604 FRAGMENTS OF SCIENCE. 



tance 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 sub- 

 sequently 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 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 distills 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 ex- 

 penditure 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 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 repeat, the 

 inexorable method of nature. 



