Description

JONES’ IMPROVED ASTRONOMICAL QUADRANT, English, early 19th century, signed “W. & S. Jones, 30 Holborn, London.” This handsome lacquered brass instrument stands 10″ (25 cm) tall on its tabletop base with three leveling screws. The base has a circumferential degree scale, and is centered by a rotating disk which carries the instrument on central pillar, and which is fitted with crossed spirit levels, internal pinion and ring gears, and one-arcminute vernier. Atop the openwork pillar is mounted the 4-1/4″ (11 cm) radius openwork quadrant with 0° – 90° scale, one-arcminute vernier, and pinion with external rack. Thus the instrument functions as a geared altazimuth theodolite. It is aligned not with sight vanes but with a right angle telescope with sliding focus to both the objective and eyepiece, fitted with solar filter. Condition is very fine, complete, and functional; the brass is spotted but retains most of its original clear lacquer finish. This is a very rare example of Jones’ improved astronomical quadrant. In his Lectures of Natural and Experimental Philosophy George Adams (and subsequently William Jones) devotes six pages to the construction and use of the simple astronomical quadrant. But in a footnote, Jones describes this improved version: “By the addition of a small telescope, with a reflecting eye-piece, vernier scales to the arc and circle, rack-work and pinion to the arc AB, and circle EF, &c. I have rendered this small instrument useful for observing angles up to the zenith, and with more ease and accuracy for angles in general.” The first example we have seen. (Featured in “Wondrous Devices” exhibition, Hudson River Museum, 2018)