534 HISTORY OF THERM OTICS. 



heat. We must therefore dismiss them, at least for 

 the present. 



3. Temperature of the Interior of the Earth. 

 The question of the temperature of the interior of 

 the earth has excited great interest, in consequence 

 of its bearing on other branches of knowledge. The 

 various facts which have been supposed to indicate 

 the fluidity of the central parts of the terrestrial 

 globe, belong, in general, to geological science ; but 

 so far as they require the light of thermotical cal- 

 culations in order to be rightly reasoned upon, they 

 properly come under our notice here. 



The principal problem of this kind which has 

 been treated of is this : If in the globe of the earth 

 there be a certain original heat, resulting from its 

 earlier condition, and independent of the action of 

 the sun, to what results will this give rise? and 

 how far do the observed temperatures of points 

 below the surface lead us to such a supposition ? It 

 has, for instance, been asserted, that in many parts 

 of the world the temperature, as observed in mines 

 and other excavations, increases in descending, at 

 the rate of one degree (centesimal) in about forty 

 yards. What inference does this justify ? 



The answer to this question was given by Fou- 

 rier and by Laplace. The former mathematician 

 had already considered the problem of the cooling 

 of a large sphere, in his Memoirs of 1807, 1809, 

 and 1811. These, however, lay unpublished in the 

 archives of the Institute for many years. But in 



