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Astrolabe
Unsigned
circa 1300; English
Brass; 462 mm in diameter

The rim of the mater is graduated 0? to 360? clockwise, numbered by 5? and subdivided to single degrees; the edge is ornamented with foliate scroll motives. The rim is riveted to the back plate. The inside of the mater is engraved as a plate for latitude 42? N ('42 GRAD{US} ROMA'). There are circles for the tropics and the equator, and azimuths and almucantars for every 2? and lines for unequal hours. None of these lines is numbered.

The throne is tri-lobed.

The Gothic rete with three quatrefoils, two trefoils and three half-quatrefoils has zoomorphic star pointers, mostly in the form of a dog's head with the tip of the dog's tongue being the actual pointer. The following 40 stars are named: 'DENEBCAITOZ', 'RIGILALSABIE', 'MIRACANDRO', 'BATENCAITOZ', 'CAPUTAR', 'MENkAR', 'ALGEMB', 'ALDEBRAN' [pointer broken off], 'AUGETENAR', 'RIGIL', 'ALhAIOC', 'BEDELGEUZE', 'ALhABOR', 'CAPUTGEMINO', 'ALGOMEIZA', 'MARkEB', 'ALFARD', 'CORLEONIS', 'EDUB', 'CONIUNCTE', 'CAUDALEONIS', 'ALGORAB', 'AChIMEC', 'BENENAZ', 'ALRAMEC', 'ALFECA', 'CORSCORPIONIS', 'IED', 'ALhAVE', 'RAZTABEN', 'ALVACA', 'ALTAIR', 'ALREF', 'ALDERAIM', 'DELFIN', 'MENKEB', 'DENEBALGEDI', 'SCEAC', 'BEDALFERAZ', 'ALFERAZ'.

The ecliptic is marked with the usual Latin names of the zodiacal signs (some abbreviated) and is divided to 12 ? 30?, numbered by 6? and further divided to 2?. The central disc has a foliate scroll decoration. The equinoctial bar is counterchanged twice: once on each side of the ecliptic and once halfway between the ecliptic and the central disk. The reverse of the rete bears construction markings.

The three plates are marked on both sides with the circles for the tropics and the equator, azimuths for every ten degrees and the almucantars every two degrees and also with the lines for the unequal hours with construction markings visible.

The plates are laid out and marked for the following latitudes ('GRAD{US}'): 1a) 48.30 'Ma'; 1b) 51; 2a) 52 'LUNDONIARUM'; 2b) 55; 3a) 53; 3b) 54. On plates 2a, 2b, 3a and 3b the almucantars are numbered by 2? and the unequal hours are numbered 1 to12. Plate 2a bears additional markings for the astrological houses in the manner of Regiomontanus.

The back is highly decorated with interwoven mythical animals and foliate scrolls. Engraved on it are the following calendrical scales (from the outside):

1) A circular band of the signs of the zodiac anticlockwise with Aries starting at the east-west line labelled with the usual Latin names of the signs, each anticlockwise graduated 0? to 30?, numbered by 5? and subdivided to single degrees, 30 minutes and 15 minutes.

2) An eccentric band of the signs of the zodiac marked with the usual Latin names with 10?45' of Capricorn corresponding to the first point of Aries on the first scale, anticlockwise graduated 0? to 360?, numbered by 6? and subdivided to 1? and 15 minutes.

3) A circular band of the signs of the zodiac marked with the usual Latin names with the first point of Aries corresponding to the first scale, graduated anticlockwise 0? to 360?, numbered by 5?, subdivided to single degrees, and graduated anticlockwise four times 0? to 90? starting with the first point of Aries: 0? to 90?, 90? to 0?, 0? to 90?, 90? to 0?.

4) An eccentric band labelled anticlockwise with the usual Latin names of the months, each divided to the corresponding number of days, numbered by 5 and divided to single days. This scale also contains the names of 48 saints and Christian feasts linked to given dates and Dominical Letters. The equinoxes are at 131/2 March and 151/2 September.

5) A circular table in the centre consists of 4 bands with the 28 years of the solar cycle, the corresponding weekdays and the Dominical Letters in a double band indicating leap years.

6) Between scales 4 and 5 in the top half of the back seven semicircles with (from the outside) the claves terminorum for Pentecoste ('T.'PE-TE'), the Easter day ('T.'PASCE'), the Quadragesimae ('T.'QaD'), the Septuagesimae ('T.'SEP'), the Claves ('CLAVES'), the Epacts ('EPACTE') and the Golden Numbers ('CICLUS').

In the vacant space in the lower half of the back are two shadow scales, each divided into 12 digits, numbered by 2.

The alidade and the ruler are missing.

The instrument was acquired in 1753 with the Sloane collection and is described in W. H. Morley, Description of a Planispheric Astrolabe Constructed for Shah Sultan Husain Safawi, King of Persia, and now preserved in the British Museum; comprising an account of the Astrolabe generally (London, 1856), (reprinted in R. T. Gunther, The Astrolabes of the World (2 vols, Oxford, 1932), vol. 1, pp. xix-50) p. 44-5, no. H; R.T. Gunther, The Astrolabes of the World (2 vols, Oxford, 1932), vol. 2, pp. 463-5, no. 290 (with plate CXXVI); 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. 112, no. 324 (with plate L).

Silke Ackermann

British Museum, London
Registration no. MLA SL54

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