A) A heated swimming pool B) A serpent-headed lion C) A six-stringed lyre D) A water clock ü
The earliest clepsydras, like those from ancient Egypt c. 2000 BC, consisted simply of a pot filled with water that emptied through a small hole, time being read from gradations in the pot as the water level declined — the same principle as a sandglass or egg timer. More complex types were gradually introduced, with elaborations such as multiple chambers, floats, and gear mechanisms. A prominent figure in clepsydra history is Ctesibius, a barber’s son who lived in Alexandria in the third century BC. He is credited with numerous advances, including a mechanism for automatically adjusting the device to the difficult requirements of the Egyptian time-keeping system, which divided both daylight and darkness into twelve hours apiece at all seasons, even though this meant that the duration of an hour changed daily, and was different in the day than at night.
