Huygens' Clocks

    Huygens licensed Salomon Coster to produce clocks to his designs. The first was made in The Hague in 1657 under Huygens' personal supervision.

    Ahasuerus Fromanteel was a member of a large clockmaking family in London. In 1657, he heard about the invention of the pendulum clock and sent his son Johannes to Holland, where he worked for Salomon Coster from September 1657 until May 1658. When he returned to London, he had learned enough to enable his father to build the first pendulum clocks in England, which were advertised in Mercurius Politicus on 27 October 1658.

    The Fromanteel family improved the design of pendulum clocks and almost every clock which they produced had some new feature. They were responsible for the basic design of the mechanism used in all table and longcase clocks in the 17th and 18th centuries.

    The first improvement to clock design after the invention of the pendulum came in the late 1660s when William Clement constructed the first successful anchor escapement. The pendulum in a clock with an anchor escapement does not need to swing as far as one in a clock with a verge escapement. This improves timekeeping because variations in the size of a pendulum's swing angle only affect its period significantly if the angle is large. This reduction in the angle made by the pendulum resulted in the development of longcase clocks.

    The anchor escapement, like the verge escapement, interferes with the pendulum's motion throughout the whole of its swing, which affects its timekeeping. The 'dead-beat' escapement, invented by George Graham in 1715, reduces this problem by giving the pendulum a short impulse when it is nearly vertical and allowing it to swing almost freely for the rest of the time.

    If a piece of metal is heated, it will expand. If this happens to a pendulum, the time which it takes to swing (its period) will increase. Raising the temperature of a clock with a steel pendulum by one degree Celsius will make it lose half a second every day. The first pendulum with temperature compensation was produced in 1721. It consisted of a steel rod with a container of mercury at the bottom as at bob. If the temperature increased, the mercury would expand more than the steel, keeping the centre of mass in the same place. Later temperature-compensated pendulums, such as John Harrison's grid iron pendulum, used rods of different metals to achieve a similar effect. Later still, pendulum rods were made of materials which hardly expanded at all.