Borda type repeating circle.

Repeating circle (Borda circle) made by Joseph Cox, London, about 1810. Circular polished brass frame and limb, a detached wooden handle. Signed on the index arm: Joseph Cox | Barbican London. Inlaid silver scale from 0° to 720° every 20". Three silver verniers to 30", zeros at the right. The index arm carries the index glass; the telescope arm carries the horizon glass. The tangent screw and clamping screw are on the back of the index arm. A second tangent screw and clamping screw is at the objective end of the telescope arm. Three index shades (two red, one green); three horizon shades (two red, one green). Index- and horizon-glass adjustment by screws. Magnifier on a 70 mm swivelling arm; a second detached magnifier can be clamped onto the limb. Two threaded telescope brackets, perpendicular adjustment on both by rising-pieces and milled knobs. Telescope (185 mm) inverted image, four cross-wires. Shaded eyepiece (red); adjusting pin. A square fitted mahogany box with remnants of a leather carrying strap.