Clock towers are a common sight in many parts of the world with some being iconic buildings like the one in London commonly called 'Big Ben' (although it is correctly called the Elizabeth Tower as Big Ben is the bell inside the tower). Clock towers are a specific type of building which houses a turret clock and has one or more clock faces on the upper exterior walls. Many clock towers are freestanding structures but they can also be adjoining or on top of another building. The tallest clock tower in the world is the recently constructed Makkah Clock Royal Tower, standing 601 m or 1,971 feet high.
It is important to distinguish between clock towers and other buildings which may have clocks or clock faces attached to them. Many buildings have had clocks added to an existing structure. Although the resulting structure is often seen to be a clock 'tower' they are not the same sort of structure. Therefore:
The mechanism inside the tower is known as a turret clock. It often marks the hour (and sometimes segments of an hour) by sounding large bells or chimes, sometimes playing simple musical phrases or tunes.
Although clock towers are today mostly admired for their aesthetics, they once served an important purpose. Before the middle of the twentieth century, most people did not have watches, and prior to the 18th century even home clocks were rare. The first clocks didn't have faces, but were solely striking clocks, which sounded bells to call the surrounding community to work or to prayer. They were therefore placed in towers so the bells would be audible for a long distance. Clock towers were placed near the centres of towns and were often the tallest structures there. As clock towers became more common, the designers realized that a dial on the outside of the tower would allow the townspeople to read the time whenever they wanted.
The use of clock towers dates back to the antiquity. The earliest clock tower was the Tower of the Winds in Athens which featured eight sundials. In its interior, there was also a water clock (or clepsydra), driven by water coming down from the Acropolis. In Song China, an astronomical clock tower was designed by Su Song and erected at Kaifeng in 1088, featuring a liquid escapement mechanism. In England, a clock was put up in a clock tower, the medieval precursor to Big Ben, at Westminster, in 1288; and in 1292 a clock was put up in Canterbury Cathedral. The oldest surviving turret clock formerly part of a clock tower in Europe is the Salisbury cathedral clock, completed in 1306; and another clock put up at St. Albans, in 1326, 'showed various astronomical phenomena'.
Al-Jazari constructed an elaborate clock and described it in his Book of Knowledge of Ingenious Mechanical Devices in 1206. It was about 3.3 metres high (11 feet), and had multiple functions alongside timekeeping. It included a display of the zodiac and the solar and lunar paths, and a pointer in the shape of the crescent moon which travelled across the top of a gateway, moved by a hidden cart and causing automatic doors to open, each revealing a mannequin, every hour. It was possible to re-program the length of day and night daily in order to account for the changing lengths of day and night throughout the year, and it also featured five robotic musicians who automatically play music when moved by levers operated by a hidden camshaft attached to a water wheel. Other components of the castle clock included a main reservoir with a float, a float chamber and flow regulator, plate and valve trough, two pulleys, crescent disc displaying the zodiac, and two falcon automata dropping balls into vases.
Line (mains) synchronous tower clocks were introduced in the United States in the 1920s.
Some clocks' towers are famously known landmarks. Five of the best-known are Elizabeth Tower built in 1859, which houses the Great Bell (generally known as Big Ben) in London, the Rajabai Tower in Mumbai, the Spasskaya Tower of the Moscow Kremlin, the Torre dell'Orologio in the Piazza San Marco in Venice, Italy, and Zytglogge clock tower in the Old city of Bern, Switzerland. The Royal Mecca Clock Tower in Saudi Arabia is the largest clock tower in the world.
Makkah Clock Royal Tower is the tallest clock tower in the world at 240m (787feet) high The Allen-Bradley Clock Tower is the tallest non-chiming four faced clock tower in the world in Milwaukee, Wisconsin.
The tallest freestanding clock tower in the world is the Joseph Chamberlain Memorial Clock Tower at the University of Birmingham in the United Kingdom. The tower stands at 100m and was completed in 1908.
- List of clock towers
- Turret clock, the mechanism used in most clock towers
- Bell tower
- Thirteenth stroke of the clock
- Street clock
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- Salim Al-Hassani (13 March 2008). "How it Works: Mechanism of the Castle Clock". FSTC. Retrieved 2008-09-06.
- "UK Parliament - Big Ben". Retrieved 2009-10-27.
- Alsharif, Asma (11 August 2010). "World's biggest clock begins ticking in Mecca". Reuters. Retrieved 14 June 2013.
- Walcott, Kingsley. "Historical Watches: Big Ben, The Great Clock". Retrieved 30 August 2013.
- "Joseph Chamberlain Memorial Clock Tower". Skyscraper News. Retrieved 15 April 2014.
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