Reflecting Circle, by Troughton, London, c. 1800

Reflecting circle of an unusual design, not the typical Troughton type. The index mirror is linked to a diametric index arm with two verniers, and the circle itself can be rotated against a fixed diametris index arm also with two verniers; both arms have clamp and tangent screws. The rotation of the circle may indicate a repeating function. There is a secondary arc on the back, with a scale on brass; the main scale is on platinum. Index mirror, horizon glass, two sets of pivoted shades, two wooden handles, one with an additional screw-fit extension, telescope. Screw attachment to a mount with two counter-weights, on pillar stand with tribrach base.