T40 POPULAR LECTURES AND ADDRESSES. 



and undoes the natural diffusion of heat ; the 

 former undoes the natural diffusion of matter. 



By a combination of the two processes, the 

 demon can decompose water or carbonic acid, first 

 raising a portion of the compound to dissociational 

 temperature (that is, temperature so high that 

 collisions shatter the compound molecules to 

 atoms), and then sending the oxygen atoms this 

 way, and the hydrogen or carbon atoms that way ; 

 or he may effect decomposition against chemical 

 affinity otherwise, thus : Let him take in a small 

 store of energy by resisting the mutual approach 

 of two compound molecules, letting them press 

 as it were on his two hands, and store up energy 

 as in a bent spring ; then let him apply the two 

 hands between the oxygen and the double hy- 

 drogen constituents of a compound molecule of 

 vapour of water, and tear them asunder. He may 

 repeat this process until a considerable proportion 

 of the whole number of compound molecules in 

 a given quantity of vapour of water, given in a 

 fixed closed vessel, are separated into oxygen and 

 hydrogen at the expense of energy taken from 



