Movement No. 68 presents a beautifully self-contained intermittent motion mechanism — a single-tooth driving wheel that advances a notched wheel by exactly one notch per revolution, while simultaneously serving as its own locking device without requiring any separate stop mechanism. The driving wheel B has a single tooth A projecting from its otherwise smooth, circular circumference. The driven wheel C has a series of evenly spaced notches cut into its circumference, and between each pair of notches, a hollow or concave recess is cut into the wheel’s surface. The operation is elegant in its simplicity: as driving wheel B rotates, its single tooth A sweeps around until it enters one of the notches of wheel C, pushing it forward by exactly one notch-space — one precise step. The rest of wheel B’s circumference is smooth and circular with no more teeth, so wheel C advances only during the brief interval when tooth A is engaged, and remains stationary for the remainder of the revolution. The ingenious self-locking feature is built into the geometry of both wheels: the smooth circular portions of driving wheel B’s circumference precisely fit into the concave hollows cut between the notches of wheel C. While tooth A is not in engagement — which is most of each revolution — the circular body of wheel B nests snugly into one of these hollows, physically preventing any rotation of wheel C. There is no separate detent, spring, or stop lever needed — the geometry of the two wheels themselves provides complete locking. This self-locking single-tooth mechanism is a direct conceptual relative of the Geneva stop mechanism used in film projectors and precision instruments, offering the same intermittent advance and positive locking through elegant geometric integration.
68. The single tooth, A, of the driving-wheel, B, acts in the notches of the wheel, C, and turns the latter the distance of one notch in every revolution of C. No stop is necessary in this movement, as the driving-wheel, B, serves as a lock by fitting into the hollows cut in the circumference of the wheel, C, between its notches.