Borda type repeating circle.

1805-1815 in Barbican
Joseph Cox
Repeating circle (Borda circle) made by Joseph Cox, London

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Repeating circle (Borda circle) made by Joseph Cox, London
Science Museum Group
© The Board of Trustees of the Science Museum

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.


Object Number:
mahogany (wood), brass (copper, zinc alloy), glass, iron, felt, leather and platinum (metal)
overall: 100 mm x 315 mm x 320 mm, 4.2kg
repeating circle
Royal Meteorological Society