PHILOSOPHY PERFECTED. 95 



of vis viva exists in matter. A single pound of water must 

 possess 508 of heat, or in other words it must possess a 

 vis viva equal to that acquired by a weight of 415,0361b. 

 after falling through a perpendicular height of one foot." 

 Joule does not here, or anywhere else in his subsequent 

 writings, make reference to having used momentum and 

 vis viva in the same sense. In whatever sense he used it, 

 however, it makes little difference. The fact that he used 

 it in other than its full mechanical sense shows that he was 

 unacquainted with mechanical philosophy when he framed 

 Tiis hypothesis. While it is equally clear that in considering 

 the results of that theory he, within the space of a year, 

 realized this philosophy in its full significance, and found 

 his hypothesis in strict accordance. 



Joule's hypothesis of whirling atmospheres itself deserves 

 more than passing notice. It was the first definite hypothesis 

 of the kinetic constitution of gas, and although Joule made 

 no attempt at its full mathematical development, the same 

 theory, with but slight modification, was revived five years 

 later by Rankine, under the title of " The Hypothesis of 

 Molecular Vortices" and in its mathematical development led 

 liim to the complete mathematical theory of the 'Mechanical 

 Action of Heat' as it exists at present. This hypothesis, 

 however, though explaining all the principal kinetic pro- 

 perties of gases, eventually failed to account for the pro- 

 perties of diffusion and viscosity, then but little known, but 

 upon which Graham was engaged in his life-long researches ; 

 while the hypothesis that the particles of gas are flying 

 about in fall directions, discussed by Daniel Bernouilly, 

 revived by Herapath in 1847, and developed first by Joule, 

 being found capable of explaining the results of Graham's 

 researches, as well as all the properties of gases explained 



