Repeating circle (Borda circle) made by George Dollond, London, abut 1850. Circular anodized brass frame, polished limb, a wooden handle; a detached U-shaped bracket holds a second handle. Signed on the bottom of the index arm: Dollond | London. Inlaid silver scale from 0° to 720° every 20' (the digits are engraved in brass). Two silver verniers to 20", zeros at the centres. The second scale is to 180° every 5° on either side of 0°, engraved in brass. The index arm carries the index glass; the tangent screw, working against a spring-loaded stop, and the clamping screw are on the back of the index arm. Three index arms, moving with a brass scale and the second vernier on the inside of the limb; they carry the telescope and the horizon glass. One arm has a tangent screw, working against a spring-loaded stop, and a clamping screw on the back of the arm. Index-glass adjustment by a screw; adjustment of the horizon glass by screw and capstan screw. Three index shades (two red, one green); three horizon shades (two red, one green). Two magnifiers on 65 mm swivelling arms. Threaded telescope bracket with perpendicular adjustment by rising-piece and a milled knob. Telescope (96 mm) erect image; telescope (158 mm) inverted image, four cross-wires; extra draw tube ( 50 mm) inverted image, four cross-wires; extra draw tube (48 mm) inverted image, four cross-wires. Sight tube 84 mm); shaded eyepiece (red). Square fitted mahogany box containing in the lid a trade label for J.D. Potter, 31 Poultry, London.
Square fitted mahogany box containing in the lid a trade label for J.D. Potter, 31 Poultry, London, for repeating circle (Borda circle) made by George Dollond, London, 1845-1852.
Repeating circle (Borda circle) made by George Dollond, London, abut 1850. Circular anodized brass frame, polished limb, a wooden handle; a detached U-shaped bracket holds a second handle. Signed on the bottom of the index arm: Dollond | London. Inlaid silver scale from 0° to 720° every 20' (the digits are engraved in brass). Two silver verniers to 20", zeros at the centres. The second scale is to 180° every 5° on either side of 0°, engraved in brass. The index arm carries the index glass; the tangent screw, working against a spring-loaded stop, and the clamping screw are on the back of the index arm. Three index arms, moving with a brass scale and the second vernier on the inside of the limb; they carry the telescope and the horizon glass. One arm has a tangent screw, working against a spring-loaded stop, and a clamping screw on the back of the arm. Index-glass adjustment by a screw; adjustment of the horizon glass by screw and capstan screw. Three index shades (two red, one green); three horizon shades (two red, one green). Two magnifiers on 65 mm swivelling arms. Threaded telescope bracket with perpendicular adjustment by rising-piece and a milled knob. Telescope (96 mm) erect image; telescope (158 mm) inverted image, four cross-wires; extra draw tube ( 50 mm) inverted image, four cross-wires; extra draw tube (48 mm) inverted image, four cross-wires. Sight tube 84 mm); shaded eyepiece (red).
