Castle clock

A "Castle clock" is a visually complicated clock originally appearing near the top of a castle and later a church tower. The original inventor was thought to be Al-Jazari and it is considered to be an early example of a programmable analog computercitation|title=Ancient Discoveries, Episode 11: Ancient Robots|publisher=History Channel|url=http://www.youtube.com/watch?v=rxjbaQl0ad8|accessdate=2008-09-06] , in 1206.

The Al-Jazari clock was a complex device that was about 11 feet high, and had multiple functions alongside timekeeping. It included a display of the zodiac and the solar and lunar orbits, 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. [Howard R. Turner (1997), "Science in Medieval Islam: An Illustrated Introduction", p. 184. University of Texas Press, ISBN 0292781490.] [Donald Routledge Hill, "Mechanical Engineering in the Medieval Near East", "Scientific American", May 1991, p. 64-69. (cf. Donald Routledge Hill, [http://home.swipnet.se/islam/articles/HistoryofSciences.htm Mechanical Engineering] )] It was possible to re-program the length of day and night everyday 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. [cite web|author=Salim Al-Hassani|title=How it Works: Mechanism of the Castle Clock|url=http://muslimheritage.com/topics/default.cfm?ArticleID=901|publisher=FSTC|date=13 March 2008|accessdate=2008-09-06]

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