412 ON THE DIFFUSION OF HEAT 



through the entire mass, and become at length equal, or near- 

 ly so, over the whole. An equilibrium of temperature must 

 therefore be established, incompatible with that system of in- 

 definitely renewed operations which is represented as the great 

 excellence of the system. This has always appeared to me 

 conclusive ; and an argument such as this, derived a priori, and 

 directed to the first principles of a geological theory, if suc- 

 cessful, is of greater weight than arguments derived from its 

 adaptation to natural phenomena, which, even when they ap- 

 pear to be just, amount only to probability, and, from our im- 

 perfect knowledge of the relations of the mineral kingdom, 

 leave often some degree of uncertainty *. 



To obviate this argument, the following reasoning has been 

 employed by Mr Pla^faiu. The diffusion of temperature, he 

 remarks, is a consequence of the tendency of heat, to pass from 

 bodies where the temperature is higher to those where it is 

 lower. It is not, therefore, a necessary result, but is only con- 

 tingent, 



* I oucht to remark, that this view of the constant existence of a central heat 

 "s not considered by all the defenders of Dr Hutton 1 s system, as a necessary 

 part of it, nor do they even regard it as a position which he himself maintained. 

 They suppose the existence only of interior local heat, which may cease for a 

 time, and be again renewed ; and to this hypothesis the above argument does not 

 so strictly apply. I must only add, that if even this view of the subject be 

 adopted, much of the difficulty will still remain in its original' force ; it be- 

 comes liable, too, if I mistake not, to other objections peculiar to itself, equally 

 important ;. and by adopting it, much of the beauty and unity of the system are 

 lost. These seem to me to require the assumption of a central heal, or general 

 reservoir of heat capable of extending its action to every part of the circumfer- 

 ence, always existing, though not equally active in its apparent effects. It is to 

 this view of the subject, consistent, I believe, with the original statement of 

 the theory by Dr Huttov, that the argument applies. It is this which Mr 

 Playfair admits, and on the admission of which, indeed, his reasoning is 

 founded ; and, strictly speaking, it is to his reasoning only that the observa- 

 tions, in this paper are directed. 



