THERMO-ELECTRIC GENERATORS. 39 



.and the possibility of heating them to a high temperature 

 without damaging the pile, made the question of thermo- 

 electric batteries enter upon a new phase, which was cultivated 

 with success by several physicists, and particularly by Farmer, 

 Bunsen, Ed. Becquerel, Clamond, Noe, &c. Piles could then 

 toe obtained having an electrical intensity comparable to 

 that of the battery cell with acids, and these piles were used 

 with much advantage, even in' electrotyping. Of all the 

 .apparatus of this kind, those which gave the greatest effects 

 were beyond dispute diamond's piles. 



From the first, that is to say, in 1870, Clamond foresaw 

 that he might one day be able to obtain the electric light 

 with this kind of battery; and here is what I said about it 

 in my Expose des applications de r electricite, tome /., p. 426, 

 published in 1871 : 



" Mure and Clamond are now constructing batteries of this 

 kind having 1,500 large elements, which they assert to have a 

 power equal to 50 Bunsen cells. If, as everything leads us to 

 expect, the expense occurs under the same conditions as in the 

 case considered (heating by coke), it will be about 30 centimes 

 per hour, and the thermo-electric pile may thus become an 

 economic source of electric light." 



This result, however, could not be attained, on account 

 of the unfavourable conditions under which the pile was 

 placed, and because the galena which Clamond then used 

 was damaged by the heat. Nevertheless, these experiments 



and the combination which develops the highest electro-motive force is that 

 pointed out by Ed. Becquerel, in which one of the bars is composed of anti- 

 mony and cadmium in equal equivalents, and the other bar of bismuth and 

 antimony, the last forming only a tenth part of the alloy. For scientific re- 

 searches this combination gives the best results, but for industrial applications 

 it cannot easily be used. In the first place, the cost of the apparatus would 

 be extremely great, and secondly, the system could not be subjected to so 

 high a temperature as one formed of other alloys. Therefore the combina- 

 tion of antimony and zinc with sheet-iron, adopted by Clamond, though not 

 of itself giving so great an electro-motive force, is capable of yielding better 

 results by reason of the greater difference of the temperatures that may be 

 imparted to it. 



