at the Stirface of the Earth, 179 



the same temperature to proceed successively over all the regions 

 ©f the globe*. Not only are these conclusions unfounded, hut 

 the changes which have occurred are probably the very reverse. 

 No heat can escape from this planet, but in consequence of a 

 high temperature being kept up at its surface by the communi- 

 cation of heat from an external soiuxe. Until this be attained, 

 it must retain the heat it receives from the sun ; and this must 

 accumulate principally towards the poles. 



That the temperature at the surface has risen above the ori- 

 ginal temperature of the earth, may be inferred not only from 

 the consideration, that solar heat has been communicated to it, 

 which could not be discliarged until a certain elevated tempera- 

 ture were attained, but also from this, that there is no natural 

 operation actually generating cold ; there is only the production 

 ©f heat ; and cold prevails where this is less powerful, or is coun- 

 teracted To account, therefore, for the low temperature at the 

 colder regions of the earth, onlv tv.o suppositions can be ad- 

 vanced. Either the original temperature must have been as low 

 as this, or lower, and have been raised higher, where it is actually 

 superior, by the reception of the sun's rays : or It must be as- 

 sunied, with Buffon and Bailly, that heat can escape from this 

 planet to an indefinite extent, and that it is in a state of pro- 

 gressive refrigeration, the effects of which are prevented from 

 being apparent at the equatorial regions by the direct communi- 

 cation of solar heat, but towards the jjolar circles are evident, as 

 not being coimteracted by the same cause. Tiiis assumption, 

 however, is precluded bv t!ie proof, that heat is not capable of 

 being carried off by the atmosphere, but can escape only by ra- 

 diation, which is dependent on an elevated temperature. The 

 conclusions seem, therefore, necessarily to follow, that the ori- 

 ginal temperature of the earth must have been at least as low as 

 the lowest natural temperature, and of course that the mean 

 temperature has been raised. 



While there is this rise, and this equalization of temperature 

 at the surface, there must be a corresponding rise in the internal 

 mass. It is obvious that no permanent rise can take place at 

 the external layer, without a portion of heat being diffused to 

 the internal matter at a lower temperature. It is obvious also, 

 that a portion of the heat received necessarily must be conveyed 

 to that matter. And as this diffusion is limited at the centre, 

 the temperature must rise until it become equal^ or nearly so, 

 through the whole, and as high, or nearly as high, as that which 

 the solar rays can excite. 



Lastly, the rise of temperature must observe certain limits ; it 



* Leltrcs mir I'Originc des Scienvcf, \>. 3?9. 



M 2 must 



