ments of rotation of these various bodies and of the sun are in the
same direction as their orbitual motions, and in planes little
different.

[Sidenote: The nebular hypothesis.] The nebular hypothesis requires us
to admit that all the ponderable material now constituting the various
bodies of the solar system once extended in a rarefied or nebulous and
rotating condition, beyond the confines of the most distant planet. That
postulate granted; the structure and present condition of the system may
be mathematically deduced.

For, as the vast rotating spheroid lost its heat by radiation, it
contracted, and its velocity of rotation was necessarily increased; and
thus were left behind from its equatorial zone, by reason of the
centrifugal force, rotating rings, the same result occurring
periodically again and again. These rings must lie all in one plane.
They might break, collapsing into one rotating spheroid, a planet; or
into many, asteroids; or maintain the ring-like form. From the larger of
these secondary rotating spheroids other rings might be thrown off, as
from the parent mass; these, in their turn breaking and becoming
spheroids, constitute satellites, whose movements correspond to those of
their primaries.

We might, indeed, advance a step farther, and show how, by the radiation
of heat from a motionless nebula, a movement of rotation in a
determinate direction could be engendered, and that upon these
principles, the existence of a nebulous matter admitted, and the present
laws and forces of nature regarded as having been unchanged, the manner
of origin of the solar system might be deduced, and all those singular
facts previously alluded to explained; and not only so, but there is
spontaneously suggested the cause of many minor peculiarities not yet
mentioned.

[Sidenote: Facts accounted for by it.] For it follows from the nebular
hypothesis that the large planets should rotate rapidly, and the small
ones more slowly; that the outer planets and satellites should be larger
than the inner ones. Of the satellites of Saturn, the largest is the
outermost; of those of Jupiter, the largest is the outermost save one.
Of the planets themselves, Jupiter is the largest, and outermost save
three. These cannot be coincidences, but must be due to law. The number
of satellites of each planet, with the doubtful exception of Venus,
might be foreseen, the presence of satellites and their number being
determined by the centrifu