Page:A history of the theories of aether and electricity. Whittacker E.T. (1910).pdf/113

 (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 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 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 François de Fourcroy (b. 1755, d. 1809), Louis Nicolas Vauquelin (b. 1763, d. 1829), and Louis Jacques Thénard (b. 1777, d. 1857) found 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