il by this motion they came upon the equator.

"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. In nearly every case the ring of vapor was broken into
several masses, each moving at similar velocities, and continuing to
rotate at the same distance around the sun. These masses would take
a spheroid form with a rotatory movement in the direction of the
revolution, because their inner molecules had less velocity than the
outer. Thus were formed so many planets in a condition of vapor. But
if one of them were powerful enough to reunite successively by its
attraction all the others around its centre of gravity, the ring of
vapor would be thus transformed into a single spheroidical mass of
vapor revolving around the sun with a rotation in the direction of its
revolution. The latter case has been that which is the most common, but
nevertheless the solar system affords us an instance of the first case
in the four small planets which move between Jupiter and Mars; at least,
if we do not suppose, as does M. Olbers, that they originally formed a
single p