PRIMITIVE HEAT OF THE EARTH. 427 
sur la Nature of Buffon, in the letters from Bailly to 
Voltaire upon the Origin of the Sciences and upon the 
Atlantide. But the ingenious romance to which it has 
served as a base, has vanished like a shadow before the 
torch of mathematical science. 
Fourier having discovered that the excess of the 
aggregate temperature of the earth’s surface above that 
which would result from the sole action of the solar rays, 
has a determinate relation to the increase of tempera- 
ture at different depths, succeeded in deducing from the 
experimental value of this increase a numerical deter- 
mination of the excess in question. This excess is the 
thermometric effect which the solar heat produces at the 
surface ; now, instead of the large numbers adopted by 
Mairan, Bailly, and Buffon, what has our colleague found ? 
A thirtieth of a degree, not more. 
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 enor- 
mous. ‘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 dissi- 
pated, 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 
