Shortt–Synchronome clock

The Shortt–Synchronome free pendulum clock is a complex precision electromechanical pendulum clock invented in 1921 by British railway engineer William Hamilton Shortt in collaboration with horologist Frank Hope-Jones,[1] and manufactured by the Synchronome Company, Ltd., of London.

The Shortt clock consists of two separate units: the primary pendulum in a copper vacuum tank 26 cm diameter and 125 cm high attached to a wall,[13] and a precision pendulum clock locked to it, standing a few feet away.

The two components were linked by wires which carried electric pulses that operated electromagnets in the mechanisms to keep the two pendulums swinging in synchronism.

The vacuum tank was evacuated by a hand-operated pump to a pressure of around 30 mmHg (40 hPa)[14] to prevent changes in atmospheric pressure from affecting the rate of the pendulum, and also to greatly reduce aerodynamic drag on the pendulum, which increased its Q factor from 25,000 to 110,000,[15] thus increasing its accuracy by a factor of four.

A pendulum swinging in a vacuum without friction, at a constant amplitude free of external disturbances, theoretically keeps perfect time.

Every 15 oscillations (30 seconds), this escapement released a gravity lever which gave the secondary pendulum a push.

The falling primary pendulum gravity lever closed a pair of contacts in a second electrical circuit, which reset that lever and provided an electrical pulse back to the hit and miss synchronizer in the secondary unit.

In 1928, American inventor Alfred Lee Loomis visited the workshop of Frank Hope-Jones and was shown an almost completed 6th clock.

[18] In 1984 Pierre Boucheron studied the accuracy of a working Shortt clock kept on display at the US Naval Observatory.

[3][19] Using modern optical sensors which detected the precise time of passage of the pendulum without disturbing it, he compared its rate to an atomic clock for a month.