DISCUSSION OF JOULE'S RESULTS. 89 



boiler from the furnace, in exact proportion to the equivalent 

 of mechanical power developed." 



" It would lengthen this paper to an undue extent were 

 I now to introduce any direct proofs of these views, had I 

 •even leisure at present to make the experiments requisite for 

 the purpose ; I shall, therefore, reserve the further discussion 

 of this interesting subject for a future communication, which 

 I shall hope to have the honour of presenting to the Royal 

 Society at no distant period," 



The opinions expressed in the several paragraphs in this 

 •remarkable quotation require separate consideration, as 

 possessing, each of them, importance in connection with 

 Joule's subsequent work, and his priority in expressing 

 views now accepted as correct. 



In the first place, it should be noticed that the two last 

 paragraphs contain the first expression Joule recorded of an 

 -opinion, or even suggestion, that the work done by the 

 steam engine is at the expense of the heat received from 

 the fire. In describing his discovery of the " Mechanical 

 Value of Heat," Joule had referred to the proportion between 

 the work done by these engines, as compared to the whole 

 mechanical equivalent of the heat of the coal consumed, 

 but he there says not a word as to the conversion of heat 

 into work by the engine. It might or might not have been 

 in his mind, for anything he says. It has already been 

 pointed out, however, that the paper contains evidence that 

 he had at that time considered electricity as the only means 

 of converting heat into work. But whether the suggestion 

 was in his mind at the time, or followed immediately after 

 writing the paper, he, for more than a year, refrained from 

 -expressing it until he had convinced himself and was in a 

 position to convince others by the results of his experiment 

 >on the condensation of air. He now advances it boldly, 



