of such a restoration completely transcends our science. How can
the little vibration which 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,