Image
Category
Maker
Object type
Place
Material
Date
Reflecting circle made by Edward Troughton, London, about 1823. Signed on the index arm: Troughton | 219 | London. Polished brass limb with inlaid silver scale from 140° to 0° to 140°; the entire circle is divided every 20'. Three silver verniers reading to 20", zeros at the left. Circular lacquered brass frame with a wooden handle. A detached U-shaped bracket holds a second handle with a brass-lined threaded hole for a third handle, which can also be screwed on the front of the frame. Three rigidly connected index arms on the back of the frame, a double-ended tangent screw and clamping screw are on the back of one of the arms. Three shades (two red, one green); three horizon shades ( two red, one green). Index glass without adjustment; adjustment of the horizon glass by a screw and a capstan screw. One detached magnifier on a 55 mm swivelling arm, for all three verniers. Threaded telescope bracket in two parts, fitted for correcting collimation error; perpendicular adjustment by rising-piece and a milled collar. Telescope (77 mm) erect image; telescope (179 mm) inverted image two parallel cross-wires; extra draw tube (90 mm) inverted image; extra draw tube (90 mm) inverted image, two parallel cross-wires. Sight tube (132 mm); sight tube (131 mm, probably from a different instrument); three shaded eyepieces (one red, two orange); a magnifying glass. Three unidentified parts. Box not seen WMB. The circle is mounted on a lacquered brass column on a tripod stand with three milled levelling screws. The counterbalanced swinging mount can be locked into the desired position by milled screws.

Brass framed reflecting circle with case.

1820-1825

Reflecting circle made by Julius Wanschaff, Berlin, Germany, about 1875. Circular dark-brown and yellow-lacquered brass frame, with two wooden handles. Signed on the limb: Julius Wanschaff. Berlin 51. Lacquered brass limb with inlaid silver scale indicating from -5° to 130° and from 180° to 290°; the entire scale is divided every 10'. Two silver verniers to 10", zeros at the right. The tangent screw, working against a spring-loaded stop, and the clamping screw, are at the bottom of the index arm. Six half-glass shades (four red, two green), the shades can be moved away from the frame by a rising-piece; no horizon shades. Index glass and horizon prism without adjustment. Magnifier on a 130 mm swivelling arm, serving both verniers, a frosted glass shade. Threaded telescope bracket, perpendicular adjustment by rising-piece and a milled knob. Telescope (168 mm) inverted image, four cross-wires; extra draw tube (130 mm) inverted image, four cross-wires; extra draw tube (57 mm) erect image and a rotating shaded eye-piece with choice of clear, two red, and one green. A prismatic eyepiece, an adjusting pin. A square fitted mahogany box. The circle is mounted on a dark-brown and yellow lacquered brass column on a tripod stand with three milled levelling screws. The counterbalanced swinging mount can be locked into the desired position by milled screws. Used by Sir David Gill (1843-1912) during his 1877 expedition to Ascension Island to observe Mars and improve the determination of solar parallax and hence the Astronomical Unit.

Prismatic reflecting circle with case.

1875-1876