A brass altitude surveying circle,
by J & J. Fayrer, Pentonville, London, circa 1860. Lacquered brass, the 13ins.(33cm) circle with silvered scale divided into four 90 degree arcs, the cruciform index arm with two opposed vernier scales reading to 10 seconds with two freely rotating magnifying lenses. The clamping arm with screw clamp and micro adjusting thread, topped by a full width spirit level. The entire instrument mounted onto a blackened brass backplate and housed in a circular brass case, with opening glass front window. 16ins.(41cm)diam.