SCIENCE AND MAN. 345 



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 communi- 

 cated to the face of the pile, but the case is worthy of 

 closer examination. In 1826 Thomas Seebeck dis- 

 covered 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 retrans- 

 muted in co 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 dis- 

 tant 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 with- 



