Fourier s Theory of Heat. 



599 



globe, and we can even assign, with great precision, the part which 

 each of them respectively performs. 



A single individual, M. Fourier, has established, in our days the 

 mathematical theory of heat. Making use of a method of calcula- 

 tion of his own invention, adapted to the new order of phenomena 

 which he was desirous to study, he arrived at a knowledge of the 

 laws by which they are regulated. No geometrican ever before 

 applied mathematical analysis so profoundly to the investigation 

 of the great phenomena of nature. No one, since Newton, has 

 opened such new paths to the study of natural philosophy. 



To give an idea of the results obtained by M. Fourier, as to the 

 heat of the globe, will be to state the amount of all that is known 

 upon the subject.* 



" Our solar system is placed in a region of the universe, all the 

 points of which have a common, and constant temperature, deter- 

 mined by the rays of light and heat which all the surrounding stars 

 emit. This cold planetary temperature is little lower than that 

 of the polar regions of the terrestrial globe. The earth would only 

 have this same temperature of the heavens, if two causes did not 

 concur to heat it ; one is the continual action of the solar rays, 

 which penetrate all its mass, and maintain the difference of climates 

 on its surface : the other, is the interior heat which it possessed 

 when the planetary bodies were formed, only a part of which has 

 been dissipated at its surface. 



" Let us proceed successively with these two last causes of the 

 terrestrial heat, considering each of them, at first, separately, as if it 

 acted alone. And first, what would have happened, if the earth, 

 primitively possessing only the temperature of the space in which 



* Tbe account which we are about to give, is extracted from a Memoir, inserted 

 by M. Fourier, in the " Annales de Chimie et de Physique," (October, 1824.) 

 If, upon some points, I have conceived it necessary to give explanations which 

 appeared to me indispensable for the readers for whom my book is intended, in 

 others, it seemed to me, that I could not do better than transcribe the actual ex- 

 pressions of M. Fourier himself. These passages are indicated by inverted 

 commas 



*** In a posterior note the author observes, that he should have here stated, 

 that the thermometer used by M. Fourier, was that of Reamur, the zero, or freezing 

 point of which, is 32°. of Farenheit, and its boiling point is marked 80, being 212°. 

 of Farenheit. — T. 



