of the tropical regions, wherein exist elephants in the present day.

It is not, however, as an explanation of the existence of elephants in
Siberia, that the idea of the intrinsic heat of the globe has entered
for the first time into science. Some savans had adopted it before the
discovery of those fossil animals. Thus, Descartes was of opinion that
originally (I cite his own words,) _the earth did not differ from the
sun in any other respect than in being smaller_. Upon this hypothesis,
then, it ought to be considered as an extinct sun.

Leibnitz conferred upon this hypothesis the honour of appropriating it
to himself. He attempted to deduce from it the mode of formation of the
different solid envelopes of which the earth consists. Buffon, also,
imparted to it the weight of his eloquent authority. According to that
great naturalist, the planets of our system are merely portions of the
sun, which the shock of a comet had detached from it some tens of
thousands of years ago.

In support of this igneous origin of the earth, Mairan and Buffon cited
already the high temperature of deep mines, and, among others, those of
the mines of Giromagny. It appears evident that if the earth was
formerly incandescent, we should not fail to meet in the interior
strata, that is to say, in those which ought to have cooled last, traces
of their primitive temperature. The observer who, upon penetrating into
the interior of the earth, did not find an increasing heat, might then
consider himself amply authorized to reject the hypothetical conceptions
of Descartes, of Mairan, of Leibnitz, and of Buffon. But has the
converse proposition the same certainty? Would not the torrents of heat,
which the sun has continued incessantly to launch for so many ages, have
diffused themselves into the mass of the earth, so as to produce there a
temperature increasing with the depth? This a question of high
importance. Certain easily satisfied minds conscientiously supposed that
they had solved it, when they stated that the idea of a constant
temperature was by far the _most natural_; but woe to the sciences if
they thus included vague considerations which escape all criticism,
among the motives for admitting and rejecting facts and theories!
Fontenelle, Gentlemen, would have traced their horoscope in these words,
so well adapted for humbling our pride, and the truth of which the
history of discoveries reveals in a thousand places: "When a thing may
be in