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Signed by Jean Giamin
Later 16th century; Rome
Iron; 282 mm in radius

Side 1: Two arcs are riveted to the limb of the instrument 30.5 mm apart to form a slot in which slides a cursor. The lower arc is decorated with a flowing foliate border, the upper arc carries a scale of 90? reading to 1? by alternating hatched and unhatched divisions. The cursor carries a doubled zodiacal calendar (with 0? Aries at 10.5 March), the months being named, the zodiacal houses being indicated by their symbols. Above this is a shadow square, the diameter of which (marked 'Vmbra reta') stretches from the apex to the 45? point on the inner degree scale. The two sides of the shadow square are labelled 'Vmbra recta' and 'Vmbra versa' and it is divided to 12 by numbered groups of three. Drawn across the shadow square are the arcs for an unequal hour diagram of the type known as a 'quadrans vetus'. The signature is placed between the umbra versa line and the degree scale arc, and the remaining free space is filled by three unequally sized circles of gold arabesque decoration within silver scroll outlines. The two sides of the instrument are decorated with repeating flowing foliate borders similar to those on the limb, and an index, graduated 0 to 90 by numbered groups of 10 subdivided to one on the bevelled fiducial edge, is pivoted from the apex/centre of the instrument. Two sights originally mounted on the edge of the instrument parallel to the umbra recta are now missing.

Face 2: The limb is decorated by six alternating, separated, sections of flowing leaf decoration and linked lozenges, each section occupying approximately 15? of the arc. Above this is a 360? scale reading to 1? by alternately hatched and unhatched divisions in four concentric arcs. Above this is a further arc of flowing leaf decoration and above this is the diagram of an horizontal quadrant, that is a stereographic projection of the celestial co-ordinates onto the plane of the observer's horizon. The diagram is in effect that found on an astrolabe plate, with the addition of the path of the ecliptic, when this is twice folded on itself to produce a quadrant. The right hand edge of the quadrant represents the meridian, the left hand edge the horizon, both being so labelled in Latin. The almucantars are drawn as arcs across the instrument for every 2( and numbered in groups of 10, 0 to 90 (equator) to 60. The two arcs of the ecliptic are drawn with the names and symbols of the signs, each sign divided to 30?, and the arc for the equinoctial is also divided to 90?. A segment of the tropic of Cancer arc is drawn below the apex and the names and positions of stars are marked. Those that can now be read are: 'Cor scorpii', 'Canis maior', 'Oculus tauri', 'Venter ceti', 'Spica', 'Caput serpentarii', 'Lucia hydr?e', 'Canis minor', 'Dexter humerus Orioni', 'Corona serpentarii', 'Vulur cadens', 'Lanx meridi', 'Lanceator', 'Hircu', 'Dexter La Perseiu', 'Caput Algol', 'Dorsum', 'Cauda' 'Umbilicus Andro{meda}'.

A rule graduated with a reversed 90? scale (portion nearest the apex), and a 231/2? obliquity scale is pivoted at the apex/centre of the instrument.

Anthony J. Turner

Istituto e Museo di Storia della Scienza, Firenze
Inventory no. 2523

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