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circa 1400; French
Brass; 152 mm in diameter

Limb attached to base plate to form mater, the shaped throne with circle decoration and suspension shackle. Degree scale on limb 0 to 360, divided to 5, subdivided to 1, 0 to 245 numbered by 5, 255 to 360 by 15.

Rete for 27 stars, pattern modified from the 'Y' type, with the tropic of capricorn terminated by a dragon's head and tail. The ecliptic has abbreviated names for the zodiacal signs, each with a 30-degree scale on the bevelled edge, divided to 5, subdivided to 1, not numbered. Diametric bar counterchanged twice. There are two characters on the verso of the rete.

There are 4 plates, engraved for latitudes 41 and 48, 45 (verso blank), 50 and 51, 52 and 53 degrees. Each has azimuths every 15 degrees and almucantars every three degrees, unnumbered. Each has meridian and east-west lines, lines for the tropic of cancer and the equator, and lines of unequal hours, numbered on only 5 of the projections.

On the back is a degree scale 90 (at the throne) to 0 to 90 to 0 to 90, divided to 5, subdivided to 1, numbered by 5. The same divisions serve for a zodiacal scale, marked on the inside with the signs, each 0 to 30, divided to 5, subdivided to 1, numbered by 5. Within this scale is an eccentric date scale, with abbreviated month names, each with a scale of days, divined to 5, subdivided to 1, numbered by 10 adjusted to each month. The vernal equinox is at 121/2 March. In the centre is a double shadow square, each quadrant with scales 0 to 12 to 0, divided to 2, subdivided to 1, numbered by 2.

Counterchanged alidade with pinhole sights, pin, counterchanged rule and wedge all modern.

Jim Bennett

Museum of the History of Science, Oxford
Inventory number 41468

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