Ixxviii KANT'S UNIVERSAL NATURAL HISTORY 



the hypothesis of Laplace, it has always been supposed that 

 the outer planets were formed first.' 1 



As regards the points of agreement between 

 Kant and Laplace, M. Wolf says : ' These two 

 conceptions have a common point of departure ; 

 both make the planetary system arise from a primi- 

 tive Nebula whose motion commands that of the 

 planets, and gives it that remarkable uniformity 

 which demonstrates the common origin of these 

 celestial bodies. It is entirely just to assign to the 

 German philosopher the glory of having first an- 

 nounced this grand idea. But there exists no 

 other common point between the two hypotheses ; 

 the Nebula of Kant differs entirely by its pro- 

 perties and its movements from the Nebula of 

 Laplace. . . . Kant supposes the primitive uni- 

 versal chaos dividing itself, by the effect of attrac- 

 tion, into a great number of isolated masses, the 

 germs of the future stars. ... In every isolated 



1 Popular Astronomy, p. 495-7. J. S. Mill discusses the logical 

 validity of the Nebular Hypothesis in his Logic, B. in., ch. xiv. ; cf. 

 John Fiske's Cosmic Philosophy, vol. I. (1874). There is an important 

 mathematical discussion of the Nebular Hypothesis by David Trow- 

 bridge, A.M., in Silliman's American Joiirnal of Science and Arts, 

 beginning in No. 114 (November, 1864), which is well worth referring 

 to. Mr. Proctor summarises the ring theory in a single sentence, thus : 

 ' Laplace conceived that the solar system may have been formed by the 

 gradual cooling and condensation of a vast, rotating nebulous globe; 

 that in the process of contraction successive rings were thrown off, to 

 form in one case a ring of small planets, but in general to break up and 

 form each a single globe ; that in the formation of such globes a similar 

 process was repeated ending in the formation of satellites, and in a 

 single case of what we now know to be a ring of small satellites.' 

 Saturn and his System, p. 2O2. 



