73. To the driving-wheel, D, is secured a bent spring, B; another spring, C, is attached to a fixed support. As the wheel, D, revolves, the spring, B, passes under the strong spring, C, which presses it into a tooth of the ratchet-wheel, A, which is thus made to rotate. The catch-spring, B, being released on its escape from the strong spring, C, allows the wheel, A, to remain at rest till D has made another revolution. The spring, C, serves as a stop.