Page:Elementary Text-book of Physics (Anthony, 1897).djvu/327

§ 271] Volta described in 1800 an arrangement for utilizing these properties of bodies for the production of continuous electrical currents. He placed in a vessel, containing a solution of salt in water, plates of copper and zinc separated from one another. When wires joined to the copper and zinc were tested, they were found to be at different potentials, and they could be used to produce the effects observed by Galvani. The effects were heightened, and especially the difference of potential between the two terminal wires was increased, when several such cups were used, the copper of one being joined to the zinc of the next, so as to form a series. This arrangement was called by Volta the galvanic battery, but is now generally known as the voltaic lattery.

Volta observed that if the terminals of his battery were joined the connecting wire became heated.

Soon after Volta sent an account of the invention of his battery to the Royal Society, Nicholson and Carlisle observed that, when the terminals of the battery were joined by a column of acidulated water, the water was decomposed into its constituents, hydrogen and oxygen.

In 1820 Oersted made the discovery of the relation between electricity and magnetism. He showed that a magnet brought near a wire joining the terminals of a battery is deflected, and tends to stand at right angles to the wire. His discovery was at once followed up by Ampere, who showed that, if the wire joining the terminals be so bent on itself as to form an almost closed circuit, and if the rest of the circuit be so disposed as to have no appreciable influence, the magnetic potential at any point outside the wire will be similar to that due to a magnetic shell.

In 1834 Peltier showed that, if the terminals of the battery be joined by wires of two different metals, there is a production or an absorption of heat at the point of contact of the wires, depending upon which of the wires is joined to the terminal the potential of which is positive with respect to the other. This fact is referred to as the Peltier effect.

271. The Electrical Current.—In 1833 Faraday showed