by his waistband and lift himself over a stone wale So that
the primitive rotating spheroidal solar nebula is not a 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.

Our attention should first be directed to the enormous waste of energy
which has accompanied this contraction of the solar nebula. The first
result of such a contraction is the generation of a great quantity of
heat, and when the heat thus generated has been lost by radiation into
surrounding space it becomes possible for the contraction to continue.
Thus, as concentration goes on, heat is incessantly generated and
incessantly dissipated. How long this process is to endure depends
chiefly on the size of