Details
A lacquered brass Douglas reflecting protractor signed Cary London Patent 185 the scale rule combined with a 0°-120° part circle, the hinged arm with sliding vernier quadrant, fitted with pin-hole sight and mirrors in fitted mahogany case with trade label 6½in(16.5)cm
Literature
Cf: J.A. Bennett The Divided Circle pp.154
The patent was designed by Sir Howard Douglas in 1811 and was used on a plane table
The patent was designed by Sir Howard Douglas in 1811 and was used on a plane table