A gridiron pendulum was a temperature-compensated clock pendulum invented by British clockmaker John Harrison around 1726.[1][2][3][4] It was used in precision clocks. In ordinary clock pendulums, the pendulum rod expands and contracts with changes in temperature. The period of the pendulum's swing depends on its length, so a pendulum clock's rate varied with changes in ambient temperature, causing inaccurate timekeeping. The gridiron pendulum consists of alternating parallel rods of two metals with different thermal expansion coefficients, such as steel and brass. The rods are connected by a frame in such a way that their different thermal expansions (or contractions) compensate for each other, so that the overall length of the pendulum, and thus its period, stays constant with temperature.
The gridiron pendulum was used during the Industrial Revolution period in pendulum clocks, particularly precision regulator clocks[1] employed as time standards in factories, laboratories, office buildings, railroad stations and post offices to schedule work and set other clocks. The gridiron became so associated with accurate timekeeping that by the turn of the 20th century many clocks had pendulums with decorative fake gridirons, which had no temperature compensating qualities.[1][4]
- ^ a b c Turner, Anthony; Nye, James; Betts, Jonathan (2022). A General History of Horology. Oxford University Press. p. 321. ISBN 9780192609366.
- ^ Baker, Gregory L. (2011). Seven Tales of the Pendulum. Oxford University Press. pp. 79–82. ISBN 9780191004841.
- ^ "Clock". Encyclopaedia Britannica, 11th Ed. Vol. 6. The Encyclopaedia Brittanica Co. 1910. p. 539. Retrieved 7 July 2024.
- ^ a b Matthys, Robert J. (2004). Accurate Clock Pendulums. Oxford University Press. pp. 8–10. ISBN 9780198529712.