Clocks Worked from the Electric Supply Mains | Nature

WHEN a house is supplied with alternating current electricity on the time-controlled system, it is possible to use an electric clock which keeps almost exact Greenwich time, the error being at the most only a few seconds per week. The principle used in their working is that of the synchronous motor, which keeps in exact step with the frequency of the alternating current, and the frequency is controlled by a ‘master controller’ regulated by Greenwich time so as to make it easy to synchronise the generators connected with the network. The clocks cost from thirty shillings upwards, depending on the size and design of the case used. The first synchronous clocks were used in the United States about twelve years ago, and, from their inventor, were called Warren clocks. In America more than six million have been sold and in Great Britain about a quarter of a million (Electrical Industries, March 16). They are made of two types. In one class the clock is self-starting and in the other it has to be started if the current stops even for a fraction of a second. In the latter class a red disc usually appears on the rare occasions when it stops. The clocks require only about half the power taken by an ordinary electric meter, and so the cost of running them is only a few pence a year. In America the sales are usually made by the electric supply companies, but in Great Britain the dealers who sell electric accessories and the clock-makers have taken up their sale. As a rule, the clocks require no attention for many months. In districts supplied by suitable alternating current, it is probable that this type of clock will supersede the escapement and pendulum type. Electric movements can be obtained to replace the ordinary clockwork movement of an existing clock.