dependent on the heat which the sun sends it. If we were deprived
of this heat we should in a few days be enveloped in a frost which
would destroy nearly all vegetation, and in a few months neither
man nor animal would be alive, unless crouching over fires soon to
expire for want of fuel. We also know that, at a time which is
geologically recent, the whole of New England was covered with a
sheet of ice, hundreds or even thousands of feet thick, above
which no mountain but Washington raised its head. It is quite
possible that a small diminution in the supply of heat sent us by
the sun would gradually reproduce the great glacier, and once more
make the Eastern States like the pole. But the fact is that
observations of temperature in various countries for the last two
or three hundred years do not show any change in climate which can
be attributed to a variation in the amount of heat received from
the sun.

The acceptance of this theory of the heat of those heavenly bodies
which shine by their own light--sun, stars, and nebulae--still
leaves open a problem that looks insoluble with our present
knowledge. What becomes of the great flood of heat and light which
the sun and stars radiate into empty space with a velocity of one
hundred and eighty thousand miles a second? Only a very small
fraction of it can be received by the planets or by other stars,
because these are mere points compared with their distance from
us. Taking the teaching of our science just as it stands, we
should say that all this heat continues to move on through
infinite space forever. In a few thousand years it reaches the
probable confines of our great universe. But we know of no reason
why it should stop here. During the hundreds of millions of years
since all our stars began to shine, has the first ray of light and