SCIENCE AND MAN 863 



without consuming tlie heat imparted to the junction. 

 This heat is the nutriment of the current. Thus the heat 

 generated by the thermo- current in a distant wire is simply 

 that originally imparted to the pile, which has been first 

 transmuted into electricity, and then retransmuted into its 

 first form at a distance from its origin. As water in a 

 state of vapor passes from a boiler to a distant condenser, 

 and there assumes its primitive form without gain or loss, 

 so the heat communicated to the thermo- pile distils into 

 the subtler electric current, which is, as it were, recon- 

 densed into heat in the distant platinum wire. 



In my youth I thought an electro -magnetic engine 

 which was shown to me a veritable perpetual motion — a 

 machine, that is to say, which performed work without the 

 expenditure of power. Let us consider the action of such 

 a machine. Suppose it to be employed to pump water 

 from a lower to a higher level. On examining the battery 

 which works the engine we find that the zinc consumed 

 does not yield its full amount of heat. The quantity of 

 heat thus missing within is the exact thermal equivalent 

 of the mechanical work performed without. Let the water 

 fall again to the lower level; it is warmed by the fall. 

 Add the heat thus produced to that generated by the fric- 

 tion, mechanical and magnetical, of the engine; we thus 

 obtain the precise amount of heat missing in the battery. 

 All the effects obtained from the machine are thus strictly 

 paid for; this "payment for results" being, I would re- 

 peat, the inexorable method of nature. 



Ko engine, however subtly devised, can evade this 

 law of equivalence, or perform on its own account the 

 smallest modicum of work. The machine distributes, but 

 it cannot create. Is the animal body, then, to be classed 



