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Signed by Giovanni Battista Giusti
Later 16th century; Florence
Gilt brass; 90 mm in radius

The quadrant side of the instrument is graduated on the limb with a 90? scale numbered in groups of five and reading to 1? by divisions that are alternately slightly cut into the medal and left level with it. Above this, in a concentric arc, is the inscription 'QUADRANS HORARIV{M} AD LATITVDINEM GRAD{I} XLII' ('horary quadrant for latitude 42?'), 42? being the latitude of Rome. Above this the left and centre of the instrument are filled with the diagram for an Italian hours dial (9 to 23 without subdivisions) the morning hours being indicated by smooth lines, the afternoon hours by dotted lines. On each side of the diagram the two halves of an undivided calendar are marked, and the remaining space at the right of the instrument carries the inscription 'LINEA PVNTORVM POS{T} MERIDIES' ('line of dots afternoon'). In the apex is the magic square of three '4 9 2' / '3 5 7' / '8 1 6' which totals 15 in all directions and has a sum of three times itself, viz. 45.

The second face of the instrument is marked with a double circle divided into eight sectors each marked with the initial two letters of the wind directions, North being placed in the apex of the instrument. Above the north indication is a well modelled head (?olus?) chiselled in relief. The circles and initial letters of Tramontanus are engraved on a hinged flap, attached at the base of the head, which covers a small pin gnomon scaphe dial for Italian hours marked with undivided hours 9 to 23. Below this dial is a partly inset compass (lacks needle and glass), and at the south point a second subsidiary bowl perhaps for a needle locking device. The free space in the corners of the quadrant and beneath the scaphe dial are filled with partly cross-hatched scrolled foliate decoration. Two engraved and moulded sights one with pinnule are set along the longer edge. The plumb and cursors line are missing. The original box has a six roll frame around the edge enclosing a central symmetrical leaf motif, single elements of this being repeated in the corners beneath a five petal flower.

Provenance: Pope Gregory XIII and thence to the Medici collections being mentioned in the Wardrobe Inventory of Ferdinand I (Inv. Guard. Med. N. 190 car 39) as 'Quadrante d'ottone dorato ordinario con oriuolo italiano che era di Papa Gregorio in custodia di corame' and in the 1654 inventory of the Uffizi as 'Un quadrante di ottone dorato, di semidiametro di P. 3, che da una parte vi ? un oriuolo orizzontale con la sua bussola e dall'altra un oriuolo a Sole con il perpendicolo quale manca e che ? fatto all'altewwa di 42, dentro custodia di corame rosso, foderata di velluto simile'.

Anthony J. Turner

Istituto e Museo di Storia della Scienza, Firenze
Inventory no. 2525

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