To make a clockwork metronome, a pendulum must be employed. The usual arrangement is to have a short lead bob pendulum, about 3 in. long, pivoted upon an arbor. The rod is extended upwards, and this upper portion is fitted with a sliding weight to adjust the speed. The higher the top weight is raised the slower the pendulum goes. The escapement is shown in the accompanying sketch. The 'scape wheel teeth are straight pins, and they rest upon two flat steel discs fixed on the pendulum arbor. These discs are cut, and the edges bevelled off, to give the impulse alternately in each direction. Thus, one of the pins of the 'scape wheel falls upon the face of disc A and, passing the bevelled edge, gives the pendulum an impulse to the right and falls upon the second disc B. As the pendulum returns, this tooth gives impulse, by means of the bevel on B, in the opposite direction to A, and the next 'scape tooth falls upon A, and so on. An American drum-clock train will do. The scape wheel must be taken away, and the next wheel before it converted into a 'scape wheel by breaking out some of the teeth, leaving one in every three, and bending them forward a little.

Clockwork Metronome.