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Inventory no. 45127 - Epact entry

Epact number: 19678

Astrolabe

Unsigned
circa 1500; Italian ?
Brass; 95 mm in diameter

Main text

This instrument has been classified as an astrolabe, but it is primarily an astrological instrument used for finding the position of planets and other celestial bodies, especially in relation to the traditional astrological houses, rather than an observational device.

It is unusual in a number of respects, including the pattern of the rete, but more especially in the series of eight concentric rotating volvelles on the back.

Source museum: Museum of the History of Science, Oxford
Museum number: Inventory no. 45,127

Detailed text

This astrological instrument consists of a thin brass plate with rete and rule riveted on one side, and a series of 8 brass volvelles with arms riveted on the other side.

There was probably a system of suspension, now missing.

The plate is engraved on the face with the rete with tropics and equator lines, almucantars and azimuth lines and unequal hour lines numbered from 1 to 12, and twilight line. The space between the horizon and the first and last hour line has been shaded. A faint inscription '33' at the centre of the plate probably indicates the latitude. The limb of the plate is graduated with four quadrants of 90°, divided by 10°, subdivided by 1°, with 90° at the zenith, numbered by 10°.

The rete has an unusual pattern; the ecliptic is engraved with the abbreviated names of the zodiac signs and with a scale of degrees divided by 30°, subdivided by 5° and by 1°. Inside is the motif of an eight-leaf flower. The 28 star pointers are in the form of round-ended lobes with a small star at the end, and there are 13 other stars which are not marked on star pointers but on the design of the rete itself.

The rule is single arm and has an unequal scale marked only 'SE' and 'ME'.

The back of the instrument is engraved on the limb with the names and numbers of the astrological houses: 'VITA ·1·', 'LVCRV ·2·', 'FERATR ·3·', 'PATER ·4·', 'FILIO ·5·', 'SERVS ·6·', 'VXOR ·7·', 'MORSE ·8·', 'ITER ·9·', 'DOMINS ·10·', 'AMICVS ·11·', 'CARCERE ·12·'. Each house is divided in 2 parts and subdivided to 8. The first volvelle has on the limb a calendar scale with 365 days and the names of the months (in an uncommon spelling). Some of the days are marked with a very small star. Placed inside this volvelle is a zodiac scale divided to one degree, numbered from 10 to 30 by 10, with the zodiacal signs named. The first point of Aries corresponds to the 16th of March. Further to the centre is a circle indicating the ruling planets, three for every sign. The next circle bears the name of the ruling planet, with the following being inscribed 'MO', 'ST', 'ME' in turn, with the indication of water, earth, fire or wind accordingly to the zodiacal signs. The following circle is divided in four parts with only these symbols.

The first volvelle has 8 arms, engraved 'OP{POSITIO}', 'QV{ADRATVS}', 'SE{XTILE}', 'TE'. The following volvelles have arms engraved 'SATVRNO', 'IVPITER', 'MARSE', 'VENVS', 'MERQRIO', 'SOL'. The latter is also divided in 29.5 parts, each further divided into four, and has a line to allow the upper volvelle, pierced and marked 'LVNA', to turn and show the lunar phases.

The last volvelle is just a double arm, shaped as the head and tail of the Dragon, inscribed 'CAPVT' and 'CAVDA'.

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

Ilaria Meliconi

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