Rare Borda Repeater Circle Signed Jecker In Paris

The repeater circle has a circular frame of varnished brass and a removable wooden handle. The index arm holds the index glass, while the telescope arm supports the horizon glass. At the rear of the index arm are a double-ended tangent screw and a clamping screw, with a second set located at the eyepiece end of the telescope arm. The instrument includes five removable shades (two red, two orange and one green) and four detachable horizon shades (one green, two red and one orange). Adjustments to the index and horizon glasses are made by means of square-headed screws and a removable key. A magnifying glass on a 60 mm pivoting arm is attached to the circle. In addition, there are two threaded telescope supports, with perpendicular adjustments facilitated by a riser and two milled knobs. The main telescope is 142 mm long and produces an inverted image. There is an additional 91 mm long drawing tube, also with an inverted image and two parallel cross-wires, and another additional 84 mm long drawing tube, which produces an upright image. Accompanying accessories include an 82 mm sighting tube, an additional 21 mm drawing tube for the magnifying glass, two red-shaded eyepieces and three additional shades (now missing), as well as two rectangular stands and an adjustment key. The brass limb of the instrument is varnished and has an inlaid silver scale ranging from 0° to 720° in 20-arc-minute increments. A brass sighting arc extends from 155° to 0° to 145° in 1° increments, with two brass stops. The repeating circle is fitted with three silver verniers that measure to 1 arc-minute, with right-aligned zeros. This Borda repeating circle is housed in a square mahogany case. This Borda circle is numbered 261 and is signed Jecker in Paris. Considering moving to Paris, Jecker chose London instead, recognizing that England was more advanced in the 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 established a business in Paris. Shortly thereafter he was drafted into the army, eventually rising to the rank of captain. He left the army as soon as he could to pursue his dream of establishing a precision machinery factory. Same model in the Greenwich Museum.