Behind The Scenes: Time, Please!

Early Chimes
The earliest clocks as we understand them date from the 14th century. The first known public clock that struck the hours was built in Milan in 1335. The oldest working clock in the world – constructed in 1386 – is at Salisbury Cathedral. Like most clocks of this type, it has no face, only a mechanism to strike the hours.

Smooth Operator
At the heart of all mechanical clocks is an escapement – a ratchet and rocking lock combination that allows movement in one direction only. Many types of escapement were invented, mostly driven by a pendulum or a spring. The most successful have been those devices that minimise friction and associated wear. Modern lubricants in high-class Swiss watches last five years before the works need attention.

Feel the Force
The first electric clocks appeared in the 19th century. They used an electric motor to power a pendulum and spring. In 1918, the synchronous electric motor was applied to clocks. A synchronous motor is designed to run in accordance with the frequency of the power source. Conveniently, domestic electricity alternates at 60 hertz (cycles per second), so a relatively simple gearing system is all that's needed to move the clock's hands. Quartz crystals, which can vibrate at 100,000 hertz when a current is passed through them, were first used in clocks in 1929. A properly maintained quartz clock is accurate to within one second over 10 years.

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