SCIENCE AND MAN 361 



still. Add together the internal and external heat pro- 

 duced by the combustion of a given weight of zinc, and 

 you have an absolutely constant total. The heat gen- 

 erated without is so much lost within, the heat generated 

 within is so much lost without, the polar changes already 

 adverted to coming here conspicuously into play. Thus 

 in a variety of ways we can distribute the items of a never- 

 varying sum, but even the subtle agency of the electric 

 current places no creative power in our hands. 



Instead of generating external heat, we may cause the 

 current to effect chemical decomposition at a distance from 

 the battery. Let it, for example, decompose water into 

 oxygen and hydrogen. The heat generated in the battery 

 under these circumstances by the combustion of a given 

 weight of zinc falls short of what is produced when there 

 is no decomposition. How far short? The question ad- 

 mits of a perfectly exact answer. When the oxygen and 

 hydrogen recombine, the heat absorbed in the decomposi- 

 tion is accurately restored, and it is exactly equal in 

 amount to that missing in the battery. We may, if we 

 like, bottle up the gases, carry in this form the heat of the 

 battery to the polar regions, and liberate it there. The 

 battery, in fact, is a hearth on which fuel is consumed; 

 but the heat of the combustion, instead of being confined 

 in the usual manner to the hearth itself, may be first lib- 

 erated at the other side of the world. 



And here we are able to solve an enigma which long 

 perplexed scientific men, and which could not be solved 

 until the bearing of the mechanical theory of heat upon 

 the phenomena of the Voltaic battery was understood. 

 The puzzle was, that a single cell could not decompose 



water. The reason is now plain enough. The solution 



SCIENCE 16 



