Portable instruments for measuring the hours of the day are first known from the New Kingdom (for a catalogue of known instruments, see
Ancient Egyptian Astronomy Database ), but a majority of the preserved examples are from the Greco-Roman era. Several principal types are known: shadow clocks and sundials, which could measure the height, length, or direction of the sun’s shadow, and water clocks, or clepsydra (see
17.194.2341).
Discovered in the Theban necropolis by Howard Carter and Lord Carnarvon, this partial shadow clock, which counted the hours by measuring the length of the sun's shadow, dates to the Ptolemaic period. Preserved here is a narrow block with three perpendicular sides and one sloping face engraved with parallel and oblique lines, with a single line of inscription around the base. The front of the base, beneath the sloping face, is partially broken away. When complete, the base would have extended forward, and a perpendicular block would have been set before the sloping face to serve as the gnomon, the part of the instrument designed to cast a shadow.
The shadow clock would have been held or placed so that it was perfectly level and faced the sun directly so that the shadow of the gnomon fell completely on the sloping face. Each of the six parallel lines on the face of our example would have corresponded with two months of the year, beginning with the month of the winter solstice at one edge, moving across the face over the course of six months and reaching the other side at the summer solstice, then traveling back during the next six months. The user would read the hour at the intersection of the line corresponding to the relevant month and the sun’s shadow, which would have fallen on or near one of the oblique lines that counted the hours. The sun’s shadow would have covered most of the sloping face in the morning, shrunk gradually until noon, then grown again during the afternoon and early evening until it shaded most of the face again.
Janice Kamrin 2017
