Image: Ellicott pendulum

Description: Drawing of an Ellicott pendulum, a temperature compensated pendulum invented by British clockmaker John Ellicott in 1752, used in some small French mantel clocks in the 1800s, from a French physics book from 1878. Around a foot long. The central rod (f) is made of iron while the two peripheral rods (c) are made of brass, which has a higher thermal expansion. With a rise in temperature, the central rod expands and gets longer, but the two brass rods expand more and press down on the levers (a), which press up on the pins (t) attached to the bob, raising the bob. This compensates for the lengthening of the central rod, keeping the bob at the same distance from the pendulum pivot. Therefore the pendulum's length to its center of mass, and its period of swing, stays constant with changes in temperature. Because of the more complicated mechanism its temperature compensation was probably inferior to the more widely used gridiron pendulum, and the Ellicott pendulum was not used in many clocks. Alterations to image: Removed caption, rotated to compensate for scanning error, converted from JPG to PNG.
Usage Terms: Public domain