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Theodolite
Unsigned
Later 16th century; English
Brass; 160 mm in diameter

Only part of the instrument survives: a brass semicircle with a thicker bar on the diameter and a single sight. There are two round holes on the plate. On one face of the semicircle is a scale of degrees on the limb, divided to 10, to 5 and to 1 by alternate shading. On the external arc the numbering is from 10 to 90 by ten with [0] at the centre, and on the internal arc the numbering is from 10 to 180 with [0] on the right hand side. In the centre of the semicircle is engraved a double shadow square with the Elizabethan arms, a lion and a dragon, and the motto 'HONI SOIT QUI MAL Y PENSE'. The shadow square is divided to 3 and to 1 by alternate shading and is numbered from 3 to 36 by 3 and from 3 to 12 by 3. It is inscribed 'VMBRA RECTA' and 'VMBRA VERSA' twice.

The other side of the semicircle is engraved with a scale of degrees on the limb, divided to 10 and to 1 by alternate shading, numbered from 10 to 90 by 10 with 90 at the centre on the external circle, and from 10 to 90 by 10 with [0] at the centre on an inner circle. The central part of the instrument is engraved with a diagram of hours, symmetric about the radial centre of the circle, numbered from 1 to 12, and an equal scale of the sun's declination engraved close to the straight edges. The symbols of the zodiacal signs are engraved. The sun's declination is also engraved on two curved lines in approximately the middle of the plate. Closer to the centre are engraved the numbers '51 30', '50', '53', '55'. Close to the centre is also engraved a table with the date of the sun's entry into the zodiacal signs, named 'Mon' with the names of the months, 'Dai' with the days of the month, 'Sun' and the word repeated, 'sig<n>e' and the symbol of the zodiacal sign.

Ilaria Meliconi

Istituto e Museo di Storia della Scienza, Firenze
Inventory no. 2528

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