Water Clock (Clepsydra)

klep-SID-rah

Definition

A water clock — its Greek name is clepsydra — is an ancient Egyptian timekeeper that tracks the seasonal hours by water moving through a calibrated vessel. The outflow type is a bowl with a single hole in the bottom, its falling water level passing inside hour-marks as it drains; the inflow type is a cylinder catching water dripping in at a steady rate. The Amenemhet inscription preserves its Egyptian words — mr3yt (water clock) and dbht (sighting instrument). It was calibrated to the standard Egyptian 14:12 ratio of longest-winter to shortest-summer night.

In Tradition

Egyptologists see the water clock as the night-time partner of the daytime shadow clock and the decanal star clock. Belmonte and Lull (2009) and Clagett (1995) record the Karnak clepsydra (made under Amenhotep III, about 1370 BCE) as the oldest example physically preserved; the courtier Amenemhet's 16-line tomb inscription describes how one was built, with a separate hour-scale per month to track the changing length of the night. Temple texts call the clepsydra both an astronomical instrument and a ritual object.

In Practice

An Egyptian astronomer-priest filled the outflow clepsydra at sunset and read the seasonal night-hour as the water level sank past inside marks calibrated for the current month — these clocks carried 12 separate sets of hour-marks, one per civil-calendar month, so they could track the 14:12 swing between the longest winter night and the shortest summer one. The inflow type, such as the cylindrical receiver from Edfu, instead measured elapsed time as the water rose against its marks. Both kinds timed temple rituals, supported astronomical observation alongside merkhet sighting work, and were used to check the decanal tables.

Historical Origin

The Karnak clepsydra (Amenhotep III, Dynasty 18, about 1370 BCE) is the oldest surviving physical example; the Amenemhet tomb inscription (Dynasty 18) records the construction procedure. The cylindrical inflow clepsydra from the temple of Edfu is Ptolemaic. Modern study: Clagett, Ancient Egyptian Science Vol II (1995), Document III.15 on the Amenemhet water clock; Belmonte and Lull, In Search of Cosmic Order (2009); Neugebauer and Parker, Egyptian Astronomical Texts.

Definition

In Tradition

In Practice

Historical Origin

Further Reading