nd
it most convenient to begin, like our authors, with a brief statement of
what the principle of continuity teaches as to the proximate beginning
and end of the visible universe. I shall in the main set down only
results, having elsewhere [2] given a simple exposition of the arguments
upon which these results are founded.

[1] The Unseen Universe; or, Physical Speculations on a Future
State. [Attributed to Professors TAIT and BALFOUR STEWART.] New York:
Macmillan & Co. 1875. 8vo. pp. 212.

[2] Outlines of Cosmic Philosophy, based on the Doctrine of
Evolution. Boston: J. R. Osgood & Co. 1875. 2 vols. 8vo.

The first great cosmological speculation which has been raised 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