. Shortly afterwards the subject was
taken up by the famous German philosopher, Kant, who dealt with the
question in a still more ambitious manner, and endeavoured to account in
detail for the origin of the solar system as well as of the sidereal
universe. Something of the trend of such theories may be gathered from
the remarkable lines in Tennyson's _Princess_:--

"This world was once a fluid haze of light,
Till toward the centre set the starry tides,
And eddied into suns, that wheeling cast
The planets."

The theory, as worked out by Kant, was, however, at the best merely a
_tour de force_ of philosophy. Laplace's conception was much less
ambitious, for it did not attempt to explain the origin of the entire
universe, but only of the solar system. Being thus reasonably limited in
its scope, it more easily obtained credence. The arguments of Laplace
were further founded upon a mathematical basis. The great place which
he occupied among the astronomers of that time caused his theory to
exert a preponderating influence on scientific thought during the
century which followed.

A modification of Laplace's theory is the Meteoritic Hypothesis of Sir
Norman Lockyer. According to the views of that astronomer, the material
of which the original nebula was composed is presumed to have been in
the meteoric, rather than in the gaseous, state. Sir Norman Lockyer
holds, indeed, that nebulae are, in reality, vast swarms of meteors, and
the light they emit results from continual collisions between the
constituent particles. The French astronomer, Faye, also proposed to
modify Laplace's theory by assuming that the nebula broke up into rings
all at once, and not in detail, as Laplace had wished to suppose.

The hypothesis of Laplace fits in remarkably well with the theory put
forward in later times by Helmholtz, that the heat of the sun is kept up
by the continual contraction of its mass. It could thus have only
contracted to its present size from one very much larger.

Plausible, however, as Laplace's great hypothesis appears on the
surface, closer examination shows several vital objections, a few of
those set forth by Professor Moulton being here enumerated--

Although Laplace held that the orbits of the planets were sufficiently
near to being in the one plane to support his views, yet later
investigators consider that their very deviations from this plane are a
strong argument against the hypothesis.

Again, it is thought tha