, a rotatory movement; and would in that state
revolve, as the planets actually do, about the sun, in
the same direction with the sun's rotation, but with
less velocity, and each of them in the same periodic
time which the sun's rotation occupied when his
atmosphere extended to that point; and this also M.
Comte has, by the necessary calculations, ascertained to
be true, within certain small limits of error. There is
thus in Laplace's theory nothing hypothetical; it is an
example of legitimate reasoning from a present effect to
its past cause, according to the known laws of that
case; it assumes nothing more than that objects which
really exist, obey the laws which are known to be obeyed
by all terrestrial objects resembling them."--Vol. II.
p. 27.

Now, it seems to us that there is quite as much of hypothesis in this
speculation of Laplace as in the undulatory theory of light. This
atmosphere of the sun extending to the utmost limits of our planetary
system! What proof have we that it ever existed? what possible
grounds have we for believing, what motive even for imagining such a
thing, but the very same description of proof given and rejected for
the existence of a luminiferous ether--namely, that it enables us to
explain certain events supposed to result from it? Nor is the thing
here imagined any the less a novelty, because it bears the old name of
an atmosphere. An atmosphere containing in itself all the various
materials which compose our earth, and whatever else may enter into
the composition of the other planets, is as violent a supposition as
an ether, not perceptible to the senses except by its influence on the
nerves of sight. And this cooling down of the sun! What fact in our
experience enables us to advance such a supposition? We might as well
say that the sun was getting hotter every year, or harder or softer,
or larger or smaller. Surely Mr Mill could not have been serious when
he says, that "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"--knowing, as we do, as
little how the sun occasions heat as how it produces light. Neither
can it be contended that because no absolutely new substance, or new
property of matter, is introduced, but a fantastic conception is
framed out of known substances and known properties, that therefore
th