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Inventory no. 81682 - Former Display Label

GERMAN MECHANICAL EQUINOCTIAL DIAL
c.1780

Brass, etc. Unsigned and undated, but certainly from the workshop of Philipp Matthaeus Hahn, of Ostmettingen, near Stuttgart. Hahn, who was a clockmaker, sold dials of this type with his clocks, the accuracy of which they served to check.

This instrument is developed from the universal ring dial. The meridian-ring, a heavy brass ring with one quadrant graduated, has a fixed steel rod at its polar axis. On the rod revolves a rectangular brass frame which has a rectangular plate at each end. On these plates are engraved scales and tablets of the signs of the zodiac, together with the equation of time. In one plate are two pin-holes. The rotating frame is geared to drive the hands of the watch-face.

In using the instrument, the frame is turned until the sun shining through the pin-holes throws spots of light on the correct points of the scale on the other rectangular plate. When this occurs the time is indicated on the watch-face.

[G.124]
Lewis Evans Collection.

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