AT THE EARTH'S SURFACE. 423 



It is, therefore, I conceive, of little importance in the 

 discussion, whether the heat supposed to be conveyed from 

 the centre to the circumference is accumulated there, or is dis- 

 charged into the regions of space. Its propagation to the 

 surface must be subversive of its accumulation in the interior. 

 Either the diffusion alone, therefore, or the diffusion attended 

 with the final result of equilibrium of temperature, is sufficient 

 for the refutation of the hypothesis. Both I conceive are esta- 

 blished. And I would still regard the argument in the light in 

 which I first advanced it, as a demonstration of the fallacy of 

 the leading principle of the Huttonian System, which as- 

 sumes the existence of an internal heat operating at renewed 

 periods for indefinite time. 



There are some other points of view under which the sub- 

 ject may be considered, in which the difficulties attending the 

 assumption of an internal heat, when connected with the law 

 which Mr Playfair has illustrated, appear in a very strong 

 light. 



It has always been found difficult to give any account of the 

 origin of the supposed internal heat, to the operation of which 

 the consolidation of minerals, and the elevation of the habitable 

 land from the bed of the ocean, have been ascribed. If the 

 view be restricted to the production even of one world, such 

 an intensity and continuance of heat are necessary for this 

 single effect, that no adequate cause can be even hypotheti- 

 cally assigned for it. If it be extended to the successive pro- 

 duction of three or four worlds, each embracing a period be- 

 tween its formation and destruction in which millions of years 

 must elapse, — an event which, according to the theory, is not 

 only possible, but has actually occurred, — the heat required is 

 altogether beyond what the imagination can conceive. But if 

 in addition to this, caloric is also diffused from the interior, 



3 H 2 and 



