Components of the first European mechanical clocks

In the most general terms, the medieval European mechanical clock consisted of four components: (i) weight drive; (ii) a mechanism for transmitting the energy through a gear train; (iii) an escapement or regulating mechanism; (iv) an indicating mechanism in the form of a striking or pointing contrivance. Only the escapement and regulating mechanism was truly an innovation. The earliest clocks used the verge-and-foliot escapement, in which the motion of a weight-driven axle is impeded in such a way that the axle’s uniform rotation is suitable for use as a time standard. An escape wheel, mounted onto the axle or linked to it via a gear train, alternately blocks and releases the verge by means of two pallets attached to the verge at a right angle to each other. Mounted on top of the vertical verge is the foliot, a scale-like beam. By pushing on one pallet, the escape wheel moves the verge and the foliot in one direction until the other pallet stops the motion and reverses the direction of the rotation. The result is a unidirectional force producing a self-reversing action.

Commentary. Philipp Nothaft (May-June 2019)