Page:Popular Science Monthly Volume 22.djvu/175

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TIME-KEEPING IN LONDON.

hollow galvanic coil, called "the accelerating or retarding coil," fastened to the clock-case and operated by a special battery. The attraction or repulsion, between the magnet and the coil, produced by sending currents in opposite directions, gives any required acceleration or

PSM V22 D175 Mean solar standard clock arrangement at greenwich.jpg
Fig. 5.—Arrangement for correcting Mean Solar Standard Clock at Greenwich.

retardation to the pendulum. Care must, of course, be taken that the correction be not made too quickly, else the clock, instead of being controlled by the current, will break away from control, and the error will be increased. It is now so arranged that the current will produce