Falling-drum water clock, c 1700.
© Science Museum / Science & Society Picture Library
Drum type water clock, made in England between 1690 and 1710. Water clocks were first used in Ancient Egypt and were among the earliest timekeepers not to depend upon the observation of celestial bodies. Early examples were stone vesels which allowed water to drip at a steady rate from a hole in the bottom. Greek and Roman horologists succeeded in making the flow more constant by regulating the presure.