GALVANOMETER

n. Gaal-va-no am'e;lt ur. From Galvani, and i*rrpov. a measure. Fr.,galva7iotnetre. Ger., O. It., galvanometro. Sp., galvanometro. Of Schweigger, an instrument for measuring the force of an electric current, consisting e entially of a magnetic needle, which is caused to deviate by the action of the current. RuhmkorfTs instrument is an astatic g., the lower needle of which is surrounded by a great number of coils of insulated copper wire, whose two ends communicate by means of binding screws with any given source of electricity. The feeblest current causes a deviation of the needles, whose extent can be read from a graduated circle placed beneath the upper needle. The entire apparatus, which is also called a multiplier, is inclosed by a gla cylinder supported on a copper stand. [B, 21 (a, 27).] Absolute g. A variety f mirror g. in which the current-strength is measured by the amount of torsion required to bring two electro-magnets, which are mutually repelled by the action of the current, back to within a certain distance of each other. fB.l Astatic g. A g. in which, instead of a single needle, two needles are used, placed parallel to each other and in the same vertical plane, but with tlieir poles turned in opposite directions. In such a combination the action of terrestrial magnetism is almost neutralized by the opposition of the poles of the two needles, and hence the two needles swing freely under the influence of a galvanic current. |B.) Differential g. A g. in which there is a double coil of wire siirroimdinK the needle. so that two separate currents can be sent through the coils, and either in the same or in an opposite direction. In the latter case the degree of deflection of the needle measures the difference of intensity of the two currents. [ B. ] Dead-beat g. A g. in which the vibrations of the needle coir.- to rest quickly. [B.] Double K- See //. hnlmltz's ,'., in which the inatrnclic needle is susjH-iided not at tlieccnlre of the vertical coil or hand. Imt on a hori/ontal axis posing through tl entreand at a distance from the latter equal to one half the radius of the vertical coil. [Pre scott. Maxwell (B).] G. of two oil-. ll< lmlM.il/'- g. A modification of G*Ugainsg., in which the magnetic needle is suspended at a point equidistant between E, he; E*. ell; G, go; I, die; I, in; N, In; N', tank; [s. 136]