ch
strikes our eye from some distant star, and which has been perhaps
thousands of years in reaching us, find its way back to its origin? The
light emitted by the sun 10,000 years ago is to-day pursuing its way in
a sphere whose surface is 10,000 light-years distant on all sides.
Science has nothing even to suggest the possibility of its restoration,
and the most delicate observations fail to show any return from the
unfathomable abyss.

Up to the time when radium was discovered, the most careful
investigations of all conceivable sources of supply had shown only one
which could possibly be of long duration. This is the contraction which
is produced in the great incandescent bodies of the universe by the
loss of the heat which they radiate. As remarked in the preceding
essay, the energy generated by the sun's contraction could not have
kept up its present supply of heat for much more than twenty or thirty
millions of years, while the study of earth and ocean shows evidence of
the action of a series of causes which must have been going on for
hundreds of millions of years.

The antagonism between the two conclusions is even more marked than
would appear from this statement. The period of the sun's heat set by
the astronomical physicist is that during which our luminary could
possibly have existed in its present form. The period set by the
geologist is not merely that of the sun's existence, but that during
which the causes effecting geological changes have not undergone any
complete revolution. If, at any time, the sun radiated much less than
its present amount of heat, no water could have existed on the earth's
surface except in the form of ice; there would have been scarcely any
evaporation, and the geological changes due to erosion could not have
taken place. Moreover, the commencement of the geological operations of
which we speak is by no means the commencement of the earth's
existence. The theories of both parties agree that, for untold aeons
before the geological changes now visible commenced, our planet was a
molten mass, perhaps even an incandescent globe like the sun. During
all those aeons the sun must have been in existence as a vast nebulous
mass, first reaching as far as the earth's orbit, and slowly
contracting its dimensions. And these aeons are to be included in any
estimate of the age of the sun.

The doctrine of cosmic evolution--the theory which in former times was
generally known as the nebular hy