Seconds pendulum

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Longcase clock with a seconds pendulum.
The seconds pendulum, with a period of two seconds so each swing takes one second

A seconds pendulum is a pendulum whose period is precisely two seconds; one second for a swing in one direction and one second for the return swing, a frequency of 1/2 Hz.

At standard gravity its length is 0.994 m (39.1 in). This length was determined (in toises) by Marin Mersenne in 1644. In 1660, the Royal Society proposed that it be the standard unit of length. In 1675 Tito Livio Burattini proposed that it be named the meter. In 1790, one year before the metre was ultimately based on a quadrant of the Earth, Talleyrand proposed that the metre be the length of the seconds pendulum at a latitude of 45°.[1] This option, with one-third of this length defining the foot, was also considered by Thomas Jefferson and others for redefining the yard in the United States shortly after gaining independence from the British Crown.[2]

In 1670 the seconds pendulum was employed by William Clement in his improved version of the original pendulum clock by Christiaan Huygens, creating the longcase clock which could tick seconds.[3]

See also[edit]


  1. ^ Seconds pendulum
  2. ^ Cochrane, Rexmond (1966). "Appendix B: The metric system in the United States". Measures for progress: a history of the National Bureau of Standards. U.S. Department of Commerce. p. 532. 
  3. ^ Long Case Clock: Pendulum