PHYSICAL THEOPJES OF HEAT. 1ST 



Without, then, deciding upon this theory, we may venture to sav 

 that it is wanting in all the prominent and striking characteristics 

 which -we have found in those great theories which we look upon as 

 clearly and indisputably established. 



Conclusion. We may observe, moreover, that heat has other bear- 

 ings and effects, which, as soon as they have been analysed into nume- 

 rical laws of phenomena, must be attended to in the formation of ther- 

 rnotical theories. Chemistry will probably supply many such ; those 

 which occur to us, we must examine hereafter. But we may mention 

 as examples of such, MM. De la Rive and Marcet's law, that the speci- 

 fic heat of all gases is the same; 11 and MM. Dulong and Petit' s law, 

 that single atoms of all simple bodies have the same capacity for heat. 12 

 Though we have not yet said anything of the relation of different 

 gases, or explained the meaning of atoms in the chemical sense, it 

 will easily be conceived that these are very general and important pro- 

 positions. 



Thus the science of Therrnotics, imperfect as it is, forms a highly - 

 instructive part of our survey ; and is one of the cardinal points on 

 which the doors of those chambers of physical knowledge must turn 

 which hitherto have remained closed. For, on the one hand, this 

 science is related by strong analogies and dependencies to the most 

 complete portions of our knowledge, our mechanical doctrines and 

 optical theories ; and on the other, it is connected with properties and 

 laws of a nature altogether different, those of chemistry ; properties 

 and laws depending upon a new system of notions and relations, among 

 which clear and substantial general principles are far more difficult to 

 lay hold of, and with which the future progress of human knowledge 

 appears to be far more concerned. To these notions and relations we 

 must now proceed ; but we shall find an intermediate stage, in certain 

 subjects which I shall call the Mechanico-chemical Sciences ; viz., 

 those which have to do with Magnetism, Electricity, and Galvanism. 



11 Ann. Chim. xxxv. (1827.) 12 Ib. s. 397. 



