VELOCITY OF GASEOUS MOLECULES. 113 



From this he then correctly deduces the corresponding 

 velocities for the molecules of oxygen, nitrogen, carbonic acid, 

 and steam as being inversely proportioned to the square 

 roots of these specific gravities. 



He then estimates, by means of his discoveries of the 

 dynamical equivalent of heat and absolute zero of tem- 

 perature, what would be the specific heats of the several 

 gases as resulting from the vis viva of these molecular 

 velocities, supposing, according to Herapath's hypothesis, 

 that the molecules are hard. These theoretical specific 

 heats he compares with the experimental results of 

 Delaroche and Berard, which he finds are invariably much 

 higher and not in simple proportion. He has thus found 

 that Herapath's hypothesis of hard particles is not capable 

 of explaining the then experimental results, but as he expects 

 the experiments undertaken by M. V. Regnault for the 

 French Government will shortly be published, he says, "Till 

 then it will be better to delay any further modifications of 

 the dynamical theory by which its deductions may be made 

 to correspond more closely with the results of experiment." 

 Considering that these results were obtained only as a con- 

 sequence of Joule's discoveries of the mechanical equivalent 

 of heat, and the absolute zero of temperature, that it was 

 more than four years before any further work was done on 

 this subject, and that not only the mean velocities, but 

 also the specific heats resulting from the linear motion 

 of the molecules are in accordance with the now accepted 

 theory, which theory is Herapath's, with an addition intro- 

 duced, first by Clausius, solely to meet the deficiency of 

 the specific heats discovered by Joule to belong to Herapath's 

 hypothesis, it appears that this memoir establishes Joule's , 

 position as the founder of the modern quantitative dynamical 

 I 



