"Let us consider now the zones of vapor successively
left behind. These zones ought, according to appearance,
by the condensation and mutual attraction of
their molecules, to form various concentric rings of
vapor revolving around the sun. The mutual gravitational
friction of each ring would accelerate some and
retard others, until they had all acquired the same
angular velocity. Thus the actual velocity of the
molecules most removed from the sun would be the
greatest. The following cause would also operate to
bring about this difference of speed. The molecules
farthest from the sun, and which by the effects of
cooling and condensation approached one another to
form the outer part of the ring, would have always
described areas proportional to the time since the
central force by which they were controlled has been
constantly directed towards this body. But this constancy
of areas necessitates an increase of velocity
proportional to the distance. It is thus seen
that the same cause would diminish the velocity
of the molecules which form the inner part of the
ring.

"If all the molecules of the ring of vapor continued
to condense without disuniting, they would at length
form a ring either solid or fluid. But this formation
would necessitate such a regularity in every part of
the ring, and in its cooling, that this phenomenon is
extremely rare; and the solar system affords us, indeed,
but one example--namely, in the ring of Saturn.