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Dated 1521 ?; German
Brass; 169 mm in diameter

The mater has been turned from one piece, with a groove in the rim, occupied by a think brass wire running round the circumference and secured at the throne. The throne comprises three ten-petalled flowers on a foliate base in the manner of Georg Hartman. The limb has an outer scale of 24 hours, numbered by 1, and an inner degree scale 0 to 360 beginning on the eastern end of the east-west line, divided to 5, subdivided to 1, numbered by 5, but the digits expressing the hundreds are not repeated after 100, 200 and 300. The inside of the mater has been engraved as a tablet of horizons, with numbered lines for latitudes between 16 and 63 degrees, and bears the date '1521'.

Rete for about 23 stars, of which 15 have individual pointers and the rest are marked on the bands of the rete. The stars are not named, but are given planetary symbols indicating their astrological significance. The ecliptic circle has symbols for the zodiacal signs, each with a scale of 30 degrees, divided to 10, subdivided to 2, numbered by 10. The east-west and meridian bars are each counterchanged once, the latter marked 'AUSTR' and 'BORIALE'.

Three plates for latitudes 38 and 41?; 42 and 45?; and 50 and 41?. There are many differences in the lines engraved on the various plates, the most complete being the first for latitude 41, the only projection with azimuths. This plate, marked 'Polus 41 Grad:', has the horizon marked 'Horizon Obliques', the east-west line 'Horizon Rettus' and the crepuscular line 'Linea Aurore Siue Crepuscoline'. There are azimuths every 5 degrees, numbered by 5 from 0 at the east and west points to 90 on the meridian north and south, and altitude lines every 2 degrees, numbered from 0 to 52 by 4 and from 60 to 90 by 10. There are lines for the houses of heaven, numbered I to XII, and for unequal hours beneath the horizon, numbered 1 to 12 by 1. There are circles for the Tropic of Cancer and the equator. The other plate for 41 degrees is marked 'Circuli Posit: a gra: 41'. It is divided according to the houses of heaven, each house divided into 6 subdivisions, alternate lined being numbered by 10 from the meridian line, 90 to 0 to 90 to 0 to 90.

The back has an outermost scale of degrees from the throne 90 to 0 to 90 to 0 to 90, divided to 10, subdivided to 1, numbered by 10. This degree division also served for a zodiacal scale, with names of the signs, each with a 30-degree scale, numbered by 10. Inside this is a calendar scale, with the names of the months, each with a scale of days, divided to 10, subdivided to 1, numbered by 10 as appropriate. The first point of Aries is at 101/2 March. Inside this scale is one for the 28 mansions of the moon, numbered by 1. The lower half of the central space has a double shadow-square, with a scale 0 to 12 to 0 to 12 to 0, divided to 3, subdivided to 1, numbered by 3. Above this is a diagram of the celestial spheres, with planetary symbols from the moon to Saturn, and the sphere of the fixed stars marked by stars.

A rule is riveted to the rete. The alidade, with vanes each having two pinhole sights, is secured by a screw and wing nut.

See: R. T. Gunther, The Astrolabes of the World (2 vols., Oxford, 1932), vol. 2, pp. 425-6.

Jim Bennett

Museum of the History of Science, Oxford
Inventory number 47657

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