History of Science Museum: Collection Database Search

Narratives

Inventory no. 51358 - Former Display Label

Roman VERTICAL DISC DIAL
?c. 250 A. D.

Bronze. Unsigned and undated.

This instrument consists of two discs, and a combined gnomon and hour-scale, held together by a bolt. The larger of the two discs is recessed to receive the smaller disc, which, like the gnomon, is free to turn.

To use the dial, the radial line, which passes under the knob on the smaller disc, was set to the appropriate latitude on the scale of latitudes, marked 'XXX' - 'LX', engraved on the raised border of the larger disc. The gnomon was then set to the correct declination on the declination-scale on the smaller disc. (At one end of the declination-scale is engraved "VIII K IAN [=25th December], and at the other end, "VIII K IVL [=24th June], representing the Winter and Summer solstices in the Julian calendar.) The dial having been adjusted, it was suspended by the small loop at the top, and turned until the horizontal bar of the gnomon cast its shadow on the curved hour-scale below, thereby indicating the time.

On the back of the instrument are engraved the latitudes of 30 provinces of the Roman Empire. The latitudes are given in degrees. For nearly every province, the latitude given is the mean of the range of latitudes given for that province by Ptolemy (died after 161 A.D.).

This dial is said to have been found near Bratislava. A similar dial was found near Rome, in the 18th century, and another in France, at CrĂȘt Chatelard (Loire).

[I. 1]
Lewis Evans Collection.

Other narratives:

Related Objects: