the material were great, subordinate rings would be formed, which when
they broke and concentrated would constitute secondary planets or
satellites, such as our moon. For some reason as yet unknown the outer
planets--in fact, all those in the solar system except the two inner,
Venus and Mercury and the asteroids--formed such attendants. All these
satellite-forming rings have broken and concentrated except the inner
of Saturn, which remains as an intellectual treasure of the solar
system to show the history of its development.

To the student who is not seeking the fulness of knowledge which
astronomy has to offer, but desires only to acquaint himself with the
more critical and important of the heavenly phenomena which help to
explain the earth, these features of planetary movement should prove
especially interesting for the reason that they shape the history of
the spheres. As we shall hereafter see, the machinery of the earth's
surface, all the life which it bears, its winds and rains--everything,
indeed, save the actions which go on in the depths of the sphere--is
determined by the heat and light which come from the sun. The
conditions under which this vivifying tide is received have their
origin in the planetary motion. If our earth's path around the centre
of the system was a perfect circle, and if its polar axis lay at right
angles to the plane of its journey, the share of light and heat which
would fall upon any one point on the sphere would be perfectly
uniform. There would be no variations in the length of day or night;
no changes in the seasons; the winds everywhere would blow with
exceeding steadiness--in fact, the present atmospheric confusion would
be reduced to something like order. From age to age, except so far as
the sun itself might vary in the amount of energy which it radiated,
or lands rose up into the air or sunk down toward the sea level, the
climate of each region would be perfectly stable. In the existing