File:On a Standard Voltaic Battery (1874) (14597897017).jpg

Identifier: philtrans00454635 (find matches)
Title: On a Standard Voltaic Battery
Year: 1874 (1870s)
Authors: Clark, L.
Subjects: Proceedings of the Royal Society of London Philosophical Transactions of the Royal Society
Publisher: Royal Society of London

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needle through a known resistance, is compared with that of theearths horizontal intensity. It was determined to measure the element by bothmethods. The electrodynamometer employed was an instrument constructed for the British-Association Committee, and referred to in their Eeport for 1867, page 478. Thisinstrument had not been previously used. In the electromagnetic system, the unit length of the unit current, acting on anothersimilar current at the unit distance, exercises the unit of attractive or repulsive force.The value of the current (C) in absolute units may therefore thus be determined fromits mechanical effect; and the resistance (R) of the circuit being known, the value of the * Taylors Scientific Memoirs, vol. iii. f British-Association Eeport, 1863, pp. 116,141. ME. LATIMEE CLAEE ON A STAND AED VOLTAIC BATTEEY. 7 electromotive force (E) follows from Ohms formula, C=; or E=CR. In the instrument in question (fig. 2) the large fixed coil is double, as in the arrange- Kg. 2.
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ment given by Helmholtz and Gaugain to the tangent galvanometer, the two coils beingin parallel vertical planes at a distance apart equal to their radius; the small coil is also 8 ME. LATIMEE CLAEK ON A STANDAED VOLTAIC BATTEEY. double, and is suspended bifilarly truly central to the fixed coils, the bifilar suspension-wires being used to convey the current between the fixed and movable coilse The top of the instrument (fig. 3) is furnished with various contrivances for facilitatingthe central adjustment of the coils; these consist of two plates, forming a slide-restmovement fitted with verniers, by which horizontal motion can be given to the suspensionin any direction. The upper plate carries a circular collar, which can be rotated by atangent screw, and is graduated to 360 degrees. Into this collar fits a brass frame, Pig. 3.

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