Epact Scientific Instruments of Medieval and Renaissance Europe

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Theodolite
Signed by Petrus ab Aggere
Dated 1560; Toledo
Brass; 101 mm square

The simple theodolite has a square plate with an inscribed circle with four geometrical quadrant scales 0 to 12 to 0, divided to 3, subdivided to 1 and to 1/4 with alternate hatching, numbered by 3, and within this a degree scale 0 to 360, divided to 10, subdivided to 5 and to 1 with alternate hatching, numbered by 10. The corners outside the circle are marked 'A', 'B', 'C' and 'D'. Within the circle pivots a circular plate with four slit sights (one is missing) and four corresponding indexes for the two scales. The plate itself has a circular scale on its edge, 0 to 360, divided to 10, subdivided to 1, numbered by 10; a quadrant-shaped aperture in the plate reveals a scale of winds beneath, while on the solid part the degree divisions are continued in a radiating pattern to the centre. The wind scale is marked for eight named winds, each with a section divided into 16 parts by a circular scale, with alternate hatching, and the reading on this scale is given by an inward pointing index inside the quadrant aperture.

Signed on the reverse: 'Absoluit Toleti Petrus ab aggere Mathematicus Regius, anno dn 1560.'

Jim Bennett

Istituto e Museo di Storia della Scienza, Firenze
Inventory no. 1278

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