NEBULAR THEORY. 359 



agined that he discovered such an origin by making this 

 triple supposition : a comet fell obliquely upon the sun ; 

 it pushed before it a torrent of fluid matter; this sub- 

 stance transported to a greater or less distance from the 

 sun according to its mass formed by concentration all the 

 known planets. 



The bold hypothesis of BufFon is liable to insurmount- 

 able difficulties. I proceed to indicate, in a few words, 

 the cosmogonic system which Laplace substituted for 

 that of the illustrious author of the Histoire Naturelle. 



According to Laplace, the sun was at a remote epoch 

 the central nucleus of an immense nebula, which pos- 

 sessed a very high temperature, and extended far be- 

 yond the region in which Uranus revolves in the present 

 day. No planet was then in existence. 



The solar nebula was endued with a general move- 

 ment of revolution directed from west to east. As it 

 cooled it could not fail to experience a gradual condensa- 

 tion, and, in consequence, to rotate with greater and 

 greater rapidity. If the nebulous matter extended 

 originally in the plane of the equator as far as the limit 

 at which the centrifugal force exactly counterbalanced 

 the attraction of the nucleus, the molecules situate at this 

 limit ought, during the process of condensation, to sepa- 

 rate from the rest of the atmospheric matter and form 

 an equatorial zone, a ring revolving separately and with 

 its primitive velocity. We may conceive that analogous 

 separations were effected in the higher strata of the 

 nebula at different epochs, that is to say, at different 

 distances from the nucleus, and that they give rise to a 

 succession of distinct rings, included almost in the same 

 plane and endued with different velocities. 



This being once admitted, it is easy to see that the 



