Image: Shortt Synchronome free pendulum clock

Description: A Shortt-Synchronome free pendulum clock belonging to the US National Institute of Standards and Technology (NIST), in the NIST Museum, Gaithersburg, Maryland, USA. Invented in 1921 by William Hamilton Shortt, it was the most accurate mechanical clock ever manufactured, achieving an accuracy of around one second per year. This example was purchased by NIST in 1929 and used by physicist Paul R. Heyl in his second determination of the gravitational constant. It consists of a master invar pendulum (left) in a copper vacuum tank and a precision pendulum clock (right). The units are connected by electric wires that operate electromagnets to keep the slave pendulum in the clock synchronized to the master pendulum. The pendulum in the clock is attached to the clock's mechanism and performs the function of moving the clock's gears, leaving the master pendulum to swing virtually free of outside influence. The pendulums make one swing per second, and every 30 swings the slave clock gives the master pendulum a push to keep it swinging. Alterations to image: brightened slightly, changed from GIF to JPEG.
Title: Shortt Synchronome free pendulum clock
Credit: Downloaded 2009-12-29 from Highlights of the NIST Museum, NIST Virtual Museum, US National Institute of Standards and Technology website. No source information or copyright notice was given. https://www.nist.gov/image/p15421coll3891fulljpg
Author: Unknown authorUnknown author
Permission: Public domain because it is work of the US National Institute of Standards and Technology. Copyright notice on the website: "These World Wide Web pages are provided as a public service by the National Institute of Standards and Technology (NIST). With the exception of material marked as copyrighted, information presented on these pages is considered public information and may be distributed or copied"
Usage Terms: Public domain
License: Public domain
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