THE DYNAMICAL THEORY OF GASES. 63 



fifth, sixth, and seventh the heating effect of fluid friction or viscosity ; and 



the last the loss of heat by conduction. The quantities on the other side of 



the equation represent the thermal effects of diffusion, and the communication 

 of heat from one gas to the other. 



The equation may be simplified in various cases, which we shall take in 

 order. 



1st. Equilibrium of Temperature between two Gases. Law of Equivalent Volumes. 



We shall suppose that there is no motion of translation, and no transfer 

 of heat by conduction through either gas. The equation (94) is then reduced 

 to the following form, 



If we put 



W-g, ....... (%), 



we find (Q t -Q l )=--(M^, + M lP A}(Q t -Q l } ......... (97), 



1 





Q,-Q>=Ce-<, where n = (M t pA + M^,) - ....... (98). 



-- 



If, therefore, the gases are in contact and undisturbed, Q 1 and Q, will 

 rapidly become equal. Now the state into which two bodies come by exchange 

 of invisible agitation is called equilibrium of heat or equality of temperature- 

 Hence when two gases are at the same temperature, 



Q 1 = Q, .................................... (99), 





