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circa 1370; English
Brass; 121 mm in diameter

The mater, including the rim, is cast in one piece. The limb has a 360-degree scale divided to 5, subdivided to 1. The scale is unnumbered, but each 3rd 5-degree division is marked by a letter of the 23-character Gothic alphabet and with a cross at the suspension shackle, these indicate the hours. Each half-hour position has a symbol of a circle within a diamond.

The throne is pierced by a slot, the shackle has a shaped accommodation for the suspension ring.

The rete has 21 star pointers, 16 for named stars, and includes a tropic of Capricorn terminated at 'Alacrab' by a zoomorphic head. The ecliptic has the zodiacal names, sometimes abbreviated, sometimes with a simple floral decoration, each sign having a 30 degree scale, divided to 6, subdivided to 2, not numbered.

Three latitude plates, marked with latitudes and cities: 'Tholet[9] [Toledo] 40', 'Roma 42'; 'Coloina [Cologne] 49', 'Pairisi[9] 59'; 'London[9] 52', 'Beruuik [Berwick] 57'. Almucantars for every 4 degrees with incomplete numbering to 48 degrees and none thereafter. Azimuth lines every 15 degrees, unnumbered. Unequal hours numbered 1 to 12. East-west line, circles for the equator and tropics.

The back has a scale of 360 degrees, divided to 5 degrees, subdivided to 1. It is numbered by 10 outside the scale, 90 (at the shackle) to 0 to 90 to 0 to 90; on the inner side it is accommodated to a zodiacal scale of named signs, with simple floral decoration, each sign having a 30-degree segment numbered by 10. A blank band separates this zodiacal scale from a calendar scale, with the names of the months abbreviated where appropriate and accompanied by the same decoration, each divided to 5 days, subdivided to single days, numbered by 10 beginning at 5. The vernal equinox is at 111/2 March, the autumnal at September 141/2. Within this are two circles giving the names and dates of 36 church festivals (3 per month) including the feasts of 6 English saints. The final circle is of dominical letters. Within this is a small double shadow square, 0 to 12 to 0 to 12 to 0, divided to 3, subdivided to 1, numbered by 3 with 12 repeated.

There is a pin, a counterchanged alidade, each vane having a notch in the edge as well as a pin-hole, a counterchanged rule tapering continuously on either side of the pivot, and a modern wedge.

See R. Taylor, "Remarks on an Astrolabe", Transactions of the Bristol and Gloucestershire Archaeological Society, 12 and R. T. Gunther, The Astrolabes of the World (2 vols, Oxford, 1932), vol. 2, pp.475-7.

Jim Bennett

Museum of the History of Science, Oxford
Inventory number 47869

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