SCIENCE AND MAN 



81 



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 of an equi- 

 valent of zinc in a single cell developes 

 not much more than half the amount of 

 heat required to decompose an equivalent 

 of water, and the single cell cannot cede 

 an amount of force which it does not 

 possess. But by forming a battery of 

 two cells instead of one, we develop an 

 amount of heat slightly in excess of that 

 needed for the decomposition of the 

 water. The two-celled battery is there- 

 fore rich enough to pay for that decom- 

 position, and to maintain the excess 

 referred to within its own cells. 



Similar reflections apply to the thermo- 

 electric pile, an instrument usually com- 

 posed of small bars of bismuth and 

 antimony soldered alternately together. 

 The electric current is here evoked by 

 warming the soldered junctions of one 

 face of the pile. Like the Voltaic current, 

 the thermo-electric current can heat 

 wires, produce decomposition, magnetise 

 iron, and deflect a magnetic needle at 

 any distance from its origin. You will 

 be disposed, and rightly disposed, to 

 refer those distant manifestations of 

 power to the heat communicated to the 

 face of the pile, but the case is worthy 

 of closer examination. In 1826 Thomas 

 Seebeck discovered thermo-electricity, 

 and six years subsequently Peltier made 

 an observation which comes with singular 

 felicity to our aid in determining the 

 material used up in the formation of the 

 thermo-electric current. He found that 

 when a weak extraneous current was 

 sent from antimony to bismuth the 

 junction of the two metals was always 

 heated, but that when the direction was 

 from bismuth to antimony the junction 

 was chilled. Now the current in the 

 thermo-pile itself is always from bismuth 

 to antimony, across the heated junction 



a direction in which it cannot possibly 

 establish itself without consuming the 

 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 vapour 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, recondensed 

 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 friction, mechanical and mag- 

 netical, 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 repeat, the inexorable method 

 of nature. 



No engine, however subtly devised, 

 can evade this law of equivalence, or 

 perform on its own account the smallest 

 modicum of work. The machine distri- 

 butes, but it cannot create. Is the 

 animal body, then, to be classed among 

 machines? When I lift a weight, or 

 throw a stone, or climb a mountain, or 

 wrestle with my comrade, am I not con- 

 scious of actually creating and expending 



