Huygens' Clocks

    Although Huygens' first clock was a better timekeeper than any previous clock, he wanted to improve it further.

    He knew that the time of swing of a pendulum was not perfectly constant. It changes slightly if the angle of swing changes. He set out to examine the working of a pendulum and by 1659, he had calculated the motion mathematically.

    He proved that if the angle of swing is small, changes to it do not have much effect on timekeeping. This gives a long pendulum an advantage over a short one.

    He also showed that the time of swing of a pendulum could be made the same for all angles of swing if the length of the pendulum was altered as it swung.

    In 1673, Huygens built a clock with a modified pendulum. The top of the pendulum was made of flexible wire which would swing against curved metal cheeks, altering the pendulum's length as it swung. By making the cheeks a special shape called a cycloid, Huygens was able to make the time of the swing equal for all angles. Because the pendulum could now swing through a large angle, there was no need for the gears which had been used in the escapement of the 1656 clock.

    Unfortunately, the pendulum moving against metal cheeks caused more problems than it solved. It went out of use when the anchor escapement was invented because this did not need its pendulum to swing through a large angle.

    Huygens spent many years producing different mechanisms to regulate the speed of clocks because he did not realise how successful his pendulum design would become. One of his interesting ideas was a kind of pendulum which swung round in horizontal circles rather than backwards and forwards. Huygens had this idea in 1659-1660 and built a working clock in 1667-1668. Because the motion of the pendulum was already circular, no escapement was needed for it to drive a clock - just gears. The result was a clock which made no ticking sound.