ire> ■;• - ( 116 > 



Mr. J. C. Maxwell on the Dynamical Theory of Gases. 207 

 and the specific heat of unit of mass at constant pressure is 

 3E_ 3 + 3/3 p 



ye — 2~ je (lld > 



The ratio of the specific heat at constant pressure to that of 

 constant volume is known in several cases from experiment. 

 We shall denote this ratio by 



whence 



^=1^1 ( 115 ) 



The specific heat of unit of volume in ordinary measure is at 

 constant volume 



J. p 



7 



and at constant pressure 



JL_Z. (117) 



where J is the mechanical equivalent of unit of heat. 



From these expressions Dr. Rankine* calculated the specific 

 heat of air, and found the result to agree with the value after- 

 wards determined experimentally by M. Regnaultf. 



Thermal Effects of Diffusion; 

 If two gases are diffusing into one another, then, omitting 

 the terms relating to heat generated by friction and to conduc- 

 tion of heat, the equation (94) gives 



/du, dvi dw, \ /dug , dv 9 , div Q \ y (US) 



By comparison with equations (78), (79), the right-hand side of 

 this equation becomes 



X (p x u x + /o 2 w 2 ) + ^{p 1 v 1 + p 2 v g ) + Z (p l w 1 + p 2 w ) 



\dx 1+ dy ^ + dz W *) \dx 2+ dy V * + dz W *J 



-^l^^+^+^^i^l-^^+^+V). 



* Transactions of the Hoyal Society of Edinburgh, vol. xx. (1850). 

 f Comptes Rendus, 1853. 



