90 JOULE IGNORES THE TRUTH OF 



clearly, and fully, and yet in no way over-states his case 

 from the present point of view. 



The reference to, and discussion of, Carnot's theory,, 

 which is contained in the second paragraph, is also of 

 great interest. It is the first reference by any of those 

 who engaged in the development of the general theory 

 of thermo-dynamics to Carnot's theory, which afterwards 

 attracted so much attention. It shows that Joule was at 

 this time aware of, and had to some extent studied,, 

 Carnot's papers. But, what is of far greater interest 

 and importance, it shows, by the light subsequently 

 thrown on the subject, the difficulty Joule was labouring 

 under in his task of reconciling his discovery with the 

 apparently conclusive but contrary testimony of the steam 

 engine itself, arising from his own want of appreciation 

 of the limits imposed by surrounding conditions to the 

 possibilities of converting heat into mechanical power. It 

 also brings out the difficulties arising from want of common 

 language in which to express newly-discovered facts. 

 Carnot had, in 1824, discovered and proved conclusively an 

 occult, but fundamental, principle respecting the relation of 

 surrounding circumstances to the possibilities of obtaining 

 power by means of heat, a principle which, as expressed by 

 him, was in strict accordance with the common experience 

 with the steam engine. In expressing this principle, Carnot 

 had to confine himself to the knowledge of his time and to 

 the language in which this knowledge was then expressed,, 

 however imperfect he himself might perceive this knowledge 

 to be. The hypothesis that heat or caloric was indestruct- 

 ible and uncreatable, on which the proof of Carnot is based, in 

 itself, contained no error, but the deduction from it, then 

 generally made, that the heat received by the engine from. 



