Galvanism, from ^Galvani to Ohm. 93 



(b. 1770, d. 1831), of Berlin discovered* that an electric current 

 can be set up in a circuit of metals, without the interposition 

 of any liquid, merely by disturbing the equilibrium of 

 temperature. Let a ring be formed of copper and bismuth 

 soldered together at the two extremities; to establish a 

 current it is only necessary to heat the ring at one of these 

 junctions. To this new class of circuits the name thermo- 

 electric was given. 



It was found that the metals can be arranged as a 

 thermo-electric series, in the order of their power of generating 

 currents when thus paired, and that this order is quite different 

 from Volta's order of electromotive potency. Indeed antimony 

 and bismuth, which are near each other in the latter series, are 

 at opposite extremities of the former. 



The currents generated by thermo-electric means are 

 generally feeble : and the mention of this fact brings us to 

 the question, which was about this time engaging attention, 

 of the efficacy of different voltaic arrangements. 



Comparisons of a rough kind had been instituted soon after 

 the discovery of the pile. The French chemists Antoine 

 FranQois de Fourcroy (b. 1755, d. 1809), Louis Mcolas 

 Yauquelin (b. 1763, d. 1829), and Louis Jacques Thenard 

 (b. 1777, d. 1857) foundf in 1801, on varying the size of the 

 metallic disks constituting the pile, that the sensations 

 produced on the human frame were unaffected so long as the 

 number of disks remained the same; but that the power 'of 

 burning finely drawn wire was altered; and that the latter 

 power was proportional to the total surface of the disks 

 employed, whether this were distributed among a small number 

 of large disks, or a large number of small ones. This was 



* Abhandl. d. Berlin Akad. 1822-3 ; Ann. d. Phys. Ixxiii (1823), pp. 115, 

 430 ; vi (1826), pp. 1, 133, 253. 



Volta had previously noticed that a silver plate whose ends were at different 

 temperatures appeared to act like a voltaic cell. 



Further experiments were performed by James Gumming (. 1777, d. 1861), 

 Professor of Chemistry at Cambridge, Trans. Camb. Phil. Soc. ii (1823), p. 47, 

 and by Antoine Cesar Becquerel (b. 1788, d. 1878), Annales de Chimie, xxxi 

 (1826), p. 371. t Ann. de Chimie, xxxix (1801), p. 103. 



