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Astrolabe
Workshop of Jean Fusoris
circa 1400; French
Brass; 72 mm in diameter

The mater of the astrolabe is made of two soldered layers of brass, one constituting the plate and the other constituting the rim and the throne. The inner part of the mater is engraved with tropic and equator lines.

The face of the limb is divided into 360? by 5? and by 1?, numbered 1 to 12 twice every 15? or an hour. The rim of the limb is roughly engraved with the letters 'M', 'A', 'M'.

The throne is simple and has two fillets on the sides, the shackle and ring are simple.

The rete bears 21 star pointers of the flambent type, all named with Gothic lettering. The ecliptic is divided on the edge into 360? by 10? and by 2? but not numbered, and on the band has the abbreviated names of the zodiacal signs. The ecliptic is connected to the Capricorn band with two ties. The east-west line is counterchanged twice on each side, as is the meridian line which is interrupted at the top end by a band similar to the equatorial line.

There are six plates, all of which, except for one which is completely blank and much thicker, are engraved with east-west and meridian lines, both tropic and equator lines.

The first plate is engraved for latitude 42?, and has engraved almucantars every 3 degrees and azimuth lines, unequal hour lines numbered every even number. The almucantar for 3? is indicated with a '3'. The back of the plate has no other lines except for the ones common to all plates.

The second plate is engraved for latitude 45? with almucantars and azimuth lines, unequal hour lines marked every even number, with a '3' on the almucantar for 3?. The back of the plate is engraved in the same way for latitude '54 g<raduus> 30 m<inutis>'.

The fourth plate is engraved in the same way for latitude 52?, but its back has only the lines common to all plates.

The fifth plate is engraved '55 g 30 m' with almucantars, azimuth lines and unequal hour lines every even number with a '3' on the almucantar for 3?. Its back is engraved in the same way for 'Paris'.

The last plate is engraved in the same way for latitude 56?. Its back has only the common lines plus horizon lines with a declination scale marked only '51' (?) twice.

The back of the mater is divided in four quadrants of 90? by 5? and by 1?, numbered by 10?, with 90? at the zenith. The same division is common to the zodiac scale, with each sign named and numbered in degrees by 10?. Further to the centre is a calendar scale with the abbreviated names of the month, divided into 365 days with the 10th, 20th and last day of the month numbered. The first point of Aries corresponds to the 11th of March. Next to the centre are, on the bottom half a double shadow square, divided by 4 and by 1 and numbered by 2, and on the top half unequal hour lines numbered 1 to 6.

The alidade is counterchanged, has decorative lines on both arms and is finished in Gothic style. The vanes have one sighting hole each. The pin is simple and the wedge is rectangular.

See R. T. Gunther, The Astrolabes of the World (2 vols, Oxford, 1932), vol. 2, p. 343.

Ilaria Meliconi

Museum of the History of Science, Oxford
Inventory number 49636

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