what seems to be a region of eternal cold, below anything that we
can produce on the earth's surface, yet radiating light, and with
it heat, like an incandescent body--can be made up of the same
kind of substance that we have around us on the earth's surface.
Who knows but that the radiant property that Becquerel has found
in certain forms of matter may be a residuum of some original form
of energy which is inherent in great cosmical masses, and has fed
our sun during all the ages required by the geologist for the
structure of the earth's crusts? It may be that in this phenomenon
we have the key to the great riddle of the universe, with which
profounder secrets of matter than any we have penetrated will be
opened to the eyes of our successors.





IV

THE EXTENT OF THE UNIVERSE


We cannot expect that the wisest men of our remotest posterity,
who can base their conclusions upon thousands of years of accurate
observation, will reach a decision on this subject without some
measure of reserve. Such being the case, it might appear the
dictate of wisdom to leave its consideration to some future age,
when it may be taken up with better means of information than we
now possess. But the question is one which will refuse to be
postponed so long as the propensity to think of the possibilities