March, 1903. 



KNOWLEDGE 



57 



MODERN COSMOGONIES. 



P.y A<iNRS M. CLERKr;. 



I.— THE NEBULAR HYPOTHESIS. 



Immanuel Kant wa.s, in 1751, still iu the pla.stic stage. 

 His period of " Pure Reason" was remote, and might have 

 appeared improbable. Such as they were, his distinctions 

 had been won in the field of concrete science, and the world 

 of phenomena invited his speculations more seductively 

 than the subtleties of logic. A seed was accordingly thrown 

 into fertile soil by his reading of Thomas Wright's " New 

 Theory of the Universe," as summarised in a Hamburg 

 journal. It set him thinking, and his thoughts proved to 

 be of the dynamic order. Wright resrarded the heavens 

 under a merely statical aspect. He laid down the first 

 definite plan of th^ir construction, showing that the stars 

 were not aggregated at random, but by method, and this 

 was much for one struggling item of humanity to have 

 accomplished unaided. But the young philosopher of 

 Kimigsberg could not rest satisfied with the idle con- 

 templation of any subsisting arrangement. His mind was 

 incapable of acquiescing in things simply as they presented 

 themselves ; it ciaved to know further how they came to 

 stand to each other in just such mutual relations. He 

 was, moreover, permeated with Epicurean doctrines. Not 

 in any reprehensible sense. He could not be reproached 

 either as a hedonist or as an atheist. His pleasures were 

 intellectual, his morals austere, his convictioas orthodox. 

 Behind the veil of material existence he divined its supreme 

 immaterial Originator, and his perception of the activity in 

 Nature of an ordering First Cause remained equally vivid 

 whether its disclosures were taken to be by immediate 

 creation or through tedious processes of modification and 

 growth. His large and luminous view embraced besides 

 the ethical significance which such jirocesses adumbrate. 

 The following sentence shows an appreciation of the place 

 of man in Nature truer and more jarofound than was 

 attained perhaps by any other thinker in the eighteenth 

 century : — " The cosmic evolution of Nature," he wi-ote in 

 memorable words, "is continued in the historic development 

 of humanity, and completed in the moral perfection of the 

 individual."* 



Nevertheless, he owned to a community of ideas with 

 Democritus as to the origin of the universe. Lucretius 

 had cast over him the spell of his lofty diction, and captured 

 his scientific adhesion with the stately imagery of his verse. 

 With reservations, however. Docile discipleship was not in 

 his line. He availed himself, then, of the Democritean 

 atoms, but by no means admitted their concourse to be 

 fortuitous. Chaos itself, as he conceived it, half concealed, 

 half revealed, the rough draft of a " perfect plan." His 

 postulates were few. He demanded only a limitless waste 

 of primordial matter, animated by no forces save those 

 of gravitation and molecular repulsion, and undertook to 

 produce from it a woi'kable solar system. The attempt 

 was no more than partiallv successful. Indeed, investi- 

 gations thrown back into the fore-time lead, at the best, 

 to precarious results, and this one, in particular, was 

 vitiated by a fundamental error of principle. Its author 

 clearly perceived that pi inetary circulation must be the 

 outcome of a vortical swirl in the nebulous matrix ; but 

 he failed to see that no interaction of its constituent 

 jiarticles could have set this swirl going. Systems cannot, 

 of themselves, add to their moment of momentum. Ex- 

 ternal force should be applied to originate rotation in 

 those naturally destitute of it. Now Kant was averse to 



* (Jiioted t)y Dr. Ilastio in the preface to his tmuslatioii of Kant's 

 " Cosmogony," Glasgow,' 1900. 



employing arbitrary expedients, and he piqued himself on 

 the simj)licity of his postulates. Yet he need not have 

 hesitated, had he only viewed things from the modern 

 standpoint, to impart a wheeling movement to his colossal 

 dust-cloud, as the upshot of the mode in which its 

 materials might have come together from the four quarters 

 of the universe ; and he would thus have escaped stumbling 

 at the threshold of his daring enquiry. 



He supposed the particles forming the initial inchoate 

 mass to fall together by gravity, but to be deviated from 

 rectilinear courses through the effects of unequal resist- 

 ance. And he derived from the combination of these 

 multitudinous encounters a common axial rotation for the 

 entire agglomeration. The futility, however, of this mode 

 of procedure was adverted to by the late M. Faye in 188.5.* 

 The deviations in question would, in fact, exactly balance 

 one another, there being no reason why movement in one 

 sense should prevail over movement in the opposite ; con- 

 sequently, a general rotatory movement could not even 

 begin to affect the seething mass, which would condense 

 in sterile rigidity. Kant should then, as Laplace did, 

 when his turn came, have assumed the gyration indis- 

 pensable to his purpose. He asked too little from Nature ; 

 nor is the modesty of a demand other than a poor excuse 

 for failure due to inadequacy of supply. 



Kant made the germ of the future sun to consist in an 

 aggregation of atoms at the core of the nebula, which, 

 growing by successive, innumerable accretions, provided the 

 motive power for the machinery of planetary construction. 

 For it was, as we have seen, the jostling of the particles 

 drawn towards the gradually preponderating centre of 

 attraction which set on foot, it was supposed, the whirl 

 eventually transformed into the tangential velocities of the 

 sun's attendant bodies. They were formed, like the sun, 

 by the perpetuation and increase of subordinate nuclei sure 

 to arise in the elemental tumult. They were formed, not 

 under the guidance of a definite law, but just where chance 

 — or what seemed like chance — favoured an accretion. 

 Nor could they have had a direct rotation. t Under the 

 given conditions retrograde systems should have originated. 

 This would have necessarily ensued from the incoherence 

 of their materials. Particles revolving iudependentlv one 

 of the others have smaller velocities the more remote thev 

 are from the focus of movement. Should they agglomerate 

 into a globe, the inner ranges must, as being the swiftest, 

 determine the direction of its rotation, which will conse- 

 quently reverse the direction of its orbital revolution. 

 Hence, it depends upon the nature of their generating 

 stuff no less than upon the advance of central condensation, 

 whether planets, in their domestic arrangements, contra- 

 vene or obey the larger law of circulation prevailing in 

 the system to which they belong ; and Kant's nebula was 

 undoubtedly such as to involve its contravention. 



Yet his scheme, with all its deficiencies, bore the 

 authentic stamp of genius — of genius imperfectly equipped 

 with knowledge, but original, ix'uetrative, divinatory. The 

 very entitling of the work " A Natural History of the 

 Heavens " was an audacity implying a radical change of 

 conception. It was here that "island-universes" made 

 their definitive appearance. Wright had indeed, five years 

 jn-eviously (in 1750) thrown out the idea that " cloud v 

 spots" might represent "external creations " ; but as a 

 mere vagary of the scientific imagination. Kant un- 

 hesitatingly laid hold of it; classed nebuhe as so many 

 separate galaxies, and I'egarded them as combining with 

 our own into a revolving system on a surpassing scale of 

 grandeur. Kant was also the first to take into account 



» " Sur I'Origine du Monde," 3» cd., p. 136. 



t This also was pointed out by M. Faye, loc. cit., p. 150. 



