28 ON THE GENERAL FORM AND 



bute the fluidity of the earth to fire, the difficulty, if it 

 be supposed one, may, in the same way as in the case of 

 solution in water, be diminished by limiting the fusion 

 to the same crust covering the inscribed sphere, of 

 which the diameter is nearly coincident with the length 

 of the Polar axis. But though it is demonstrable that 

 the great mass of the superficial rocks has been depo- 

 sited from water, that fact, as of more recent date* 

 is not incompatible with such a theory. Adopting 

 this supposition, we must however explain the 

 loss of that heat which must have been extricated 

 on the cooling of such a mass. For this purpose, 

 recourse has been had to the chemical changes and 

 combinations in which heat is absorbed or becomes 

 latent ; and if this explanation is attended with diffi- 

 culties, it is conceived that the doctrine of radiation 

 offers a satisfactory solution. 



That the planetary bodies, as well as the solar ones, 

 must and do radiate their heat into free space, is 

 a doctrine to which we cannot well refuse our assent; 

 and thence the mean temperature of the ambient void, 

 imperfectly indicated by that of our own polar regions. 

 It is almost unnecessary to say, that if the earth was 

 even that heated body which this theory supposes, it 

 must, like a solar one, have radiated its heat until its 

 surface, at least, had subsided to that temperature ; 

 omitting here any consideration of the solar action. 

 Hence, the cooling of the earth from a high state of 

 former heat, is not the impossibility which has been 

 imagined ; while the laws which regulate its progress 

 through conducting bodies, would permit the co- 

 existence of the present superficial temperature with 

 any imaginable one in its interior parts. 



But another hypothesis to explain the statical figure 

 of the earth has been proposed, founded on the changes 



