424 JOSEPH FOURIER. 



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 envel- 

 opes 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 de- 

 tached 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 Giro- 

 magny. It appears evident that if the earth was for- 

 merly 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 hypo- 

 thetical 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 con- 

 stant 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 admit- 

 ting and rejecting facts and theories ! Fontenelle, Gen- 

 tlemen, would have traced their horoscope in these words, 

 so well adapted for humbling our pride, and the truth of 



