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Signed by Adrianus Descrolieres
Dated 1580; Paris
Gilt brass; 271 mm in diameter

The rim of the mater bears an equal 24-hour scale on the outside numbered twice from I to XII starting at the throne, divided to 4 minutes subdivided to 2 minutes. The inside has a 360? altitude scale, graduated, 0? to 90?, 90? to 0?, 0? to 90?, 90? numbered by 10? starting from the east and west points, divided to single degrees and subdivided to half degrees. The rim is rivetted to the backplate. The inside of the rim has a recess at 12 o'clock underneath the throne to accommodate the tongues of the plates.

The inside of the mater is engraved with a Quadratum Nauticum, the compass directions are indicated by the names of the winds in the three bands with the cardinal directions marked as: 'Septe<n>trio', 'Oriens', 'Meridies', 'Occidens'. Reading north, east, south, west they are centre band: 'Tramontana', 'Graeco tra{montana}', 'Graeco, Graeco leu{ante}', 'Leuante', 'Scirocco leu{ante}', 'Scirocco', 'Ostro sci{rocco}', 'Ostro', 'Ostrogar{bino}', 'Garbino', 'Ponente gar{bino}', 'Ponente', 'Ponente maes{tro}', 'Maestro', 'Maestro tra{montana}'; in the middle band: 'Aparctias', 'Aquilo', 'Cecias', 'Subsolanis', 'Eurus', 'Phenix', 'Auster', 'Libonotus', 'Africus', 'Zephirus', 'Corus', 'Circius'; and in the outer band: 'Grecus', 'Syrochus', 'Lybicus', and 'Magistralis'.

The outsides of the squares have scales from 0 ? to 90 ?, numbered by 30? and subdivided to 3?. On top of the squares are the inscriptions (reading from the north): 'Longitudo maior vel Orientalior', 'Latitudo minor et Australior', 'Longitudo minor sive Occidentalior'.

The throne is fixed to the rim by two screws. It consists of a base in the shape of the section of a ring carrying two reclining sartyrs (male on the left, female on the right) supporting a compass (magnetic deviation c. 12? east, compass needle missing) inset into a shield shaped suspension surmounted by the shakle. The swivel pin and the suspension ring are missing. The base ring is signed 'Adrianus Descrolieres facit' and dated 'Lutetie anno 1580'.

The rete follows the typical pattern of Arsenius type astrolabes. The names of 43 stars are given with their corresponding planetary temperaments and their magnitudes. Some star names are abbreviated so that instead of the name of the zodiacal sign the symbol is given: 'Cauda ceti [Saturn] 3', 'ndro<medae> u<m>bilic<us> [Venus] 3', 'Venter ceti [Saturn]', 'Luba ceti', 'Meduse caput [Saturn] [Jupiter] 2', 'Nares ceti 3', 'Persei lat{us} dex{trum}', 'Oculus [Taurus] [Mars] 1', 'Hircus [Mars] [Mercury] 1', 'Ori{onis} si<nister> hu<m>e{rus}', 'Orionis sin{nister} pes [Jupiter] [Saturn] 1', 'Orio<n>is dex{ter} hu<m>er<us> [Mars] [Mercury] 1', 'Canis maior [Jupiter] [Mars] 1', 'Canicula [Mars] 1', 'Cor [Leo] [Mars] 1', 'Hydre clara, Cervix [Leo] [Saturn] 2', 'Ursa maior [Mars] 2', 'Crateris fu<n>d<us> 4', 'Cauda [Leo] [Saturn] [Venus] 1', 'Corui ala dex{tra} [Jupiter] [Mars] 2', 'Spica [Virgo] [Mars] [Mercury] 1', 'Arcturus [Jupiter] [Mars] 1', 'Bootis si<nister> hu<m>{erus} [Mercury] [Jupiter] 3', 'Lanx boree clarior, Corona S{eptentrionalis} [reengraved]', 'Cor [Scorpio] [Jupiter] [Mars] 2', 'Ophiuchi sin{nistra} man<us>', 'Caput herculis [Mars] [Mercury] 2', 'Ophiuchi caput [Saturn] [Venus] 3', 'Ophiuchi ma{nus} dex{tra}', 'Caput draco{nis} [Saturn] [Mars] 3', 'Lyra [Venus] [Mercury] 1', 'Aquila [Mars] [Jupiter] 2', 'Cauda cigni [Venus] [Mars] 2', 'Cauda [Capricorn] [Jupiter] [Saturn] 3', 'Cephei dex{ter} hu{merus} [Jupiter] [Saturn]', 'Pegasi rictus [Mars] [Mercury] 2', 'Crus [Aquarius] 3', 'Pegasi hu<m>er<us> [Jupiter] [Mercury] 2', 'Crus pegasi [Mars] [Jupiter] 2', 'Ala pegasi, Cassi{opeie} pec{tus}'.

The ecliptic is marked with the usual Latin names of the zodiacal signs (some abbreviated) with their symbols and the Latin names of the months. Each sign is divided into single degrees, each month is divided into single days.

There are three plates which are each marked on both sides (except 3b) with the circles for the equator (marked 'AEquinoctialis' or 'AEquator') and the tropics (marked 'Tropicus Cancri' and both Tropicus Capricorni' and 'Circulus Capricorni'), azimuths for every 5? (numbered by 10?), the almucantars for every 2? (numbered by 10?), the lines for the unequal hours (marked in Arabic numerals from 1 to 12), and the markings for the astrological houses in the manner of Regiomontanus (marked in Arabic numerals from 1 to 12). The 'Horizon Obliquus' and the 'Horizon rectus' are indicated and marked. Three cardinal directions are marked as 'Oriens', 'Septentrio and 'Occidens'. Some of the markings are abbreviated or give the symbol where the name of the zodiacal sign would be expected.

The plates are laid out and marked for the following latitudes ('Pro elevatione poli'): 1a) 39; 1b) 42?; 2a) 45? (with mistake in the first letter(s) of 'Aequator'); 2b) 48?; 3a) 51?.

Plate 3b) bears markings for the Horizontale catholicum with horizons for every 2?, numbered by 10?. The 'HORIZO<N> RECTUS' , the 'Aequinoctialis' and the cardinal points 'Oriens', 'Occidens' and 'Septe<n>trio' are marked. The bottom half of the vacant space outside these circles is taken up by a double shadow scale marked 'UMBRA RECTA' and 'UMBRA VERSA' to the base of 12 and 60 respectively, divided into 0.2 digits and single digits respectively, numbered 1 to 12 and 10 to 60 respectively. The top half inside the horizons contains an hour diagram for converting equal hours into unequal hours and vice versa. The unequal hour ('Hore inequales') are marked 1 to 12 and divided by 4 minutes. The equal hour lines ('HORAE AEQUALES') are given for every half hour and marked 1 to 12 to 1 'Hore ante meridiem' and 'Hore post meridiem'. The equal hour lines are laid out in the form of segments of vertical hyperbolic spirals.

The back of the instrument is engraved with Gemma Frisius' universal projection with the position of 21 stars marked with a star, but not identified. The ecliptic is marked with the symbols of the zodiacal signs. The four quadrants are each marked on the outside on the rim 0? to 90?, numbered by 10? and subdivided to 5?. The tropics are graduated1 to 12.

The rule is graduated along both margins, starting at the top in the centre from 0? to 90?, continuing from 90? to 270? along the whole length on th bottom and from 270? to 360? back on the top numbered by 10?. The zodiacal signs are represented by their symbols. In the vacant space between the lines for the zodiacal signs the following star names are given (starting at the tropic of Capricorn): 'Spica [Virgo] 8', '40 Eridanus postrema', '32 Extr [Aquarius] fuse', '36 Cauda [Scorpio]', '51 Canopus', '15 Canis maior', '9 Orionis sin{nister} pes', and 'Mori stelle'.

The alidade mounted on the front and fixed with a winged screw. It is marked with the 'Hore Ortus [Sun]' (numbered 1 to 10) and the 'Hore occasus' (numbered from 1 to 12) on one arm. On the other arm are markings for the 'Declinatio septentrionalis' from 0? to 90?, numbered by 10?, and for the 'Declinatio Meridion{alis}' from 0 ? to 23 1/2 ?, numbered by 10 ?.

The instrument came from the Spitzer collection and was purchased in 1893. It is described in 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. 117, no. 337.

Silke Ackermann

British Museum, London
Registration no. MLA 1893,6-16.1

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