Striking clock
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A striking clock is a clock that sounds the hours on a bell or gong.
The striking feature of clocks was at one time sometimes more important than their clock faces; some early clocks struck the hours, but had no public dials to enable the time to be read. Many early clocks struck up to 24 strokes, particularly in Italy, where the 24 hour clock, keeping Italian hours, was widely used in the 14th and 15th centuries. The 12 hour clock, and consequently 12 hour striking, became more widespread, particularly in Northern Europe and England, and eventually became the standard.
A typical striking clock will have two gear trains, because a striking clock must add a striking train that operates the mechanism that rings the bell in addition to the timekeeping train that measures the passage of time.
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[edit] Passing strike
The most basic sort of striking clock simply sounds a bell once every hour. This sort of striking clock is called a passing strike clock. It is far simpler to create such a clock; all that must be done is to attach a cam to a shaft that rotates once an hour; the cam raises and then lets fall a hammer that strikes the bell. Such clocks were the earliest striking clocks; they rang once for each canonical hour, and were used as reminders to summon monks or nuns to their prayers. This sort of striking is still found in some skeleton clocks. It does not require a separate gear train to arm and release the single stroke sounded.
However, early in the history of European clocks, it was considered desirable to have striking clocks that struck the bell multiple times to count the hours. Some of the earliest clocks, such as the astronomical clock designed by Richard of Wallingford, struck up to 24 times. The famous clock of the Beata Vergine (later San Gottardo) in Milan, built around 1330, was one of the earliest recorded that struck a bell a number of times to tell the time (not just striking once on each hour). In 1335, Galvano Fiamma writes: "There is there a wonderful clock, because there is a very large clapper which strikes a bell 24 times according to the 24 hours of the day and night, and thus at the first hour of the night gives one sound, at the second two strokes, and so distinguishes one hour from another, which is of greatest use to men of every degree."
[edit] Counting the hours
[edit] Countwheel
Two technologies have been devised by clockmakers to enable striking clocks to correctly count out the hours. The earlier technology is called countwheel striking. This uses a wheel that contains notches on its side, spaced by unequal, increasing arc segments. This countwheel governs the rotation of the striking train. When the striking train is released by the timekeeping train, a lever is lifted from a notch on the countwheel; the uneven notches allow the striking train to move only far enough to sound the correct number of times, after which the lever falls back into the next notch and stops the striking train from turning further.
The countwheel has the disadvantage of being entirely independent of the timekeeping train; if the striking train winds down, or for some other reason the clock fails to strike, the countwheel will become out of synch with the time shown by the hands, and must be resynchronized by manually releasing the striking train until it moves around to the correct position. Countwheel striking was the original method of counting the hours. It has existed since the fourteenth century.
[edit] Rack striking
In the late seventeenth century, rack striking was invented. Rack striking is so called because it is regulated by a rack and snail mechanism. The distance a rack is allowed to fall is determined by a snail-shaped cam, thereby regulating the number of times the bell is allowed to sound.
The snail-shaped cam is a part of the timekeeping train that revolves every twelve hours; often, the rack is attached to the part that drives the hour hand of the clock. Like the countwheel, the cam stops the striking train when the appropriate count has been reached. The diameter of the cam is largest at the one o'clock position, permitting the rack to move only a short distance, after which the striking train is stopped; it is smallest at the twelve o'clock position, which allows the rack to move the farthest.
Because it is linked to the timekeeping train, rack striking seldom becomes desynchronized from the hands. Rack striking also made possible the repeating clock, which can be made to repeat the last hour struck by pressing a button.
[edit] Types of striking clocks
Specialized types of striking clocks include chiming clocks, which play fragments of a melody on the hours and quarter hours such as the Westminster Quarters; musical clocks, which play tunes on a music box in addition to counting the time; and automaton clocks, with mechanically animated figures that periodically perform various displays, usually as a part of the clock striking the hours. The cuckoo clock is a specific type of automaton clock, which displays an animated bird and plays imitation birdcalls in addition to striking on a bell or gong. A ship's bell clock strikes the ship's bells of a nautical watch instead of the hours.
Some quartz clocks also contain speakers and sound chips that electronically attempt to imitate the sounds of a chiming or striking clock. Other quartz striking clocks use electrical power to strike bells or gongs.
[edit] References
- Eric Bruton, The History of Clocks and Watches (Time Warner, repr. 2002) ISBN 0-316-72426-2
- David Landes, Revolution in time: Clocks and the making of the modern world Harvard University Press (1983) ISBN 0-674-76802-7
