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THE POPULAR SCIENCE MONTHLY.— SUPPLEMENT. 



heat is absorbed. Mix the liberated hydrogen f 

 with the oxygen and cause them to recombine, 

 the heat developed is mathematically equal to 

 the missing heat. Thus in pulling the oxygen 

 and hydrogen asunder an amount of heat is con- 

 sumed which is accurately restored by their re- 

 union. 



.This leads up to a few remarks upon the vol- 

 taic battery. It is not my design to dwell upon 

 the technic features of this wonderful instru- 

 ment, but simply by means of it to show what 

 varying shapes a given amount of energy can 

 assume while maintaining unvarying quantitative 

 stability. When that form of power which we 

 call an electric current passes through Grove's 

 battery, zinc is consumed in acidulated water, and 

 in the battery we are able so to arrange matters 

 that when no current passes no zinc shall be con- 

 sumed. Now the current, whatever it may be, 

 possesses the power of generating heat outside 

 the battery. We can fuse with it iridium, the 

 most refractory of metals, or we can produce with 

 it the dazzling electric light, and that at any ter- 

 restrial distance from the battery itself. 



We will now, however, content ourselves with 

 causing the current to raise a given length of plat- 

 inum wire, first to a blood-heat, then to redness, 

 and finally to a white heat. The heat under these 

 circumstances generated in the battery by the 

 combustion of a fixed quantity of zinc is no longer 

 constant, but it varies inversely as the heat gen- 

 erated outside. If the outside heat be nil, the in- 

 side heat is a maximum ; if the external wire be 

 raised to a blood-heat, the internal heat falls 

 slightly short of the maximum. If the wire be 

 rendered red-hot, the quantity of missing heat 

 within the battery is greater, and, if the external 

 wire be rendered white-hot, the defect is greater 

 still. Add together the internal and external 

 heat produced by the combustion of a given 

 weight of zinc, and you have an absolutely con- 

 stant total. The heat generated without is so 

 much lost within, the heat generated within is 

 so much lost without, the polar changes already 

 adverted to coming here conspicuously into play. 

 Thus, in a variety of ways, we can distribute the 

 items of a never-varying sum, but even the sub- 

 tile agency of the electric current places no cre- 

 ative power in our hands. 



Instead of generating external heat we may 

 cause the current to effect chemical decomposition 

 at a distance from the battery. Let it, for exam- 

 ple, decompose water into oxygen and hydrogen. 

 The heat generated in the battery under these cir- 

 cumstances by the combustion of a given weight 



of zinc falls short of what is produced when there 

 is no decomposition. How far short ? The ques- 

 tion admits of a perfectly exact answer. When 

 the oxygen and hydrogen recombine, the heat ab- 

 sorbed in the decomposition is accurately restored, 

 and it is exactly equal in amount to that missing 

 in the battery. We may, if we like, bottle up the 

 gases, carry in this form the heat of the battery, 

 to the polar regions, and liberate it there. The 

 battery, in fact, is a hearth on which fuel is con- 

 sumed, but the heat of the combustion, instead 

 of being confined in the usual manner to the 

 hearth itself, may be first liberated at the other 

 side of the world. 



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 vol- 

 taic battery was understood. The puzzle was, 

 that a single cell could not decompose water. 

 The reason is now plain enough. The solution 

 of an equivalent of zinc in a single cell develops 

 not much more than half the amount of heat re- 

 quired 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 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-elec- 

 tric pile, an instrument usually composed of small 

 bars of bismuth and antimony soldered alter- 

 nately 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, magnetize iron, and deflect a mag- 

 netic 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 ob- 

 servation 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 



