A striking clock is a clock that sounds the hours on a bell, gong, or other audible device. In 12-hour striking, used most commonly in striking clocks today, the clock strikes once at 1:00 am, twice at 2:00 am, continuing in this way up to twelve times at 12:00 mid-day, then starts again, striking once at 1:00 pm, twice at 2:00 pm, and the pattern continues up to twelve times at 12:00 midnight. The striking feature of clocks was originally more important than their clock faces; the earliest clocks struck the hours, but had no dials to enable the time to be read. The development of mechanical clocks in 12th century Europe was motivated by the need to ring bells upon the canonical hours to call the community to prayer. The earliest known mechanical clocks were large striking clocks installed in towers in monasteries or public squares, so that their bells could be heard far away. Though an early striking clock in Syria was a 12-hour clock, 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. As the modern 12-hour clock became more widespread, particularly in Great Britain and Northern Europe, 12-hour striking eventually became the standard. In addition to striking on the hour, many striking clocks play sequences of chimes on the quarter-hours. The most common sequence is Westminster Quarters. Today the time-disseminating function of clock striking is almost no longer needed, and striking clocks are kept for historical, traditional, and aesthetic reasons. Historic clock towers in towns, universities, and religious institutions worldwide still strike the hours, famous examples being Big Ben in London, the Peace Tower in Ottawa, and the Kremlin Clock in Moscow. Home striking clocks, such as mantel clocks, cuckoo clocks, grandfather clocks and bracket clocks are also very common. A typical striking clock will have two gear trains, because a striking clock must add a striking train which operates the bell-ringing mechanism to the timekeeping train that measures the passage of time.
Passing strike
The most basic sort of striking clock simply sounds a bell once every hour; this is called a passing strike clock. Passing strike was simple to implement mechanically. All that must be done is to attach a cam to a shaft which rotates once per hour; the cam raises and then lets a hammer fall that strikes the bell. The first tower clocks, mounted in towers in cathedrals, abbeys, and monasteries to call the community to prayer, which originated in Medieval Europe before the invention of the mechanical clock in the 13th century, were water clocks that used the passing strike mechanism; they rang once for each canonical hour. In Ancient Egypt and later Ancient Rome, sundials were typically used during the day and water clocks were preferred for keeping the time at night. The Tower of the Winds in Athens, the only surviving tower clock of classical antiquity, built in the 1st century BC during Roman Greece, has visible sundials on its exterior and evidence that a water clock and weather vane were also used. The ancient Han Chinese developed water-driven astronomical clocks with automatically rotating armillary spheres starting with the Han dynasty era scientist Zhang Heng (78–139). The Tang dynasty Chinese Buddhist monk and inventor Yi Xing (683–727) created a rotating celestial globe that was turned by a water clock mechanism driven by a waterwheel. This featured two wooden gear jacks on its horizon surface with a drum and a bell, the bell being struck automatically every hour and the drum being struck automatically every quarter-hour. It is recorded that Confucian students in the year 730 were required to write an essay on this device in order to pass the Imperial examinations. The use of clock jacks to sound the hours were used in later clock towers of Song dynasty China, such as those designed by Zhang Sixun and Su Song in the 10th and 11th centuries, respectively. A striking clock outside of China was the clock tower near the Umayyad Mosque in Damascus, Syria, which struck once every hour. It is the subject of a book, On the Construction of Clocks and their Use (1203), by Riḍwān ibn al-Sāʿātī, the son of a clockmaker. The Florentine writer Dante Alighieri made a reference to the gear works of striking clocks in 1319. One of the older clock towers still standing is St Mark's Clocktower in St Mark's Square, Venice. The St Mark's Clock was commissioned in 1493, from the famous clockmaker Gian Carlo Rainieri from Reggio Emilia, where his father Gian Paolo Rainieri had already constructed another famous device in 1481. In 1497, Simone Campanato moulded the great bell, which was put on the top of the tower where it is alternately beaten by the Due Mori (Two Moors), two bronze statues handling a hammer.
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