THOMSON ON CARNOT'8 



primitive physical state as to density, temperature, 

 and molecular constitution, it must contain the 

 same quantity of heat as that which it initially pos- 

 sessed; or, in other words, we suppose that the 

 quantities of heat lost by the body under one set 

 of operations are precisely compensated by those 

 which are absorbed in the others. This fact has 

 never been doubted ; it has at first been admitted 

 without reflection, and afterwards verified, in many 

 cases, by calorimetrical experiments. To deny it 

 would be to overturn the whole theory of heat, in 

 which it is the fundamental principle. It must be 

 admitted, however, that the chief foundations on 

 which the theory of heat rests, would require a 

 most attentive examination. Several experimental 

 facts appear nearly inexplicable in the actual state 

 of this theory." 



7. Since the time when Carnot thus expressed 

 himself, the necessity of a most careful examina- 

 tion of the entire experimental basis of the theory 

 of heat has become more and more urgent. Es- 

 pecially all those assumptions depending on the 

 idea that heat is a substance, invariable in quan- 

 tity; not convertible into any other element, and 

 incapable of being generated by any physical 

 agency; in fact the acknowledged principles of 

 latent heat, would require to be tested by a most 



