quite above the plane of guesswork by making no other assumption
than that of the uniformity of nature, is the well-known Nebular
Hypothesis. Every astronomer knows that the earth, like all other
cosmical bodies which are flattened at the poles, was formerly a
mass of fluid, and consequently filled a much larger space than
at present. It is further agreed, on all hands, that the sun is a
contracting body, since there is no other possible way of
accounting for the enormous quantity of heat which he generates.
The so-called primeval nebula follows as a necessary inference
from these facts. There was once a time when the earth was
distended on all sides away out to the moon and beyond it, so
that the matter now contained in the moon was then a part of our
equatorial zone. And at a still remoter date in the past, the
mass of the sun was diffused in every direction beyond the orbit
of Neptune, and no planet had an individual existence, for all
were indistinguishable parts of the solar mass. When the great
mass of the sun, increased by the relatively small mass of all
the planets put together, was spread out in this way, it was a
rare vapour or gas. At the period where the question is taken up
in Laplace's treatment of the nebular theory, the shape of this
mass is regarded as spheroidal; but at an earlier period its
shape may well have been as irregular as that of any of the
nebulae which we now see in distant parts of the heavens, for,
whatever its primitive shape, the equalization of its rotation
would in time make it spheroidal. That the QUANTITY of rotation
was the same then as now is unquestionable; for no system of
particles, great or small, can acquire or lose rotation by any
action going on within itself, any more than a man could pick
himself up by his waistband and lift himself over a stone wale So
that the primitive rotating spheroidal solar nebula is not a