Temperature of the Terrestrial Globe. 17 



Although the effect of internal heat may be no longer sensible at 

 the surface, the sum total of this heat which escapes in a given time, 

 as in a year or a century, is measurable, and has been ascertained. 

 That which escapes in a century through a square metre, and is dis- 

 sipated in the celestial space, would melt a column of ice, of which 

 the base should be a square metre, and height three metres. 



This result is derived from a fundamental proposition, which can 

 be applied to all questions relating to the motions of heat, and espe- 

 cially to that of terrestrial temperature. 1 allude to the differential 

 equation, which expresses for each moment the state of surface. 

 This equation, the truth of which is plain, and easily demonstrated, 

 establishes a simple relation between the temperature of an element 

 of the surface and the normal motion of heat. What renders this 

 result of theory very important, and more valuable than any other 

 for throwing light upon the questions which form the subject of this 

 article, is, that it exists independent of the form and dimensions of 

 bodies, and of the nature of the substances, whether homogeneous 

 or not, of which the internal mass may be composed. The results 

 of this equation are absolute : they are the same, whatever may have 

 been the material constitution or original state of the globe. 



We have published in the ^'Annales de Chimie et de Physique," 

 the abstract of a memoir, which has not yet been printed, and the 

 object of which is to apply to the terrestrial globe the analyses of 

 the motions of heat in a sphere or plane solid, of great dimensions. 

 In that extract the principal formulas were exhibited, particularly 

 those which express the variable state of a solid uniformly heated at 

 a determinate and very great depth, or in its whole depth. If the 

 original temperature, instead of being the same to a very great depth, 

 results from successive immersions in several media, the consequen- 

 ces are not less simple or remarkable. But this case, and several 

 others which we have considered, are comprised in the general ex- 

 pressions which have been mentioned. 



After having explained separately the principles of the inquiry 

 respecting the temperature of the earth, in order to form a correct 

 idea of these phenomena united, we ought to give, in a general 

 statement, all the effects we have just described. 



The earth receives the rays of the sun, which penetrate its mass, 

 and are converted into non-luminous heat : it likewise possesses an 

 internal heat with which it was created, and which is continually 

 dissipated at the surface : and lastly, the earth receives rays of light 



Vol. XXXIL— No. 1. 3 



