Page:Encyclopædia Britannica, Ninth Edition, v. 6.djvu/35

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It should be understood that under this term two, or wo may say three, very different things are comprehended. The first is a mere clock movement, i.e., the works of a clock without either weight or pendulum, which is kept going by electrical connection with some other clock of any kind (these ought to be called electrical dials, not clocks) ; the second is a clock with a weight, but with the escape ment worked by electrical connection with another clock instead of by a pendulum ; and the third alone are truly electrical clocks, the motive power being electricity instead of gravity; for although they have a pendulum, which of course swings by the action of gravity, yet the requisite impulse for maintaining its vibrations against friction and resistance of the air is supplied by a galvanic battery, instead of by the winding up of a weight. If you take the weight off a common recoil escapement clock, and work the pallets backward and forwards by hand, you will drive the hands round, only the wrong way ; consequently, if the escapement is reversed, and the pallets are driven by magnets alternatively made and unmade, by the well-known method of sending an electrical current through a wire coil set round a bar of soft iron, the contact being made at every beat of the pendulum of a standard clock, the clock without the weight will evidently keep exact time with the standard clock ; and the only question is as to the best mode of making the contact, which is not 