CONDUCTION AND RADIATION. 535 



1820, when the accumulation of observations which 

 indicated an increase of the temperature of the 

 earth as we descend, had drawn observation to the 

 subject, Fourier gave, in the Bulletin of the Philo- 

 mathic Society 15 , a summary of his results, as far as 

 they bore on this point. His conclusion was, that 

 such an increase of temperature in proceeding 

 towards the center of the earth, can arise from 

 nothing but the remains of a primitive heat ; that 

 the heat which the sun's action would communicate, 

 would, in its final and permanent state, be uniform 

 in the same vertical line, as soon as we get beyond 

 the influence of the superficial oscillations of which 

 we have spoken ; and that, before the distribution 

 of temperature reaches this limit, it will decrease, 

 not increase, in descending. It appeared also, by 

 the calculation, that this remaining existence of the 

 primitive heat in the interior parts of the earth's 

 mass, was quite consistent with the absence of all 

 perceptible traces of it at the surface ; and that the 

 same state of things which produces an increase of 

 one degree of heat in descending forty yards, does 

 not make the surface a quarter of a degree hotter 

 than it would otherwise be. Fourier was led also 

 to some conclusions, though necessarily very vague 

 ones, respecting the time which the earth must 

 have taken to cool from a supposed original state of 

 incandescence to its present condition, which time 

 it appeared must have been very great; and respect- 

 15 Rullvi. ikx Sr. 1820, p. 58. 



