426 ON THE DIFFUSION OF HEAT 



Leaving the consideration of this subject, in so far as it is 

 connected with the argument on the Huttonian Theory, J may 

 add a few observations of a more general nature, which the 

 preceding reasoning suggests with regard to the temperature 

 of the globe, and its relation to solar heat. From the nature 

 of the agency of the atmosphere in diffusing heat, the conclu- 

 sions seem to me almost necessarily to follow, — that there is 

 a tendency to equalization of temperature over the whole sur- 

 face of the earth, — that this continues to operate in such a 

 manner, that in the progress of time the difference at different 

 parts must become less than what existed at a preceding pe- 

 riod ; and that, ultimately, a temperature nearly uniform shall 

 be established over the whole. 



At the hotter parts of the earth's surface, the temperature 

 cannot increase, or must increase very slowly, and to no great 

 extent ; for if it were to rise higher, the ascent of heated air 

 from it, and the transfer of this to the colder parts of the sur- 

 face, would only become more rapid. But the temperature at 

 the colder regions may rise higher ; for the direct ascent of 

 heated air is there less abundant, and what recedes in a lateral 

 direction, does so, deprived of caloric, which it has yielded to 

 the earth. Whatever discharge of caloric, too, may take place 

 by radiation, must be principally from the hotter parts of the 

 surface ; from the colder it must be much less considerable, 

 for the quantity radiated is less as the temperature is low : it 

 increases, too, at a higher ratio than the increase of tempera- 

 ture ; and hence, if increased radiation from increased tempe- 

 rature, did take place at both, being greater at the former than 



at 



