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Mathematical Compendium
Signed by Hans Christoph Schissler jr
Late 16th century; German
Gilt brass and silver; 198 x 200 x 90 mm

The instrument is built in the form of a clock, with a rectangular brass plinth on four feet and four turned pillars rising to a top plate with four silver finials (one missing). Hinged at one end of the top plate is an alidade with pinhole and window sights and a hinged vertical scale at the other end graduated in degrees 0 to 40, divided to 5, subdivided to 1, numbered by 5, and having also a geometrical quadrant scale 0 to 12, divided to 1, subdivided to 1/4, numbered by 1. Between the pillars at one side is a plumb-line. The front of the plinth has a pivoted folding square, one arm with a linear scale 0 to 100, divided to 5, subdivided to 1, numbered by 5, the other with the radiating divisions of a geometrical quadrant scale 0 to 45, similarly divided and numbed.

The front side has a square plate hinged at the top. The outside face has an hour circle 1 to 12 twice, divided to 1 hour, subdivided to 1/2 hour, numbered with Roman numerals to 1. The spandrels are pierced and engraved with figures and foliate decoration. Behind is a silvered plate with circles for the daily path of the sun marked for different signs of the zodiac and crossed by hour lines. A gilt brass planisphere is marked with the equator and tropics, names of continents and five cities. On top of the planisphere and hour plate is a pivoted index with a latitude scale. The other face of the plate has a similar hour circle and a plain index, but with a pivoted ecliptic ring, with zodiacal symbols and a 30-degree scale for each sign, and the plate beneath with an astrolabe projection of the horizon and lines for unequal hours. The front of the hinged plate is marked 'Meridies', 'Septentrio', 'Oriens' and 'Occidens' and has the signature 'H C [as a monogram] Sch?ssler'.

The back has a circular plate with a table of ruling planets for daytime and night-time hours, which hinges down to reveal a sundial with a folding pin-gnomon. A silvered circular plate has a set of hour lines crossing circles marked for the sun's position in the zodiac, and an offset target line for a magnetic compass needle. This plate is glazed and rotates with the folding gnomon about a degree scale 0 to 360, divided to 10, subdivided to 2, numbered by 10, with an index at the position of the gnomon. Above this a second glass plate is carried by a brass rim and 6 turned pillars. This upper level appears to have no function at present, and something may be missing.

There is a shaped case, in two halved held by pivoted catches, lined with leather, covered with leather with gold decorative tooling.

Jim Bennett

Istituto e Museo di Storia della Scienza, Firenze
Inventory no. 2467

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