Shadow Clock

Definition

A shadow clock is an ancient Egyptian daytime timekeeper that tells the hour from a shadow cast by a horizontal crossbar onto a marked base. The standard Set-I form has a base 5 palms long (the mertut) with hour-marks at 12, 9, 6, and 3 units, and a crossbar 2 fingers tall (the mrhyt) at one end. You face the crossbar east in the morning, then turn it west at noon. A 13-line inscription in the Cenotaph of Seti I preserves its Egyptian vocabulary — s3t (shadow clock), mrtwt (base), mrhyt (crossbar), hp (accepted rule), wpt (opening).

In Tradition

Egyptologists see the shadow clock as the daytime counterpart of the night-time water clock and star clock — together they covered a full day of seasonal hours. Clagett published the Set I instrument in Ancient Egyptian Science Vol II (1995), Document III.16; Frankfort first published it in Cenotaph of Seti I at Abydos (1933); Bruins (1965) proposed an alternative seasonal-strip reading. Belmonte and Lull take the L-shaped setjat as the standard form, with merkhyt the broader word for a measuring instrument.

In Practice

In the morning you set the clock flat with its crossbar pointed at the rising sun. As the sun climbs, the shadow falls across the marked base and reaches the 12, 9, 6, and 3-palm marks in turn. At noon, when the shadow lies straight along the clock's axis, you turn the whole device 180 degrees so the crossbar faces west — and the shadow retraces the same marks in reverse through the afternoon. The Egyptians always divided daylight into 12 hours whatever the season, so these are seasonal hours, longer in summer and shorter in winter; the shadow clock approximates them rather than measuring equal hours.

Historical Origin

The Set I shadow clock is attested in the cenotaph of Seti I at Abydos (Dynasty 19, about 1290 BCE), with a 13-line inscription describing its construction and use. An earlier physical example is the priest-Hor instrument, Berlin 14085 (6th century BCE; Borchardt 1899). Modern study: Clagett, Ancient Egyptian Science Vol II (1995), Document III.16; Frankfort, Cenotaph of Seti I at Abydos (1933); Bruins, Janus 52 (1965), pages 127-37.

Definition

In Tradition

In Practice

Historical Origin

Further Reading