OBSCURES GENERAL LAWS. 1 25. 



From this mechanical hypothesis of heat and the con- 

 stitution of matter, Rankine, by his remarkable innate 

 mathematical facility, developes as general equations the re- 

 lations between pressure, volume, temperature and heat, of 

 the matter so constituted. Using the "Experimental 

 Results of Regnault," published in 1847 ; the experiments 

 of De la Roche and Berard, as to specific heat, together 

 with the velocity of sound, and Laplace's extension of 

 Newton's theory, as data from which to determine the 

 values of his symbols, Rankine at once applies the theory 

 to determine relations hitherto not experimentally deter- 

 mined, or not determined with sufficient accuracy, for air 

 and steam, and this with great success. 



These equations of Rankine, if they truly express the 

 thermodynamical condition which holds in any particular 

 mechanical arrangement, must implicitly conform to the 

 general laws, which hold for all arrangements of matter ; 

 but they obscure rather than indicate the generality or 

 importance of such laws. Based on a definite hypothetical 

 mechanical constitution of matter, they implicitly con- 

 formed to the law of the conversion of that form of energy 

 named heat to that called mechanical energy, but they 

 did not explicitly call attention to the general importance of 

 this law, or to the importance of the mechanical equivalent 

 of heat. In the same way Rankine's equations conformed 

 to Carnot's law, but in no way indicated its generality or 

 importance. Thus it was that Rankine, having failed to 

 recognize the general truth of Carnot's law, did not know that 

 it was to be obtained from his equations until he looked for it 

 after its importance had become known to him. 



To the importance of Joule's mechanical equivalent of 

 heat, Rankine's attention had already been called by Joule's 



