Big clocks

    There was a mechanical clock working in Milan by 1335. It is the first for which there is firm evidence although there are suggestions that there were some mechanical clocks in existence before 1300. By 1350, several mechanical clocks were working in Italy. The oldest surviving mechanical clock in Britain and probably anywhere was installed in Salisbury Cathedral in 1386. By 1392 another mechanical clock was installed at Wells Cathedral.

    The mechanism for the Well's clock was replaced in 1838. However the original is now in the Science Museum, along with steel bells added in the 1880s.

    Mechanical clocks brought about a change in the way in which time was measured. Before the 14th century, the system of dividing a period of one day and one night into 24 equal hours was only used by astronomers. For most people, the periods of daylight and darkness were each divided into 12 "temporal hours", which varied in length throughout the year. This is convenient with sundials but the speed of a mechanical clock does not vary in this way. By the end of the 15th century, most people in Europe had switched to the modern system and the design of sundials had changed to use it as well.

    In 1386, a large mechanical clock was installed at Salisbury Cathedral. It is the oldest surviving mechanical clock in Britain and probably anywhere. Bishop Erghum moved from Salisbury to Wells in 1388, four years before the Wells Cathedral Clock is thought to have been constructed. It seems likely that he had the two clocks made by the same people.

    The Salisbury Clock is not as advanced as the one at Wells. It has no face and only strikes the hours. Like the Wells Cathedral clock, it originally used a foliot balance with a verge escapement. At the end of the 17th century, these were replaced by a pendulum and a recoil escapement. Holes on the clock's frame show that these were later replaced again. In the 18th century, the bell tower which had housed the clock was demolished so the clock was moved to the Cathedral's central tower. In 1884, a new clock was installed and the old one was forgotten. It was re-discovered in the tower in 1929 and put on display in the Cathedral's North transept. In 1956, the clock was restored to its original condition and made to work again. Its pendulum and recoil escapement were replaced by a new foliot balance and verge escapement.

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