. The practical telephone handbook and guide to the telephonic exchange . mploy a reflecting galvanometer such as the Kelvin Astatic Galvanometer. A very good form of this, made by MessrsNalder, is shown inFig. 425. It consistsof four fine wire coilshinged to an uprightbrass plate, two at thetop and two below, soas to form, as it were,two larger coils, thewhole being wound toabout 6000 these coils aresuspended, by meansof a fibre of raw silk,two sets of very smallmagnets, one in eachcoil, each set beingcemented on the backof a circular disc about f inch in diameter, an aluminiumvan
. The practical telephone handbook and guide to the telephonic exchange . mploy a reflecting galvanometer such as the Kelvin Astatic Galvanometer. A very good form of this, made by MessrsNalder, is shown inFig. 425. It consistsof four fine wire coilshinged to an uprightbrass plate, two at thetop and two below, soas to form, as it were,two larger coils, thewhole being wound toabout 6000 these coils aresuspended, by meansof a fibre of raw silk,two sets of very smallmagnets, one in eachcoil, each set beingcemented on the backof a circular disc about f inch in diameter, an aluminiumvane intended to steady the movements being connected tothe combination. The two sets of magnets are rigidly joinedtogether in the same plane, but so that the north poles of thetop set are over the south poles of the lower set, this formingan astatic combination, by means of which the earths actionis neutralised. In the centre between the two double coilsis an opening, in which is a small glass mirror fastened so asfco move with the magnet needles. The coils are so joined. iii jok Fig. 425.—Kelvin Mirror Galvanometer ELECTRICAL MEASUREMENTS 45* up that a current passing through all, tends to turn thecombination in the same direction. The terminals of theinstrument are fixed on an ebonite base, fitted with spiritlevels and levelling screws, and the coils, etc., are covered witha case having glass sides. On top of the instrument is apair of scissors adjusting magnets, by means of which theastatic system can be very readily directed, and the sensibilityaltered. About 3 feet away from the front of the instrument is set a
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Keywords: ., bookcentury1900, bookdecade1900, booksubjecttelephone, bookyear19
