Water clock

A water clock or clepsydra (from Ancient Greek κλεψύδρα (klepsúdra) 'pipette, water clock'; from κλέπτω (kléptō) 'to steal', and ὕδωρ (hydor) 'water'; lit. 'water thief') is a timepiece by which time is measured by the regulated flow of liquid into (inflow type) or out from (outflow type) a vessel, and where the amount is then measured.

For the individual water clock at The Children's Museum of Indianapolis, see Water clock (Indianapolis).

Water clocks are one of the oldest time-measuring instruments. The bowl-shaped outflow is the simplest form of a water clock and is known to have existed in Babylon, Egypt, and Persia around the 16th century BC. Other regions of the world, including India and China, also have early evidence of water clocks, but the earliest dates are less certain. Water clocks were also used in ancient Greece and ancient Rome, described by technical writers such as Ctesibius and Vitruvius.

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