atmosphere, and the rotation of both round an axis, La Place
sought to give a scientific form to the speculations of Sir William
Herschell on the condensation of Nebulae, by proving simply the
_dynamical possibility_ of the formation of a planetary system by such
means, according to the known laws of matter and motion; but he did not
affirm the scientific certainty of his conjecture, and far less the
actual production of the solar system in this way. He has been followed
by M. Comte, who has attempted to furnish, if not a complete
demonstration, at least a plausible mathematical verification, of the
hypothesis.[29] Utterly excluding all supernatural agency in the work of
creation, he equally excludes from the problem which he attempts to
solve, the origin of the sun and its atmosphere; and confining himself
to the task of accounting, in the way not of demonstrative certainty,
but merely of plausible hypothesis, for the formation of the planets and
satellites of our solar system, he conceives the theory of La Place to
be susceptible of such a numerical verification as is sufficient to give
it a high degree of verisimilitude. Assuming that the periodic time of
each planet must be equal to that of the portion of the solar atmosphere
of which it was formed at the era when it was thrown off, and combining
the theorems of Huygens on the measure of centrifugal forces with
Newton's law of gravitation, he establishes a simple equation between
the time of the rotation of each zone or section of the solar
atmosphere, and the distance of the corresponding planets. On applying
this equation to the various bodies of our system, he found that the
periodic time of the moon agrees, at least within the tenth of a day,
with the duration of the earth's revolution, when her atmosphere is
supposed to have extended to the moon; and that the periodic times of
the planets maintain a similar correspondence with what must have been
the duration of the solar revolution when they were severally thrown off
from its atmosphere. It is the less necessary, however, to enter on a
detailed exposition of his argument, because he admits that it can
afford at the utmost only a probable proof of an hypothesis; and
further, because it is expressly limited to the production of the
planets and their satellites, while not only is the existence of the
solar atmosphere presupposed, but also its existence in _a certain
state_, and with _several determinate conditions_