Inventory no. 31514 - Epact entry
Epact number: 39280
Signed by Giovanni Antonio Magini
Late 16th century; Italian
Brass; 297 mm in radius
This very unusual and richly elaborated quadrant is essentially a planisphere, but very similar to the 'new' quadrant devised in the 13th century by Profatius Judaeus.
On one side is a projection of the heavens, in fact a folded astrolabe, indicating the equator, the tropics, the ecliptic and 37 stars. On the back of the quadrant is a stereographic projection of the northern hemisphere.
The instrument was probably not used for observation, but as a model of the heavens and as a calculating device for the same tasks as an astrolabe.
Source museum: Museum of the History of Science, Oxford
Museum number: Inventory no. 31,514
This quadrant is essentially a planisphere, very similar to the 'new' quadrant devised by Profatius Judaeus in the 13th century, which is basically a folded astrolabe. The quadrant is rather big, and has at the apex a ring for suspension.
A radial rule is made of two brass parts soldered together at the ends, so that the same rule is used for both sides of the instrument. Its ends are decorated. One the side of the qudrant where the polar projection is, the rule has an unequal scale of latitudes divided to 5 and to 1, subdivided to |1/4| on the edge, numbered from 5 to 90 by 5 from the centre to the limb and from the limb to the centre.
This side of the quadrant has a polar projection of the celestial sphere, with lines every degree. The lines of celestial latitude are numbered on one edge from 5 to 90 and from 90 to 5 by 5. A further division to |1/2| and |1/4| is engraved near the scale. The same scale is engraved also for celestial longitude 45 degrees (in the centre of the quadrant) and 90 degrees (on the limb). On this edge is also engraved the inscription 'QVADRANS PLANISPHAERII GENERALIS IO ANTONII MAGINI'. The ecliptic has divisions to 30, to 5, to 1 and to 1/4 degree, numbered from 5 to 30 by 5. The symbols of the zodiacal signs are engraved next to the ecliptic. The latitudes 23.5 and 66.5 are engraved with dotted lines. The longitude lines are engraved by 1, and are numbered on the other edge in bustrophedic way, from 0 to 90 (from the apex to the limb), then from 90 to 180 (from the limb to the apex), then from 180 to 270, then from 170 to 360. The scale on the edge is divided to 1, subdivided to 1/2 and to 1/4, numbered by 5. The numbers 0 and 180 cannot be seen since they are covered by the sliding rule. The astrological houses are numbered from I to VI to XII. The edges and the limb of the quadrant are decorated.
The other side of the rule has a unequal scale of celestial latitude, divided to 5 and to 1, subdivided to 1/2 and to 1/4 on the edge of the rule. It is numbered from 85 to 5 by 5, from the apex to the equator, inscribed 'DECLINATIO SEPTENTRIONALIS', and from 5 to 30 by 5, from the equator to the limb, inscribed 'DECLINATIO MERIDIANA'.
The limb of the quadrant is engraved with a scale of right ascension engraved 'Ascensio recta', with a scale of degrees divided to 5, to 1, to 1/2 and to 1/4, numbered in bustrophedic way from 5 to 90 (from left to right), then from 275 to 360 (right to left), then from 180 to 270, then from 95 to 180, by 5. All these numberings go from the limb towards the centre of the instrument. The symbols of Aries and Aquarius are also engraved to the left of the scale, and of Cancer and Capricorn to its right. The main part of the quadrant is inscribed with a projection of the heavens. The ecliptic is divided to 5, to 1, to 1/2 and to 1/4 degrees, numbered from 5 to 30 by 5. The lines of celestial longitude corresponding to each degree are also engraved, as are the lines of celestial latitude, up to 6 degrees above and below the ecliptic. The names and symbols of the zodiacal signs are engraved along the ecliptic. On both the folded parts of the ecliptic are engraved 'LATITVDO BOREALIS' and 'LATITVDO MERIDIONALIS'. Superimposed to this projection is another geocentric projection, engraved with the meridian 'Meridianus' on the left edge, and the Horizon 'Horizon Rectus' on the right edge. The equinoctial land tropic lines are engraved 'AEQVINOCTIALIS' and 'TROPICVS |Cancer|' and 'TROPICVS CAPRICORNI'. The almucantars are engraved every 3 degrees from 9 to 90, numbered from 9 to 87 by 3, and are engraved 'HORIZONTES' and elsewhere 'OBLIQVI'. On the left edge is an unequal scale of latitudes, divided to 5, to 1, to 1/2 and to 1/4, numbered from 65 to 90 to 10 (from the limb to the centre) and engraved 'ELEVATIONES POLARES SEV CIRCVLI POSITIONVM'. On the right edge is another unequal scale of latitudes divided to 5, to 1, to 1/2 and to 1/4 degrees, numbered from 85 to 5 and from 5 to 25 from the apex to the limb. It is inscribed 'DECLINATIO SEPTENTRIONALIS' and 'DECLINATIO MERIDIANA'. The names of 31 stars and their constellations are engraved. In the centre of the quadrant is engraved a coat-of-arms with a pyramid, standing on a rectangular base, between two stars. The edges of the quadrant are decorated with a geometrical motif.