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Eighteenth-century craftsmen marked out the degree scales on scientific instruments with great accuracy, using basic geometrical principles, compasses and hand tools. However, this was a time-consuming task.
During this period, navigating accurately at sea was a
pressing problem. Dividing engines were devised to produce the octants and sextants which were increasingly used to find the altitude of the Sun or stars. In combination with an accurate chronometer (or using a complex 'lunar distance' method) these instruments could give both the latitude and the longitude, fixing the position of a ship exactly.
The first circular dividing engine was completed in about 1774 by Jesse Ramsden, earning an award from the Board of Longitude - the body that ultimately rewarded the chronometer pioneer John Harrison. This machine is believed to be a close copy of Ramsden's engine, completed by John Troughton in 1778.
Although using a dividing engine was faster than hand-dividing, it was backbreaking work for the operator, who had to lean over the engine. John's brother Edward wrote that, 'it had done no good either to his health or that of my own'. However, it was a profitable business and Troughton became one of London's major instrument makers.