REPEATING CIRCLE . BORDA CIRCLE SIGNED JECKER A PARIS

The repeating circle features a circular varnished brass frame and a detachable wooden handle. The index arm holds the index glass, while the telescope arm supports the horizon glass. Located on the back of the index arm are a double-ended tangent screw and a clamping screw, with a second set found at the ocular end of the telescope arm. The instrument includes five detachable shades (two red, two orange, and one green) and four detached horizon shades (one green, two red, and one orange). Adjustments for the index and horizon glasses are made using square-headed screws and a detachable key.

A magnifier on a 60mm swiveling arm is attached to the circle. Additionally, there are two threaded telescope brackets, with perpendicular adjustments facilitated by a rising piece and two milled knobs. The main telescope is 142 mm long and produces an inverted image. There is an extra draw tube, 91 mm in length, also with an inverted image and two parallel cross wires, and another extra draw tube, 84 mm long, that produces an erect image. Accompanying accessories include an 82 mm sight-tube, a 21 mm extra draw tube for the magnifier, two red-shaded eyepieces, and three additional detached shades (now missing), as well as two rectangular brackets and an adjusting key.

The instrument’s brass limb is varnished and features an inlaid silver scale ranging from 0° to 720° in 20-arc minute increments. A brass finder arc spans from 155° to 0° to 145° in 1° increments, with two brass stops. The repeating circle is equipped with three silver verniers that measure to 1 arc minute, with zeros aligned to the right.

This repeating circle is stored in a square, fitted mahogany box. This borda circle is numbered 261 and signed Jecker à Paris.

Considering a move to Paris, Jecker instead chose London, recognizing that England was more advanced in mechanical arts. In 1786, he began an apprenticeship with Ramsden, a renowned instrument maker. According to Barker, Jecker and Ramsden became lifelong friends.

In 1792, Jecker returned to France and started a business in Paris. Shortly thereafter, he was drafted into the army, eventually rising to the rank of Captain. He left the military as soon as he could to pursue his dream of establishing a precision machine works.

Same model in Greenwich Museum.