66 POPULAR LECTURES AND ADDRESSES. 



and the kinetic theory of Clausius and Maxwell, 

 scarcely yet afford us sufficient data for estimating 

 the rapidity with which the vapour proceeding 

 from one of the liquids will diffuse itself through 

 the air and reach the surface of another liquid at a 



FIG. 32. 



lower level. With air at anything approaching to 

 ordinary atmospheric density to resist the process, 

 it is probable it would be too slow to show any 

 results unless in very long continued experiments. 

 But if the air be removed as perfectly as can be 



