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supported on spring catch K. Once every half-minute the lever is let down (in the act of giving an impulse to the pendulum P) upon the armature A. Current from any available source then passes through the series circuit of dials and the magnet M, which attracts the armature A and throws up the lever G on to its catch again.

The pendulum releases the switch by means of the 15-toothed wheel C which carries a vane D engaging with the catch K at each revolution. The hook B pivoted upon the pendulum P turns this wheel once every 30 seconds. At the moment of its release the little roller R on the gravity arm G is just above the curved end of the pallet J, down which it runs, giving an impulse to the pendulum at the moment when it passes through its zero or central position. Thus the pendulum is free at all times except in the middle of its swing ; not only is the escapement detached, but it operates while the pendulum is passing its equilibrium position, thus approximating to the conditions necessary for isochonism.

The shape of the impulse surface of the pallet J is such as to yield an impulse, beginning with extreme gentleness, increasing to a maximum at the centre of the pendulum’s swing, and diminishing in identical ratio. The switch cannot stop in closed circuit. The dials can be readily set to time by merely removing the lever from normal to retard or accelerate.

Battery warning.—A valuable feature of the system is the automatic warning of impending failure of the battery long before such failure can cause any irregularity in the working of the time circuit. When the current is insufficient to enable the magnet M to replace the gravity lever G the pendulum on its return swing to the left finds the gravity lever in its path and assists the magnet to raise it, thus prolonging the duration of the contact to a full second, which is clearly noticeable on every dial. The electrical contact, occurring at each half-minute precisely, is the only contact in the system, and it is a very perfect one. The whole of the energy required to keep the pendulum swinging being transmitted through its surfaces.

It is so designed that at each operation it transmits to aU the dials sufficient current to propel them. By a novel application of the phenomenon of self-induction, it becomes impossible for the switch to operate without doing so.

A 4240. 0.

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