadmitted that, because matter cannot be eternal and self-existent, it\nmust have been created.' The discovery that atoms disintegrate into\ncorpuscles does not, then, bring us any nearer to the heart of the\nmystery; but it is eminently suggestive as regards secondary processes.\n\nAcquaintance with ultra-atomic matter, begun within the narrow\nprecincts of 'Crookes's tubes,' has advanced rapidly since 'radiology'\ntook its place among the sciences. For, from the time when Becquerel\nfirst saw a plate darkened by the photogenic projectiles of uranium,\nand Madame Curie sifted radium from the refuse of the mines of\nJoachimsthal, the lines of proof steadily converged towards the\nconclusion that chemical atoms are not only divisible, but that their\ndecay progresses spontaneously, irresistibly, in fire, air, earth, and\nwater, as part of the regular economy of Nature.\n\nTo explain further. Radio-active bodies are composed--according to\nRutherford's plausible hypothesis--of atoms in unstable equilibrium.\nThe gradual changes incidental to their own internal activities\nsuffice to bring about their disruption. And their explosive character\nis obviously connected with unwieldy size, since uranium, thorium,\nand radium, the three substances pre-eminent for radio-activity,\npossess the highest atomic weights known to chemistry. The precarious\nbalance, then, of each of these complex, though infinitesimally\nsmall systems is successively overthrown, regardless of external\nconditions or environment, their constituent parts being hurled abroad\nwith the evolution of an almost incredible amount of energy. Their\nproducts include cathode-rays; matter in the 'fourth state,' matter\na thousand times finer than hydrogen, is ejected in torrents from\nthe self-pulverized atoms of radium. Moreover, the issuing rays are\nequivalent to currents of negative electricity. Each corpuscle bears\nwith it an electron, or is itself an electron, for the choice between\nthe alternatives is open. In either case, we are confronted with\nmatter apparently in its ultimate form; and to that form ordinary,\nsubstantial bodies tend to become reduced. Electrons may fairly be\ncalled ubiquitous. They occur in flames, near all very hot masses,\nwherever ultra-violet light impinges on a metallic surface;[61] they\nare freely generated by R\u00f6ntgen and cathode-rays; they are the agents\nof electrical transmission in conductors.\n\nEverywhere throughout the universe, atoms are thus in course of\ndegradation into corpuscles. But no information is at hand as to\nthe scene or mode of their reconstitution. The waste and decay are\npatent; the processes of compensation remain buried in obscurity.\nIndeed, Sir William Crookes anticipates the complete submergence,\nat some indefinitely remote epoch, of material substance in protyle,\nthe 'formless mist' of chaos. He assumes an identity between the past\nstate and the future, leaving, however, the present unexplained. The\nbreak-up of matter, in fact, does not render its construction the\nmore intelligible. Running-down is an operation of a different order\nfrom winding-up. It is an expenditure of a reserve of force. It needs\nno effort; it accomplishes itself. But to create the reserve for\nexpenditure demands foresight and deliberate exertion; it implies a\ndesigned application of power.\n\nNow each atom is a storehouse of energy, representing the force\nprimitively applied to reduce some thousands of free electrons to the\nbondage of a harmoniously working system. Its disruption is accompanied\nby the dissipation of the energy previously accumulated in it; and that\natomic systems are not calculated for indefinite endurance is one of\nthe most surprising of modern discoveries. The secret of their original\nconstruction is, none the less, impenetrable. That they are composed\nof protyle--that their clustering members are corpuscles moving under\nstrong mechanical control--is more than probable. And the law of order\nadumbrated by what are called the 'periodic' relations of the chemical\nelements shows that their concourse was very far from being fortuitous.\nBut beyond this point there is no holding-ground for distinct thought.\nWe are ignorant, too, whether the process of building matter out of\nprotyle is at present going on, or was completed once for all in the\nabysmal fore-time, decay being now definitive. Nor is it likely that\nwe shall ever succeed in capturing with recognition a brand-new atom\nfreshly minted for cosmical circulation.\n\nFOOTNOTES:\n\n[Footnote 52: First introduced by Basilius Valentinus. See Fowler's\nedition of the _Novum Organum_, p. 576, note.]\n\n[Footnote 53: Thus recurring, as Mr. Fowler remarked (_loc. cit._), to\nGeber's earlier view.]\n\n[Footnote 54: _Dictionary of National Biography_, vol. xlvi., p. 426.]\n\n[Footnote 55: Crookes, _Philosophical Transactions_, vol. clxx., p.\n163.]\n\n[Footnote 56: J. J. Thomson, _The Discharge of Electricity through\nGases_, p. 195; _Philosophical Magazine_, vol. xliv., p. 311.]\n\n[Footnote 57: _Science_, June 26, 1903.]\n\n[Footnote 58: _Proceedings of the Chemical Society_, March 2, 1888.]\n\n[Footnote 59: _Times_, March 30, 1888.]\n\n[Footnote 60: _Encyclop\u00e6dia Britannica_, article 'Atom.']\n\n[Footnote 61: Fleming, _Proceedings Royal Institution_, vol. xvii., p.\n169.]\n\n\n\n\nCHAPTER X\n\nUNIVERSAL FORCES\n\n\nWe find it equally impossible to conceive of matter without force,\nas of force without matter. The two modes of action, or of being,\nare inseparable. Yet our minds strongly distinguish between them;\nthey impart a dual aspect to the world. Phenomena are not simple\nmanifestations of disembodied energy, if such a thing could be; they\nhave a substantial basis which, nevertheless, eludes apprehension,\nand seems to slip away into nothingness if we try to empty it of its\nimmaterial contents. Nor do these energize in the void. They and the\nbodies they animate are knowable only in combination, and exist, to our\napprehension, only on the condition of mutual dependence. All we can do\ntowards discriminating them is to fix our attention predominantly on\none or the other side of things, and so facilitate thought by drawing\nideal lines of demarcation.\n\nJust as there are many forms of matter--all springing, we are led to\nbelieve, from an undifferentiated, fundamental world-stuff--so there\nare various kinds of force, reducible, possibly without exception, to\none universal principle. Their correlation, indeed, has been already\nin large measure demonstrated; heat, light, electricity, and kinetic\npower are known to be equivalent and interchangeable; but there\nare outstanding activities, which resist assimilation, and seem to\noriginate under different conditions from the rest. Forces manifest\nthemselves chiefly through attractive and repulsive effects, varying\nin accordance with their natures and the modification of attendant\ncircumstances. The minute particles of matter, for instance, cohere;\nthey cling together tenaciously; yet no pressure avails to bring them\ninto actual contact; at a certain point of mutual approach, they\ndevelop an invincible power of resistance to any further encroachments\nupon their separate molecular domains. And it is this faculty which\ngives to matter its distinctive property of hardness. It is rendered\ntangible to sense just by its recalcitrance to constraint.\n\nNeither the mode of operation nor the nature of the forces by which\nmolecules are organized into masses is known; while the power acting on\nthe masses thus organized, and regulating by its action the mechanism\nof the universe, is fully as baffling to comprehension. Wonder at\nits results is blunted by familiarity; presented to us as novelties,\nthey should be pronounced to outrage reason. The relations of gravity\nare of the utmost simplicity; and they are, on that very account,\nsupremely perplexing. They are governed by one steadfast law, the same\neverywhere, and under all varieties of conditions within the range of\nexperiment or precise observation. It governs impartially every kind\nand quality of matter, taking no notice of its states or combinations,\nignoring its subjection to chemical, thermal, magnetic, or electrical\ninfluences. Gravity is not only indifferent, but inevitable and\ninexorable; there is no resisting its sway; no screen serves as a\nshelter against its persuasions; it spreads equably in all directions,\nbecoming enfeebled, like wave-motion, in the strict proportion of its\ndiffusion from a centre over successive spherical surfaces. Its most\nsingular peculiarity, however, is its apparent unconcern with time. The\ngravitational pull is virtually instantaneous; its transmission--if\nit be transmitted--takes place millions of times faster than that of\nlight; the finest tests have, so far, failed to elicit symptoms of\ndelay. These would be found in minute discrepancies between calculated\nand observed perturbational effects in the heavens.\n\nThe action of gravity, if propagated with finite velocity, should\ndiffer for bodies preserving an invariable distance from its source,\nand for bodies travelling towards or away from it. Their movement would\nmodify the law of attraction.[62] Yet, up to the present, it has proved\nimpossible to detect the slightest deviation from the plain rule of\ninverse squares. Again, the penetrative faculty of this strange force\nseems absolute and unlimited. We know by ordinary experience that we\ncannot diminish the weight of an object by interposing any kind of\nshield between it and the earth; and no refinement in experimentation\navails to alter this result. That it is so, is a fortunate circumstance\nfor the harmony of the world. We can dimly imagine the riot of\nconfusion that would ensue if a transiting globe could intercept the\nattraction, as it does the light, of a central governing mass. But\nfrom the wonderfully adjusted universal order gravitational eclipses\nare excluded; nor does the densest body throw even the faintest\ngravitational shadow.\n\nThe nature of a power so singularly conditioned is almost\ninconceivable; yet attempts have not been wanting to fathom the mystery\nthat surrounds it. Professor Osborne Reynolds, in the Rede Lecture for\n1902, claimed to have arrived at 'a complete, quantitative, purely\nmechanical explanation of the cause of gravitation,' based on the\n'dilatancy' of a granular medium in close piling. But his working model\nof the universe will probably be remembered only as a lesson in the\n'inversion of ideas,' showing that with skill and ingenuity a fairly\nconcordant outcome of phenomena may be derived from antagonistic\nhypotheses. In this author's view matter is equivalent to a deficiency\nof mass, the spaces where his cosmic grains are relatively few,\nbecause their arrangement is out of gear, being driven towards one\nanother by the pressure of the surrounding medium, in which they are\ncompactly stowed, and therefore numerous. Thus, the acting forces in\nnature are made to depend upon the compression by the denser medium\nof interspatial tracts of rarer consistence, forming what we call\nmatter. The theory is difficult, if not impossible of acceptance, not\nbecause it involves the overthrow of conceptions which may be rooted in\nhabitual modes of thought, rather than in absolute truth, but because\nof its startling postulates and large vacuities. To be valid, it should\nbe complete; and there are obvious chasms in the vast expanse of ground\nwhich it covers with surprising, though only partial success.\n\nThe _multa renascentur_ of the poet is verified by the revolutions no\nless of thought than of speech. Flights of minute material particles\nhave served the turn of theorists often, and in more ways than one,\nand have as frequently been consigned to discredited oblivion; but\nthey are in vogue once more. George Louis Lesage, of Geneva, devoted\nsixty-three of the seventy-nine years of his life, which came to\nan end in 1803, to the elaboration of a mechanical rationale of\ngravity, first given to the world in the _Transactions_ of the Berlin\nAcademy of Sciences for 1782, and with details of amplification in\nhis _Trait\u00e9 de Physique M\u00e9canique_, edited by Pierre Pr\u00e9vost in\n1818.[63] The explanation it offered of molar attractions was by the\nsupposed unceasing impacts of 'ultramundane corpuscles,' speeding in\ncountless numbers and at fabulous velocities, from nowhere everywhere,\nand thus enforcing the mutual approach of masses of gross matter.\nThis involved the supposition of an infinitesimal screening effect,\nproducing a small inequality in the strength of the bombardment on\nthe sheltered and unsheltered sides of the bodies exposed to it. This\ninequality, in fact, was taken to be the _causa causans_ of gravity.\nYet its production encountered a difficulty. There was required for\nit a trifling degree of opacity in every kind of matter, while\nperfect gravitational transparency is asserted by the most delicate\nobservations. Lesage, then, reduced the arrests laid upon his particles\nto a minimum; one in ten thousand, for instance, might at the utmost\nbe intercepted by the terrestrial globe.[64] Even this insignificant\nminority, however, would suffice, through the surrender of their\nmomentum to the impeding bodies, to endow them with the noted property\nof gravitation.\n\nClerk Maxwell urged the objection that the accompanying loss of kinetic\nenergy by the corpuscles should, if transformed into heat, render all\ngravitating bodies white-hot. But Professor J. J. Thomson holds that\nthe transferred corpuscular energy might, instead of reappearing in\nthermal form, be converted into some highly penetrative species of\nradiation capable of escaping unperceived into surrounding space.[65]\n'A simple calculation,' he adds, 'will show that the amount of kinetic\nenergy transformed per second in each gramme of the gravitating body\nmust be enormously greater than that given out in the same time by\none gramme of radium.' This consequence of Lesage's theory takes\none's breath away; the 'fables of the Talmud' seem, by comparison,\neasy of belief; nevertheless, Lord Kelvin[66] declared it in 1873 to\nbe more complete in the expository sense, and not more arduous in its\nassumptions, than the kinetic theory of gases.\n\nIts fundamental postulate, at any rate, has been curiously verified in\nthe course of recent researches into the arcana of physics. Entities\nin some degree corresponding to the ultramundane corpuscles of the\nGenevese philosopher do actually exist. Electrons are being continually\nexpelled from bodies in all parts of the universe; they issue forth\nunder all conceivable conditions and in unlimited numbers. Space is\nperhaps thronged with them; no material object can be exempt from their\nmultitudinous buffetings, which are beginning to be taken account of\nin many cosmical speculations, and cannot certainly be ignored in\nefforts to solve the most obvious to superficial apprehension, the most\nintricate on a profound consideration, of all cosmical problems. But\nthere is one fatal objection to an electronic theory of gravitation.\nThe agency appealed to travels too slowly to be available for the\nrequired purpose. The velocity of light, there is reason to believe,\nsets a limit impossible to be surpassed or even attained by the\nvelocity of electrons; yet it is incomparably smaller than the rate of\ngravitational transmission.\n\nTisserand estimated at six million times the quickness of luminous\ntravel the minimum speed at which the sun's attraction must be\npropagated in view of the imperceptibility in planetary observations\nof effects corresponding to a time-inequality;[67] and this value\nmay be taken as authentic. So colossal a discrepancy excludes any\nkind of impact-rationale of the mutual pull of heavy masses; Lesage's\ncorpuscles remain 'ultramundane'; their identification with known\natoms or sub-atoms appears to be precluded; no products of ionic\ndisintegration possess the qualities necessarily to be ascribed to them.\n\nWe turn, then, inevitably to the menstruum of mysteries, the bank of\nthe insolvent in speculation, to the all-serviceable ether. Ethereal\nradiations exercise an impulsive power; light-pressure has secured\na recognised status among cosmic agencies; and every vibrational\nsystem of the luminous type undoubtedly shares the faculty by which\nlight tends to drive minute particles forward along the lines of its\npropagation. Professor J. J. Thomson, accordingly, considered that but\nfor the drawback of their insufficient velocity, 'very penetrating\nR\u00f6ntgen rays' might with advantage be substituted for corpuscular\nstreams as the cause of gravity.[68] They would, in some slight\ndegree, be absorbed by encountered masses, to which they would impart\na proportionate amount of momentum. Two bodies mutually shadowing one\nanother would, under such circumstances, be drawn together with a force\nvarying as the inverse square of distance; and if further they absorbed\nthe impinging rays strictly in the measure of their density (as\nobservation shows to be approximately the case), the attraction would\nincrease in the same ratio as the product of their masses. But R\u00f6ntgen\nrays travel with the precise velocity of light; they are, in truth,\nultra-invisible light; and they must hence be regarded as hopelessly\nincompetent to explain an influence transmitted at least six million\ntimes more rapidly.\n\nThis was fully admitted by Dr. H. A. Lorentz,[69] who, five years\nago, weighed the vibrational hypothesis of gravity in the balance of\nrigorous calculation, and found it wanting. His equations yielded the\nunexpected result that, if its postulates were granted, the noted\nattractions between massive bodies could subsist only on the terms\nof an incessant waste of electro-magnetic energy. But this is of\ncourse inadmissible. The theory involving such a consequence stands\nself-condemned, to say nothing of the wholly inadequate rate of\npropagation afforded by it.\n\nImpulsion hypotheses, whether by corpuscles or rays, being hopelessly\ndiscredited, Dr. Lorentz reverted to a half-forgotten speculation\nby Mosotti, which, though sixty years old, struck him as capable of\nbeing adapted to modern requirements. It was of an electrical nature,\nand, in the novel shape given to it, supposed gravitational action to\ndepend upon strains of the ether due to the disturbing effects of the\npositive and negative ions constituting ordinary matter. These 'states'\nof the medium are distinct in kind; they cannot neutralize one another;\nand the familiar law of attraction represents their resultant effect.\nTo bring it about much has to be taken for granted; yet the hypothesis\ncan lay claim to one singular prerogative. Although the disturbances\ninvoked by it traverse the ether with no more than the standard speed\nof light, it appears from Dr. Lorentz's investigation that, owing to\ncertain modifications in the properties of the medium produced by\nmoving matter, the planetary perturbations betraying loss of time in\ngravitational transmission would, on the electrical theory, be so\nsmall as to evade detection. As regards this crucial point, the Dutch\nphysicist has hit upon a felicity of explanation entirely original,\nand, as it were, unsought.\n\nAn 'undulatory theory' of gravity, adumbrated, rather than advanced\nby Mr. Whittaker in 1902,[70] excited hopes that the ideal aim of\nscience--a complete unification of the forces of Nature--might at\nlast be within reach. Based upon a striking mathematical research,\nit exhibited the attraction between masses as, in a manner, the\nintegration of innumerable wave disturbances, propagated at a rate\nnot strictly definable, but perhaps immensely surpassing that of\ngravity. No suggestion was made as to the primary mode or cause of\nagitation, yet it seemed much to learn that the medium we are cognizant\nof in space might be capable of transmitting the pull of gravity.\nUnfortunately, however, the physical foundation of this reassuring\ncongruity proves to be weak or unsound. The mathematical mill works\nmagnificently, but the grist put into it is of dubious quality.\nStripping Mr. Whittaker's result of its purely analytical form, Dr.\nJohnstone Stoney showed that an assumption of extreme improbability lay\nconcealed in his equations, which could not, he concluded, be seriously\ntaken to correspond with the reality of things.[71]\n\nThere would then seem to be no alternative but to accept _ad interim_\nthe electro-dynamical view of the nature of gravity. If not true, it\nis at least not obviously false. Through its subtlety it escapes direct\nconfutation. And the method of exclusions, by eliminating competitors,\nhas left it in virtual possession of the field.\n\nNothing is more curious in the history of recent science than the\ncontinual and irresistible growth which it records in the importance\nof electrical phenomena. All others tend to become merged in them; the\nmost varied data of experience claim to be translated into electrical\nterminology. They are not, assuredly, rendered more intelligible by\nthe process, but it at any rate abolishes the confusion incidental\nto multitudinous points of view. Thus, in the last resort, we find\nelectrical forces (if they may be so designated) swaying the world.\nWhat they essentially consist in, we cannot tell; the utmost that may\nreasonably be hoped for is to arrive at a clear conception of modes\nof action reduced to antagonistic stresses, by which the play and\ncounterplay of the universe may be kept up. And to this extent we find\nit possible to understand how electricity works the ethereal machinery.\nIt is strongly dualistic. The nearer we get to the foundations of\nnature, the more sharply positive and negative charges appear to be\ndifferentiated.\n\nThe opinion is nevertheless held by some inquirers that negative\nelectricity is the only substantive kind, and that its complement is\nordinary matter deprived of some of its negative particles. This, in\nfact, revives Franklin's 'one fluid theory,' only with the substitution\nof negative for positive electricity as the active principle.[72] But\nwe are met by the doubt whether 'ordinary matter' can be said to exist\nin and by itself. If it do, the mode of its existence becomes more and\nmore baffling to comprehension, as the association of mass with charge\nmakes its way into the foreground of thought.[73] Moreover, a charge\nis, or produces, a 'state of the ether' (to use the unsatisfactory\ncurrent phrase); and the ether being capable of opposite distortions,\nthe effects upon it of opposite charges are contrary and similar,\nthough perhaps not equivalent; whence the 'two fluid theory' obtains\na _prim\u00e2 facie_ recommendation as the simplest, though a crude\ninterpretation of electrical phenomena. These are ubiquitous; destitute\nthough we are of sense-organs for their perception, we still indirectly\nrecognise their presence on every side. If the unification of the\nforces in nature be attainable, the unifying formula will doubtless\nbe derived from them. Electricity is the _mot de l'\u00e9nigme_; yet it is\nitself the most inscrutable of enigmas.\n\nFOOTNOTES:\n\n[Footnote 62: Lorentz, _Proceedings Amsterdam Academy_, 1900, p. 565.]\n\n[Footnote 63: Sir W. Thomson, _Philosophical Magazine_, vol. xlv.,\nfourth series, 1873. Many hints have been taken, in what is above\nwritten, from this valuable paper.]\n\n[Footnote 64: Sir W. Thomson (Lord Kelvin), _loc. cit._, p. 323.]\n\n[Footnote 65: _Electricity and Matter_, p. 159.]\n\n[Footnote 66: _Loc. cit._, p. 331.]\n\n[Footnote 67: _Trait\u00e9 de M\u00e9canique C\u00e9leste_, tome. iv., p. 495.]\n\n[Footnote 68: _Electricity and Matter_, p. 160.]\n\n[Footnote 69: _Proceedings Amsterdam Academy of Sciences_, 1900, p.\n559.]\n\n[Footnote 70: _Monthly Notices_, vol. lxii., p. 619; vol. lxiii., p.\n258.]\n\n[Footnote 71: _Monthly Notices_, vol. lxiii., p. 424.]\n\n[Footnote 72: J. J. Thomson, _Electricity and Matter_, p. 88.]\n\n[Footnote 73: _Ibid._, p. 47.]\n\n\n\n\nCHAPTER XI\n\nTHE INEVITABLE ETHER\n\n\nEther is the fundamental postulate of physics. Its existence, nowise\napparent, is in all manner of ways implied. The properties that must\nbe assigned to it are certainly arduous of conception. We need the\naid of forced analogies to enable us to realize, even imperfectly and\nindistinctly, the mode in which it discharges functions obviously\nsomehow discharged. But in the last resort everything is obscure;\nif our thought-borings go deep enough, they always reach the\nincomprehensible.\n\nThe original ether was the 'quintessence' of the ancients--a kind of\nmatter vaguely imagined as pure and incorruptible enough to serve for\nthe raw material of the heavenly bodies, the four common elements being\nreserved exclusively for sublunary use. The distinction, however,\neventually broke down. All the spheres, from the _primum mobile_ to\nthe very surface of our low earth, are pervaded by a subtle mode of\naction, demanding for its transmission machinery of a finer kind than\ncould be constructed out of gross everyday matter. The phenomena of\nlight, when they came to be attentively studied, imperatively required\na medium, universally diffused, evasive to sense, accessible only by\nprocesses of reasoning. Hooke and Newton accordingly brought the ether\nthrough the Horn Gate of dreamland into a region of reality, where it\nbecame a subject of legitimate speculation to men of science. The task,\nnevertheless, of definitely specifying its qualities was not taken\nseriously in hand until the beginning of the nineteenth century, when\nthe establishment of the undulatory theory of light supplied tangible\nholding-ground for ideas regarding the vehicle of propagation, and\nrendered the ether a fixture of thought.\n\nA great deal is demanded from it. We cannot afford to set up an\nestablishment of ethers; one factotum must suffice. Incongruous offices\nare devolved upon it. It has to be Atlas and Mercury in one. It is\nthe universal supporter and the universal messenger. Whatever kind of\ninfluence or form of energy can pass from world to world is conveyed\nby its means. If 'action at a distance' be inadmissible (as Newton\nhimself held it to be), the pull of gravity must be exerted through\na medium; and common-sense insists upon its identification with the\ntransmitting medium of light, as well as upon the identification of\nthat with the transmitting medium of electricity. A genuine conformity\nto these demands of reason is vouched for, not only by Hertz's\ndiscovery that an electrical explosion starts an undulatory disturbance\nindistinguishable, except in scale, from luminous waves; but also by\nDr. Lorentz's indicated conclusion that strains of the same ethereal\nessence bear the all-pervading mandates of gravity. The unity of the\nmedium may, then, be regarded as finally ascertained; the complex\ninteractions of sundry different 'fluids' need no longer be taken into\naccount. To provide one with the capabilities implied by the services\nwe perceive it to render is, indeed, a sufficiently formidable task.\n\nIn popular apprehension the ether of space figures as a finer kind of\nair. No idea could be more misleading. The elasticity by which air\ntransmits the longitudinal waves of sound is totally different from the\nelasticity by which ether propagates the transversal waves of light.\nAir yields to pressure; disturbance hence produces in it undulatory\ncondensations due to oscillations of the gaseous molecules along the\nline in which the audible commotion travels. Ether, on the contrary,\nappears to be entirely incompressible; it conveys no vibrations\ndirected lengthwise. Now this is extremely perplexing. We have no\nexperience of a kind of matter absolutely rigid to pressure, while\nyielding, albeit with intense reluctance, to distortional stresses.\n\nA jelly-like solid makes the nearest, though a very distant, approach\nto fulfilling the indispensable conditions; and a solid ether was\naccordingly in vogue until long past the middle of the nineteenth\ncentury. For a solid it had very peculiar qualities; that, for\ninstance, of offering no resistance to motion. It was, in truth,\nobviously a mere temporary expedient--a scientific fiction which\nmight pass muster until replaced by something corresponding less\ndistantly with the fundamental fact. At last, on the advent of the\nelectro-magnetic theory of light and the modified conceptions which it\nbrought in its train, the solid ether withdrew behind the scenes. Its\nproperties, though inconsistent and unconvincing, had not been chosen\narbitrarily; they were imposed by the necessities of the situation;\nand when these varied, speculators naturally had recourse to fresh\ninventions.\n\nThe most plausible is that of a medium neither solid, liquid, nor\ngaseous in the ordinary sense, but in the ideal state of a 'perfect\nfluid.' Out of such an ether Lord Kelvin, with exquisite ingenuity,\nconstructed his 'vortex-atoms,' which 'had their day and ceased to be.'\nOther ideas now prevail. 'The present tendency of physical science,'\nthe late Mr. Preston wrote in 1890,[74] 'is to regard all the phenomena\nof Nature, and even matter itself, as manifestations of energy stored\nin the ether.' The more closely we look into the things around us,\nthe more strongly the persuasion is forced upon us that what we call\nether, electricity, and matter are really varied forms of one primal\nsubstance.\n\nTwo comprehensive schemes of molecular physics, resting upon the basis\nof this unifying thought, have lately been elaborated--one by Dr.\nLarmor, the other by Professor Osborne Reynolds. They have nothing in\ncommon beyond the largeness of their synthesis. In every respect they\nare radically unlike, save in regarding the intangible ether as the\none material reality. Dr. Larmor, however, is not quite confidently\nexplanatory. He presents no cut-and-dried theory of the universe; its\nhaunting mysteries are not ignored in his efforts to rationalize them.\nHe is vividly aware of the difficulties besetting the endowment of the\nether with the type of elasticity which it is recognised to possess. He\ncan only surmise that it results from particular modes of motion--from\n'kinetic stability' ensuing upon a special dynamical state. The medium\nmay thus be thought of as pervaded by 'a structure of tangled or\ninterlaced vortex filaments, which might resist deformation by forming\na stable configuration.'[75] But the details of any such scheme of\naction are evidently far too intricate to be easily unravelled; what\nconcerns us here is to point out that no simple structureless fluid can\navail to maintain cosmical communications.\n\nReduced to its lowest terms, Dr. Larmor's conception of the ether is\nthat of a 'rotationally elastic medium.'[76] In other words, it resists\nbeing turned round an axis. The forces continually acting upon it are\nnevertheless of a gyratory nature; and hence arise strains, betrayed\nto our apprehension by electrical manifestations. Each 'electron' is\nheld to be the nucleus of some kind of distortion or displacement,[77]\nand carries with it, as it moves, a field of force. Out of these 'point\ncharges' material atoms are variously built up. They are 'structures in\nthe ether,' encompassed by 'atmospheres of ethereal strain,' not--as\nthey were formerly taken to be--'small bodies exerting direct action at\na distance on other atoms according to extraneous laws of force.'[78]\nObviously the new view brings to the front extremely subtle questions\nregarding the nature of 'dynamical transmission'[79]--what the\npropagation of energy essentially consists in, and by what mechanism\nit is effected; and they are, for the present, unanswerable.\nElectricity is, on the theory we are attempting to sketch, positive\nor negative according to the direction of the originating strain.\nA positive electron might be imagined to resemble a spiral nebula\nof the right-handed sort, a negative one a left-handed spiral, or\n_vice vers\u00e2_. The analogy is, perhaps, fanciful; yet it helps towards\nobtaining a mental picture of objects which, insignificant and elusive\nthough they appear, may be the initials and ultimates of this strange\nworld.\n\nThe forces, at any rate, by which it is at present kept going are\nevoked _ad libitum_ by the pioneers of modern research from the\nethereal plenum. The actualities of matter are potentialities in the\nether. 'All mass,' in Professor J. J. Thomson's opinion, 'is mass of\nthe ether, all momentum, momentum of the ether, and all kinetic energy,\nkinetic energy of the ether.[80] Only if this be so,' he adds, 'the\ndensity of the ether must be immensely greater than that of any known\nsubstance.'\n\nThe condition is startling, but in dealing with such subjects we must\nbe prepared to meet with anomalies. They come, as the ghosts appeared\nto Odysseus in Hades, at first one by one, then in an awe-inspiring\nswarm. Yet, in spite of the perplexities they occasion, we can discern,\nwith growing sureness of insight, the amazing reality of the universal\nmedium. It is, in a manner, the only reality. For what is manifest to\nsense is subject to change. We can conceive that the visible framework\nof material existence might crumble and dissolve, like 'the baseless\nfabric of a vision,' into seeming nothingness. But a substance that is\ninapprehensible is, to our limited ideas, imperishable. The ether is\nassuredly the seat of intense activities, which lie at the root, most\nlikely, of all the processes in Nature. An absolutely uniform medium,\nhowever, can scarcely be imagined to energize or react. Some kind of\nheterogeneity it must possess; and the heterogeneity produced, in Dr.\nLarmor's view, by strains, is associated, in Professor Reynolds's\ntheory, with intrinsic texture.\n\nThe 'Sub-Mechanics of the Universe' are here made to depend upon the\nfitting together of ineffably small, ideally rigid grains. A misfit\ngives rise to matter, which might hence be defined as 'ether out of\njoint'; and the misfit can be propagated endlessly from one range of\ngranules to the next. This propagation through the ether of an abnormal\narrangement of its constituent particles, without any transference of\nthe particles themselves, explains the phenomena of matter in motion. A\nconcrete existence belongs to the ether alone. It is composed of round\naboriginal atoms, the diameters of which measure the _seven hundred\nthousand millionth part_ of the wave-length of violet light.[81] They\nare packed closely together, yet not so closely but that free paths are\nleft to them averaging in length the _four hundred thousand millionth\npart_ of their diameters.\n\nThis inconceivably small relative motion suffices, nevertheless, to\nrender the medium elastic; is, indeed, 'the only cause of elasticity\nin the universe, and hence is the prime cause of the elasticity of\nmatter.' The medium so formed is ten thousand times denser than\nwater; it exerts a mean pressure of 750,000 tons on the square inch;\nthe coefficient of its transverse elasticity is 9 + 10^{24} (in C.G.S.\nunits); which gives a velocity of transmission identical with that\nof light for vibrations of the same type, while longitudinal waves\nare propagated 2\u00b74 times more rapidly. The scheme further includes a\nplausible rationale of gravity and of electrical effects; so that there\nis much to warrant the claim of its author to have excogitated 'the one\nand only conceivable purely mechanical system capable of accounting for\nall the physical evidence, as we know it, in the universe.'\n\nThe machine, to be sure, lacks motive power; but that is a want which\nno human ingenuity can supply. Its source is obscured in the primal\nmystery of creation. And as regards the preliminary assumptions\nrequired for the constitution of an atomic ether, inclined though we\nmight be to cavil at them, we should, perhaps, act more wisely in\nfollowing Dr. Larmor's advice by abstaining from attempts to explain\n'the simple group of relations which have been found to define the\nactivity of the ether. We should rather rest satisfied,' he tells us,\n'with having attained to their exact dynamical correlation, just as\ngeometry explores or correlates, without explaining, the descriptive\nand metric properties of space.'[82] Yet one cannot help remarking\nthat the properties of space are not ordinarily modified to suit the\nneeds of demonstration, while those of the ethereal medium are varied\nat the arbitrary discretion of rival cosmogonists. In the future, when\nthey come to be more clearly ascertained, they will, perhaps, form\nthe basis of a genuine new science. Already, the study of ethereal\nphysics excites profound interest and attention. Nor is it possible to\nignore the gathering indications that it will impose qualifications\nupon principles consecrated by authority and hitherto regarded as\nfundamental.\n\nThe grand modern tenet of the conservation of energy, for example,\nmay need a gloss; it may prove to be admissible only with certain\nrestrictions. The second bulwark of the scientific edifice is even more\nseriously undermined. For the 'strain theory' of atomic constitution\nnecessarily includes the conception of opposite distortions\ncorresponding to positive and negative electricity. And the further\ninference lies close at hand that these, by combining, may neutralize\none another. The coalescence, then, of a positive and negative electron\nshould result in the smoothing out of the complementary strains they\nstand for; and there would ensue the annihilation of a pair of the\nsupposed ultimates of matter. The event might be called the statical\nequivalent of the destruction of light through interference. That\nits possibility should be contemplated even by the most adventurous\nthinkers is a circumstance fraught with meaning as to the subversive\ntendencies of recent research.\n\nAlready, in May, 1902, Professor J. A. Fleming[83] pointed out that 'if\nthe electron is a strain-centre in the ether, then corresponding to\nevery negative electron there must be a positive one. In other words,\nelectrons must exist in pairs of such kind that their simultaneous\npresence at one point would result in the annihilation of both of\nthem.' The consequence thus viewed in the abstract finds concrete\nrealization, if Mr. Jeans's suggestion be adopted,[84] in the processes\nof radio-activity, which possibly consist 'in an increase of material\nenergy at the expense of the destruction of a certain amount of matter.\nThere would, therefore, be conservation neither of mass nor of material\nenergy.'\n\nNo longer ago than at the opening of the present century such notions\nwould have been scouted as extravagant and paradoxical; now there\nis no escape from giving them grave and respectful consideration.\nScientific reason has ceased to be outraged by hypotheses regarding\nthe disappearance of mass and the development of energy. Mass and\nenergy may, after all, be interchangeable; they are, at any rate, kept\nless rigidly apart in our meditations than used formerly to be the\ncase. Nor can we assert with any confidence that partial subsidences\ninto or emergences from the surrounding medium are for either a sheer\nimpossibility; the universal framework, on the contrary, presents\nitself to us in the guise of an iridescent fountain leaping upward\nfrom, and falling back towards, the ethereal reservoir.\n\nTo the very brink of that mysterious ocean the science of the twentieth\ncentury has brought us; and it is with a thrill of wondering awe that\nwe stand at its verge and survey its illimitable expanse. The glory\nof the heavens is transitory, but the impalpable, invisible ether\ninconceivably remains. Such as it is to-day, it already was when the\n_Fiat Lux_ was spoken; its beginning must have been coeval with that\nof time. Nothing or everything, according to the manner in which it\nis accounted of, it is evasive of common notice, while obtrusive to\ndelicate scrutiny. Its negative qualities are numerous and baffling.\nIt has no effect in impeding motion; it does not perceptibly arrest,\nabsorb, or scatter light; it pervades, and may even share in the\ndisplacements of gross matter; yet its motion (if it do move), is\nwithout effect on the velocity of light.\n\nLooking, however, below the surface of things, we find the\nsemi-fabulous quintessence to be unobtrusively doing all the world's\nwork. It embodies the energies of motion; is, perhaps, in a very real\nsense, the true _primum mobile_; the potencies of matter are rooted in\nit; the substance of matter is latent in it; universal intercourse is\nmaintained by means of the ether; cosmic influences can be exerted only\nthrough its aid; unfelt, it is the source of solidity; unseen, it is\nthe vehicle of light; itself non-phenomenal, it is the indispensable\noriginator of phenomena. A contradiction in terms, it points the\nperennial moral that what eludes the senses is likely to be more\npermanently and intensely actual than what strikes them.\n\nFOOTNOTES:\n\n[Footnote 74: _Theory of Light_, second edition, p. 28.]\n\n[Footnote 75: _Encyclop\u00e6dia Britannica_, vol. xxv., p. 106.]\n\n[Footnote 76: _Report of the British Association_, 1900, p. 626.]\n\n[Footnote 77: _\u00c6ther and Matter_, p. 26.]\n\n[Footnote 78: _Nature_, vol. xlii., p. 453.]\n\n[Footnote 79: Larmor, _Report British Association_, 1900, p. 625.]\n\n[Footnote 80: _Electricity and Matter_, p. 51.]\n\n[Footnote 81: _The Structure of the Universe_, Rede Lecture, June 10,\n1902, p. 14.]\n\n[Footnote 82: _Nature_, June, vol. lxii., p. 451.]\n\n[Footnote 83: _Proceedings of the Royal Institution_, vol. xvii., p.\n177.]\n\n[Footnote 84: _Nature_, vol. lxx., p. 101.]\n\n\n\n\nCHAPTER XII\n\nTHE FORMS OF NEBUL\u00c6\n\n\nSir William Herschel's celestial surveys first made the classification\nof nebul\u00e6 practicable. Until he began grinding specula at Bath very\nfew such objects were known, and those too imperfectly for the\neffectual discrimination of their differences. Arrangement presupposes\ncomparison, and comparison some variety of specimens to be compared,\nwhich became available only through Herschel's scrutiny. The rapidity\nand penetrative power of his observations in this field almost passes\nbelief. He detected with discernment. Discovery and enrolment did not\nsatisfy him; he was, besides, keen to note analogies and contrasts,\nlikenesses and dissimilitudes. He could not see without at the same\ntime setting in order what he saw; and the law of order that commended\nitself to him was founded on an evolutionary principle. The contents\nof the heavens seemed to fall spontaneously, as he regarded them,\ninto genetic sequences; and the nebul\u00e6 with particular facility. The\ncriterion adopted was that of progressive condensation. Development\nmust clearly, he judged, be attended by contraction and local\nbrightening. Diffused milky tracts represented cosmic formations in\ntheir most rudimentary form; they assumed, through the unremitting\naction of gravity in drawing their particles together, a more compact\ntexture, more definite shapes, and a heightened lustre.\n\nBut things have changed somewhat in aspect during the last hundred\nyears. Herschel's simple regulative plan, although of unquestioned\nvalidity, needs to be supplemented and controlled. Much auxiliary\nknowledge has been acquired since it was formulated. In attempting\nto estimate the comparative antiquity of nebul\u00e6, we no longer depend\nexclusively upon one set of indications. The conclusions drawn from\ntheir immediate inspection can at least be checked by the study of\ntheir spectra and distribution.\n\nThe Milky Way might be figuratively described as the nursery-garden\nfrom which the parterres of the universe are stocked. A primitive\ncondition is usually assigned, not without good reason, to any class\nof objects markedly tending to collect in its plane. And this is the\ncase with gaseous or 'green' nebul\u00e6. Moreover, their materials appear\nto be in a highly elementary state (if it be permissible to speak of\none kind of matter as more elementary than another); their spectra\nincluding no rays due to metallic incandescence, but mainly those\nof nebulium, hydrogen, and helium. These substances, inconceivably\nattenuated, constitute the vast irregular formations placed by\nHerschel at, or near, the start of cosmical development. And so far\nhe has been justified by the outcome of modern research. But he has\nnot been justified in his description of planetary nebul\u00e6 as 'very\naged, and drawing on towards a period of change or dissolution.' For,\ndespite their determinate shape and definite boundaries, they do not\nappreciably differ in composition from nebul\u00e6 of the irregular class,\nand must be reckoned as, in a manner, coeval with them.\n\nThere is, on the whole, a concurrence of evidence that gaseous nebul\u00e6\nare at a very early stage of growth. They are the least elaborated of\nsidereal objects; they seem, many of them, barely to have crossed the\nthreshold of creation. Yet their mutual relations in time are by no\nmeans obvious. They cannot easily be disposed in any kind of rational\nsequence. Each of the great nebul\u00e6, at any rate, exhibits features and\noccupies a position shared by none of its fellows. The most discerning\ncosmologist cannot pretend to say that the Argo nebula, say, is of\ngreater or less antiquity than the Orion or the 'America' nebula.\nThey are individual growths, simultaneous, not successive. The line\nof development suggested by their relationships is rather towards the\nformation of star-clusters than of diverse nebular species. Thus, the\nPleiades illustrate not improbably the future condition of the Orion\nnebula, the contained stars having gained predominance over their misty\nenvelopments, though fragmentary swaddling-bands, later, presumably, to\nbe shaken off, still adhere to many of them.\n\nPlanetary nebul\u00e6 have much more in common than irregular nebul\u00e6, and\ntheir minor varieties might, with some plausibility, be associated with\ndifferences in relative age. They are marked chiefly by the character\nof the nuclear star which, in nearly all such objects, appears to act\nas the pivot of the surrounding vaporous structure. The supposition\nlies close at hand that it is designed as a provision for the\nnourishment of the star--that the star gains in mass and light at the\nexpense of the nebula, which it is eventually destined wholly to absorb\nand supersede. On this view, planetaries like the green glow-lamp at\nthe pole of the ecliptic (N.G.C. 6,543) should be regarded as the\nmost advanced, while Webb's planetary in Cygnus (N.G.C. 7,027) would\nexemplify an inchoate condition. In the former the central star is of\n9\u00b76 magnitude, and sharply stellar; in the latter it is double and\ndiffuse,[85] perhaps a wide binary system in embryo.\n\nThe question is, however, still open as to the real nature of the\nconnection between planetaries and their central stars. The pabulum\ntheory is a promising conjecture; but no facts with which we are\nacquainted stringently enforce it. Ideas on the subject will need\ncomplete revision if the traces of spirality noted from time to time in\nsome of these peculiar objects prove to be of radical significance. The\n_oculi_, distinctive of the 'Owl nebula' (N.G.C. 3,587), as originally\nshown by the Parsonstown reflector, consisted of luminous traceries\ncoiled round _two_ interior stars,[86] but the appearance was either\ndue to illusion, or became effaced by change, since the camera has\nrefused to endorse it as genuine. The 'helical' planetary in Draco[87]\nis doubtless essentially a spiral conformation;[88] and Professor\nSchaeberle, by means of exposures with a 13-inch reflector of 20\ninches focus, has compelled, not only the Ring nebula in Lyra,[89] but\nthe Dumb-bell in Vulpecula, to betray the surprising secret of their\nwhorled structure. Both these nebul\u00e6 give a spectrum of bright lines,\nand inventiveness is at a loss to devise means for building up gaseous\nmaterials into edifices of strongly characterized architectural forms.\nThe materials, indeed, may not be wholly gaseous;[90] or we possibly\nsee (as Professor Darwin long ago suggested) merely illuminated\nstream-lines of motion furrowing an obscure mass. But if this be indeed\nso, there is the further question to be asked: What direction does the\nmotion take? Do the tides set inward or outward?\n\nOur spontaneous impressions are all in favour of concentrative\ntendencies. We cannot easily shake off centripetal prejudices. Our\nlives are passed under a regimen of central attraction, and we\nnaturally incline to universalize our experience. Herschel's scheme\nof sidereal evolution invites accordingly at first sight ready\nacceptance. Stars seem as if they could not act otherwise than as\nfoci of condensation in nebul\u00e6; the lucid stuff involving them must,\napparently, with the lapse of ages, settle down towards their surfaces,\nand become absorbed into their substance. Such processes, indeed,\nbelong, unless counteracted by different modes of action, to the\ninevitable order of nature; but these may, and probably do, exist.\nFrom sundry quarters the conviction is pressed upon us that cosmic\nbodies can drive out matter as well as draw it in. Repulsive forces\ninsist upon recognition, and their effects become more palpable the\nmore attentively they are considered. Under certain conditions they get\nthe better of gravity; and stars may possibly, like cocoon-spinning\ninsects, expend their organic energies in weaving themselves faintly\nlucent envelopes, the products of subtle and unaccountable activities.\n\nThe example of Nova Persei is fresh in every mind, but we make\nno pretension to decide the controversy it raised. A dogmatic\npronouncement is unadvisable where the unknown elements of the question\nobscure and outweigh those that are known. A less slippery foundation\nfor reasoning is afforded by the permanently visible spiral nebul\u00e6, and\nfeatures charged with an emphatic meaning have been revealed in them by\nphotographic means.\n\nLooking at the entire contents of the nebular heavens, we find the\nspiral type very largely predominant. It claims more specimens, and\nemerges more distinctly with each development of delineative power. Its\nchief prevalence is among 'white' nebul\u00e6, showing continuous spectra.\n\nThey are vastly numerous. Gaseous nebul\u00e6 are reckoned by the score,\nwhite nebul\u00e6 by tens of thousands. Moreover, they collect near the\npoles of the Milky Way,[91] while the gaseous variety crowd towards\nits plane, both branches of the family thus manifesting galactic\nrelationships, though of an opposite character. Now, these facts of\ndistribution have some bearing on the question of relative age. There\nis, as already remarked, a consensus of opinion that objects showing\na marked preference for the Milky Way are in a more primitive state\nthan those withdrawn from it, and the inference is supported by the\ncircumstance that nebul\u00e6 situated in high galactic latitudes shine with\ncontinuous light, those near the galactic equator with vivid lines. Yet\nit would be rash to assume that any individual nebula traverses these\nsuccessive stages. The series would be satisfactorily established only\nif we could point to a number of intermediate instances, which seem\nto be almost wholly lacking. We cannot trace in nebular as we can in\nstellar growth the insensible gradations of progressive change. They\nare perhaps complicated in nebul\u00e6 by influences of a different kind\nfrom those which have gained the ascendancy in stars. Diffusive effects\nmay in them be more conspicuous than concentrative effects;[92] or a\nbalance may be temporarily struck between antagonistic tendencies.\n\nSpiral conformation is the real crux of nebular cosmogony. The\nconditions from which it arises are met with only in the sidereal\nheavens, but are there widely prevalent. Though remote from our\nexperience, they are fundamental in the realms of space. If we could\ndefine and comprehend them, we should be in a better position for\ndetermining the cosmical status of nebul\u00e6.\n\nThe choice is open between two rival theories of nebulous spirals.\nThe first is the more obvious, and readily falls in with admitted\nmechanical principles. Sir Robert Ball has adopted and ingeniously\nadvocated this view.\n\nA globular collection of promiscuously revolving particles inclines,\nif left to itself, to flatten down into a disc. The reason is this: In\na system of the kind moment of momentum is invariable, while energy\nconstantly diminishes. To render the contrast intelligible we have\nonly to consider that moment of momentum is the algebraic sum of all\nthe products of mass and motion in the aggregation, reduced to, or\nprojected upon, its 'principal plane,' while energy is independent of\nthe varied directions of velocity. Collisions consequently involve no\ndiminution of moment of momentum, but combine with radiative waste to\nproduce a steady loss of energy. Inevitably, then, the system will\nassume the form in which it possesses the minimum of energy that is\nconsistent with the maintenance of its original momentum; and it is\nthat of a disc extended in the principal plane. Retrograde movements\nwill by the time this shape is definitively arrived at have become\neliminated; the constituent particles circulate unanimously in one\ndirection; and Sir Robert Ball adds that their circulation, owing to\nthe more rapid rotation of the central mass, is along spiral paths.[93]\nThey would accordingly present the twisted conformation so commonly\nobserved in the heavens, and might even include subordinate centres of\nattraction, fitted to ripen and strengthen into a full-blown retinue\nof planets. Such are spiral nebul\u00e6 regarded in their direct mechanical\naspect. Spherical nebul\u00e6 are their immediate progenitors; suns, with or\nwithout trains of dependent worlds, their lineal descendants.\n\nLet us, however, consult some autographic records and weigh attentively\nwhat these peculiar objects tell us about themselves. We see at once\nthat their curving lines, far from being laid down at the dictate of\nchance, follow a strictly defined plan. Spiral nebul\u00e6 are not formed\nlike watch-springs by the windings of a single thread. They are always\ntwo-branched. From opposite extremities of an elongated nucleus issue\na pair of nebulous arms, which enfold it in double convolutions.\nTheir apparent superposition and interlacements occasion, in the Lyra\nnebula, the noted effect of a fringed and ruptured annulus, and it is\nof profound interest to perceive that even in gaseous masses the same\nconstructive rule prevails as in the great Whirlpool in Canes Venatici.\n\nYet this circumstance is well-nigh irreconcilable with the hypothesis\nthat an influx of material is in progress.[94] Falls due to gravity\ncould not be limited to two narrow areas on the central body. Matter\nejected from it might, on the other hand, quite conceivably follow this\ncourse. Interior strain could easily be supposed to cause yielding\nalong a given diameter, and nowhere else. Solar disturbances partially\nand dimly illustrate such a kind of activity. Diametrically opposite\nprominences are not unknown. They indicate the action of an explosive\nforce right across the solar globe. Similarly, the formation of a\nspiral nebula cannot be rightly apprehended otherwise than as the\noutcome of long-continued, oppositely-directed eruptions.\n\nThe history of the heavens involves the law of spirality. The scope\nof its dominion continually widens as research becomes intensified.\nThe Huygenian 'portent' in the Sword of Orion now figures as merely\nthe nucleus of the 'great winding Nebula' photographed by Professor\nW. H. Pickering in 1889. That the vast nebulosity encompassing the\nPleiades is an analogous structure seems eminently probable, though\nthe brilliancy of the enclosed stellar group obliterates most traces\nof its ground-plan. The magnitude of the mixed system, we are told by\nProfessor Barnard,[95] who detected it in 1893 by means of a ten hours'\nexposure with the Willard lens, transcends our powers of realization.\nIt covers 100 square degrees of the sky with intricate details. Again,\nsome four minutes of arc to the north-west of the Ring in Lyra lies\na small nebula discovered visually by Professor Barnard in 1893, and\nphotographically resolved by Keeler into a delicate spiral. It is a\ntwo-branched, left-handed spiral, as the large adjacent object has also\nproved to be. One is, in fact, the miniature of the other, and they\nare now shown, by Professor Schaeberle's short-focus reflector, to be\nlinked together by curving folds of nebulosity into a compound spiral\nsystem. The Dumb-bell is held, on the same authority, to be similarly\nconditioned, and the analogy frequently noted between its aspect and\nthat of the Ring nebula has thus become incalculably widened in scale.\n\nThe galactic relations of the Magellanic Clouds are not easily defined.\nThey are within the Milky Way, yet not of it. Enigmatical excrescences\nupon the universe, they suggest an origin from gigantic eddies in\nthe onflowing current of sidereal arrangement. Their miscellaneous\ncontents are, to all appearance, disposed along eddying lines. Mr. H.\nC. Russell's photographs[96] rendered this, in 1890, to some extent\nmanifest, and their indications were ratified by the Arequipa plates,\nfrom the study of which Professor Pickering gained the conviction that\nthe great Looped Nebula, 30 Dorad\u00fbs, is the structural nucleus of the\nNubecula Major. 'It seems,' he wrote,[97] 'to be the centre of a great\nspiral, and to bear the relation to the entire system that the nebula\nin Orion bears to the great spiral nebula which covers a large part of\nthat constellation.'\n\nOn all sides, in the sidereal heavens, we can discern the signs of the\nworking of a law of convolution. Sometimes they are patent to view;\nsometimes half submerged; but they can generally, with attention,\nbe disentangled from overlying appearances. They are exhibited by\nstars no less than by nebul\u00e6, as the late Dr. Roberts pointed out\nfrom convincing photographic evidence; the 'hairy' appendages of\nglobular clusters betray them by their curvilinear forms; they meet\nus in every corner of the wide nebular realm. Many investigators\nrecognise in the Milky Way itself the stamp of spirality. Stephen\nAlexander, of New Jersey,[98] regarded the majestic galactic arch as\na four-branched spiral, resulting from catastrophic breaches in a\nprimitive, equatorially loaded spheroid, the currents of matter ejected\nby which should, owing to their lower angular rotation, lag behind as\nthey retreated from the nucleus, and thus flow along helicoidal lines.\nR. A. Proctor subsequently devised convoluted galactic streams, which,\nhowever, corresponded imperfectly with what the sky showed. And Dr.\nEaston[99] has designed by way of simple illustration an elaborate\nseries of spires, originating possibly from a central galactic\ncondensation, the projection of which upon the sphere may, he thinks,\naccount for the known peculiarities of the Milky Way.\n\nOur interior situation, nevertheless, makes it extremely difficult to\ndetermine the real relations in space of the star-streams circling\naround it. The observed facts are, perhaps, equally compatible with\nmany other structural schemes besides those based on the idea of\nspirality; and it will be prudent to adopt none, for the present,\nwith settled conviction. We can, however, gather one sufficiently\ndefinite piece of information regarding the history of the Cosmos.\nAll the inmates of the heavens, stellar and nebular, represent quite\nevidently the d\u00e9bris of a primitive rotating spheroid. Its equator is\nstill marked by the galactic annulus, its poles by a double canopy\nof white nebul\u00e6. The gyrating movement which it once possessed as a\nwhole doubtless survives in its parts, but ages must elapse before the\nfundamental sidereal drift can be elicited.\n\nFOOTNOTES:\n\n[Footnote 85: Keeler, _Lick Publications_, vol. iii., p. 214.]\n\n[Footnote 86: Rosse, _Transactions Royal Dublin Society_, vol. ii., p.\n93.]\n\n[Footnote 87: First detected as such by Holden and Schaeberle in 1888,\n_Monthly Notices_, vol. xlviii., p. 388.]\n\n[Footnote 88: Deslandres, _Bulletin Astronomique_, February, 1900.]\n\n[Footnote 89: _Astronomical Journal_, Nos. 539, 547.]\n\n[Footnote 90: Maunder, _Knowledge_, vol. xix., p. 39.]\n\n[Footnote 91: Dr. Max Wolf places the point of nebular concentration in\nR.A. 12h 53m, D. +61\u00b0 20\u00b4, that assigned to the galactic pole being\nin R.A. 12h 49m, D. +62\u00b0. _K\u00f6nigstuhl Publ._, Bd. I., p. 174.]\n\n[Footnote 92: T. J. J. See, 'Repulsive Forces in Nature,' _Popular\nAstronomy_, No. 100, December, 1902.]\n\n[Footnote 93: _The Earth's Beginnings_, pp. 243-247.]\n\n[Footnote 94: _Cf._ Moulton, _Astrophysical Journal_, vol. xxii., p.\n165.]\n\n[Footnote 95: _Monthly Notices_, vol. lx., p. 259.]\n\n[Footnote 96: See _Knowledge_, vol. xiv., p. 50.]\n\n[Footnote 97: _Harvard Annals_, vol. xxvi., p. 206.]\n\n[Footnote 98: _Astronomical Journal_, vol. ii., p. 100, 1852.]\n\n[Footnote 99: _Astrophysical Journal_, vol. xii., p. 158.]\n\n\n\n\nCHAPTER XIII\n\nTHE PROCESSION OF SUNS\n\n\nPhenomena are functions of time, and the form of the function has to\nbe determined in each particular case. That is what the historical\nmethod comes to, and its use is prevalent and almost compulsory. We can\nno longer be satisfied with a simple bird's-eye view of the universe;\nour thoughts are irresistibly driven to grope into its past, and to\ndivine its future. Statical conceptions sufficed for our intellectual\nforefathers. They aimed at establishing the equilibrium of things,\nwhile we see them in a never-ending flux. One aspect of them calls up\nthe next, and that another, and so on _ad infinitum_; we cannot, if we\nwould, balance our ideas on the pivot of the transient present.\n\nThe immutable heavens of the ancients strike us to-day as the\ninvention of a strange race of beings. We see them, on the contrary,\nwith Shelley as a 'frail and fading sphere,' a 'brief expanse,' the\nseat and scene of change. The 'fixed' stars long ago broke away from\ntheir moorings, and began to flit at large through space. Of late a\nless obvious, more intimate kind of mobility has been attributed to\nthem. Grooves of individual development have been assigned to them,\nalong which they appear to shift as the tardy ages go by; and since\neverything that grows must decay, the orbs of heaven, too, incur\nthe doom of mortality. But modern science has done much more than\nextend to them the dismal philosophy of the phrase, 'Tout passe,\ntout casse, tout lasse.' The grandiose enterprise has been not\nunsuccessfully essayed of tracing in detail the progress of sidereal\nevolution, and of marshalling the vast stellar battalions in order of\nseniority. This has been rendered feasible by the disclosures of the\nspectroscope. Apart from their guidance, the track might have been\nseen by elusive glimpses, but could never have been laid down with any\napproach to definiteness. Herschel found for it a _terminus \u00e0 quo_\nin nebul\u00e6 of various forms, but attempted to pursue it no further.\nWe do not hesitate to run it on, from station to station, right down\nto the _terminus ad quem_. Not, it is true, without the perception\nof outstanding difficulties and insecurities, which yet seem to be\noutweighed by a certain inevitableness of self-arrangement in the\nrelated facts.\n\nThe argument from continuity is that mainly relied upon. An unbroken\nsuccession of instances is strongly persuasive of actual transition,\nprovided only that a principle of development (so to call it) may\nreasonably be assumed as influential. A series of mineralogical\nspecimens, however finely differenced, does not suggest the progressive\nenrichment of one original mass of ore. In the stars, on the other\nhand, a species of vitality may be said to reside. They are not\nfinished-off products, but spontaneously-acting machines. They are\ncentres of energy, which they dispense gratis, supplying the cost out\nof their own funds. And the process is not only obviously terminable,\nbut must be accompanied by constitutional alterations, which might be\ntraceable by subtle methods of inquiry. They _are_ traceable, unless\nwe are deceived by illusory appearances.\n\nSecchi's classification of the stars was unwarped by any speculative\nfancy. It was purely formal; it aimed only at providing distinct\ncompartments for the convenient arrangement of a multitude of\ndifferently characterized items of information. Then, by degrees,\nthe closeness of the gradations between one class and the next came\nto be noticed; partitions melted away; the methodized array showed\nitself to be in movement; and the bare framework took shape, under the\nauspices of Z\u00f6llner and Vogel, as a cosmic pedigree. The white stars\nwere set forth as the progenitors of yellow, yellow of red stars; and\nthe insensibly progressive reinforcement of the traits of relationship\nbetween the successive types went far towards demonstrating some\npartial, if not a complete, correspondence of the indicated order\nwith the truth of things. It has since been found necessary to divide\nthe first stellar class into helium and Sirian stars; and here,\ntoo, essential diversity shades off imperceptibly into likeness\napproximating to identity. All the groups hang together; the entire\nscheme is on an inclined plane of change. Helium stars, as they\ncondense, pass into Sirian, these into solar stars, which finally,\nreddening through the increase of absorption, exhibit the badge of\npost-meridional existence in fluted spectra. The finality of the red\nstage is, indeed, very far from being absolute, but what lies beyond is\nmatter of conjecture.\n\nThere are several good reasons for taking helium stars to be the\n'youngest' or most primitive of the amazing assemblage that sparkle in\nthe vault of heaven. The first is their affinity with nebul\u00e6. Every\nstar, perceived to be involved in folds or effusions of shining haze,\nhas yielded--if bright enough for profitable examination--a spectrum\nof helium quality. Further, they are remarkably tenuous bodies. It has\nbeen ascertained with approximate certainty, from the investigation of\nstellar eclipses, that helium stars are commonly, perhaps invariably,\nof far slighter consistence than the sun. Radiation, however, is\nmaintained by contraction; hence, orbs at the outset of their course\nmust be, on the whole, the most diffuse. A third note of youth is\nmembership of embryo systems, and this is affixed very markedly to\nhelium stars. One-third certainly, probably one-half of those lately\nsubmitted to trial by Professors Frost and Adams proved to have\nspectroscopic companions. They are pairs believed to have been recently\ndivided by the fission of a single parent-globe. And this is an\noperation which must, we should suppose, be undergone early, or not at\nall.\n\nThe spectra of helium stars are peculiar and suggestive. Those\nbelonging to Miss Maury's earliest groups--many of them visibly\nnebulous--bear next to no traces of metallic absorption, showing\ninstead lines of oxygen, of nitrogen, and of hydrogen in all its\nthree series. The conditions, accordingly, needed to produce the\n'cosmic' modification of hydrogen are realized in these inchoate\nbodies. What those conditions actually are we cannot tell, yet it may\nbe confidently surmised that they will prove to be of an electrical\nnature. Hydrogen resembles the metals in being electro-positive; it\ncollects at the negative pole during the electrolytic decomposition\nof water. There is, however, an unmistakable tendency in primitive\nsidereal objects to display absorption rays of electro-negative\nrather than of electro-positive elements. It is conceivable that\nhydrogen may be capable of altering its behaviour in this respect,\nand that the molecules radiating the Pickering and Rydberg series, in\naddition to the more familiar Huggins series, have, in fact, through\nsome corpuscular re-arrangement, assumed the electro-negative quality\nproperly characterizing a non-metallic substance. The association of\nthis form of hydrogen with oxygen and nitrogen in early helium stars\nwould thus be naturally related to the simultaneous quasi-disappearance\nfrom them of the spectral badges of metals.\n\nThe helium-line most distinctive of this stellar family is situated\nwell up in the blue. It appertains to the same vibrational sequence\nwith D3, which is also represented in Rigel, one of the more\n'advanced' Orion stars. In Rigel, too, we meet a fairly prominent\nmagnesium ray, lying below the blue helium emanation, while as yet iron\nis unapparent. Numerous fine, faint streaks, due to its absorption,\nonly emerge when the Sirian type is fully reached, and they are mostly\nof the 'enhanced' kind. When the spark discharge is substituted for\nthe arc as the source of illumination, certain lines in the resulting\nspectrum brighten relatively to the others, and these have been\ndistinguished by Sir Norman Lockyer as 'enhanced.' Now, the rule is\nstrikingly prevalent that the absorption rays in white stars are of\nthis class; yet it can no longer be interpreted as indicating for them\nan excessively high temperature. Rather, it would seem that electrical\nconditions still imperfectly defined are in question, and their\ngradual removal or subsidence is, beyond doubt, largely instrumental\nin bringing about the transition to the solar stage. The effacement of\nhelium-absorption is even more perplexing. No sooner does iron begin to\nshow than it vanishes. There is still a faint trace of its 'blue' line\nin Vega; none survives in Sirius.\n\nIn spectra of the solar type two great bars of violet light are stopped\nout by calcium; otherwise metallic arc-lines predominate, while those\nof hydrogen are no longer so powerfully emphasized as in white stars.\nMoreover, the whiteness of the unveiled Sirian photospheres has become\ntinged with yellow owing to the development of a shallow envelope\npartly impermeable to blue rays. For this reason the comparative\nextension of their ultra-violet spectra affords, for stars of different\ntypes, no secure criterion of relative temperature. Sound in principle,\nit becomes inapplicable when the unknown factor of general absorption\ncomes into play. The energy-curve of the solar spectrum, as it is, can\nbe determined; the energy-curve of the solar spectrum, as it would\nbe if unaffected by general absorption, has to be constructed from\ninference. But only photospheres bare to space give comparable results.\nHence, there are no valid grounds for asserting that Sirius is hotter\nthan the sun, or the sun than Betelgeux. It may be so, but the evidence\nat present available is inconclusive. The appearances expounded in this\nsense may bear quite different meanings.\n\nThe reasons for holding that solar mature into Antarian stars are of\nthe same character, and of equal cogency with those tending to prove\ntheir own development from luminaries of Sirian type. There is a\nsimilar continuity of specimens. They can be ranged one after another\nin an unbroken series, in which, as we run down the line, primrose\nshades into orange, and orange into red; general absorption arrests an\nincreasing percentage of the blue radiations, while specific absorption\nbecomes strengthened by dusky channellings of titanium. Carbon stars\nare less easily located. Dr. Vogel regards them as co-ordinate with\nthe Antarian class. The two varieties of red stars with banded spectra\ndescend, in his opinion, from the common stock exemplified by our sun.\nProfessor Hale also favours this view, some attendant difficulties\nnotwithstanding. His photographs have certainly established for carbon\nstars links of relationship both with the Antarian and the solar\nfamilies; yet the fact remains indisputable that the carbon type is,\nto a great extent, isolated from all the rest. Tokens of a genuine\nmigration towards it are few and obscure.\n\nThe ultimate fate of both tribes of red stars can only be conjectured.\nMost of the objects constituting them vary in brightness, some to\nthe verge of periodical extinction; and variability may be a symptom\nof interior dilapidation. But the organization of such bodies is\nprofoundly enigmatical. They are exceptionally remote, and offer slight\nholding-ground for inquiry. No indications have been gathered as to\ntheir density or intrinsic light-power. Very little is known about\ntheir movements. They rarely form binary combinations, and those that\nthey do form are almost always relatively fixed. No red star travels\nin a computed orbit; only one, \u03b7 Geminorum, occurs on the long list of\nspectroscopic binaries. The revolutions of this curious system ought\nto prove, when thoroughly investigated, replete with interest and\ninstruction.\n\nCoupled stars present special opportunities to students of cosmogony.\nThey are obviously contemporaries; they have started fair in the\nevolutionary race; identical influences have acted upon them; hence,\ndifferences in their standing can only result from dissimilarities\nin mass or composition. It is commonly taken for granted that a body\ncontaining less matter than its fellow must develop faster, and incur\nthe final quenching sooner. But Sir William and Lady Huggins have\nadverted to the probability of the very opposite being the case.\nPowerful surface-gravity may, they consider, serve to hasten the\ntransition from a Sirian to a solar spectrum; and we should then\nhave giant suns like Capella, advanced in type while at a very early\nstage of condensation. This perhaps explains the remarkable spectral\nrelations of contrasted stellar pairs. Always, so far as we yet know,\nthe Sirian spectrum is yielded by the lesser star, the mass of which,\njudging by analogy, must be even smaller than would be indicated by the\nproportion of its faintness. It is true that the distribution of mass\nin binary systems is often widely different from what might have been\nanticipated. Certain purplish satellites, for instance, of undetermined\nspectral quality exercise a gravitative sway of surprising force. Some\nresults of this kind lately obtained by Mr. Lewis and others are likely\nto prove of fundamental importance to theories of stellar evolution.\n\nWhat we know of 'dark stars' has been mainly derived from the\nobservation of stellar systems. They are assumed to be the denizens of\na stellar Hades, dim wanderers amid the shades, who 'have had their\nday, and ceased to be' as suns. In the 'cold obstruction' of these\nviewless orbs the grand cosmical procession is held to terminate.\nTheir presence attests the downward progress of decay, and gives\nlogical completeness to the argument for development. Yet there are\ncircumstances warning us against too full an assurance that their\nstatus is really that of skeletons at the feast of light. They are very\nfrequently found to be in close attendance upon brilliant white stars.\nThus intimately, if incongruously, coupled, they circulate and compel\ncirculation in brief periods, as members of systems just, it might be\nsaid, out of the shell. What are we to think, for instance, of the\nobscure body spectroscopically discovered to control the revolutions of\nthe chief star in the Orion trapezium? It is evidently comparable in\nmass with that imperfectly condensed luminary. Is it credible that it\nhas already traversed all the stages of stellar existence, and cooled\ndown to planetary rank? So violent an assumption should at least not\nbe made without due consideration; and we may more prudently hold our\njudgment in suspense as to whether globes so circumstanced--and they\nabound--should be regarded as effete, or as abortive suns.[100]\n\nSpeculations on the exhaustion of stellar vitality have lately become\ninextricably involved with the complex problem of elemental evolution.\nA dim inkling has been acquired of the activity in the universe of\nobscure forces, availing, we can just see, to falsify many forecasts.\nThe theory, among others, of the dissipation of energy needs to be\nrevised or qualified. Nor was it propounded by Lord Kelvin with\ndogmatic certainty. He carefully noted the possibility that in 'the\ngreat storehouses of creation' reserves of energy might be provided\nby which the losses incurred through radiation could be, wholly or in\npart, made good.[101] The anticipated possibility is perhaps realized\nin the phenomena of radio-activity. But if we inquire how, we are met\nat the threshold by difficulties connected with the origin of helium.\nHelium appears to result from the disintegration of radium, its\ngeneration being accompanied by the setting free of enormous quantities\nof energy. Its copious presence, then, argues long-continued and lavish\nexpenditure of heat and light. Yet it is as a constituent of highly\nprimitive orbs that it is chiefly conspicuous. Gaseous nebul\u00e6, too,\ninclude immeasurable supplies of it, while it is incompatible with\nwhatever we seem to know about them to suppose that radium at any time\nentered into their composition.\n\nThe genesis of the elements has, in truth, not yet been made the\nsubject of coherent speculation. Current ideas regarding it imply a\ndouble course of change, by aggregation first, and subsequently by\ndisintegration. And this should give us a twofold series of elements.\nOn one side there should be fixed survivals from the advancing process,\non the other, products of decomposition, continuously evolved, and\neven now accumulating. If the claim of helium to take rank among these\nlast should be finally established, our conceptions of the nature and\nhistory of nebul\u00e6 might have to undergo a strange inversion; but the\noutcome of the researches in progress is still uncertain, and may be\nfar off.\n\nIt is, nevertheless, quite clear that the electronic theory of matter\nsupplies no genuine explanation of the source of energy in the\nuniverse. What is given out when the atoms go to pieces must have been\nstored up when they were put together. Whence was it derived? This is\nthe fundamental question which underlies every discussion concerning\nthe maintenance of the life of suns. It is unanswered, and probably\nunanswerable.\n\nFOOTNOTES:\n\n[Footnote 100: It must at the same time be borne in mind that their\ntotal darkness is not proved. All that is certain is that their spectra\nare not bright enough to leave any impression on the exposed plates.]\n\n[Footnote 101: Thomson and Tait, _Natural Philosophy_, Appendix E, p.\n494, edition 1890.]\n\n\n\n\nCHAPTER XIV\n\nOUR OWN SYSTEM\n\n\nOur sun is clearly middle-aged. It bears none of the marks associated\nwith juvenility in stars, while its decrepitude is in the distant\nfuture. It is crossing, most likely, a level tract where recuperation\nso nearly balances expenditure that radiation can be maintained for an\nindefinite time at a high and fairly uniform standard. Stars of the\nsolar type pursue the even tenor of their way with particularly few\ninterruptions. They show little tendency to intrinsic variability.\nTheir periodicity, when it exists, is due to the presence of a\ncompanion. Variables, in other words, belonging to the spectral family\nof our sun, are binary systems; and they are usually, if not always,\nnon-eclipsing binaries, on the pattern of \u03b4 Cephei. Light changes can\nthus be impressed upon sunlike stars by external influence; they do\nnot conspicuously arise through native instability.\n\nOur planet, accordingly, is attached to a safe and steady luminary,\none subject, not to destructive spasms, but to vicissitudes so mild as\nto evade distinct meteorological recognition.[102] It is, moreover,\ngoverned by a polity settled on a broad basis of tranquillity and\npermanence. All this is as it should be. The conditions specified were\na pre-requisite to the unfolding of human destinies. Nor can it be\nconfidently asserted that they have been realized anywhere else. Our\nsystem may be unique; while, on the other hand, replicas of it might,\nimperceptibly to us, be profusely scattered through the wide realms of\nspace. It is certain that a telescopic observer on Sirius or \u03b1 Centauri\nwould see our sun unattended; not even Jupiter could be brought into\nview by optical appliances in any degree comparable to those at our\ndisposal.\n\nThere are, nevertheless, strict limitations to the possible diffusion\nof planetary worlds like those that wander amid the zodiacal\nconstellations. We have become aware of incapacitating circumstances,\nby which a multitude of stars are precluded from maintaining retinues\nof subordinate globes. Spectroscopic discoveries have compelled a\nrevision of ideas as to cosmical arrangements. Especially the large\nproportion established by them of binary to single stars makes it\nimpossible any longer to regard the solar system as a pattern copied at\nlarge throughout the sidereal domain. We cannot, then, compare it with\nany other; the mechanism of which the earth forms part must, perforce,\nbe studied in itself and by itself, and it may, for aught that appears,\nbe the outcome of special and peculiar design.\n\nThe machine in question is self-sustaining and self-regulating; no\nextraneous power noticeably affects its working. This immunity from\ndisturbance is the fortunate consequence of its isolation. A great\nvoid surrounds it. The span of Neptune's orbit is but a hand-breadth\ncompared with the tremendous unoccupied gulf outside--unoccupied, that\nis to say, by bodies of substantial mass. The feebleness of starlight\nrelatively to sunlight affords some kind of measure of the impotence of\nstellar attractions to compete with the over-ruling gravitational power\nthat sways the planetary circulation. This it is which gives to it such\nremarkable stability. The incomparable superiority of the sun over his\ndependent orbs not only safeguards them against foreign interference,\nbut reduces to insignificance their mutual perturbations. Hence the\nstrong concentration of force exemplified in our system--the absolutely\ndespotic nature of the authority exercised--makes for a settled order\nby excluding subversive change.\n\nThe organization of the solar kingdom, as disclosed by modern research,\nis greatly more varied and complex than Laplace took it to be. His\ngenetic scheme was, indeed, no sooner promulgated than deviations from\nthe regularity and unanimity of movement upon which it was based began\nto assert their inconvenient reality. They have since multiplied; and,\nemerging to notice under the most unlikely aspects, they occasion\nincongruities which tax, for their explanation, all the resources and\naudacities of the most inventive cosmogonists. Let us briefly consider\ntheir nature.\n\nThe swarm of asteroids that bridge the gap between Mars and Jupiter\nrevolve, it is true, with the general swirl of planetary movement; but\nthey use a large license as regards the shape and lie of their orbits.\nAnd their partial exemption from the rules of the road becomes entire\nfor comets and meteors, which have nevertheless proved themselves\nto be aboriginal in our system by their full participation in its\nproper motion. Finally, several of the major planets set convention at\ndefiance in the arrangement of their several households, and thereby\nintimate departures from the supposed normal course of development so\nfrequent and so considerable as to shake belief even in its qualified\nprevalence. Thus, the anomalously short period of the inner satellite\nof Mars, besides throwing doubt over its own mode of origin, tends\nto obscure the history of its more sedately circulating associate.\nDeimos cannot have been thrown off from its primary under conditions\nmaterially different from those attending the birth of Phobos.\n\nThe sub-systems of Uranus and Neptune exhibit, moreover, eddies of\nretrograde movement suggesting primitive disturbances of a fundamental\nkind; while the surprising disclosures connected with Saturn's\nfirstborn and furthest satellite, photographically detected by\nProfessor W. H. Pickering in 1898, have added one more knotted thread\nto the tangled skein we would fain unravel. Until acquaintance was made\nwith Ph\u0153be, counterflows of revolution within the same satellite-family\nwere unknown, and, if contemplated at all, would have been scouted\nas impossible. One ternary star, to be sure--\u03be Scorpii--had been\nrecognised as probably owning an immediate and a more remote attendant,\nin oppositely directed orbital movement;[103] but the cases are in many\nways disparate, and the analogy, though instructive, is imperfect.\n\nIf the ninth Saturnian moon is to be regarded as sprung from the\ncondensing mass of the planet, a total change in the state of the\nparent body must have supervened during the long interval between\nits separation and that of its successor, Iapetus. The change, in\nProfessor W. H. Pickering's opinion,[104] was nothing less than a\nreversal of axial movement. The nebulous spheroid destined to develop\ninto the wonderful Saturnian system had, presumably, when Ph\u0153be\nbecame detached from it, a diameter of sixteen million miles, and\ngyrated tranquilly from east to west, in a period of about a year and\na half. But the action of sun-raised tides availed first to destroy\nand finally to invert this movement; for the natural outcome of tidal\nfriction is synchronism, and this implies agreement, both in period and\ndirection, between the rotation and revolution of the body acted upon.\nAcceleration through contraction did the rest; and by the time another\nsatellite was ready to separate, the originating globe span normally in\nseventy-nine days, the actual revolutionary period of Iapetus. The view\nthat such was the course of events is plausible at first sight; yet the\ndoubt remains whether the cause alleged was adequate to the effect\nproduced. At the distance of Saturn, solar tidal friction exerts only\nabout 1/20000 its power on the earth;[105] its efficacy would, on the\nother hand, be greatly enhanced by the distension of the mass subjected\nto it; but approximately to what extent, our powers of calculation are\nimpotent to determine.\n\nThis is not all. Exhaustive photographic research promises to unfold\nintricacies of construction in secondary systems demanding the\npatient industry of many generations for their complete unravelment.\nThe families of the great planets will perhaps be found to include\ncrowds of inferior members which pay slight heed in their circulatory\narrangements to the trammels of convention. In those of both\nJupiter and Saturn the phenomenon has lately been brought to light\nof 'asteroidal' satellites, as they may be termed, minute bodies\ntravelling round their primaries at nearly the same mean distances,\neach group evidently representing the unagglomerated materials of a\nsingle full-sized satellite. The pigmy components of such groups\ndoubtless exist in multitudes; each great planet, most likely,\nis encompassed by at least one zone of moonlets; but so far only\nspecimen-objects have been picked up. The tenth Saturnian satellite,\ndiscovered, like its predecessor, by Professor W. H. Pickering, is thus\nassociated, by its period and locality, with Hyperion, the seventh and\nleast prominent of Saturn's visual train, the apparent insignificance\nof which suggested to Sir John Herschel that it might have many\nco-occupants of the wide gap between Titan and Iapetus.[106] But the\nsurmise had to await verification until methods were intensified beyond\nwhat seemed possible in the middle of the nineteenth century.\n\nThe corresponding Jovian pair found by Professor Perrine circulate\nfar outside the boundaries of the original Galilean realm, in\norbits which interlock as a consequence of their marked difference\nin eccentricity.[107] They are mutually inclined at an angle of\n27 degrees, nor are they supposed actually to intersect, so that\ncollisions are apparently out of the question. Direct movement is\nindicated, but cannot yet be claimed to belong quite certainly to both\nobjects. We are only beginning to make acquaintance with the submerged\npopulations of the Saturnian and Jovian kingdoms; they are perhaps\nmultitudinous; they are certainly peculiar, and we await impatiently\nand curiously the further developments of their remarkable behaviour.\n\nThe one certain inference derivable from the diversity of facts\nascertained within the last hundred years is that our world is not (so\nto speak) machine-made. The _modus operandi_ employed to disengage\nthe planets from their nebulous matrix was not of cast-iron rigidity;\nit was adaptable to circumstances; it left room for the display of\nboundless inventiveness in details. This was made, nevertheless, to\nconsist with the perfect preservation of the main order, both in design\nand operation. The general plan is broadly laid down and unmistakable;\nthe springs of the machine are undisturbed in their free play, and for\nthe primary reason that departures from regularity, which might, in any\nway, prove a menace to stability, affect bodies of negligible mass.\nThe great swing of settled movement goes on irrespectively of them. 'De\nminimis non curat lex.'\n\nSo the erratic procedure of comets is harmless only because of their\ninsignificance. If imitated by substantially attractive masses, it\ncould not fail to jeopardize the planetary adjustments. Even the\nasteroids would be unsafe neighbours but for their impotence; and it\nis remarkable that Mercury, by far the smallest of the major planets,\ncirculates along a track of the asteroidal type. It would seem as if an\nimportant size carried with it an obligation to revolve in an orbit of\nsmall eccentricity, inclined at a low angle to the principal plane of\nthe system. The reason why this should be so is not obvious; but were\nit otherwise the equilibrium, now so firmly established, would subsist\nprecariously, or not at all.\n\nThe assertion, indeed, that it is firmly established can only be\nmade under reserve. We are ignorant of any causes tending towards\nits overthrow; yet they may supervene, or be already imperceptibly\nactive. One such lurking possibility is the presence of a resisting\nmedium in interplanetary space. Waifs and strays of matter must,\nbeyond doubt, be encountered there--outlawed molecules, self expelled\nfrom the gaseous envelopes of feeble globes; thin remnants of cometary\nparaphernalia, driven off amid the fugitive splendours of perihelion;\nproducts of ionic dissociation set flying by the impact of ultra-violet\nlight--and all disseminated through an ethereal ocean, which 'is cut\naway before and closes from behind' as moving bodies traverse it. That\nits indifference is shared by ordinary material substances, when in the\nlast stage of attenuation, is a plausible but unverified conjecture. It\nis only safe to say that retardation of velocity in what may pass for\nempty space is insensible or null.\n\nThere may, nevertheless, be springs of decadence in the solar system.\nSome of them have been discussed by M. Poincar\u00e9,[108] whose confidence\nin the reassuring demonstrations of Laplace and Lagrange is inversely\nproportional to the magnitude of the terms they were forced to neglect.\nThey dealt with fictitious globes, devoid of appreciable dimensions,\nand swayed by the strict Newtonian law. But the real planets and\ntheir satellites are acted on by other forces as well, frictional,\nmagnetic, radio-repulsive, the joint effects of which may not be\nwholly evanescent. The tidal drag on rotation undoubtedly occasions\na small but irretrievable loss of energy. The moon, for instance, as\nM. Poincar\u00e9 states, now gains, by the reactive consequences of tidal\nfriction in widening its orbit, no more than 1/28 the _vis viva_ of\nwhich the earth is deprived by the infinitesimal slowing down of its\nrotation; and the remaining 27/28, being dissipated abroad as heat, are\nfinally abstracted from the system.\n\nThe ultimate state, we are told, towards which the planetary\nmechanism tends is that of the synchronous revolution, in a period\nof about twelve years, of all its members. This might, apart from\nthe possibility of a resisting medium, have indefinite permanence;\notherwise precipitation to the centre would gradually ensue, and\none solitary sphere, cold, stark, and unilluminated, would replace\nthe radiant orb of our cerulean skies, with its diversified and\nexquisitely poised cort\u00e8ge. Unsecured drafts upon futurity, however,\nare not among the most valuable assets of science, and a consummation\nso immeasurably remote may be anticipated by a score of unforeseen\ncontingencies. What can be and has been ascertained is the relative\ndurability of the scheme with which the visible destinies of the human\nrace are so closely connected. It will unquestionably last long enough\nfor their accomplishment. Curiosity that would seek to pierce the\nulterior darkness is likely to remain ungratified.\n\nBut there is a further outlook. Other and incalculable items remain\nto be taken into account. The sun, although an autocrat within his\nown dominion, is himself subject to external influences. As a star,\nhe is compelled to follow whithersoever the combined attractions of\nhis fellow-stars draw him; nor can we thoroughly interpret the summons\nwhich he obeys. The immediate upshot in the transport of the solar\nsystem towards the constellation Lyra has, it is true, been determined,\nbut the eventual scope and purpose of the journey remain profoundly\nobscure. The pace is to be reckoned as leisurely: twelve miles a\nsecond is little more than half the average stellar speed. We should,\nhowever, probably suffer no inconvenience from being whirled through\nthe ether in the train of such a stellar thunderbolt as Arcturus. Only\nthe excessive velocities of any adventitious bodies we might happen to\npick up would betray to ordinary experience the fact of our own swift\nprogress. As it is, our sweepings from space appear to be scanty.\n\nIf shreds from inchoate worlds, or dust of crumbled worlds, strewed\nthe path of our system, they should be annexed by it in its passage,\ntemporarily or completely, and we should then expect to find the apex\nof the sun's way marked, if no otherwise, by the predominant inflow\nfrom that quarter of comets and meteors. Yet there is no trace of such\na preference in the distribution of their orbits. Hence the enforced\nconclusion that the sun has attached to him, besides the members of his\nimmediate household, an indefinite crowd of distant retainers, which,\nby their attendance upon his march, claim with him original corporate\nunity. To this rule there may be a few exceptions. An occasional\naerolite probably enters the earth's atmosphere with hyperbolic\nvelocity, and takes rank accordingly as, in the strictest sense, a\nforeign intruder; but the broad truth can scarcely be challenged that\nthe sun travels through a virtual void.\n\nWe can, however, see no necessity why he should for ever continue to do\nso. Widely different conditions seem to prevail near the centre and out\ntowards the circumference of the sidereal world. What may be designated\nthe interior vacuity of the Milky Way is occupied mainly by stars of\nthe solar type, including one to our apprehension super-eminent over\nthe rest; they are separated by vast, apparently clear intervals; they\nare non-nebulous, and of stable constitution. This secure habitat is\nours for the present, although it may at some future time be exchanged\nfor one less exempt from disturbance. The shape and size of the sun's\norbit are utterly unknown; the changes of environment, accordingly,\nthat will accompany the description of it defy conjecture. Our actual\ncourse is inclined at a small angle to the plane of the Milky Way. It\nwill presumably become deflected, but perhaps not sufficiently to keep\nour system clear of entanglement with the galactic star-throngs. In\nour ignorance of their composition no forecast of the results can be\nattempted: they are uncertain and exorbitantly remote. Moreover, the\ncomparative slowness of the sun's motion in a manner guarantees the\npermanence of his subsisting cosmical relations. For anything that\nscience can tell, they may ultimately be subverted by some preordained\ncatastrophe; but the possibility lies outside the sphere of rational\nforecast.\n\nThe universe, as reflected in the mind of man, gains extent as the\nmirror acquires polish. Early astronomers conceived of but one solar\nsystem and one 'd\u00e6dal earth,' upon which the 'pale populace of heaven'\nrained influences sinister or propitious. Later, human egotism took\nanother form. The whole universe was assimilated to our particular\nlittle settlement in it. Terrestrial conditions were universalized.\nNone divergent from them were counted admissible or profitable. But one\nanswer seemed possible to the perpetual _Cui bono?_ with which restless\nthought assailed the heavens. But one purpose was regarded as worthy\nof fulfilment, that of multiplying, in distant sidereal climes, copies\nof our own planet, and of providing suitable locations for myriads\nof intellectual beings, as little alien to ourselves as might be\ncompatible with the minimum of diversity in their material surroundings.\n\nThe spread of this astral philanthropy has been in some measure\nchecked by the advance of knowledge. Our position and circumstances\nhave been shown by it to be, if not quite peculiar, at any rate very\nfar from inevitable. It has reduced, by a process of exclusions, to\na relatively limited number the class of stars that can fairly be\nregarded as possible centres of vitality; it has immensely widened the\nscope of discernible variety in cosmical arrangements, and held out\nwarnings against errors of exposition due to inborn prejudices. And we\nshall surely not wander from the truth by recognising our inability to\npenetrate all the depths and complexities of Infinite Design.\n\nFOOTNOTES:\n\n[Footnote 102: The uncertainty affecting the best attainable\nresults in weather-cycle investigation is rendered strikingly\napparent by a comparison of the able and laborious papers by H. W.\nClough (_Astrophysical Journal_, vol. xxii., p. 42), and C. Easton\n(Petermann's _Geogr. Mittheilungen_, 1905, Heft VIII., and _Proceedings\nAmsterdam Academy of Sciences_, June 24, 1905).]\n\n[Footnote 103: R. T. A. Innes, _Reference Catalogue_, p. 155A.]\n\n[Footnote 104: _Harvard Annals_, vol. liii., p. 61, where, however, the\nreversal is explained by a shifting of the plane of rotation.]\n\n[Footnote 105: G. H. Darwin, _Philosophical Transactions_, vol.\nclxxii., p. 526; Moulton, _Astrophysical Journal_, vol. xi., p. 110.]\n\n[Footnote 106: _Monthly Notices_, vol. ix., p. 91.]\n\n[Footnote 107: F. E. Ross, _Lick Bulletin_, No. 82.]\n\n[Footnote 108: _Annuaire du Bureau des Longitudes_, 1898.]\n\n\n\n\nCHAPTER XV\n\nREMNANTS AND SURVIVALS\n\n\nIf the sun and planets were, in sober truth, wrought into their present\nshape out of a primordial nebula, the comparatively void surrounding\nspace should naturally be strewn with fragments of unappropriated\nmaterial. For the process of englobement could hardly, one would think,\nbe carried out with such neatness and precision as to leave no shreds\nor shavings lying about the great atelier. Residual stuff there must\nbe, unless our preconceived ideas are grossly erroneous; nor have we\nfar to look in order to find it. We find it, apparently, under two\nforms presenting curious dissimilarities, yet belonging fundamentally,\nwe can scarcely doubt, to the same order of things. These two kinds of\nwaste product may be identified in the innumerable army of comets and\nin the strange, pale cone of the zodiacal light.\n\nOne of the most important and secure additions to knowledge in the\ndepartment of cosmogony made during the nineteenth century was the\nestablishment of comets in a position of entire, perennial, and\naboriginal dependence upon the sun. That is to say, a vast majority, if\nnot the whole of them, attend him on his sidereal journey. They are,\naccordingly, and have immemorially been his clients, and they can lose\nthat status only through the effects of violent disturbance compelling\nthem to depart irrevocably from their closed orbits along hyperbolic\ntracks. A trifling leakage of comets from our system is thus possible,\nwhich may or may not be compensated by annexations of adventitious\nmembers of the class, similarly banished from the precincts of remote\nstars. But this is a secondary consideration; the essential point to\nbe borne in mind is that comets are native-born subjects of the sun,\nthat they make an integral part of his cort\u00e8ge, that they own the same\nsubstantial origin, are dominated by his power, and must share his\nfortunes. Their study should then prove strongly illuminative as to\nthe pre-history of our system, and for this especial reason, that they\nseemingly belong by right to that vanished world which it is the chosen\ntask of cosmogony to reconstruct. They are, we can infer, the genuine\nprimitives of the solar company; they retain something of prairie\nwildness, not having been broken in by steadily enforced gravitational\ndiscipline. Each perihelion passage is an adventure; between it and the\nnext, fateful incidents may occur. Forces negligible on dense planetary\nglobes act sensibly on their tenuous materials; they in part strikingly\nillustrate, and in part fantastically invert, the common modes of\nnatural procedure. But it is their antiquarian significance that mainly\nconcerns us here.\n\nAdmitting for the inchoate solar nebula such a constitution as that\ndevised by Kant, and adopted with amendments by M. du Ligond\u00e8s, we\nfind ourselves confronted with the almost inevitable consequence\nof symptomatic survivals. Wisps of crude matter, in other words,\nwhich escaped being drawn into the vortices of embryo planets should\ncontinue to circulate, as they had from the first circulated, in all\npossible planes, and with no partiality for either a right-handed or\na left-handed direction. These waifs and wastrels should, in fact, be\nindistinguishable from comets--'les seuls t\u00e9moins,' according to the\nFrench cosmogonist, 'qui nous restent sur le mode de la circulation\npremi\u00e8re.'[109] The identification is seductive to the imagination, and\ndoes not fall far short of convincing the reason.\n\nThere is clear evidence that what we may venture to call the native\nmode of cometary circulation is absolutely exempt from the rules\nwhich impress the movements of the planets with an unequivocal stamp\nof congruity. The few comets showing some degree of compliance with\nthe general plan are those which have been subjected to manifold\nperturbations, and can hence no longer be called as unbiassed\nwitnesses; while their untrained associates, left relatively free to\nfollow the impulsion of their start, betray no geometrical preferences\nin their manner of travelling. They revolve indifferently with or\nagainst the course of the signs; their paths are inclined at every\npossible angle to the ecliptic; they approach the sun in sensibly equal\nnumbers from all quarters of the sky; they agree only in pursuing\nellipses so elongated as to verge towards the parabolic limit. But\njust in this way, and no otherwise, we should expect to find bodies\ncirculating which, having been aggregated at random (as Kant supposed)\nin the beginning, had departed to the least possible extent from the\ninitial conditions of their systemic union. A good _prim\u00e2 facie_ case\ncan, then, be made out for regarding comets as samples of the used-up\nnebula, as superannuated constituents of an inconceivable chaos, which,\nevading the operation of laws of change, have floated down the stream\nof ages virtually intact and undisturbed.\n\nYet the question has other aspects besides this purely mechanical\none. They should all be harmonized by truth, which cannot be more\nsecurely guaranteed than by consilient testimony; nevertheless, there\nare difficulties in effecting the accommodation. Comets are not, in\na chemical sense, closely related to nebul\u00e6. They are fundamentally\nof carbonaceous composition--free hydrogen makes no spectroscopic\nshow in them--while they include metallic ingredients occasionally\nrendered glowing by the powerful excitement of a perihelion rush-past.\nBut gaseous nebul\u00e6 shine mainly with the light of certain unknown\nsubstances, reinforced by rays of hydrogen and helium. Carbon flutings\nand metallic lines are alike alien to their spectra. Nor is there any\ncommunity that we yet know of between the chemistry of white nebul\u00e6\nand that of comets. The nebular hypothesis of cometary origin is thus\ndiscountenanced by the results of light-analysis. Still, there are\npossibilities of reconcilement. Spectral conditions must be subject to\nchange. The quality of light emitted by a body of mixed composition\ncannot fail to alter with the inevitable alteration of physical state\nbrought about by external influences or internal change.\n\nSelective illumination is beyond doubt largely concerned in modifying\nthe information we are able to obtain as to the composition of remote\nmasses, and its modes of action seem capricious because they are very\nimperfectly understood. Hence, spectral modifications may take place\nmerely through the substitution of some elements for others in carrying\n(let us suppose) an electric discharge, though all were from the first\nsimultaneously present in unvaried proportions. Moreover, chemical\nimmutability can no longer be taken for granted. We have learned\nof late that even elementary individuality breaks down under the\nbattering-ram of time. Sooner or later the stamp, however apparently\ninviolable, will be defaced, transformations of species will ensue, and\nnovel combinations of material will subtly accommodate themselves to\nthe needs of a growing world. These things, it is true, are involved in\nmuch obscurity, but we have caught glimpses of instability clear enough\nto convey an emphatic warning against dogmatic interpretations of\nspectral characters. Physical science may then license M. du Ligond\u00e8s'\ntheory of comets with a provisional _Nihil obstat_.\n\nThe zodiacal light suggests a different set of considerations. Comets\nbeing of pre-planetary origin, the ecliptical glow must be supposed\npost-planetary. It belongs to a later epoch, being composed, according\nto an accepted opinion,[110] of superfluous materials left over from\nthe construction of the train of globes to which our own belongs. It\nmight be compared to whey from which the curd has been separated.\nAll the good has been got out of it; we might be tempted to throw it\naside upon the rising rubbish-heap of the skies, with the importunate\nasteroidal throng, a few dozen undistinguished comets, and some\nhundreds of ill-defined meteoric systems. But celestial refuse is\nalways worth sifting, above all, for tokens of genealogical descent,\nand we should be unwise to neglect the chance of finding them in the\npeculiar relations of the zodiacal light.\n\nA triple phenomenon, it consists, when completely seen, of a cone, a\nband, and a counterglow. The connection of these parts into a whole\nis obvious, though enigmatical. Usually, however, only the cone is\nvisible. It appears about the time of the spring and autumn equinoxes,\nafter sunset and before sunrise respectively, as a faint lenticular\nillumination, tapering upward from the sun's place below the horizon\nto an apex high up near the meridian. Under the name of the 'False\nDawn' it was familiar, probably from an early age, to Oriental peoples.\nBut they looked for it at the opposite end of the night from that\nfavoured by European observers; nor did the phenomenon attract any\nparticular notice here in England until 1660, when Joshua Childrey\npublished a description of it in his _Britannia Baconica_. Yet it\nhad been specifically observed about seventy years previously by\nChristoph Rothmann of Hesse, and must have been less intelligently\nperceived by numberless spectators, who most likely included it,\nwith such miscellaneous objects as comets' tails, auroral beams, and\nmeteor-trails, in the undefined class of appearances known from of old\nas _trabes_.\n\nThe light is ordinarily much feebler than the Milky Way, which\nit nevertheless on occasions unmistakably outshines.[111] Real\nfluctuations of brightness seem implicated in these changes; yet they\nfollow no traceable law of periodicity, and are certainly independent\nof the sunspot cycle.\n\nThe counterglow, first remarked by Pez\u00e9nas in 1730,[112] soon fell into\noblivion, and had to be rediscovered after six-score years by Brorsen,\nwho bestowed upon it its current title of the 'Gegenschein.' Of late\nit has been pretty constantly observed, particularly by Professor\nBarnard, to whom it presented itself, owing to the scantiness of\nthe available records, as a surprising novelty.[113] Surprising it\ncertainly is. The appearance of the Gegenschein is that of a large\nelliptical patch of diffuse light, measuring about 12 by 9 degrees,\nand situated diametrically opposite to the sun.[114] Now and again,\nthough somewhat rarely, it is perceived to be united to the cone by\nthe 'zodiacal band,' a strip of evanescent luminosity nearly following\nthe line of the ecliptic. We cannot, then, be mistaken in recognising\nthe great pyramidal beam centred on the sun, with the counterglow and\nits linking band, as sections of a single formation, constituting in a\nmanner the substratum of the solar system. A recent observation made\nby Professor Newcomb under unique conditions proves it to be much less\nexclusively 'zodiacal' than had been supposed. Looking north from the\nsummit of the Rothhorn, at midnight, on July 29, 1905, he perceived a\nwell-marked glow spreading 35 degrees from the sun's place.[115] It was\nthe light in its thwartwise aspect, which had never before been seen,\nor even looked for; and we learn from it the remarkable fact that the\nsun is enclosed in a vast, dimly luminous sphere, with a girth not much\nsmaller than the orbit of Venus, and indefinitely diffused along the\nequatorial plane.\n\nNotwithstanding its dim indefiniteness, neither the spectroscope nor\nthe camera is wholly ineffective for the scrutiny of this extraordinary\nappurtenance. We have learned positively that its radiance is of the\ncontinuous sort, the origin of which through the reflection of sunlight\nfrom small solid bodies seems more than probable. The whole structure\nmust accordingly be of a pulverulent or meteoric nature; it consists\nof independently moving particles. But to the further question, Under\nwhat regimen do these particles circulate? no decisive answer is as\nyet forthcoming. M. Hansky[116] and others hold the light to be a\ntrue solar appendage, an extension of the corona, in which case it\nwould have a formal, but no material permanence. It would represent\nthe continually changing aggregate of multitudinous minute bodies\nissuing from or repelled by the sun, and in large proportion falling\nback towards his surface. Yet some difficulty is raised to this view\nby the vast dimensions of the problematical glow. That it extends far\nbeyond the earth's orbit is rendered patent by the phenomena of the\nGegenschein and the band. True, the scope of the sun's repulsive action\ncannot be limited; still, we might naturally expect its products to\nbecome too attenuated for recognition beyond a radius of perhaps fifty\nmillion miles.\n\nAdmitting, on the other hand, the residual character of the zodiacal\nlight, we should attribute to it a constitution analogous to that of\nSaturn's rings. Each one of the cosmic atoms collected in it would\nrevolve round the sun on its own account, scarcely disturbed by\nits neighbours. Nor need we despair of determining with reasonable\ncertainty which way the truth lies in this matter. The rival hypotheses\nmay be tried by a criterion the application of which is by no means\nremotely feasible. It is furnished by the geometrical relations of the\nzodiacal light. Evidently, if the sun can claim organic connection\nwith it, its axis should coincide with the plane of the solar\nequator; while, if it represent wastage from the Kantian nebula, it\nshould stretch along the principal plane of our system--the plane of\nmaximum moment of momentum--the plane towards which the primitive\nagglomeration of revolving particles collapsed as it condensed. The\nquestion of planes is, then, crucial. Is the zodiacal effluence placed\nsymmetrically as regards the solar equator, or does it appertain\nproperly to the ecliptic, which deviates very slightly from the\nfundamental plane of the solar system? The evidence is, unfortunately,\ncontradictory. Most observers have located the dim equinoctial\ncone right along the pathway of the sun; some, under exceptionally\nfavourable circumstances, have perceived in it a marked departure from\nthe track of the Signs.\n\nM. Marchand's determinations from the Pic du Midi, for instance,\nindicated a probable coincidence between the solar equatorial plane and\nthe axis of the light;[117] and Dr. Max Wolf succeeded, in 1889, in\ngetting a photographic impression which, though partial and imperfect,\ntended to corroborate Marchand's inference.[118] Again, on November\n16, 1904, when the cone showed a remarkable lustre, it was distinctly\nperceived at K\u00f6nigstuhl to sheer off and separate from the ecliptic as\nit mounted the sky. Now, however, that a beginning has been made in\nphotographing this enigmatical tenant of the sphere (the feat has been\nperformed at Flagstaff as well as at Heidelberg), we may confidently\nexpect a speedy reconcilement of inconsistent statements regarding\nits whereabouts. Until then we cannot venture to assert that it is in\nactual reality what it appears to be, a nebulous survival.\n\nFOOTNOTES:\n\n[Footnote 109: Ligond\u00e8s, quoted by l'Abb\u00e9 Moreux, _Le Probl\u00e8me\nSolaire_, p. 67.]\n\n[Footnote 110: Moreux, _Le Probl\u00e8me Solaire_, p. 133; Ledger,\n_Nineteenth Century_, March, 1905.]\n\n[Footnote 111: Humboldt, _Cosmos_, vol. iv., p. 563 (Ott\u00e9's\ntranslation); Maunder, _Journal of the British Astronomical\nAssociation_, vol. viii., p. 174; Max Wolf, _K\u00f6nigstuhl Report_ for\n1904.]\n\n[Footnote 112: _Paris Memoirs_, 1731, quoted by R. Wolf, _Geschichte\nder Astronomie_, p. 695.]\n\n[Footnote 113: _Popular Astronomy_, vol. i., p. 337.]\n\n[Footnote 114: Nijland, _Astr. Nach._, No. 4,008.]\n\n[Footnote 115: _Astrophysical Journal_, vol. xxii., p. 209.]\n\n[Footnote 116: _Comptes Rendus_, 1905, No. 6; _Nature_, February 23,\n1905.]\n\n[Footnote 117: _Comptes Rendus_, tom. cxxi., p. 1134.]\n\n[Footnote 118: _Sitzungsberichte_, Munich, Bd. XXX., p. 197.]\n\n\n\n\nCHAPTER XVI\n\nLIFE AS THE OUTCOME\n\n\nThe making of worlds, we are assured, was not purposeless, and its most\nobvious purpose to our minds is the preparation of suitable abodes\nfor organic life. No other seems of comparable importance; no other,\nindeed, comes within the full grasp of our apprehensive intelligence.\nYet its limitations must not be forgotten. The human standpoint is not\nthe only one from which the sum of things may be surveyed; and although\nwe be unable to quit it, we can still admit that the view obtainable\nfrom it is probably not all-embracing. We only know with certainty that\nthe end which appears to us supreme has, in one case, been successfully\nattained; how far it was sought to be compassed elsewhere must always\nremain a matter of speculation.\n\nOn our own globe the presence of life is none the less mysterious for\nbeing profuse and familiar. We can trace the strange history of its\nslow unfolding, but the secret of its initiation baffles our utmost\nscrutiny. The cooled rind of a once molten globe serves as the stage\nfor the drama; beneath it primeval heat still reigns. Temperature\nrises steadily with descent into the interior of the earth; at a\ndepth of about two miles it must reach the boiling-point of water at\nthe sea-level. This temperature, which is absolutely prohibitive of\nvitality, was formerly, beyond question, that of the surface. At some\nlong past epoch, accordingly, our future oceans hung suspended as a\nprodigious envelope of vapour above a hot crust of slag and lava; our\nteeming planet lay barren; it harboured no promise, no potency, no\nvisible possibility of life.\n\nSo it should have remained had the law of continuity been rigidly\nenforced; but there came a time for a new beginning, and a new\nbeginning was made. A momentous alteration took place; inert Nature\nwas quickened; what had been sterile became all at once fruitful; an\nimmeasurable gulf was bridged, and movement was started along an\nendless line of advance. That the advance was set on foot and directed\nby an intelligent Will is the only inference derivable from a rational\nsurvey of the known facts.\n\nLife can be studied in its manifestations, not in itself. Attempts\nto define it have served only to show our inability to 'lift the\npainted veil.' We can, however, see that its presence is attended by\ncharacteristic effects, brought about in harmony with the laws of\ninorganic nature, although not in blind submission to them. Their\noperation is somehow restrained, and appears to be subtly though\nsecurely guided towards determinate ends prescribed by the vital\nneeds of each animal or plant. This modifying principle unmistakably\nregulates the economy of every living organism; the cessation of its\nactivity means death.\n\nScience has made no real progress towards solving the enigma of\nvitality. Its evasiveness becomes, on the contrary, more apparent as\ninquiry is rendered more exact. Under a laxer discipline of thought\nthe contrast between life and death seemed less glaring. It was\neasily taken for granted that creeping things were engendered by\ncorruption, aid being invoked, if required, from the _virtus c\u0153lestis_\nof the eighth sphere. Thus, the birth of mice from the damp earth\nwas, in the ninth century, held to be signified by the word _mus_\n(=humus);[119] and Van Helmont, at the height of the revival of\nlearning, published without misgiving a recipe for the creation of the\nsame animals.[120] Yet there was already better knowledge to be had\nfor the asking; and Francesco Redi, in 1668, crystallized Harvey's\nopinion in the celebrated maxim, '_Omne vivum ex vivo._' Its truth is\nincontrovertible. Challenged and tested again and again, it has as\noften been vindicated, and may now be said, despite certain anomalous\neffects of radium on veal broth, to stand outside the legitimate range\nof debate. 'That life is an antecedent to life,' Lord Kelvin declared\nin 1871, 'seems to me as sure a teaching of science as the law of\ngravitation.'[121]\n\nBut the succession is not easy to start within the terms of a strictly\nuniformitarian convention. The expedient is tempting, if scarcely\nsatisfactory, of demanding from the past what we dare not claim from\nthe present. Two and a half millenniums ago it was already in vogue.\nHerodotus dismisses a genealogical embarrassment with the remark,\n\u03b3\u03ad\u03bd\u03bf\u03b9\u03c4\u03bf \u03b4'\u03ac\u03bd \u03c0\u1fb6\u03bd \u03ad\u03bd \u03c4\u1ff6 \u03bc\u03b1\u03ba\u03c1\u1ff6 \u03c7\u03c1\u03cc\u03bd\u03c9, which may be freely translated, 'In\nthe long run of time anything may happen.' Conditions, we are apt to\nthink, may have been more elastic long ago. The proven impossibility\nof to-day becomes vaguely thinkable seen through the mist of uncounted\nyesterdays. 'If it were given to me,' Professor Huxley said,[122] 'to\nlook beyond the abyss of geologically recorded time to the still more\nremote period when the earth was passing through physical and chemical\nconditions which it can no more see again than a man can recall his\ninfancy, I should expect to be a witness of the evolution of living\nprotoplasm from non-living matter.' To these first vital compounds he\nattributed a fungoid nature and mode of growth, and the choice deprived\nhis speculation of any plausibility that might otherwise have belonged\nto it. Fungi are not self-supporting; they cannot supply themselves\nwith nourishment from the raw materials of the mineral world; they\ndepend upon the hospitality of differently organized beings. They\nwere, then, certainly not among the 'first mercies of nature.' Mr.\nHerbert Spencer, too, was inclined to regard spontaneous generation\nas a superannuated process. The leap from the non-vital to the vital,\nnow admitted by the saner kind of biologists to be impracticable,\nmight have been taken, it seemed to him, when 'the heat of the earth's\nsurface was falling through those ranges of temperature at which the\nhigher organic compounds are unstable.' But the 'reason why' is to\nseek. A sterilized solution is precisely one which has cooled from\na high thermal grade; a baked brick is similarly circumstanced. Why\nshould the appearance of life in primeval times have been favoured by a\nstate of things fatal to it here and now?\n\nThe essence of the biological crux resides in 'protoplasm.' The word\nwas coined by Von Mohl in 1846, with the object of emphasizing the\nimportance of the substance it signified, which indeed forms the bulk\nof every organism, animal and vegetable, man, mushroom, and am\u0153ba.\nHuxley rightly termed it 'the physical basis of life,' adding, however,\nthe infelicitous conjecture that its production might have been one\nof the lucky hits of nature. It would have been a hit of incalculable\nmoment, but of incalculable improbability. 'Odds beyond arithmetic'\nwere against that particular throw coming out of the Lucretian\ndice-box. The 'primal slime' (to use Oken's phrase) is composed of\noxygen, nitrogen, hydrogen, and carbon, with minute percentages of\nphosphates and other salts. But these constituents are put together in\na highly artificial manner. Eight or nine hundred elementary atoms,\nin fact, go to the making of one molecule of protoplasm, forming a\nstructure of extreme complexity, most delicately balanced and eminently\nunstable. It results, accordingly, from the employment of specially\ndirected forces, and stores, for the benefit of the producing organism,\nthe energy expended in its construction. Left to itself, it promptly\ngoes to pieces, and yields back its component particles to their native\ninorganic sphere. The laws there ruling are in truth adverse to the\nexistence of protoplasm; abandoned to their unmitigated action, it\nperishes. We should then as reasonably suppose that in the geological\npast rivers flowed uphill as that inorganic nature stumbled blindly\nupon this wonderful postulate and product of life.\n\nProfessor Huxley affirmed life to be 'a property of protoplasm,' the\ninevitable outcome of 'the nature and disposition of its molecules,'\nand he sought to cover the absurdity of the dictum by claiming as\nanalogous a case wholly disparate. Water, he argued, has qualities\ntotally unlike those of oxygen or hydrogen, and protoplasm may\nsimilarly, by mere intricacy of arrangement, and the evoking of latent\naffinities, become endowed with the transcendant powers connected\nwith animated existence. 'What better philosophical status, then,' he\nexclaimed, 'has _vitality_ than _aquosity_?'[123] 'True,' he added,\n'protoplasm can only be generated by protoplasm, in a manner that\nevades our intelligence, but does anybody quite comprehend the _modus\noperandi_ of an electric spark which traverses a mixture of oxygen and\nhydrogen?' The illustration is inapt. The electric spark fulfils no\nconstructive function. It simply agitates the molecules so as to bring\ntheir native affinities into play. It acts like a mechanical blow on\ndynamite. Further, water is a stable compound, because its formation is\nattended by loss of energy; it represents a plane permanently occupied\nbecause reached by a steep descent; but protoplasm is, in this respect,\nthe antitype of water. It needs force for its composition; water needs\nforce for its decomposition. Protoplasm needs force plus a suitable\napparatus; it can be turned out only by an artfully adapted machine\nwith a head of steam on. It is thus continually manufactured by plants\nunder the stimulus of light. They provide the apparatus, sunbeams the\nenergy. If the supply of power is cut off, the machinery comes to a\nhalt, protoplasm ceases to be generated, the organism dies of inanition.\n\nMany German biologists find themselves compelled, by the impossibility\nof explaining vital activities in terms of chemistry or physics, to\nassociate protoplasm with some kind of psychical activity.[124]\nIndividuality, at least, implies an ultra-material principle, and it\nasserts itself at the very base of the animal creation. An am\u0153ba is the\nsimplest of living beings. Formerly called the 'Proteus animalcule,' it\nis 'everything in turn, and nothing long.' It can be round or radiated,\nspherical or lenticular, as momentary convenience prescribes. Organs it\nhas none, its limbs are conspicuous by absence, it is 'sans everything'\nthat belongs to the ordinary outfit of an animated creature. Yet\nsuch-like nucleated globules of protoplasm have flourished exuberantly\nduring countless ages. Adaptability insured survival. An am\u0153ba is at\nhome in almost any environment. What it has not ready-made, it can\nsupply at a moment's notice. Out of any part of its substance it can\nimprovise feelers and tentacles for the capture of its prey, as well as\na stomach for its digestion, and it thus effectively goes through the\nfull round of animal economy. Some varieties, too, are noted builders.\nThose called Foraminifera have the faculty of secreting carbonate of\nlime from sea-water, and construct with it fairy dwellings, perforated\nin all directions to allow of the protrusion of exploratory filaments.\nFossil chambered shells of this type are extraordinarily abundant.\nTheir dense conglomeration in the chalk elicited Buffon's exclamation\nthat 'the very dust had been alive!'[125] The _calcaire grossier_ of\nwhich Paris is built consists mainly of them, and to this day, in\noceanic depths, the materials of future capitals are in course of\npreparation by the monumental industry of these unpretending creatures.\n\nSuch as they are, they maintain a status incomparable with that of\nnon-living things. Incomparable, for instance, as regards the water in\nwhich they float. The contrast is startling despite its familiarity. An\nam\u0153ba incarnates a purpose; it embodies a spark of personal existence,\nunconsciously swaying the forces of inorganic nature towards the\nends of its own well-being. The subordination is most real, though\nprofoundly mysterious. In the organic and the inorganic worlds the same\nlaws hold good; the same ultimate atoms exert their preferences in\neach; in neither is an uncaused effect possible. A bullet can no more\nbe fired from a gun that has no charge than a man can lift a finger\nwithout a corresponding outlay of food-products. Accordingly, while\nplants store and animals expend energy, plants and animals are equally\nincompetent for its origination. What they can do is to appropriate\nand specifically apply it; and herein resides the essence of life. 'It\nwould seem,' Sir George Stokes wrote in 1893,[126] 'to be something\nof the nature of a directing power, not counteracting the action of\nthe physical forces, but guiding them into a determined channel.'\nWhat the power is in itself it would be futile to seek to define. We\nare only sure of its being extra-physical. Matter cannot evolve a\nprinciple which disposes of it as its master. Evolution means only the\nunfolding into self-evidence of something already obscurely present.\nThe 'latent process' (to use a Baconian term) of the hatching of an egg\nis typical and instructive. Yet it is not the less recondite for being\ndaily conducted before our eyes. A concourse of suns, indeed, fails to\nimpress us with the unutterable wonder of the 'flower in the crannied\nwall' apostrophized by the last great poet of the nineteenth century.\n\nThe two wide kingdoms of life lack a 'scientific frontier.' The\nboundary-line is ill-marked and irregular. So much so that a few\nnaturalists have set up a neutral zone, or no man's land, inhabited\nby creatures of mixed or uncertain nature, by plant-animals, or\nzoophytes in the literal sense of the word. But the expedient avails\nto shelter ignorance rather than to advance knowledge. For it seems\nprobable that there is no organism so imperfectly characterized as to\nbe genuinely incapable of giving a categorical answer to the question,\n'Under which king, Bezonian?' Fungi might, perhaps, on a superficial\nview, be taken for hybrids. They share the nature of animals so far\nas to be unable to elaborate their own food, while appearing in other\nrespects to be authentic vegetables. They are, in fact, parasites\nand scavengers. Not the smallest reason exists for supposing them to\nconstitute a genetic link between the two chief hierarchies. These\nare, in all likelihood, fundamentally distinct. Only by a gratuitous\nhypothesis can they be credited with a common ancestor. Each seeks\na different kind of perfection; their ideals, so to speak, follow\ndivergent tracks. That the tracks were marked out from the beginning\nmay be safely affirmed; and this implies radical separation. Plants\ncame first, since animals pre-suppose and imperatively require them;\nthe antecedence having quite possibly been by a vast interval of time.\nOn this point, geological evidence, though inconclusive, is suggestive.\nThe Laurentian beds, which are among the very earliest stratified\nformations, contain no recognisable fossils. They were once supposed to\nenshrine the remains of a lowly organism dubbed _Eoz\u00f6on Canadense_; but\nthe markings that simulated animal forms are now known to be of mineral\norigin. Laurentian graphite, on the other hand, occurs plentifully;\nand graphite may be described as coal at a more advanced stage of\nmineralization. Such deposits, we are led to believe, consist of\naltered vegetable substances; and it seems to follow that these hoary\nrocks are the burying ground of a profuse succession of virgin forests.\nThat they flourished beneath the sea--were, in fact, composed of\nalg\u00e6--was the opinion of Professor Prestwich,[127] and it is not easily\ngainsaid.\n\nPrimitive animal life was unquestionably marine, and the Huronian\nstrata, which overlie the Laurentian, afford traces of it in a few\nsponge-spicules, the cast of an annelid, and such-like scanty leavings.\nHigher up, the Cambrian series swarms with oceanic invertebrates;\nfishes, the first type of vertebrates, came upon the scene in Silurian\ntimes; and so, by a various and surprising progression, life advanced\nthrough the ages, until the ascending sequence culminated with a being\ncast in a diviner mould, who walks the earth, even now, with face\nuplifted to the stars.\n\n 'Natus homo est; illum mundi melioris origo\n Finxit in effigiem moderant\u00fbm cuncta deorum.'\n\nIn the vegetable kingdom the vital law of development has wrought with\nless conspicuous effect. The superiority of recent to ancient floras\nis more significant than striking. A tree-fern or a sigillaria bears\ncomparison with an oak much better than a trilobite or a plesiosaurus\nwith an eagle, horse, or lion. The geological variations of plants,\nhowever, have unmistakably tended to make them more serviceable to\nman--more serviceable to his material needs, and also more gratifying\nto his \u00e6sthetic instincts. For him, flower-petals were painted and\nperfumes distilled; for him, the grasses of the prairie laid up stores\nof sustaining nutriment; in preparation for his advent, choice fruits\nripened and reddened under Tertiary sunshine; while the barren and\nsombre vegetation of the Carboniferous epoch had already done its part\nby dying down into seams of coal for the eventual supply of power for\nhuman industry and warmth for human comfort.\n\nIt would be an abuse of our readers' patience to discuss the futile\nconjecture of an extra-terrestrial origin for life on our globe. The\nagency, in this connection, of germ-laden aerolites was first invoked\nby Richter of Dresden; and Lord Kelvin gave currency to the notion by\nan incidental reference to it in 1871 from the Presidential Chair of\nthe British Association. Its adoption would oblige us to regard the\ndenizens of our planet, fauna and flora alike, as salvage from the\nwreck of some unknown world in space. _Credat Jud\u00e6us Apella._ To our\nminds, the adventures of Baron Munchausen appear more credible than\nthe pre-natal history of the primal organism implied by this 'wild\nsurmise.' Inquiry into the nature of the supposed organism serves\nto draw closer the web of embarrassment. The remarkable aridity of\nmeteorites excludes the possibility of its having had an aquatic\nhabitat. Members of the fungoid order are unsuited to act as pioneers,\nowing to their helplessness in the matter of commissariat; and the\nspores or lichens or mosses could scarcely be expected to survive\nthe vicissitudes of such a journey as they must have performed if\nmeteor-borne to terrestrial shores. The immigration hypothesis,\nmoreover, even if it were plausible, could not be made useful.\nDifficulties do not vanish on being pushed into a corner; the problem\nof life is as formidable in one world as in another; we should not\nexpect to find it easier to square the circle in Mars than Deinostratos\nfound it in Greece; matter, we are convinced, has no more psychical\ninitiative in the system of Arcturus than can be ascribed to it in the\nsystem of the sun. Profitless conjectures may then be dismissed; they\ndo not help us out of the slough of intellectual impotence.\n\nThis need not, indeed, be absolute. The determination to regard things\nmechanically alone renders them unintelligible. Science becomes\nunscientific when it refuses to be guided by experience; and we have\nthe plainest testimony of consciousness to the working in ourselves of\noriginative faculties independent of, and irrepressible by, physical\nagencies. Here we hold the clue to the labyrinth. The intimation\nconveyed is distinct of a Power outside nature, continually and\ninscrutably acting for order, elevation, and vivification.\n\nFOOTNOTES:\n\n[Footnote 119: Hewitt, _Problems of the Age_, p. 105.]\n\n[Footnote 120: Pasteur, _Annales de Chimie et de Physique_, tome xliv.,\np. 6, 1862.]\n\n[Footnote 121: _Popular Lectures and Addresses_, vol. ii., p. 198.]\n\n[Footnote 122: _Report British Association_, 1870, p. 84.]\n\n[Footnote 123: _Collected Essays_, vol. i., p. 153]\n\n[Footnote 124: Neumeister, _Betrachtungen \u00fcber das Wesen der\nLebenserscheinungen_, 1903.]\n\n[Footnote 125: Owen, _Pal\u00e6ontology_, pp. 11, 14.]\n\n[Footnote 126: _Gifford Lectures_, p. 46.]\n\n[Footnote 127: _Geology_, vol. ii., p. 22.]\n\n\n\n\nINDEX\n\n\n Alexander, structure of the Milky Way, 214\n\n Am\u0153ba, versatile organization, 274-5\n\n Anaximander, generalized matter, 5\n\n Anaximenes, air as the 'Urstoff,' 4, 151\n\n Aristotle, conception of nature, 8;\n   solid spheres, 13\n\n Asteroids, orbital relations, 236\n\n\n Babinet, objection to Laplace's cosmogony, 44\n\n Bacon, elemental triad, 151\n\n Ball, Sir Robert, mechanics of a condensing nebula, 79, 209-10\n\n Barnard, discoveries of nebul\u00e6, 212;\n   observations of the Gegenschein, 259\n\n Becquerel, detection of radio-activity, 157, 162\n\n Bessel, astronomy of the invisible, 141\n\n Bode's law of planetary distances, 26\n\n Brorsen, the zodiacal counterglow, 259\n\n Bruno, a platonic pantheist, 9\n\n Buffon, cometary impacts, 61;\n   fossil foraminifera, 275\n\n\n Campbell, system of \u03b6 Geminorum, 113;\n   number of spectroscopic binaries, 143;\n   density of nebulium, 153\n\n Chladni, meteoric cosmogony, 118\n\n Comets, position in Cartesian system, 12-13;\n   in that of Laplace, 136;\n   origin, 73-4, 252-4;\n   meteoric relations, 122-4, 133;\n   solar dependants, 133, 140, 236, 251;\n   nebular affinities, 137, 254-5;\n   insignificant mass, 242\n\n Cosmogony, primitive, 1-3, 14;\n   philosophical, 3-7;\n   scientific, 7, 15;\n   of Descartes, 11-13, 60;\n   Kant's, 21-28, 61-2, 252, 254;\n   Laplace's, 29-33, 38-53, 57-61, 138, 235;\n   Herschel's, 35-7, 136, 199-201;\n   Faye's, 68-76, 81, 129;\n   Lockyer's, 125-134;\n   sidereal, 105-7, 145-7, 217-230\n\n Crookes, Sir William, protyle, 5, 149;\n   radiant matter, 154, 156-7;\n   future of the world, 163\n\n Curie, Madame, discovery of radium, 162\n\n\n Dalton, combining equivalents, 152\n\n Dark stars, 141, 226-7\n\n Darwin, condensation of nebulous rings, 42, 51;\n   history of earth-moon system, 87-92, 94, 97, 142;\n   equilibrium of rotating globes, 102, 104-5, 112, 143;\n   fluid pressure on meteor-swarms, 129, 131;\n   spiral nebul\u00e6, 205\n\n Delambre, on cosmic speculations, 14, 15\n\n Democritus, mechanical theory of the world, 5, 22\n\n Descartes, theory of vortices, 11-13\n\n Dissipation of energy, 229\n\n Double stars, genesis and development, 98-9, 106-7, 142-5, 226-7;\n   occulting, 108-113;\n   variable, 113-115, 143;\n   'dumb-bell' type, 115, 116, 143;\n   frequency of occurrence, 144, 234\n\n\n Earth, effective rigidity, 86;\n   critical situation, 87;\n   antique disruption, 89, 91;\n   tidal effects upon, 90, 244;\n   meteoric intakes, 119-120, 133;\n   internal heat, 266\n\n Easton, the galactic spiral, 214\n\n Eclipses, stellar, 107-8;\n   questionable occurrence, 109-113;\n   criterion of reality, 114\n\n Electricity, discharge through vacua, 154;\n   relations with disintegrated matter, 155, 159-160, 163;\n   gravity explained by, 177-8, 179;\n   dual properties, 180-181;\n   fundamental in nature, 182;\n   ethereal transmission, 185\n\n Electrons, copious production, 174;\n   strain-centres, 189-190, 195;\n   ultimates of matter, 231\n\n Elements, ancient and medi\u00e6val ideas regarding, 5, 151;\n   genesis, 152, 230-231\n\n Empedocles, four elements, 5, 151\n\n Ether, in Cartesian philosophy, 12;\n   evasive character, 159, 183, 197-8;\n   relation to gravity, 175, 185;\n   properties, 184, 191, 193-4\n\n Evolution, of solar system, 22, 241, 250;\n   of stars, 35-6, 217-225;\n   of stellar systems, 98-9, 106-7, 142-5, 226-7;\n   of nebul\u00e6, 145-6, 200-211;\n   of the chemical elements, 151, 230-231\n\n\n Faye, objections to Laplace's cosmogony, 25;\n   modified scheme, 68-73, 81, 129;\n   duration of the sun, 76\n\n Fleming, nature of electrons, 195\n\n Frost and Adams, spectroscopic binaries, 143, 221\n\n\n Galileo, first law of motion, 12\n\n Goldstein, cathode-rays, 155\n\n Gravitation, mode of action, 168, 185;\n   velocity of transmission, 169, 175, 177;\n   explanatory hypotheses, 170-179\n\n\n Hale, relationships of carbon stars, 225\n\n Halley, nature of nebul\u00e6, 36\n\n Hansky, status of zodiacal light, 261\n\n Harvey, life from life, 268\n\n Helium, present in the sun, 55;\n   origin by atomic decay, 158, 230;\n   absorption in stars, 220, 222-3;\n   a constituent of nebul\u00e6, 230\n\n Helmholtz, maintenance of solar heat, 31, 34, 35, 74-5\n\n Helmont, spontaneous generation, 268\n\n Heracleitus, elemental evolution, 151\n\n Herodotus, omnipotence of time, 269\n\n Herschel, Sir John, nature of atoms, 156;\n   Saturn's satellites, 240\n\n Herschel, Sir William, Uranian system, 29;\n   sidereal evolution,\n  35-6, 37, 136;\n   observations of nebul\u00e6, 199;\n   history of their growth, 200-201\n\n Huggins, Sir William, discovery of gaseous nebul\u00e6, 54, 153\n\n Huggins, Sir William and Lady, stellar development, 226\n\n Huxley, origin of life, 269, 271, 272\n\n Hydrogen, molecular velocity, 55;\n   the unit-atom, 152;\n   tenuity, 153;\n   absorption in stars, 221-2\n\n\n Island-universes, 54\n\n\n Jeans, figures of equilibrium, 104-5;\n   nature of radio-activity, 196\n\n Jupiter's system, 240-1\n\n\n Kant, cosmological speculations, 20-28, 60-62, 252, 254;\n   tidal effects, 27, 84-5;\n   Saturn's rings, 49;\n   status of comets, 73\n\n Kelvin, Lord, Lesage's theory of gravitation, 174;\n   vortex-atoms, 187;\n   dissipation of energy, 229;\n   origin of life, 268, 280\n\n Kepler, physical astronomy, 10\n\n Kirkwood, objection to nebular hypothesis, 50, 51;\n   effects of solar tidal friction, 67\n\n\n Lambert, sidereal construction, 17-18\n\n Langley, mass of meteoric infalls, 119\n\n Laplace, hypothesis of planetary origin, 25, 29-31, 33, 36-42,\n 52-3, 58-9, 60-62, 235;\n   Saturn's ring-system, 49;\n   _M\u00e9canique C\u00e9leste_, 57;\n   status of comets, 73, 136\n\n Larmor, scheme of molecular physics, 188;\n   definition of ether, 189, 193\n\n Lenard, cathode-rays, 157\n\n Lesage, rationale of gravity, 172-3, 175\n\n Lewis, masses of double stars, 226\n\n Ligond\u00e8s, scheme of planetary growth, 77-8, 81, 252;\n   comets as survivals, 253, 256\n\n Lockyer, Sir Norman, meteoritic hypothesis, 125-7;\n   enhanced lines, 223\n\n Lorentz, electrical hypothesis of gravity, 177-8, 185\n\n\n Magellanic clouds, spiral conformation, 213\n\n Marchand, plane of the zodiacal light, 263\n\n Mars, rotation of, 47-8\n\n Maxwell, origin of matter, 161;\n   corpuscular theory of gravitation, 173\n\n Mayer, J. R., effects of tidal friction, 87\n\n Mercury, action upon of solar tides, 88, 96;\n   eccentric orbit, 242\n\n Meteoritic formation of planets, 28-9, 119-122, 125, 128, 131-3;\n   of comets, 122-4;\n   of nebul\u00e6, 126-7, 134\n\n Meteors, abundance, 119, 133;\n   mineralogy, 121-2, 134;\n   hyperbolic orbits, 133;\n   attendance on the sun, 236\n\n Meteor-swarms, progressive dispersal, 72, 124;\n   constitution, 122-4, 128-131;\n   primitive existence, 134\n\n Milky Way, theories regarding, 16-17, 215;\n   undeveloped condition, 201, 207;\n   relation to sun's movement, 247\n\n Mohl, protoplasm, 270\n\n Moment of momentum, 23, 40, 44, 45, 65, 209\n\n Moon, origin, 87-92, 97, 139, 145;\n   retreat from the earth, 244\n\n Moulton, nebular cosmogony, 44, 51, 82\n\n Myers, systems of \u03b2 Lyr\u00e6 and U Pegasi, 109-110\n\n\n Nebul\u00e6, gaseous composition, 37, 153, 201, 205;\n   illusory resolution, 53;\n   spiral structure, 79-80, 106, 146, 190, 204-208, 211-214;\n   classification, 199;\n   development, 200-202, 205, 207-211;\n   relation to stars, 202-3, 205;\n   helium ingredient, 230, 255\n\n Nebular hypothesis, propounded by Kant, 22-8;\n   by Laplace, 29-31, 38, 52-3, 61;\n   difficulties, 39-52, 54-6;\n   amendments, 60-82\n\n Nebulium, a constituent of nebul\u00e6, 54, 153, 201\n\n Neptune, retrograde system of, 43, 52, 237\n\n Newcomb, transverse observation of the zodiacal light, 260\n\n Newton, transmission of gravity, 184, 185\n\n Nova Persei, nebulous appurtenance, 206\n\n\n Perrine, new Jovian satellites, 240\n\n Pez\u00e9nas, notice of the counterglow, 259\n\n Phobos, anomalous revolution, 47-8, 237\n\n Ph\u0153be, retrograde motion, 96, 237-8\n\n Pickering, E. C., binary nature of V Puppis, 112;\n   structural relations of the Looped Nebula, 213\n\n Pickering, W. H., origin of Ph\u0153be, 97, 238;\n   photograph of a great nebula, 212;\n   satellite discoveries, 237, 240\n\n Plato, conception of a world-soul, 8\n\n Poincar\u00e9, rotational equilibrium, 101, 105, 110, 143;\n   destiny of the solar system, 243-4\n\n Prestwich, Laurentian graphite, 279\n\n Proctor, structure of the Milky Way, 214\n\n Protoplasm, its properties, 270-273\n\n Protyle, supposed discovery, 149, 154-7;\n   function and qualities, 152;\n   cosmic relations, 164-5\n\n Prout, unity of matter, 152\n\n\n Radio-activity, possible effects, 33-4, 229;\n   discovery, 157;\n   nature and cause, 158-9, 162-3, 196\n\n Red stars, affinities, 224-6\n\n Redi, transmission of life, 268\n\n Reynolds, explanation of gravity, 170;\n   molecular physics, 188, 192-3\n\n Richter, germ-laden aerolites, 280\n\n Roberts, A. W., systems of R2 Centauri and of V Puppis, 111, 113\n\n Roberts, Isaac, spiral arrangements of stars, 214\n\n Roche, planet-making expedients, 48;\n   reconstruction of Laplace's hypothesis, 62-67\n\n Roche's limit, 63, 115-6\n\n R\u00f6ntgen rays, discovery, 157;\n   ethereal nature, 158, 176;\n   electronic effects, 163;\n   suggested connection with gravity, 176\n\n Rothmann, early notice of the zodiacal light, 256\n\n Russell, photographs of Magellanic Clouds, 213\n\n Rutherford, atomic disintegration, 162\n\n\n Satellites, periods of revolution, 46;\n   anomalies of movement, 47-8, 52, 96, 236-9;\n   effects on of tidal friction, 93-4, 96, 97, 238;\n   origin by fission, 105;\n   'asteroidal,' 239-40\n\n Saturnian system, an example to cosmogonists, 41, 71;\n   anomalies, 49, 52, 96, 237-240\n\n Schaeberle, photographs of nebulous spirals, 204, 212\n\n Secchi, star-classification, 219\n\n See, tidal friction in stellar systems, 98, 142\n\n Shelley's Demiorgon, 9\n\n Solar system, origin, 22, 39-42, 69-82, 241;\n   anomalies, 29, 43-52, 236-241;\n   mechanism, 30, 234-5;\n   stability, 235, 242;\n   springs of decadence, 243-5;\n   translation, 245-8\n\n Spectroscopic binaries, 98, 112-114, 142-4, 221\n\n Spencer, status of nebul\u00e6, 54;\n   spontaneous generation, 270\n\n Spinoza, pantheistic views, 9\n\n Stars, relations to nebul\u00e6, 35-6, 202-3;\n   distribution, 147;\n   relative ages, 217-221, 225;\n   spectra, 221-5\n\n Stokes, Sir George, nature of life, 276\n\n Stoney, criticism of gravitational hypothesis, 179\n\n Sun, mode of development, 25, 31;\n   maintenance of heat, 31-5;\n   helium-constituent, 55-6;\n   stellar relationships, 224-5;\n   actual standing, 232-3;\n   motion in space, 245-8\n\n Swedenborg, cosmic evolution, 4, 6, 15\n\n\n Thales, ideas of cosmic evolution, 4, 14, 151\n\n Thomson, J. J., mass of corpuscles, 158;\n   gravitational effects, 173;\n   R\u00f6ntgen rays and gravity, 176;\n   ether and matter, 190\n\n Tidal friction, effects in earth-moon system, 28, 87-92, 94, 97, 244;\n   in other sub-systems, 48, 50, 93-7, 238-9;\n   on binary stars, 98-9, 108, 142;\n   modifying power, 46-7, 67-8, 83-7\n\n Tisserand, transmission-rate of gravity, 175\n\n\n Uranian system, retrograde motion, 43, 52, 70, 237\n\n\n Variable stars, 108-115\n\n Venus, mode of rotation, 96\n\n Vogel, stellar development, 219, 225\n\n\n Whewell, status of nebul\u00e6, 54\n\n Whittaker, undulatory theory of gravity, 178-9\n\n Wilson, radium in the sun, 34\n\n Wolf, C., motion of Phobos, 48;\n   solar tidal friction, 67;\n   criticism of Faye's cosmogony, 73\n\n Wolf, Max, photographs of the zodiacal light, 263\n\n World Soul, function in cosmogony, 8-9\n\n Wright, theory of the Milky Way, 16-17, 18, 20\n\n\n Zodiacal light, origin, 256-7, 261, 264;\n   triple aspect, 257-60;\n   transversal dimensions, 260;\n   constitution, 262;\n   plane of extension, 262-3\n\n\nBILLING AND SONS, LTD., PRINTERS, GUILDFORD","title":"Modern cosmogonies","tradition":"philosophy-ethics","translated_text":null,"word_count":50882}