the
student who does not approach it in a somewhat professional way. We
shall therefore now turn to a description of the portion of the starry
world which is found in the limits of our solar system. There the
influences of the several spheres upon our planet are matters of vital
importance; they in a way affect, if they do not control, all the
operations which go on upon the surface of the earth.

THE SOLAR SYSTEM.

We have seen that the matter in the visible universe everywhere tends
to gather into vast associations which appear to us as stars, and that
these orbs are engaged in ceaseless motion in journeys through space.
In only one of these aggregations--that which makes our own solar
system--are the bodies sufficiently near to our eyes for us, even with
the resources of our telescopes and other instruments, to divine
something of the details which they exhibit. In studying what we may
concerning the family of the sun, the planets, and their satellites,
we may reasonably be assured that we are tracing a history which with
many differences is in general repeated in the development of each
star in the firmament. Therefore the inquiry is one of vast range and
import.

Following, as we may reasonably do, the nebular hypothesis--a view
which, though not wholly proved, is eminently probable--we may regard
our solar system as having begun when the matter of which it is
composed, then in a finely divided, cloudy state, was separated from
the similar material which went to make the neighbouring fixed stars.
The period when our solar system began its individual life was remote
beyond the possibility of conception. Naturalists are pretty well
agreed that living beings began to exist upon the earth at least a
hundred million years ago; but the beginnings of our solar system must
be placed at a date very many times as remote from the present day.[1]

[Footnote 1: Some astronomers, particularly the distinguished Professor
Newcomb, hold that the sun can not have been supplying heat as at
present for more than about ten million years, and that all geological
time must be thus limited. The geologist believes that this reckoning is
far too short.]

According to the nebular theory, the original vapour of the solar
system began to fall in toward its centre and to whirl about that
point at a time long before the mass had shrunk to the present limits
of the solar system as defined by the path of the oute