the general contrivance in a timepiece, by which the pressure of the wheels, which move always in one direction, and the vibratory motion of the pendulum or balance-wheel, are accommodated to each other. By this contrivance the wheelwork is made to communicate an impulse to the regulating power, which in a clock is the pendulum and in a watch the balance wheel, so as to restore to it the small portion of force which it loses in every vibration, in consequence of friction and the resistance of the air. The leading requisite of a good escapement is that the impulse communicated to the pendulum or balance wheel shall always be the same, notwithstanding any irregularity in the train of wheels. See CLOCK; WATCH.