102 G. F. Becker — Kant as a Natural Philosopher. 



originally disseminated in an elementary state, as atoms r 

 throughout the entire space belonging to the system. The 

 material is not supposed to be heated or in motion, the average 

 density of the nebula is many times smaller than that of the 

 terrestrial atmosphere, and the conditions are explicitly the 

 simplest conceivable.* 



He proceeds to develop from this hypothesis not merely the 

 conditions of the solar system but of the star cluster bounded 

 by the Milky Way and other star clusters which he supposes 

 to be represented by the nebulae. As the solar system is to 

 the cluster of which it is an insignificant member, so is this to 

 a greater group of clusters ; and infinite space is occupied by a 

 rotating group of similar constitution but of an infinite order 

 of magnitude and of complexity.! 



For the solar system he deduces many remarkable conclu- 

 sions. The shrinking nebula acquires rotary motion, he erro- 

 neously supposed, in consequence of irregular impact of the 

 component particles and their elasticity.^: Tendencies to 

 motions in all directions, excepting in one resultant plane, are 

 suppressed by mutual interferences of the free particles. Most 

 of the material accumulates at the center, in the sun, but a 

 wide, thin disc of heterogeneous matter remains. This disc 

 consists of discrete particles each of which has acquired such a 

 velocity and direction as to maintain the appropriate orbital 

 motion. On the whole the inner zones of the disc will con- 

 tain a larger proportion of denser substances than are to be 

 found in the outer ones ; while the outer rings, being of rela- 

 tively large circumference, will be of greater mass than the 

 inner ones. Mutual attraction and adhesion, beginning at 

 relatively massive particles, cause the agglomeration of the 

 particles in any zone or ring to single planets or to groups of 

 planetary bodies. The direction of axial rotation is deduced 

 from the mode of formation, the outer part of any accumula- 

 ting planetary mass moving with greater velocity than the inner 

 portion. § (The proof offered for this last proposition is unsatis- 

 factory.)! 



* Kant's Werke, vol. i, p. 247. f Kant's Werke, vol. i, p. 290. 



% Though Kepler's law of areas was well known to Kant, he did not realize the 

 more general theorem, that the moment of momentum of a system on which no 

 external forces act is constant. 



§ Kant's Werke, vol. i. pp. 267 and 258. 



I Mr. H. Faye (L'origiue du monde, 1884. pp. 117 and 143) rejects Laplace's 

 nebular hypothesis on the ground that the latter is in error in his deduction as to 

 the rotation of the plauets. Mr. Faye thinks that because the inner numbers of a 

 swarm of panicles tend to revolve with a higher velocity than the outer ones, 

 retrograde rotation would ensue. This is a case where simple explanations are 

 tempting but misleading The problem rigorously dealt with involves the solu- 

 tion of the problems of three or more bodies. It does not appear to me that Mr. 

 Faye has given any satisfactory proof of his position. The same may be said of 

 Laplace, but it may be suspected that this great man had solved some particularly 



