128 JAMES CLKKK MAXWELL 



mean velocity of the molecules. Since the absolute 

 temperature is proportional to the square of the 

 velocity, it follows that the coefficient of viscosity is 

 proportional to the square root of the absolute 

 temperature. 



The second part of the paper deals with the 

 process of diffusion of two or more kinds of moving 

 particles among one another. 



If two different gases are placed in two vessels 

 separated by a porous diaphragm such as a piece of 

 iingla/ed earthenware, or connected by means of a 

 narrow tube, (i rah am had shewn that, after sufficient 

 time has elapsed, the two are mixed together. 

 The same process takes place when two gases 

 of different density are placed together in the same 

 vessel. At first the denser gas may be at the bottom, 

 the less dense above, but after a time the two arc 

 found to IK; uniformly distributed throughout. 



Maxwell attempted to calculate from his theory 

 the rate at which the diffusion takes place in these 

 cases. The conditions of most of Graham's experi- 

 ments were too complicated to admit of direct com- 

 parison with the theory, froni which it appeared that 

 there is a relation between the mean free path and 

 the rate of diffusion. One experiment, however, was 

 found, the conditions of which could be made the 

 subject of calculation, and from it Maxwell obtained 

 as the value of the mean free path in air .J t - w of an 

 inch. 



The number was close enough to that found from 

 the viscosity to afford some continuation of his 

 theory. 



