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Proportional Instrument
Signed by James Kynvyn
Dated 1597; London
Brass; 310 mm in diameter

Circular brass plate with a suspension ring, and a degree scale on the edge 0 to 360, divided to 10, subdivided to 5, to 1, to 1/2 and to 1/4, numbered by 10. The central area is divided into four quadrants, two of which (90 to 180) have two sinecal quadrants whose sides have scales 0 to 40, divided to 5, subdivided to 1/2 with alternate hatching, numbered by 10. Dotted lines extend across the quadrant from the scales for every unit and continuous lines for every ten. The quadrant from 0 to 90 has parallel lines for every degree for a decreasing scale 0 to 90, numbered by 5, with every 5 line indicated by arrows; lines for only every 2 degrees are included between 70 and 80 and none between 80 and 90. It gives sines of angles for radii up to 200. A scale 0 to 200 on the left coincides with one on the pivoted index, divided to 10, subdivided to 2 and to 1, numbered by 10. The quadrant between 270 and 360 has a shadow square, the sides with scales 0 to 60 to 0, divided to 5, subdivided to 1, numbered by 5, and 0 to 12 to 0, divided to 3, numbered by 3.

The other arm of the counterchanged index, with shaped ends, has a scale 0 to 45, divided to 5, subdivided to 1/2 with alternate hatching, numbered by 5; this is for use with the sinecal quadrants. The index arm has two upright screws, and a shaped brass piece can be secured by two wing nuts. This may be the remains of a sighting device.

The remainder of the top face has decorative engraving of plants, dragons and an angel, and the signature: 'James Kenvyn fecit 1597'.

The underside has a socket for mounting on a tripod or staff, and is blank except for some practice engravings: 'Jacobu:', 'Iames' and (?)'Job'.

Jim Bennett

Istituto e Museo di Storia della Scienza, Firenze
Inventory no. 3174

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