There are now two rival systems of electric clocks in this country—one invented by Wheatstone,- patented 1869, and "exploited" by the British telegraph company; the other invented by Ritchie, clock-maker, Edinburgh (patented 1872).
Wheatstone's primary clock is a gravity clock with a pendulum bob like Bain's, with fixed magnet or magnets coincident with the arc of the pendulum. When the bob is driven by the weights of the clock from the one end to the other, a current is induced in the coil of the bob, according to the well-known principles of magneto-electricity (q.v.). When the bob returns, a current is created in the opposite direction. The copy ing clocks or dials have a mechanism similar to Wheatstone's step-by-step telegraph, and each oscillation of the primary pendulum, by generating a current, drives them one step onwards. The pendulum of the primary clock, along with the magnets, is a magneto-electric machine driven by the weight of the clock, and moving all the copying clocks. The work the pendulum has to do, however, interferes with its isochronism, and hence the primary clock has to be kept under the control of a standard clock by an ingenious contrivance. Ritchie takes advantage of the important feature of Jones's sys tem, viz., that of having a standard clock free from all electric impulses, an ordinary astronomical clock whose pendulum only makes and breaks contact in a galvanic circuit. Thus all the perfection of clock-making is fully utilized. The standard clock, as in Jones's system, is placed in circuit with the copying clocks. But here his system differs.
Instead of having weights and a train of wheel-work in the copying clocks, he has simply a Bain's pendulum driving an escapement (also patented) similar to Bain's original clock. The mechanism is thus simple and cheap, and each clock has got in its pendu lum a store-house, so to speak, of individual energy under electric maintenance and control, and cannot without a grave accident be put out of order. It is inferior to Wheatstone's system in having battery power to maintain. But this does not cost much. From 3 to 5 Daniell's cells will work a copying clock in any part of the same town, and need only to be renewed once in six months, Ritchie's system is in some respects more trustworthy than Wheatstone's. The delicate action of the step-by-step motion is liable to accidental derangement. Now Ritchie's sympathetic clock has a heavy pendulum, and can be used in public dials to withstand even the action of the wind on the hands. Again, there is no need of a magneto-electric clock and a standard clock. The standard clock does all. The perfect success of Ritchie's system has been proved in Edinburgh and elsewhere. In Edinburgh, several public clocks on the sympathetic system have been in action for some years, and have not varied a second. The success of Ritchie's system is much indebted to an invention of Edward Sang, by 'which the length of the suspend ing spring of the standard pendulum can be altered, and the rate of the clock regulated without stopping it. Ritchie in 1864 also patented a magneto-electric system which, however, he has never worked.