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Instrument type

circa 1370; English
Brass; 154 mm in diameter

The mater consists of two riveted layers of brass, one constituting the plate and the other the rim and throne.

The limb has a scale of degrees from [0?] to 360?, divided by 5 and by 1?, numbered by 5?, with 360? at the zenith. The inner side of the mater has engraved the east-west and the meridian line.

Suspension is by means of a three-lobed throne, shackle and ring, with an additional ring.

The rete is of Gothic type with a quatrefoil inside the ecliptic and a half-quatrefoil between the tropic of Capricorn and the equinoctial line. The 32 star pointers, named, are in the flambent form and some of them are double, making a sort of 'whale-tail'. The ecliptic is engraved with the names of the zodiac signs and is divided on the edge by 3? but is not numbered, and it is linked to the Capricorn band with two ties. The east-west line is counterchanged twice on each side, as is the meridian line. The Capricorn band has engraved the head and the tail of the Dragon.

The four plates are all engraved, except for one, with both tropic and equator lines, east-west and meridian lines, almucantars and azimuth lines. Plate 1 is engraved for latitude 33? and 36?, but has no other marks. Plate 2a is engraved for latitude 38?, with no other marks, and plate 2b for latitude 45?, with astrological houses numbered from 1 to 12, twilight line and unequal hour lines engraved, and almucantars engraved by 3? but numbered from 12? to 72? by 12?. A '3' is marked next to the horizon line. Plate 3a is engraved for latitude 42? with no other marks, and plate 3b has no indication of the latitude and no azimuth lines engraved. Plate 4 has engraved full horizon lines, engraved by 4? but marked by 8?; starting from the top, '33', '41', '49', '42', '34', '32', '40', '48', '45', '37', '31', '39,' '47', '44', '36', '30', '38', '46', '43', '35'. Plate 4b is blank.

The back of the mater is engraved with a scale of degrees on the limb, in four quadrants of 90? with 90? at the top, divided to 5? and to 1?, numbered by 5?. Next to it is a zodiac scale with each sign divided from [0?] to 30? sharing the same divisions of the scale of degrees, numbered by 5 with the names of the signs engraved further to the centre. Further to the centre is a calendar scale with the names of the months and the 10th, 20th and last day engraved. The first point of Aries corresponds to the 11th of March.

On the bottom half of the plate, next to the centre, is engraved a double shadow square, divided by 4 and by 1 but not numbered, and on the top half are unequal hour lines, not numbered.

The alidade is counterchanged on each side and has on each arm with an unequal scale numbered [0] to 6 by 1, and ends in Gothic style. There are two sighting vanes, each with two holes. The pin is in the form of a four-leaf flower and is kept in place by a ring.

See R. T. Gunther, The Astrolabes of the World (2 vols, Oxford, 1932).

Ilaria Meliconi

Museum of the History of Science, Oxford
Inventory number 47615

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