matter of assumption, but is just what must once have existed,
provided there has been no breach of continuity in nature's
operations. Now proceeding to reason back from the past to the
present, it has been shown that the abandonment of successive
equatorial belts by the contracting solar mass must have ensued
in accordance with known mechanical laws; and in similar wise,
under ordinary circumstances. each belt must have parted into
fragments, and the fragments chasing each other around the same
orbit, must have at last coalesced into a spheroidal planet. Not
only this, but it has also been shown that as the result of such
a process the relative sizes of the planets would be likely to
take the order which they now follow; that the ring immediately
succeeding that of Jupiter would be likely to abort and produce a
great number of tiny planets instead of one good-sized one; that
the outer planets would be likely to have many moons, and that
Saturn, besides having the greatest number of moons, would be
likely to retain some of his inner rings unbroken; that the earth
would be likely to have a long day and Jupiter a short one; that
the extreme outer planets would be not unlikely to rotate in a
retrograde direction; and so on, through a long list of
interesting and striking details. Not only, therefore, are we
driven to the inference that our solar system was once a vaporous
nebula, but we find that the mere contraction of such a nebula,
under the influence of the enormous mutual gravitation of its
particles, carries with it the explanation of both the more
general and the more particular features of the present system.
So that we may fairly regard this stupendous process as veritable
matter of history, while we proceed to study it under some
further aspects and to consider what consequences are likely to
follow.