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Late 14th century ?; English
Brass; 123 mm in diameter

The rim has an equal 24-hour scale and a 360? altitude scale. The hour scale is calibrated by letters instead of numerals ('A, B, C, D, E, F, G, h, I, k, L, M, N [reversed], O, P, Q, R, S, T, V, X, Y, Z'). The altitude scale is numbered 0? to 360?, numbered by 10?, divided to 5? and subdivided to single degrees. The rim is soldered to the back plate.

The mater is empty except for some construction markings.

The throne is trilobal.

On the rete with its distinctive Y inside the ecliptic, 23 stars are indicated, some names now illegible. The star pointers are partly zoomorphic (dragon's head and dog's head), partly worm-shaped and partly in the form of bent swords.

The star names are given as follows: [illegible], 'Batukaito', 'Algenib [?]', 'Menkar [?]', 'Aldeb', 'Alaior', 'Rigil', 'Algomeiza', 'Alhabor', 'Vrsa', 'Alfard', 'Corvus', [illegible], 'Alram', 'Alchim{e}c', 'Alacrab', 'Elfeca', 'Al[illegible and broken off]', 'Wega', [illegible], 'delfin', 'Denebalgedi', [illegible].

The ecliptic bears the usual Latin names of the zodiacal signs. Each sign is divided to 30?, numbered by 10? with divisions to 2?.

The three plates have markings for the equator and the tropics, azimuths for every 221/2?, almucantars for every 2? (numbered by 6?), and lines for the unequal hours (numbered 1 to 12). They are laid out and marked for the following latitudes: 1a) 'Dover' 51?; 1b) 'Oxoni{ensis}' 52?; 2a) 'Notin<n>gh<a>m' 53?; 2b) 'Ebo<rum>' 54? [York]; 3a) 'Novu<m>cas{trum}' [Newcastle] 55?; 3b) 'Berwik' 56?.

The back has several circular concentric scales as follows (from the outside): 1) A 360? altitude scale, marked four time 0? to 90? starting at the east-west line, numbered by 10?, divided to 5? and subdivided to single degrees; 2) A scale with the usual Latin names of the zodiacal signs except 'Wirgo', each sign divided to 30?, numbered by 10?, divided to 5? and subdivided to single degrees; 3) A Julian calendar scale marked with the usual Latin names of the months, each month divided to the corresponding number of days, numbered by 10, divided to 5 and subdivided to single days, the equinoxes corresponding to March 11 and September 13; 4) to 6) Three bands with the names of saints and feast days, the corresponding dates and the corresponding day letters, amongst which are the English saints Dunstan (19 May) and Augustin of Canterbury (26 May).

The lower half of the vacant space inside these circles is taken up by a double shadow scale to the base 12, numbered by 3 and divided to single digits.

The counterchanged rule and alidade as well as the screw and the pin are replacements, all except the screw are marked '1888', the year of their replacement.

The instrument was presented by Maurice Rosenheim in 1914 and is described and illustrated in C. Ferguson, "On an Astrolabe Planisphere of English Make", Archaeologica 52 (1889), pp. 75-84; F. A. B. Ward, A Catalogue of European Scientific Instruments in the Department of Medieval and Later Antiquities of the British Museum (London, 1981), p. 113 ff., no. 327.

Silke Ackermann

British Museum, London
Registration no. MLA 1914,2-19.1

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