414 ON THE DIFFUSION OF HEAT 



rier, then an accumulation of it at the surface, and at last a 

 uniform distribution of it through the whole mass, would ine- 

 vitably be the consequence. But if heat may be lost and dis- 

 sipated in the boundless fields of vacuity, or of ether, which 

 surround the earth, no such equilibrium can be established. 

 The temperature of the earth will then continue to augment, 

 only till the heat which issues from it every moment into the 

 surrounding medium, become equal to the increase which it 

 receives every moment from the supposed central reservoir. 

 When this happens, the temperature at the superficies can un- 

 dergo no farther change, and a similar effect must take place 

 with respect to every one of the spherical and concentric strata 

 into which we may conceive the solid mass of the globe to be 

 divided. Each of these must in time come to a temperature 

 at which it will give out as much heat to the contiguous stra- 

 tum on the outside, as it receives from the contiguous stratum 

 on the inside, and when this happens, its temperature will re- 

 main invariable *." 



The principle on which this reasoning rests will not be dis- 

 puted. Admitting it therefore, my objects in attempting to 

 support the original argument will be to shew,^^, That such 

 a discharge of heat from the surface of the earth as is here sup- 

 posed does not take place ; and, secondly, That if it did, this 

 would be as subversive of the system, as if the heat were 

 retained. 



There are two modes in which caloric may be supposed to 

 be conveyed from the surface of the earth ; one is by radiation, 

 the other by slow communication by the medium of the elas- 

 tic fluid which surrounds it. Each of these may be briefly 

 considered. 



The 



* Transactions of the Society, vol. vi. p. 356, 



