The Unseen World and Other Essays | Page 6

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 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 the contracting mass, as small bodies radiate heat
much faster than large ones. The moon seems to be already thoroughly
refrigerated, while Jupiter and Saturn are very much hotter than the
earth, as is shown by the tremendous atmospheric phenomena which
occur on their surfaces. The sun, again, generates heat so rapidly,
owing to his great energy of contraction, and loses it so slowly, owing
to his great size, that his surface is always kept in a state of
incandescence. His surface-temperature is estimated at some three
million degrees of Fahrenheit, and a diminution of his diameter far too
small to be detected by the finest existing instruments would suffice to
maintain the present supply of heat for more than fifty centuries. These
facts point to a very long future during which the sun will continue to
warm the earth and its companion planets, but at the same time they
carry on their face the story of inevitable ultimate doom. If things
continue to go on as they have all along gone on, the sun must by and
by grow black and cold, and all life whatever throughout the solar
system must come to an end. Long before this consummation, however,
life will probably have become extinct through the refrigeration of each
of the planets into a state like the present state of the moon, in which