124 .IAMKS ri.KHK MAXWKIJ. 



the two sets respectively, /,, r* their mean velocities 

 we must have finally 



This is the second of the two great laws enunciated 

 by Waterston in 1845. and 1851, but which, as wo 

 have seen, had remained unknown until 1859, when 

 it was again given by Maxwell. 



Now, when gases are mixed their temperatures 

 become equal. Hence we conclude, in Maxwell's 

 words, "that the physical condition which determines 

 that the temperature of two gases shall be the same, 

 is that the mean kinetic energy of agitation of the 

 individual molecules of the I wo gases are equal.' 1 



Thus, as the result of Maxwell's more exact re- 

 searches on the motion of a system of spherical 

 particles, we find that wo again can obtain the 

 equations 



.> vr * ' 



""- S NT == j f> - 



From these results we obtain as before the laws of 

 Boyle, Charles and Avrogadro. 



Again if 9 bo the specific heat of the gas at 

 constant volume, the quantity of heat required to 

 raise a single molecule of mass ni one degree will bo 



a i,i. 



Thus, when a molecule is heated, the kinetic 

 energy must increase by this amount. But the 

 increase of temperature, which in this case is 1, is 

 measured by the increase of kinetic energy of the 



