S6 DYNAMICAL THEORY OF HEAT. 



latent heat that Joule drew the conclusion that the heat 

 respectively evolved and absorbed in the first and third 

 series was the equivalent of the work done respectively on 

 and by the gas in these experiments, and thus afforded an 

 independent proof of the convertibility of heat into 

 mechanical effect, as well as a verification of the close 

 approximation to the true value of his previous determina- 

 tion of the mechanical equivalent. 



As regards Joule's position in the history of the discovery 

 of the conversion of heat and work, the appreciation which 

 he showed of the possibility of phenomena of air being 

 complicated by latent heat, and his proof of its non- 

 existence, are very important. It is certain that at this time 

 Joule was unaware that Mayer had in 1842 brought forward 

 the heat absorbed in the expansion of air as in itself 

 affording a proof of the convertibility of heat into work. 

 Had he done so he could not have conceived experiments 

 better contrived to show the hypothetical character of 

 the proof assumed by Mayer than those described in this 

 paper, or have furnished those who, in the discussion which 

 arose years afterwards, defended his position with more 

 crushing arguments. 



The conclusion of this paper has great interest as con- 

 taining the expression of facts and opinions, the influence 

 of which on Joule's subsequent work was considerable. 

 Speaking of these experiments, he says that they " afford 

 a new and, to my mind, powerful argument in favour of 

 the dynamical theory of heat, which originated with Bacon, 

 Newton, and Boyle, and has been, at a later period, so well 

 supported by the experiments of Rumford, Davy, and Forbes.. 

 With regard to the detail of the theory, much uncertainty 

 at present exists. The beautiful idea of Davy that the heat 



