The surface of the earth, which originally was perhaps incandescent, has cooled then in the course of ages, so as hardly to preserve any sensible trace of its primitive heat.  However, at great depths, the original heat is still enormous.  Time will alter sensibly the internal temperature; but at the surface (and the phenomena of the surface can alone modify or compromise the existence of living beings), all the changes are almost accomplished.  The frightful freezing of the earth, the epoch of which Buffon fixed at the instant when the central heat would be totally dissipated, is then a pure dream.  At the surface, the earth is no longer impregnated except by the solar heat.  So long as the sun shall continue to preserve the same brightness, mankind will find, from pole to pole, under each latitude, the climates which have permitted them to live and to establish their residence.  These, Gentlemen, are great, magnificent results.  While recording them in the annals of science, historians will not neglect to draw attention to this singular peculiarity:  that the geometer to whom we owe the first certain demonstration of the existence of a heat independent of a solar influence in the interior of the earth, has annihilated the immense part which this primitive heat was made to play in the explanation of the phenomena of terrestrial temperature.

Besides divesting the theory of climates of an error which occupied a prominent place in science, supported as it was by the imposing authority of Mairan, of Bailly, and of Buffon, Fourier is entitled to the merit of a still more striking achievement:  he has introduced into this theory a consideration which hitherto had been totally neglected; he has pointed out the influence exercised by the temperature of the celestial regions, amid which the hearth describes its immense orb around the sun.

When we perceive, even under the equator, certain mountains covered with eternal snow, upon observing the rapid diminution of temperature which the strata of the atmosphere undergo during ascents in balloons, meteorologists have supposed, that in the regions wherein the extreme rarity of the air will always exclude the presence of mankind, and that especially beyond the limits of the atmosphere, there ought to prevail a prodigious intensity of cold.  It was not merely by hundreds, it was by thousands of degrees, that they had arbitrarily measured it.  But, as usual, the imagination (cette folie de la maison) had exceeded all reasonable limits.  The hundreds, the tens of thousands of degrees, have dwindled down, after the rigorous researches of Fourier, to fifty or sixty degrees only.  Fifty or sixty degrees beneath zero, such is the temperature which the radiation of heat from the stars has established in the regions furrowed indefinitely by the planets of our system.