EXTREMELY RARE MINIATURE BRASS SEXTANT BY FAMED MAKER JESSE RAMSDEN. Circa 1785. Fully signed on t-bar, in beautiful script engraving, "Ramsden London". Reverse with serial number "866".  4" long index arm with top mounted tangent screw and a beveled scale divided 0-30 degrees. Index mirror.  4" radius with a beveled scale that's divided 0-130 degrees. Horizon mirror with an adjusting arm. Removable telescope mount, swing away magnifier, 2 telescopes and a ebony handle that all store neatly in the shaped mahogany storage case when not in use. Overall condition superb with the majority of the brass retaining its original lacquer finish. The meticulously fashioned case was made using beautifully grained mahogany. Jesse Ramsden is considered to be the premier instrument maker of his time. He was awarded substantial prizes for the innovation of his improved dividing machine. His instruments were carried by Captain Cook. The workmanship on this little gem of an instrument is remarkable throughout. (I-0980)
Condition: The instrument is complete with all its parts. It is in excellent condition as is the original box.
Biography - Jesse Ramsden was an English mathematician, optician, physicist, and astronomical instrument maker. He is known for constructing the dividing engine, Ramsden eyepiece, surveying instruments, and optical telescopes. Ramsden was one of the finest scientific instrument makers in Britain in the last half of the 18th century.
Jesse Ramsden was born at Salterhebble near Halifax, Yorkshire, England on October 6, 1735. He was the son of a Halifax innkeeper and the great-nephew of Abraham Sharp, mathematician, instrument maker, and assistant to the Astronomer Royal, John Flamsteed. Having attended the free school at Halifax for three years, he was sent at the age of twelve to his uncle at Craven in the North Riding, and there studied mathematics under the Rev. Mr. Hall. After serving his apprenticeship with a cloth-worker in Halifax, he went in 1755 to London, where in 1758 he was apprenticed to a mathematical instrument maker. After four years’ study of mathematics, Ramsden was apprenticed at sixteen to a clothworker in Halifax. In 1755, upon finishing this service, he moved to London, where he worked as a clerk in a cloth warehouse. In 1758 he apprenticed himself to the mathematical instrument maker Burton. Ramsden opened his own shop in the Haymarket in 1762, moving to larger quarters at 199 Piccadilly in 1775. His great skill brought him commissions from the foremost practitioners of the period, including J. Sisson, J. Adams, J. Dollond, and E. Nairne. In 1774 Ramsden published Description of a New Universal Equatorial Instrument, which improved on the design of Short’s portable telescope mounting. Ramsden's mounting was quickly accepted and served to enhance his growing reputation.
A passion for precision was the motivating force behind Ramsden’s development of the dividing engine, his greatest contribution to the technology of the era. His first machine, built around 1766, produced only moderate improvement in the accuracy he sought, but the machine constructed in 1775 reduced the error to less than one-half second of arc as compared to the three seconds of arc of the first machine. This achievement earned him a grant from the Commissioners of the Board of Longitude in 1777. Ramsden’s shop grew until the staff numbered about sixty workmen. At no time, however, did he permit the quality of his output to diminish. By 1789 he had produced someone thousand sextants, as well as theodolites, micrometers, balances, barometers, and the many philosophical instruments required by the physicists of the period. It appears that the demand far exceeded his capacity for production. In 1784 William Roy, who was conducting the trigonometric survey that linked England with the Continent, ordered a three-foot-diameter theodolite from Ramsden, who took three years to complete it. The Royal Society awarded him the Copley Medal (1795) for “various inventions and improvements in philosophical instruments.” Many of Ramsden's instruments have been preserved and may be seen at the Smithsonian Institution, the Science Museum and the National Maritime Museum in London, the Museum of the History of Science in Florence, Teyler’s Museum in Haarlem, the Conservatoire National des Arts et Metiers in Paris, and in many other museums.