Huygens' Clocks

It is thought that, in 1582, Galileo watched a lamp swinging from a long rope in Pisa Cathedral. By timing the swings against his pulse, he found that their period hardly changed, however far the lamp was swinging. In 1637, he had the idea of using a swinging weight to control the speed of a clock by allowing a wheel to rotate by a certain amount every time the weight swung in one direction.

In 1637, he had the idea of using a swinging weight to control the speed of a clock by allowing a wheel to rotate by a certain amount every time the weight swung in one direction. By that time, he had gone blind so he developed his idea with his son Vincenzo and his pupil Viviani, who drew this diagram in 1659. Galileo himself had died in 1642 and his son died in 1649. The son had begun to construct the clock but nothing survives from that time. Models of it have been made more recently.

Although it was not successful, Galileo's work is important because it was the first known attempt to use a pendulum to control a clock.

The first pendulum clock was produced in December 1656 and was far more accurate than any previous clock. This clock could run for about three hours with an error of only one second whereas clocks with foliot balances would gain or lose that much every few minutes.

Although Galileo had imagined a new kind of escapement when he had the idea of using a pendulum in a clock, Huygens' real clock used the traditional verge escapement, powered by a weight which fell five centimetres per hour. The oscillating part of a verge escapement needs to swing through a large angle and Huygens realised that if a pendulum swung through such a large angle, its timekeeping would suffer. To avoid this problem, he used a pair of gear wheels at the top of his clock to make the verge swing through a larger angle than the pendulum.

The timekeeping of the clock could be regulated by twisting the nut at the bottom of the pendulum to move the lead weight up or down.

Before the invention of the pendulum, few clocks had minute hands because, even if they were checked against the sun or stars once every day, the time which they showed could still be wrong by several minutes. Huygens' new clock was reliable enough for him to fit it with a minute hand and a second hand but, because they were relatively new, it was not obvious where they should go.

On this clock, the hour hand is the shorter hand in the main dial and rotates twice every day as usual. The minute hand rotates anticlockwise once every hour in the small dial at the bottom of the clock. The longer hand in the main dial is the second hand, which takes five minutes to revolve. Second hands did not become common until the anchor escapement further improved clock accuracy.