, the odds are four thousand
millions to one, that this coincidence in the direction of so many
movements is not the effect of accident.

It was Buffon, I think, who first attempted to explain this singular
feature of our solar system. Having wished, in the explanation of
phenomena, to avoid all recourse to causes which were not warranted by
nature, the celebrated academician investigated a physical origin of the
system in what was common to the movements of so many bodies differing
in magnitude, in form, and in distance from the principal centre of
attraction. He imagined 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 substance 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 insurmountable 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 possessed a very high temperature, and
extended far beyond the region in which Uranus revolves in the present
day. No planet was then in existence.

The solar nebula was endued with a general movement of revolution
directed from west to east. As it cooled it could not fail to experience
a gradual condensation, 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
separate 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 indefinite
stability of the rings would have required a regularity of structure
throughout their whole contour, which is very imp