d to be a
very unsatisfactory condition. But a condition, we think, very
superior to the astronomical speculation of Laplace, which Mr Mill,
after scrutinizing the preceding hypothesis with the utmost
strictness, is disposed to treat with singular indulgence.

"The speculation is," we may as well quote throughout Mr
Mill's words, "that the atmosphere of the sun originally
extended to the present limits of the solar system: from
which, by the process of cooling, it has contracted to
its present dimensions; and since, by the general
principles of mechanics, the rotation of the sun and its
accompanying atmosphere must increase as rapidly as its
volume diminishes, the increased centrifugal force
generated by the more rapid rotation, overbalancing the
action of gravitation, would cause the sun to abandon
successive rings of vaporous matter, which are supposed
to have condensed by cooling, and to have become our
planets.

"There is in this theory," Mr Mill proceeds, "no unknown
substance introduced upon supposition, nor any unknown
property or law ascribed to a known substance. The known
laws of matter authorize us to suppose, that a body
which is constantly giving out so large an amount of
heat as the sun is, must be progressively cooling, and
that by the process of cooling it must contract; if,
therefore, we endeavour, from the present state of that
luminary, to infer its state in a time long past, we
must necessarily suppose that its atmosphere extended
much further than at present, and we are entitled to
suppose that it extended as far as we can trace those
effects which it would naturally leave behind it on
retiring; and such the planets are. These suppositions
being made, it follows from known laws that successive
zones of the solar atmosphere would be abandoned; that
these would continue to revolve round the sun with the
same velocity as when they formed part of his substance,
and that they would cool down, long before the sun
himself, to any given temperature, and consequently to
that at which the greater part of the vaporous matter of
which they consisted would become liquid or solid. The
known law of gravitation would then cause them to
agglomerate in masses, which would assume the shape our
planets actually exhibit; would acquire, each round its
own axis