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Astronomical Ring Dial
16th century; German
Brass; 75 mm in diameter

A relatively simple ring dial whose hour scales are without divisions although the latitude scale is divided to degrees. Around the central flat rings is a second flat ring slotted around the pivots so that it may be slid over the first ring. The inner ring is also slotted and diametrically opposite pin-holes are set in the outer ring. One of these holes is aligned with the slot running through the declination scale for the appropriate date, thus opening the sighting hole opposite. The two rings are then adjusted until sun-light passes through the two holes, when the time is read off from the position of the double ring against the hour scales.

Anthony J. Turner

Istituto e Museo di Storia della Scienza, Firenze
Inventory no. 2452

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