- Museum number
- SLMathInstr.54
- Title
- Object: The Sloane Astrolabe
- Description
-
The rim of the MATER is graduated 0° to 360° clockwise; 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°. 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 almucantars every two degrees and with 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 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°.
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, graduated anticlockwise 0° to 360.
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 four times 0° to 90° starting with the first point of Aries.
4) An eccentric band labelled anticlockwise with the usual Latin names of the months, each divided to the corresponding number of days. This scale also contains the names of 48 saints and Christian feasts linked to given dates and Dominical Letters. The equinoxes are at 13½ March and 15½ September.
5) A circular table in the centre consisting 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.
The ALIDADE and the RULER are missing.
- Production date
- 1290-1300
- Dimensions
-
Diameter: 462 millimetres
-
Thickness: 12 millimetres
- Curator's comments
-
Sir Hans Sloane’s ‘Miscellanea’ catalogue is a bound volume in Central Archives containing seven separate catalogues: ‘Miscellanies’, ‘Antiquities’, ‘Seals’, ‘Pictures’, ‘Mathematical Instruments’, ‘Agate Handles’ and ‘Agate Cups, Bottles, Spoons’. Each contains numbered entries that list and describe objects collected by Sloane between the 1680s and 1750s. Each catalogue begins with object number one.
Text from Sloane Miscellanea catalogue: Miscellanea Mathematical Instruments 54 "54. A brasse astroblade made at London for the latitudes of Rome, London &c wt. a perpetuall almanack upon it. 2. 11. 6."
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This unusually large, very accurately and elegantly engraved instrument had been in the possession of Sir Hans Sloane and was therefore part of the founding collections of the British Museum in 1753. It is the earliest and largest English astrolabe to have survived from the Middle Ages but shows a knowledge of Arabic astronomy and instrumentation. The presence of the names of three saints of particular English significance (Dunstan 19th May, Augustine of Canterbury 26th May, Edmund 20th November) in the list on the back and the plate marked for London make an English origin most likely. One plate is marked for 48º 30', the latitude of Paris.
Note by M Caygill 7.1.11:
The rediscovery of the astrolabe is recorded in the Journals of Sir Frederic Madden (1801-73), Keeper of Manuscripts at the British Museum 1837-66, as follows:
"Thursday 19th [May 1853] Fine weather. Mr Franks came to my house, and shewed me a very curious Astrolabe of brass, in the most perfect condition , made in England about the year 1330, and lately found in the cellars among refuse, covered with rust!! It formed part of the Sloane Collection, and has been thrown aside and neglected for just a Century! ...
'Mr Franks' was Augustus Wollaston Franks (q.v.) newly-appointed Assistant in the Department of Antiquities, one of whose early tasks was to identify survivors of the Sloane collection. Madden's journals were bequeathed to the Bodleian Library, Oxford (MS.Eng.hist.c.140-182. This extract: c.166).
- Location
- On display (G1/fc12)
- Exhibition history
-
1999 1 Dec-2000 24 Sep, London, The Queen’s House, The Story of Time
- Acquisition date
- 1753
- Department
- Britain, Europe and Prehistory
- Registration number
- SLMathInstr.54
- Additional IDs
-
Sloane Miscellanea Catalogue number: 54 (Mathematical Instruments)
