A Rare Medieval Brass Astrolabe, Probably Italian, Late 13th/Early 14th Century,
CCA 4556.
Rete
The fully symmetrical strapwork is arranged around a central trefoil placed between the arcs representing the tropics and a mitre within the ecliptic. The positions of thirty-one named stars are indicated by slender curved pointers arising from squat bases which carry a number indicating the magnitude of the star except in the cases of Menkar, Rigel, Alphard, and Cor Leonis where the base is pierced by two small holes thus causing the magnitude number to be placed after the name. Most, but not all, of the star names are enclosed within a pair of dots. A segment of the Capricorn arc has broken away thus removing the pointer and magnitude for Deneb. Several of the stars marked employ contracted forms indicated by a symbol that has not been reproduced in the following list:

Stars outside the ecliptic
VENT CETI - 3 - Venter ceti - γ Ceti
DENEB - lost Deneb kaitoz - β Ceti
MENCAR - 2 - Menkar - α Ceti
RIGEL - 1 - Rigil - β Orionis
ALHABOR - 1 - Alhabor - α Canis Maior
ALFARID - 1 - Alphard - α Hya
CORV - 2 - Corvus - γ Cru
ALCHIM - 1 - Alchimec -α Virgo
COR SCOR - 1 - Cor scorpionis - α Scorpionis
COR TAV - 1 - Cor Tauri - α Tauri
HVMER - 2 - Humerus - α Orionis
ALCOMEISA - 1 - Algomeisa - α Canis minoris
COR LEO - 1 - Leo - α Leonis

Stars inside the ecliptic
ALTAIR - 2 - Altair - α Aquilonis
DELF - 3 - Delphinus - γ Delphinis
CAPUT S - 2 - Caput serpentari - α Ophiucus
WEGA - Vega - α Lyræ
ARAM - 1 - Aramec - α Bootes
CORO -Corona - α Corona Borealis
CAP D - 3 - Caput draconis - γ Draconis
CAUDA LEO - Cauda leonis - β Leo
BE[ ]C - 1 - Benenæ - η Ursa majoris
SELLA - 2 - Stella - μ Ursa majoris
VRSA - 2 - Ursa - α Ursa majoris
MIRAT - 2 - Mirach - β Andromedæ
ALGE - 2 - Algemb - α Persei
EQ - 1 - Equus - α Andromedæ
EMFALFA - 2 - Emif Alkferaz - ε Pegasi
BARAZ - 2 - Bed Alferaz - β Peg
GALLINA - 1 - Gallina - α Cygni
IRC - 1 - Hircus - α Aurigæ

The ecliptic ring carries abbreviated names for the signs each divided to two degrees and numbered by groups of six. There is a rectangular Capricorn pointer with a central index line.

Limb
Separately cast and attached to the backplate by seventeen rivets (some loose), the limb is engraved with a degree scale in four quadrants arranged 0-90-0-90-0, reading to 1° by numbered groups of six. That the metal composition is somewhat different from that of the rest of the instrument, that the division is by sixes rather than by fives as on the back, and that the lettering is not identical, lead to the possibility that the ring is a slightly later renewal.

Mater
This is plain apart from inscribed circles for the tropic of Cancer and the Equator. Burin pecks resulting from the division of the limb after it had been attached to the back are visible.

Throne
A low, simple, construction composed of five roundels: two larger supported by two smaller ones symmetrically disposed around a higher one that carries the shackle for the suspension ring (probably a replacement). Three of the roundels are open, the fourth metal-filled. That all four originally carried a decorative motif is possible.

Back
The circumference is engraved with a degree scale in four quadrants arranged 90-0-90-0-90, that is the opposite of the arrangement on the front, the somewhat uneven divisions numbered by groups of five. Within this is a zodiacal scale, the signs divided to degrees by numbered groups of five and within this an eccentrically drawn calendar, the named months divided to single days (February 28; 0°Aries approximately 13½ March); the lower half contains a double shadow square of twelve numbered every two division; the centre is engraved with four concentric circles, the outer with an ill-defined division probably into twelve, the next two into twenty-eight while that at the centre is blank. These were probably intended to carry calendrical data such as the solar cycle, and the dominical letters.

Plates
There are five plates that are marked both for latitude and for the climates, the value for the latter being marked both on the fixing lug at the top of the plate and at the centre. Only two of the plates however retain their whole lug, the others offering only a residual excrescence.
The plates are drawn for

Clima 1 latitude 15 scraped down and re-engraved for 43 g[radus] 45 m[inutae], appropriate for Florence or Pisa/Clima 2 latitude 24
Clima 3 latitude 30/Clima 4 latitude 36
Clima 5 latitude 39/Clima 5 latitude 41
Clima 6 latitude 43/Clima 6 latitude 45
Clima 7 latitude 47/Clima 7 latitude 48 The latter side of this plate has been scraped down so that now only some of the numbers for the unequal hour lines are visible and virtually none of the lines for either these or for the projection.

All the plates carry the usual almucantars and azimuth lines except those for climates 2, 3 and 4 which have no azimuth lines. Neither set of lines is numbered. The almucantars are drawn for every five degrees though somewhat unevenly. Numbered unequal hour arcs are drawn beneath the horizon.

Rule
The single arm rule is too long for the instrument, it is stamped with more recent numeral forms than those found on the instrument, and is a replacement.

Alidade, ring and pin.
The plain, counter-changed alidade is, like the ring, probably a replacement though not a modern one. The pin however is likely to be original.

12 2/3in x 10 1/4in x 1/2in (32cm x 26cm x 1 1/5cm)
Footnotes:
Provenance
A European noble household located in Italy
Christie's South Kensington sale 29 September 1994, lot 136.
Private collection, UK.

Commentary
Since its appearance in 1994 this astrolabe has attracted a considerable degree of scholarly research. The first description of it, prepared by Gerard Turner for Christie's sale catalogue established its early date on the basis of the letter forms employed and similarities with other known early instruments. David King and John Davis have both subsequently remarked that the marking of 'climates' (the seven geographical bands of the Ancient World the centres of which were identified by the lengths of maximum daylight in hours) as well as latitudes on the plates is also an early feature and links the astrolabe into a long tradition stemming from Greece. Turner noted some problems with the positions of the star pointers and some of their names, problems that have since been elucidated by Elly Dekker who showed firstly that the ecliptic had been divided using a faulty construction, secondly that the positions adopted derived from John of London's star table of 1246, and thirdly that incorrect plotting of the star ecliptic coordinates had led to incorrect positioning. If the instrument was thus of little use qua se, these errors nonetheless have historical importance for revealing the difficulties faced by metal-workers to produce astrolabes in the workshop postulated to have produced this one. These difficulties were not confined to the calculation and design of the instrument. Analysis of the metal by John Davis leads to the conclusion that the metal production process was also not fully controlled. Both problems reinforce an early date for the instrument. That this was in Italy is suggested not only by the recent provenance of the instrument but by the Lombardic lettering and some similarities, such as the delimiting of the star names by dots, and the characteristic letter 'A', of this astrolabe with the products of a mid-fourteenth century Lombard workshop (Tomba group astrolabes for which see Davis et al) to which it seems to be a precursor.

[A copy of recent investigation of the instrument by Dr. John Davis using XRF analysis is included with the lot].

An imposing, early European astrolabe of historical importance for revealing some of the construction difficulties posed by such instruments in the first period of their manufacture in workshops. Already a source of enlightening evidence, the instrument nonetheless offers potential for further research and discoveries.

Bonhams is very grateful to Anthony Turner for his extensive assistance in compiling the catalogue entry for this lot.

Bibliography
CCA = Derek J. de Solla Price et al, A Computerized checklist of astrolabes, New Haven (Conn.), 1973.
John Davis, 'An early Italian Latin astrolabe' (in preparation).
John Davis, Bert Degenaar, Arie de Ruiter, Rob van Gent, Arie Pappot and Angelo Agostini, 'A previously unrecorded medieval Latin astrolabe and evidence for a mid-fourteenth century Instrument workshop', Bulletin of the Scientific Instrument Society, 146 2020, 6-23.
Elly Dekker, 'Exploring the retes of astrolabes', in Koenraad van Cleempoel, Astrolabes at Greenwich, a catalogue of the astrolabes in the National Maritime museum, Greenwich, Oxford 2005, 63-69.
David A. King, In Synchrony with the heavens: studies in astronomical timekeeping and instruments in Medieval civilization, 2 vols, Leiden 2005, ii 384-5.
[Gerard l'E Turner], 'A rare medieval brass astrolabe' in Christie's South Kensington, Fine scientific instruments, 29 September 1994, lot 136.
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