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Instrument type

circa 1400; French
Brass; 112 mm in diameter

The mater is made of a single piece of brass. The limb is engraved with a scale of degrees starting below the throne from 0 to 360, divided to 5, subdivided to 1 and numbered by 15.

The throne is three-lobed and engraved with decorative double lines on the border and a symbol on one of the lobes. The shackle and ring are simple.

The rete is derived from the 'Y' type, with the abbreviated names of the zodiac signs on the ecliptic, connected to the Capricorn band by two ties. The ecliptic has further division to 2?, not numbered, on the edge of the band. The east-west line is counterchanged twice whereas the meridian line is straight. The star pointers (one of which is broken) are for 16 stars, named in Lombardic script, and are of the 'wavy-flame' type.

The four plates all have east-west and meridian line, both tropic and equator lines, unequal hour lines and almucantars every 4? but none of them is numbered. The first plate is for latitude 38? and has lines for the astrological houses, but does not have zenith lines. On the back it is engraved in the same way, for latitude 40?. The second plate is for latitude 42? and has azimuth lines, though not numbered. Its back is engraved in the same way for latitude 44?. The third plate is engraved for latitude 47?, also with azimuth lines. Its back, for latitude 49?, is engraved in the same way and also marked '49 PIS' [Paris]. On this face the almucantars are engraved with a dotted line every 12? and the hour lines every other degree. The fourth plate is engraved for latitude '51 40'' (London), with azimuth lines and astrological houses lines. Its back is engraved for latitude 60?.

The back of the mater has a scale of degrees divided in four quadrants by 5? and by 1?, numbered by 15? with 90? at the zenith. The zodiac scale has the names of the zodiacal signs abbreviated and divided from 0? to 30? by 5? and by 1?, numbered by 10?. Further to the centre, a calendar scale has engraved the abbreviated names of the months divided by the day with the 10th, 20th and last day numbered. The first point of Aries corresponds to the 12.5 March.

In the top half of the plate, next to the centre, are engraved unequal hour lines, not numbered, and on the bottom half is a shadow square, not numbered.

The alidade is counterchanged and is decorated with foliage. The pin is simple and plain, as is the wedge.

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

Ilaria Meliconi

Museum of the History of Science, Oxford
Inventory number 54330

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