Water Clock

Water Clock. ΚΛΕΨΥΔΡΑ. This monumental water clock was constructed at the end of the 4th cent. B.C. in a prominent location at the southwest corner of there Agora square, on the street leading from the Agora up to the Pnyx. Water was drawn by a stone drain. The device was at first a simple outflow clock, a stone tank or cistern accessible through a flight of steps, with a small bronze outlet hole at the bottom which allowed the tank to drain slowly. Some flotation device would record the passing hours as the water level fell. The full tank would take some 17 hours to empty. The plug would be pulled at dawn each day. , In the 3rd cent. B.C. two supplementary tanks were added, set at different levels, which were filled gradually. The time was no longer estimated by emptying the main tank but by the gradual filling of one supplementary tank. At the end of the day the main tank would be emptied through a large outlet hole set at its bottom. With this system all the problems caused by water pressure changes would be avoided. , This water installation was dismantled in the 2nd cent. B.C. It is the forerunner of the water clock in the Tower of the Winds, the clock the astronomer Andronikos Kyrrestes.