So long ago as the year 1840 Sir Charles Wheatstone read a paper before the Royal Society in which he described an apparatus for controlling any number of clocks by one standard clock at a distance away. The principle was, that at each beat of the standard clock an electric current was sent from it through a wire to the clocks to be worked by it or governed; and this current made an electro-magnet attract a piece of iron each time it was sent; and this piece of iron moved backwards and forwards two pallets, something like those of an ordinary clock, which turned a wheel, and so worked the clock. Instead of a spring or weight being used to work it regulated by the pallets, the pallets moved the clock themselves, and of course keep time with the standard clock. Sir Charles Wheatstone in this most valuable pioneer paper, indicates several modifications of this plan. He proposed to the Astronomer-Royal to test his method by using the then new telegraph line to Slough, but the idea was not carried out.
This method of _driving_ clocks by electricity naturally required considerable battery power, and in the more modern systems the clocks are simply _controlled_, and not _driven_, by electric currents.
A very pretty method of regulating clocks by a standard clock is that in use at Edinburgh. On the pendulum rod of the clock to be regulated, and low down on the same, is a coil of fine covered wire wound round a short tube. Two permanent magnets are placed in line with each other, with their N or S ends close together and the other ends attached to the clock-case, in such a manner that the coil, on swinging with the pendulum, can slide over the magnets without touching. The terminal wires of the coil are led up to near the point of suspension of the pendulum, so as not to affect its swing, and the regulating current is sent through a wire like a telegraph wire from the standard clock, and from this wire round the coil and then to the earth, or back by another wire. Currents are sent through the wires in contrary directions during each successive second, so that the current in the coil flows in one direction during its swing from, say, right to left, and in the contrary direction when swinging from left to right; the effect of the current flowing in one direction is to cause one magnet to repel the coil off it, and the other to attract it over it, so that there is a tendency to throw the coil from one side of its swing to the other, and back again when the current is reversed. A little consideration will make it clear that if the pendulum tries to go too fast the coil will tend to commence its return swing before the current assisting the previous swing has stopped, and it will therefore meet with resistance, and be brought back to correct time.