gal van ology

[Pref. galvano-, and Gr. logos discourse.] A description of galvanism; a treatise on its phenomena. găl-văn-ô-măg-net'-ic, a . [Pref. galvano- , and Eng. magnetic .] Elect. The same as Electromagnetic (q. v.). găl-van-om-é-ter, s. [Pref. galvano- , and Gr. metron =a measure.] Elect. Machine : A multiplier; a very delicate apparatus for determining the existence, direction, and intensity of currents. It was invented by Schweigger, in Germany, in 1819, just before Ersted, in Denmark, in the same year, discovered the law of directive action, which a fixed current excites at a distance on a magnetic needle. In connection with the construction of the Indicator telegraph (q. v.), Ampére, Arago, Schilling, Geu , Weber, Alexander, all used the principle, but it was carried out in a superior manner to any by Cooke and Wheat stone in 1837. The galvanometer consists of a magnetic needle suspended by a filament of silk, and surrounded in the plane of the magnetic meridian by a copper wire, forming a complete circuit round the needle in the direction of its length. The actions of the four branches of the circuit, give the North Pole the same direction. The coiling of the copper wire in the direction of the needle multiplies the current. By making several, though not an indefinite number of circuits, all insulated, the action of the instrument becomes more powerful, and the deflection of the needle greater. If there their coils carefully insulated by means of silk and shellac, currents of high intensity will be generated. IMG:content-0301.png:[blocks in formation] (1) Differential galvanometer : Elect. Mach.: An instrument designed to ascertain a difference in the intensity of two currents. It consists of a needle like that in an ordinary galvanometer, round the frame of which are coiled two wires of the same kind and size, completely isolated from each other, and with binding screws, so that separate currents can be pa ed through each of them. If the currents are of the same intensity, but in different directions, there is no de flection, but, where the needle is deflected, one of the two currents differs from the other. (2) Marine galvanometer . Elect. Mach .: A galvanometer designed to test the insulation of submarine cables, and at the same time unaffected by the pitching and rolling of the ship. It consists of several you sand coils of copper wire-insulating. In the center of the coil is a slide carrying the magnet; it is attached to a mirror of thinly silvered gla . A single fiber of silk is stretched acro the slide; to this the mirror and magnet are attached in such a manner that the fiber exactly pa es in every position through the center of gravity. The slide fits into a groove in iron case, with the aperture in front, and a wrought the coil, and the whole is inclosed within a wrought iron lid on the top. There are also an adjusting magnet and a scale.