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Signed by Thomas Gemini
Dated 1559; London
Brass; 357 mm in diameter

The mater of this large astrolabe is made of three riveted layers of brass.

The face of the limb is divided into hours, numbered I to XII twice, and into 360? to 10?, subdivided to 5? and to 1? by alternate shading, numbered by 10?, with 0? at the east point.

The suspension ring is broken and a piece is missing. The throne is decorated with two scrolls on the sides of a circle, inscribed 'Elizabeth Dei Gratia Anglia Franciae & Hiberniae Regina &c.' and on the back is her coat-of-arms between the initials 'E R'.

The inner side of the mater has a 'QUADRATVM NAVTICVM' with, at its centre, a wind rose with 32 directions, named in English. Enclosing the wind rose is a shadow square, divided to 10 and to 1, numbered by 10 with 90 at the edges. Between the wind rose and the square are the names of the main winds, in Latin and Greek characters. Outside the square are the inscriptions 'Longitudo minor siue Occidentalior' and 'Longitudo maior seu Orientalior', and 'Latitudo minor uel Australior' and 'Latitudo maior aut Borealior'. At the bottom of the square is the signature 'Thomas II [Gemini] 1559'.

The rete is of typical Flemish pattern, similar to that of the Arsenius workshop in Louvain. The brass bands constituting the decoration are superimposed to one another and not derived from a single plate. The 22 star pointers are of the flambent design and end in a small star shape. They are all named. The ecliptic is divided on its edge into 360? to 5? and to 1?, grouped by 10? and numbered by 5?. The zodiacal signs are indicated with names and symbols. Some stars are indicated on the ecliptic band and on the Capricorn band.

The only plate is engraved on both sides and does not have a notch but a small hole which fits on a pin on the inner part of the mater. On one side it has a zodiac scale on the limb, divided to 10?, subdivided to 5? and to 1? by alternate shading and numbered by 5?. The zodiacal signs are named and numbered from Aries with their symbols. There is a corresponding calendar scale in which the first point of Aries is on the 11th of March. The months are named and numbered from January. Closer to the centre is a calendar scale, divided to five and to the single day by alternate shading, numbered by 5 to the last day of the month as appropriate. There is a small space at the end of the year, indicated '1/4'. Next to the centre is, on the bottom half, a double shadow square, divided to 1 and subdivided to 1/2 and to 1/8, numbered by 2, indicated 'Umbra Recta' and 'Umbra versa', 'Horae ante meridiem' and 'Horae post meridiem'. On the top half of the plate are unequal hour lines numbered I to XII with further divisions of each hour into 15 parts, and indicated 'Horae inae quales'.

The other side of the plate is engraved with east west and meridian lines, indicated 'HORISON RECTVS' and 'Linea meridiana', and full horizon lines engraved every 2? and numbered by 10?. Each 10th degree line is dotted with little arrows. The equator line is indicated 'Equinoctialis'. At the bottom of the plate is engraved 'Horizontiale Catholicum' twice, and the tropic line is indicated 'Tropicus Capricorni'.

The space in the middle of the plate between the horizon lines is engraved '1659 Acad. Oxon. in usum praecipue Prof. Savilianorum: Ex dono Nic Greaves S.T.D. In memoriam {Tho. Bambridge M.D. Jo Greaves A.M.N. fra:} olim Astronomiae Prof. Savil'.

The back of the mater has a scale of degrees in four quadrants from [0?] to 90? with 90? at the zenith, divided to 10?, subdivided to 5? and to 1? by alternate shading, numbered by 5?.

The whole plate is engraved with an 'astrolabium catholicum' in the style of Gemma Frisius. The ecliptic is divided in degrees to one by alternate shading and numbered from [0?] to 30? by 10?. The symbols of the zodiacal signs are also engraved on it. The stereographic projection has lines every 2? in both longitude and latitude, and every 10? the line is marked with small arrows. The equator is divided into 12 parts, numbered in both directions 1 to 12. The stars are indicated with a small star symbol.

The rule is divided into two lines, each representing 180?, divided and numbered by 10? with 0? at the centre. It has a decoration at both ends. The sliding cursor is missing from the rule.

The alidade is counterchanged and has an arabesque decoration at the centre. It is graduated on one arm with an unequal scale of latitudes, indicated 'Latitudo meridionalis' and 'Latitudo Septentrionalis' from [0?] to 70? and from [0?] to 20?, both divided to 2? and numbered by 10?. On the other arm it is graduated with an equal scale of hours, indicated 'Horae ortus solis' and 'Horae occasus solis', numbered 1 to 10 and 2 to 12.

The pin has been replaced by a screw with square washer.

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

Ilaria Meliconi

Museum of the History of Science, Oxford
Inventory number 42223

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