Jesse Ramsden FRS FRSE (6 October 1735 – 5 November 1800) was a British mathematician, astronomical and scientific instrument maker.

His reputation was built on the engraving and design of dividing engines which allowed high accuracy measurements of angles and lengths in instruments.

[1] Having attended the free school at Halifax from 1744 to 1747, he was sent at the age of twelve to his maternal uncle, Mr Craven, in the North Riding, and there studied mathematics under the Rev.

His three-year delay in providing William Roy with the theodolite for the Anglo-French Survey (1784–1790) provoked a public row within the portals of the Royal Society and in its Philosophical Transactions.

[7] The Copley Medal of the Royal Society was bestowed upon him in 1795 for his 'various inventions and improvements in philosophical instruments.’ Ramsden's health began to fail and he traveled to Brighton on the south coast to try to benefit from its better climate; he died there on 5 November 1800.

In about 1785, Ramsden provided General William Roy a new large theodolite[9] which was used for the measurement of the latitude and longitude separations of London (Greenwich) and Paris and later for the Principal Triangulation of Great Britain.

In its simplest form it consists of two planoconvex lenses with the curved sides facing each other and separated by a gap of about 2/3 of their focal length.

[11][12] His most celebrated work was a 5-feet vertical circle, which was finished in 1789 and was used by Giuseppe Piazzi at the Palermo Astronomical Observatory in constructing his catalogue of stars and in the discovery of the dwarf planet Ceres on 1 January 1801.

[11][13][14] He was the first to carry out in practice a method of reading off angles (first suggested in 1768 by the Duc de Chaulnes) by measuring the distance of the index from the nearest division line by means of a micrometer screw which moves one or two fine threads placed in the focus of a microscope.