164 POPULAR LECTURES AND ADDRESSES. 



thickness of each piece of metal and of each 

 intervening space be i/ioo,ooo,oooth of a centi- 

 metre, instead of i/ioo,oooth. The work would 

 be increased a million-fold unless i/ioo,ooo,oooth 

 of a centimetre approaches the smallness of a mole- 

 cule. The heat equivalent would therefore be enough 

 to raise the temperature of the material by 62 

 This is barely, if at all, admissible, according to 

 our present knowledge, or, rather, want of know- 

 ledge, regarding the heat of combination of zinc 

 and copper. But suppose the metal plates and 

 intervening spaces to be made yet four times 

 thinner, that is to say, the thickness of each to 

 be i /4OO,ooo,oooth of a centimetre. The work 

 and its heat equivalent will be increased sixteen- 

 fold. It would therefore be 990 times as much 

 as that required to warm the mass by one degree 

 Centigrade, which is very much more than can 

 possibly be produced by zinc and copper in enter- 

 ing into molecular combination. Were there in 

 reality anything like so much heat of combination 

 as this, a mixture of zinc and copper powders 

 would, if melted in any one spot, run together, 



