.

Now, admitting the ring to have possessed, by some seemingly accidental
arrangement of its heterogeneous materials, a constitution nearly
uniform, then this ring, _as_ such, would never have ceased revolving
about its primary; but, as might have been anticipated, there appears to
have been enough irregularity in the disposition of the materials, to
make them cluster about centres of superior solidity; and thus the
annular form was destroyed.[5] No doubt, the band was soon broken up
into several portions, and one of these portions, predominating in mass,
absorbed the others into itself; the whole settling, spherically, into a
planet. That this latter, _as_ a planet, continued the revolutionary
movement which characterized it while a ring, is sufficiently clear; and
that it took upon itself also, an additional movement in its new
condition of sphere, is readily explained. The ring being understood as
yet unbroken, we see that its exterior, while the whole revolves about
the parent body, moves more rapidly than its interior. When the rupture
occurred, then, some portion in each fragment must have been moving
with greater velocity than the others. The superior movement prevailing,
must have whirled each fragment round--that is to say, have caused it to
rotate; and the direction of the rotation must, of course, have been the
direction of the revolution whence it arose. _All_ the fragments having
become subject to the rotation described, must, in coalescing, have
imparted it to the one planet constituted by their coalescence.--This
planet was Neptune. Its material continuing to undergo condensation, and
the centrifugal force generated in its rotation getting, at length, the
better of the centripetal, as before in the case of the parent orb, a
ring was whirled also from the equatorial surface of this planet: this
ring, having been ununiform in its constitution, was broken up, and its
several fragments, being absorbed by the most massive, were collectively
spherified into a moon. Subsequently, the operation was repeated, and a
second moon was the result. We thus account for the planet Neptune, with
the two satellites which accompany him.

[5] Laplace assumed his nebulosity heterogeneous, merely that
he might be thus enabled to account for the breaking up of the
rings; for had the nebulosity been homogeneous, they would not
have broken. I reach the same result--heterogeneity of the
secondary masses immedi