GREEK WATER CLOCKS

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Ctesibius built a complex water clock. A tank was kept full by wasting excess water down a spillway. The constant pressure at the bottom filled a bucket with water. The bucket would tip, dumping its contents into a lower tank and.rotating an axle 60 degrees. A statue of a naked soldier floated on the water in the lower tank, his spear pointing to lines on a wide cylinder. Once a day, the water level in the lower tank tripped a syphon, emptying the lower tank.
The rotating axle connected to a train of gears that rotated the wide cylinder once every 360 days. The curved lines on the wide cylinder marked sunrise as zero hour, noon as 6 and sunset as 12 and the next sunrise as 24. Rotation of the cylinder gave the correct time of sunrise and sunset for each day of the year

Another Greek clock design turned a hand like that on the face of modern non-digital clocks.

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clepsydra-diagram-fancy

3RD CENTURY BC GREEK WATER CLOCK
Many centuries before Islam, Greeks built some very sophisticated water clocks.
This 19th century clock was an attempt to build a replica of a clock built by Ctesibius (3rd century BC Greek living in the Roman colony of Alexandria Egypt), but has some errors.

Missing from this illustration is the tank used by Ctesibius that delivered a constant flow of water to the clock. His tank wasted water by adding too much water, and using a spillway to remove the excess water.

Thus he maintained a constant water height, and thus constant pressure to deliver a constant flow of water to the clock. (Later Greek clocks used a float valve, similar to the modern valve in a toilet tank, to cut off its water input when the tank became full.)
The rising water in the clock raises the float on which is mounted a small statue of a man with a spear that points to the time on a 24 hour clock display.

(In the original Ctesibius clock, the man was naked.)

The tank fills until it trips a siphon, causing the tank to empty itself once every 24 hours, causing the water wheel below to rotate 60 degrees once every 24 hours. A 60:1 ratio gear train converts this motion into rotating the cylinder at the top right once every 360 days.

The actual cylinder was very wide. The line markings on the cylinder were not horizontal as in this 19th century attempt of a reconstruction, but steeply curved, giving different time values for each astrological month of the year, serving to convert 24 hours from dawn to dawn into sundial time of 12 hours from sunrise to sunset, and 12 hours from sunset until sunrise.

Another Greek clock design turned a hand like that on the face of modern non-digital clocks.

Image by unknown artist in “a New Universal Dictionary of Arts and Sciences” (1819), via Wikimedia Commons.
Image credit https://commons.wikimedia.org/wiki/File:Clepsydra-Diagram-Fancy.jpeg

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