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 
