ELECTRIC CLOCES. An electric clock is one whose mechanism is, in some way, either actu ated or controlled by electricity. There are two types of electric clocks—(1) Independent clocks, whose mechanism is kept in operation by elec tricity : (2) systems of clocks Nthich are con nected with a central or primary clock by an electric circuit, and are so arranged that either (a) the primary clock regulates its movements, at stated intervals, by forcibly moving the hands by an electric current into the proper position, or (h) the primary clock directly the hands of the secondary clocks, which are simply dials without independent machinery.
Clocks of the first class usually have some electromagnetic attachment applied to the mech anism, which keeps them constantly wound up: in other words, they are constructed like ordi nary clocks, except that they are self-winding. The first self-winding clocks were made as early as H55 by Alexander Bain, who applied electro magnetic attachments to the bob of the pendu lum, which, in obedience to contacts connected with the pendulum itself, attracted it to and fro. Since that time many other means of applying the electric current to keep a clock running have been devised, and hundreds of patents for the same have been taken out in England and America : but, as yet. this form of electric clock has proved of little practical value. An other form of independent electric clock was put in operation in 1:=;96, in the laboratory of Durham College, North Carolina. The clock is run directly by electromagnets, which are actu ated by a current from an earth battery. The Pendulum is swung by the electric current, and it is this which moves the clock. The works and dial are placed on the pendulum and swing with it.
In the second class of electric clock the object is to keep a system of clocks correct by an automatic connection with a central and standard timekeeper. It is probable that this
method of time-service will be rapidly extended, until not only public buildings, but private offices are supplied with time from a central clock, as they now receive a common service in heat, light, power, water, etc. Instead of employing the central clock simply as a regula tor, it may be adopted as an actual propeller of the clocks on its circuit, and the secondary clocks become mere dials for indicating time.
Certain difficulties have been encountered in the electric connection between the main and sec ondary clocks, due, among other things, to in duced currents from crossed telephone or other electric wires. In view of these difficulties, it has been proposed by prominent electricians that the Marconi wireless system be applied to clocks, and thus obviate the faults of the old system. Though the general adoption of elec trically controlled clocks is a development of the close of the nineteenth century. they have long been the subject of experimentation. In 1S37 Alexander Bain began to experiment on electrically driven synchronous clocks, and in 1846 his system was in use between Glasgow and Edinburgh.
I'xixmATic CLocKs. A system of synchronous clocks which ate connected with the central controlling clod: by compressed air instead of electricity is called pneumatic. The clockwork in the City Hall at Philadelphia, described above, is of this type. The movement of the cen tral clock compresses air in the connecting tubes. and causes a bellows to expand at each dial, thus moving the hands.