Page:Popular Science Monthly Volume 22.djvu/350

336, and a system adopted whereby the clock is automatically "set to time" every hour, or at such intervals as may be arranged. The apparatus can here be described only in brief. There are three essential parts, the standard clock, the distributor, and the synchronizer.

The standard clock is an astronomical regulator with mercurial pendulum and dead-beat escapement, and closes an electric circuit at the sixtieth second of each hour. Another regulator, technically called "Lobby," is for use in case of accident to "Standard." They are so connected that a single failure of "Standard" to send out a signal at the proper time brings "Lobby" into action for the next signal, and, in order that "Lobby" may always be ready for service, an intentional breakdown of "Standard" occurs automatically at eight each morning, and the nine o'clock signal is sent out by "Lobby"; which of the two is in operation is shown by indicators connected with the clocks (Fig. 10). Should a breakdown occur, the indicator of "Standard" would show missed, and that of "Lobby" at work.



The error of the standard clock is determined daily by comparison with the Greenwich signal. An ordinary dotting chronograph is set to the standard clock, and the Greenwich signal makes a dot on the chronograph-dial which gives at once the error of the standard and can be read off at leisure. It is corrected by electric means. The pendulum carries a small permanent magnet which swings over a resistance-coil about inch distant. The coil is connected with the commutator in the test-box (Fig. 11), consisting of a clock commutator with plugs for "Standard" and "Lobby," a current commutator with plugs for "Fast" and "Slow," and a small time-piece, shown at the top. The time-piece has only a minute-hand, and is made so as to stop itself and break circuit at XII, but closes circuit when running. The working is thus: Suppose "Standard" is found to be slow. Plugs are inserted for "Standard" and "Slow," and the hand of the time-piece is set back a required number of minutes. It then runs to XII and stops. In this interval the action between the magnet and the coil has exactly corrected the standard clock. For every second of