362 FRAGMENTS OF SCIENCE 



of an equivalent of zinc in a single cell develops not 

 much more than half the amount of heat required to de- 

 compose an equivalent of water, and the single cell can- 

 not 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 therefore rich enough to pay for 

 that decomposition, and to maintain the excess referred 

 to within its own cells. 



Similar reflections apply to the thermo-electric pile, 

 an instrument usually composed 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 Yoltaic current, the 

 thermo-electric current can heat wires, produce decom- 

 position, magnetize 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 tha 

 two metals was always heated, but that whea the direc- 

 tion was from bismuth to antimony the junction wag 

 chilled. Now the current in the thermo-pile itself is al^ 

 ways from bismuth to antimony, across the heated junc- 

 tion — a direction in which it cannot possibly establish itself 



