15. The arc of vibration is more equal in this than in any other gravity escapement.
16. It is not so liable to stop in consequence of a diminution of arc from the variation of motive force in train.
17. It will answer for regulators as well as for turret clocks, its arc of vibration being from 1° to 3°.
DOUBLE THREE-LEGG'D ESCAPEMENT.
This escapement is chiefly designed for turret clocks with heavy dial-work requiring much power on the scape-wheel. The peculiarity consists of two locking wheels with one set of lifting pins between them. The wheels are set so that the pallets may lie between, and the pallets fall with the pendulum clear of all other contact. The pallet D for instance has its stop in front for the wheel A B C to act upon, and the E stop is acted upon only by a b c, the E and A being on different planes. In this escapement, by making the teeth longer and the pallets shorter, the resistance of the pendulum is much reduced, and the stride of the pallets being wider, the actual weight required of them is considerably lessened,—a point of some importance.
THE REMONTOIRE.
is an invention which, being derived from the French, still bears its French title, and consists of either a train remontoire, or a gravity or remontoire escapement, in which latter the impulse is not given to the pendulum directly by the clock-train or weight, but by some small weight lifted up or a small spring bent up by the clock-train at every beat of the pendulum, so as to secure a uniform and constant impulse, the remontoire weights being lifted either faster or slower according to need. The train remontoire differs from the escapement but slightly, the chief difference being that the small weight or spring which gives the impulse to the pendulum is not wound up at every beat, but at some larger interval, seldom more than half a minute. Its effect is to counteract the various errors to which large clocks driving heavy hands are always liable, and to diminish the friction which arises from the use of heavy weights—these being in very large clocks almost incredibly heavy; for instance, the weights used by me for my clock in the Great International Exhibition of 1862 amounted to more than two tons. Whatever the cause of inequality of movement in the clock, whether it be dust or dirt, or insufficient oil, or whether it be wind delaying or expediting the progress of the hands on the dial, the remontoire regulates and counteracts.