Thermo -electricity

(-e-lek-tris'e-te.) (Phys.) The electricity developed by change of temperature, discovered by Seebeck in 1822. It is most probably that electricity which, being developed by the succe ive heating and cooling of the earth's surface during rotation on its axis, causes the earth to be a magnet. If two pieces of copper wire are attached to a delicate galvanometer, on bringing the free ends together, between the finger and thumb, sufficient electricity will be set free to deflect the needle. The phenomena may be shown by the apparatus represented in Fig.637, which consists of a plate of copper, mn, the ends of which are bent and soldered to a plate of bismuth, op. In the interior of the circuit is a magnetic needle movm n a 0 Fig. 637. ing on a pivot. When the apparatus is placed in the magnetic meridian, and one of the solder ings gently heated, as shown in the figure, the needle is deflected in a manner which indicates the pa age of a current from n to m, that is, from the heated to the cool junction in the copper. If, instead of heating the junction n, it is cooled by ice or by placing upon it cotton wool moistened with ether, the other junction remaining at the ordinary temperature, a current is produced, but in the opposite direction; that is to say, from m to n. In both cases the current is more energetic in proportion as the difference in temperature of the solder ings is greater. Seebeck gave the name thermo-electric to this current, and the couple which produces it, to distinguish it from the hydro-electric or ordinary voltaic current and couple. [s. 892]