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circa 1500 ?; Italian
Brass; 197 mm in diameter

Mater comprised of limb and attached plate, inner face blank. Three-lobed throne attached to the limb be two screws. Shackle and suspension ring. The face of the limb has a degree scale 0 to 360, divided to 5, subdivided to 1, numbered by 5. The rim of the limb has an 24-hour scale, divisions 2 to 22 being visible and numbered.

Rete for 15 named stars in a form of the Y-pattern with a continuous diametric bar. Ecliptic circle with named constellations, each with a 30 degree scale divided to 5, subdivided to 1, numbered by 5. The hours 1 to 16 are marked on the outer band, for the tropic of Capricorn.

Four plates marked for latitudes 33 and 36?; 39 and 42?; 45 and 48?; 51 and 54?. Each has azimuths every 10 degrees, numbered from 90 at the meridian to 0 east and west, and beyond, and almucantars every 2 degrees, numbered every 10, lines for unequal hours, numbered 1 to 12 below the horizon, lines for the houses of heaven, equator and tropics.

The back has an outermost 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 degree divisions serve a zodiacal scale with each sign named and having a 30 degree scale divided to 5, subdivided to 1, numbered by 5. Within this is a calendar scale with the months named in Latin, each divided to 5 days, subdivided to 1, numbered by 5 as appropriate. The first point of Aries is at 101/2 March. The upper half of the central circular space is occupied by an unequal-hour diagram, with lines for hours 1 to 12, marked 'Hore Inequales'. The lower half has a double shadow square, marked 'Scala Altimetra' with scales 'Vmbra Versa' 0 to 24, divided to 4, subdivided to 1, numbered by 4, and continuing with similar division and numbering for 'Vmbra Recta' 24 to 0, 'Vmbra Recta' 0 to 24, 'Vmbra Versa' 24 to 0. The diagonal lines to the 24 points are both marked 'Diameter'.

The rule with shaped end has a declination scale 24, 20 to 0 (at the equator) to 70, divided to 10, subdivided on the bevelled edge to 2, numbered by 10; the divisions are carried over on to the back of the rule. Alidade (sights missing), pin and wedge.

R. T. Gunther, The Astrolabes of the World (2 vols, Oxford, 1932), vol. 2, pp. 327-8.

Jim Bennett

Museum of the History of Science, Oxford
Inventory number 35146

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