280 Reviews — Professor T. C. Chamberlin — 



his well-known planetesimal theory. The author tells us of the 

 development of his interest in cosmography, and shows us the gradual 

 growth of his present conclusions. He was first led into what he 

 calls the " cosmographic fens and fogs " by his desire to reconcile 

 the existence of former glacial periods with faith in an originally 

 molten globe. He, therefore, with the aid of various mathematical 

 friends, notably Professor Moulton, inquired whether the earth could 

 have been in the condition of incandescent gas ; and he was forced to 

 abandon Laplace's nebular hypothesis. In the first series of chapters 

 he points out the objections to it; he claims that it is inconsistent 

 with the kinetic theory of gases, and that if the temperature were 

 high enough to keep the very refractory constituents of the earth in 

 a gaseous state they could not have been held together by gravity. 

 He further holds that if the solar system had originated from a con- 

 tracting nebula the equatorial velocity of the sun should be 270 miles 

 per second, whereas it is only 1£ miles per second. In reference to 

 the support given to the nebular theory by the practical agreement 

 of the average inclination of all the planets and planetoids to the 

 plane of the solar equator with the requirement that they should 

 revolve in that plane, he objects that the divergence of 5° is greater 

 than should occur. A weightier objection is that though the sun is 

 744 times as great as all the planets together, yet they, rlr of the 

 mass, own 98 per cent of the momentum. The criticisms of Laplace's 

 theory are undeniably very weighty. Professor Chamberlin admits 

 its attractiveness, and remarks (pp. 61-2) that its long acceptance 

 was the natural result " of its unsurpassed simplicity and beauty, 

 and of the great service it has rendered the progress of thought", 

 and of the "long list of general harmonies between the salient 

 features of the solar system and the broader terms of the hypothesis. 

 On such general harmonies the hypothesis was founded, and from 

 these it gathered to itself a wide adherence". 



The older forms of the meteoritic theory Professor Chamberlin 

 also regards as unsatisfactory. He insists that Sir George Darwin's 

 well-known demonstration that a swarm of small meteorites would 

 behave physically as a gas in which each meteorite would act as 

 a molecule rests on the doubtful assumption that the separate 

 meteorites should have an elastic recoil like molecules. Professor 

 Chamberlin's presentation of his own hypothesis is not free from 

 serious difficulties, and is perhaps less attractive than in its original 

 form. The planetesimals now play a comparatively small part. 

 Professor Chamberlin regards the meteorites as fragments of an old 

 world rather than as the germs of a new. He derives the solar 

 systems from spiral nebulae ; and he attributes the latter to the 

 scattering of the material of compact stars by that process of dynamic 

 disruption the possibility of which was indicated by Roche. If two 

 bodies approach one another their mutual attraction produces an 

 internal tide that may break the surface and lead to the escape of 

 a large mass of material through a solar prominence. The matter thus 

 drawn upward may fall back to the parent body as a colossal deposit 

 of volcanic agglomerate ; or it may be raised so high as to remain 

 suspended between the two bodies and revolve around the parent as 



