n the lavas of Vesuvius, nor influence
the thunders of Krakatoa by one appreciable note. So far as a human
life or the life of the human race is concerned, the decline of a
tenth of a degree per century in the earth's internal heat is
absolutely void of significance. I cannot, however, impress upon you
too strongly, that the mere few thousands of years with which human
history is cognizant are an inappreciable moment in comparison with
those unmeasured millions of years which geology opens out to us, or
with those far more majestic periods which the astronomer demands for
the events he has to describe.

An annual loss of even one-thousandth of a degree will be capable of
stupendous achievements when supposed to operate during epochs of
geological magnitude. In fact, its effects would be so vast, that it
seems hardly credible that the present loss of heat from the earth
should be so great as to amount to an abatement of one-thousandth of a
degree per annum, for that would mean, that in a thousand years the
earth's temperature would decline by one degree, and in a million
years the decline would amount to a thousand degrees. At all events,
the illustration may suffice to show, that the fact that we are not
able to prove by our instruments that the earth is cooling is no
argument whatever against the inevitable law, that the earth, like
every other heated body, must be tending towards a lower temperature.

Without pretending to any numerical accuracy, we can at all events
give a qualitative if not a quantitative analysis of the past history of
our earth, in so far as its changes of temperature are concerned. A
million years ago our earth doubtless contained appreciably more heat
than it does at present. I speak not now, of course, of mere solar
heat--of the heat which gives us the vicissitudes of seasons; I am
only referring to the original hoard of internal heat which is
gradually waning. As therefore our retrospect extends through
millions and millions of past ages, we see our earth ever growing
warmer and warmer the further and further we look back. There was a
time when those heated strata which we have now to go deep down in
mines to find were considerably nearer the surface. At present, were
it not for the sun, the heat of the earth where we stand would hardly
be appreciably above the temperature of infinite space--perhaps some
200 or 300 degrees below zero. But there must have been a time when
there was sufficient