PRIMITIVE HEAT OF THE EARTH. 427 



snr 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 



