Abstract
III.
FROM this property of the Gramme machine it may be employed to measure by the method of opposing currents any electromotive force. For this purpose it is only necessary to ascertain the velocity of rotation of the ring when the equilibrium between the currents is established. This may be measured in one of two ways-by the velocimeter of Deschiens, or by a chromoscopic diapason. The mode of operating with the latter when applied to the Gfamme machine is thus described in M. Breguet's work. On the axis of the ring is mounted a small plate whose plane surface is covered with lamp-black by holding it over a candle. A tuning-fork vibrating one hundred times in a second, and carrying at one end a little style, is held in the hand, or, still better, fixed on a special support. At the precise moment that the two electromotive forces are shown by the galvanometer to be equal, the style is brought into contact with the blackened surface of the plate, upon which it traces a sinuous line. A very short contact is sufficient to give the required result. On stopping the machine, it will be seen to what fraction of the circumference ten sinuosities of the line traced on the plate correspond, from which it may be inferred in how many hundredths of a second the entire revolution of the ring has been accomplished. It is stated that if the ring in the Gramme machine be turned at a perfectly steady rate, the current produced will be more rigorously constant even than that of a DanielFs battery in good working order. Fig. 7 represents a machine constructed with electro-magnets in 1872 by M. Gramme, which, with six others of the same kind, is in use in the well-known galvanoplastic establishment of Chrislofle and Co., of Paris. These machines weigh 750 kilogrammes, and the weight of copper used in their construction is about 175 kilogrammes. With a small engine of one-horse power, one of them will deposit 600 grammes of silver per hour. By some recent modifications in its construction this machine has been improved so as to increase the weight of silver deposited per hour to 2,100 grammes, or above 41/2lbs. In Figs. 8 and 9 we have the forms of the Gramme Machine now in use for the production of the electric light. They are improvements on the machine which was tried on the Clock Tower of Westminster Palace. This machine had the defect of becoming heated while at work, and of giving sparks between the metallic bundles of copper wire and the conductors from the helices. In the machine represented in Fig. 8 these defects are said to have been completely remedied. The entire machine weighs 700 kilogrammes, and there are 180 kilogrammes of copper in the electro-magnets, and forty kilogrammes in the two rings. It produces a normal light of 500 Carcel burners; but, by augmenting the velocity, it is asserted that the amount of light may be doubled. It does not become heated, nor does it produce any spark where the brushes are applied.
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Magneto-Electric Machines * . Nature 12, 170–172 (1875). https://doi.org/10.1038/012170a0
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DOI: https://doi.org/10.1038/012170a0