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circa 1350; English
Brass; 341 mm in diameter

The limb of the single plate has a degree scale 0 to 360, divided to 5, subdivided to 1, numbered by 5 except that every 15 degrees are numbered for equal hours 1 to 24.

The latitude projection for 51 degrees has numbered almucantars for every 2 degrees from 0 to 30, every 3 degrees from 30 to 60 and every 5 degrees from 60 to 90. There are numbered azimuth lines every 15 degrees from 90 on the meridian to 0 to 90 to 0 to 90. There are numbered unequal hour lines, meridian and east-west lines, and arcs for the equator and tropics below the horizon.

The 'Y' pattern rete has the names for 18 stars, 14 with pointers (one broken), the others indicated by the tracery. The ecliptic circle has abbreviated named for the zodiacal constellations, each with a scale of 30 degrees, divided to 5, subdivided to 1, numbered by 5. The outer band, for the tropic of capricorn, has a calendar scale (the first point of Aires is at 11 March) extending from 19 January to 3 November, with abbreviated named of the months, divided to 5 and subdivided to single days, numbered, as appropriate, by 5.

The back has a quadrant with a degree scale on the limb in the manner of a 'nautical ring', 0 to 90, divided to 5, subdivided to 5 and to 0.5, numbered by 5. A quadrant arc centred on the point of suspension is divided equally 0 to 12 to 0 by 3, subdivided to 1, numbered by 3. Within this arc are lines for unequal hours alternately numbered for morning and afternoon'.

See R. T. Gunther, The Astrolabes of the World (2 vols, Oxford, 1932), vol. 2, p. 473.

Jim Bennett

Museum of the History of Science, Oxford
Inventory number 47901

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