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Jesse Ramsden

Jesse Ramsden was a famed mathematical instrument maker and optician of London who was widely considered the most skilled at using the dividing engine. Ramsden was born in Salterhebble near Halifax in Yorkshire to an innkeeper, likely on 6 October 1735. He completed an apprenticeship to a local clothworker before moving to London. Unusually for a 21 year-old, he then apprenticed himself to the mathematical instrument maker Mark Burton of Denmark Street in the Strand. In 1763 he began working under his own name in the same street, already being admired for his dividing skills. He also learned optical instrument making skills from the famous Dollond family of opticians, into which he soon married. (Ramsden in fact received a share in John Dollond's valuable patent on the achromatic lens as a partial dowry!) He opened a shop in Haymarket under the sign of the Golden Spectacles.

In 1767, Ramsden invented his first dividing engine because of the need for small, affordable and yet accurately divided sextants for use with the lunar-distance method. It is likely that he was also inspired by the reward which the Board of Longitude had recently given to John Bird for his method of hand-dividing. Some sources claim that the engine - to be used on instruments with circular scales including sextants, octants and theodolites - was inspired by that of the clockmaker Henry Hindley of York. Ramsden built an improved version of this engine in about 1775. (The first version was used by his wife and apprentices before being sold and illegally exported to France.)

On 25 June 1774, Ramsden submitted a memorial [RGO 14/5:262] to the Board 'representing that he had invented an Instrument for dividing Sextants &c, the construction of which is as leaves no dependance upon the Workman, as a Boy can use it with the same exactness as the most experienced hand ; and in the most speedy manner. And expressing his wish that the said Instrument which as [sic] cost him upwards of £250 and another which he is constructing to divide streight Lines may be the property of the Board on their paying him for them and giving such a Gratuity to him as, in their Opinion he may deserve, And the said Mr Ramsden having been called in and discoursed with upon the Subject, The Professors who were present were desired to go to his House (taking with them Mr Bird if he was inclinable to for) in order to see a Quadrant divided by the above instrument, And to report their opinion of it to the Board'.

The Commissioners ultimately awarded Ramsden £300 in 1777 and paid another £315 for the rights to the circular dividing engine. In return, the instrument maker was to divide sextants for them at six shillings each and to explain its construction on paper and to nominated craftsmen. (This allowed John and Edward Troughton, who were also associates of the Board, to build engines in the style of that of Ramsden.) The Board published his Description of an Engine for Dividing Mathematical Instruments later that year. Ramsden next used his straight line dividing engine, a description of which he published in 1779, to more precisely divide linear mathematical scales as well. The Board rewarded him with £400 in total for it, much as they had for the circular dividing engine.

During the 1770s, Ramsden went on to improve the accuracy of precision astronomy dramatically by graduating full circles rather than the large mural quadrants previously in vogue in European observatories. He also pioneered more stable equatorially mounted telescopes and improvements to a variety of other smaller instruments. Ramsden was able to expand his workshop even further into Piccadilly in 1780, giving him room to make large observatory instruments and to host an unusually large workforce. It numbered sixty, and each man had his own locked drawer of tools. By 1789, the instrument maker had graduated more than a thousand sextants alone, which helped to revolutionise navigation and the search for the longitude. (This would have benefited his own son, John, who became a commander in the East India Company's navy.) Like John Bird, he was known for sometimes horrible delays in completing commissions, due to perfectionism as well as to the high demand for his services.

Ramsden was so admired by astronomers and scientists across Europe that the Royal Society elected him a Fellow in 1786. It awarded him the Copley medal in 1795, for his ‘various inventions and improvements to philosophical instruments’. When the instrument maker died in 1800, the Board ensured that his engines passed to his longtime foreman Matthew Berge rather than to his former apprentice Thomas Jones. Jones, however, got them once Berge died in 1819.

In a number of the digitised volumes, there are records related to Ramsden's reward and publication and to his commissions and repairs, expert advice, and other activities for the Board. These of course include the surviving minutes of communal meetings of the Commissioners in RGO 14/5 [RGO 14/5], RGO 14/6 [RGO 14/6], RGO 14/7 [RGO 14/7] and RGO 14/8 [RGO 14/8]. Other examples include the records of payments made to the craftsmen by the Board in volume RGO 14/18 [RGO 14/18]. Volume RGO 14/30 [RGO 14/30] encompasses later reports by William Hyde Wollaston, an early nineteenth-century Commissioner of Longitude, on Ramsden's circular dividing engine. The instrument maker additionally appears in the collections of individuals' papers, such as those of the astronomer William Gooch in MS Mm/6/48 [Mm.6.48].

Many of the instruments divided by Ramsden, or on his engines, survive around the world and at the National Maritime Museum. There are a number of the sextants which were divided on Ramsden's circular engine including this [RMG icon] and this [RMG icon] , both circa 1780. His workshop made a pretty penny selling about forty sextants a year in addition to dividing other people's instruments.

Alexi Baker
History and Philosophy of Science
University of Cambridge