er to explain the prime movements of the planetary system,"
he says, "there are the five following phenomena: The movement of the
planets in the same direction and very nearly in the same plane; the
movement of the satellites in the same direction as that of the planets;
the rotation of these different bodies and the sun in the same
direction as their revolution, and in nearly the same plane; the slight
eccentricity of the orbits of the planets and of the satellites; and,
finally, the great eccentricity of the orbits of the comets, as if their
inclinations had been left to chance.

"Buffon is the only man I know who, since the discovery of the true
system of the world, has endeavored to show the origin of the planets
and their satellites. He supposes that a comet, in falling into the sun,
drove from it a mass of matter which was reassembled at a distance in
the form of various globes more or less large, and more or less removed
from the sun, and that these globes, becoming opaque and solid, are now
the planets and their satellites.

"This hypothesis satisfies the first of the five preceding phenomena;
for it is clear that all the bodies thus formed would move very nearly
in the plane which passed through the centre of the sun, and in the
direction of the torrent of matter which was produced; but the four
other phenomena appear to be inexplicable to me by this means. Indeed,
the absolute movement of the molecules of a planet ought then to be in
the direction of the movement of its centre of gravity; but it does not
at all follow that the motion of the rotation of the planets should be
in the same direction. Thus the earth should rotate from east to west,
but nevertheless the absolute movement of its molecules should be
from east to west; and this ought also to apply to the movement of the
revolution of the satellites, in which the direction, according to the
hypothesis which he offers, is not necessarily the same as that of the
progressive movement of the planets.

"A phenomenon not only very difficult to explain under this hypothesis,
but one which is even contrary to it, is the slight eccentricity of the
planetary orbits. We know, by the theory of central forces, that if
a body moves in a closed orbit around the sun and touches it, it also
always comes back to that point at every revolution; whence it follows
that if the planets were originally detached from the sun, they would
touch it at each return towards it, and