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Al-Jazari (1136 – 1206) borrowed from another Muslim the idea of attaching a string between a large candle and a counterweight. As the candle burned away, the counterweight caused a small statue of a man to rise, causing the sword in his hand to point to a horizontal line labeled with the hour.
Pre-Islamic candle clocks instead had markings on the candle to show how much candle had burned away. The idea of using a statue with a weapon tip pointing to the hour had been used earlier by Ctesibius in one of his water clocks.

Al-Jazari invented a push-and-twist “bayonet fitting“ to hold the candle. This fitting is used today as an alternative to screw-in lightbulbs.

Al-Jazari’s book described a mercury clock in which a pulley rope was wrapped around a small barrel half-filled with mercury. The barrel contained compartments connected to each other by small holes. The rate at which the pulley rope fell was determined by how fast mercury could flow through holes between compartments.

Ibn Yunus could not have built a pendulum clock because pendulum clocks require the Verge escapement mechanism (derived from a European Christian invention for ringing a bell).
The source of this false claim about ibn Yunus was a translation error made in 1684 by the English scholar Edward Bernard.

Abū Ishāq Ibrāhīm al-Zarqālī (Arzachel) (1029-1087) in Muslim Spain built a device that “by magic” displays the correct phase of the moon.
The height of the water in the device controlled the movement of the moon plase display.
I assume that (in another room) someone sets the height of a water spillway, which (by means of a hidden siphon) controls the water level in the moon phase display device.

The alchemist Geber wrote a 4 volume work on building water clocks, probably based on him having read about the water clocks of Greeks such as Pseudo-Archimedes, Hero of Alexandria and Ctesibius.

Taqi al-Din completed in 1577 an observatory near Istanbul that contained a “mechanical clock”. I assume it was a Pseudo-Archimedes water clock for measuring the time interval between the sightings of two stars. If the sightings were less than 8 minutes apart from each other, and assuming the water clock had an accuracy of plus or minus one percent, the water clock would have had an error of only plus or minus a twelfth of a minute in measuring the time interval.

Image by al-Jazari, via Wikimedia Commons.
image credit

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