Jesse Ramsden
Template:Short description Template:Use dmy dates Template:Infobox scientist 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. He produced instruments for astronomy that were especially well known for maritime use where they were needed for the measurement of latitudes and for his surveying instruments which were widely used for cartography and land survey both across the British Empire and outside. An achromatic eyepiece that he invented for telescopes and microscopes continues to be known as the Ramsden eyepiece.
Life
Ramsden was born at Salterhebble, Halifax, West Riding of Yorkshire, England<ref name=odnb/> the son of Thomas Ramsden, an innkeeper and his wife Abigail née Flather.<ref name=odnb>Template:Cite ODNB</ref>
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. Mr. Hall. After serving his apprenticeship as a cloth-worker in Halifax, he went to London where, in 1755, he became a clerk in a cloth warehouse. In 1758 he was apprenticed to a mathematical instrument maker<ref>The workshop of Mr Burton in Denmark Street.</ref> and he proved so proficient that he was able to set up his own business only four years later.Template:Sfn The quality and accuracy of his instruments established his reputation as the most able instrument maker in Europe for the next forty years until his death in 1800.<ref name=anita>Template:Harvnb Jesse Ramsden (1735–1800).</ref><ref name=odnb />
In 1765, Ramsden married Sarah Dollond, daughter of John Dollond, the famous maker of high quality lenses and optical instruments. Ramsden received a share in Dollond's patent achromatic lens as dowry.<ref name=odnb /> Little is known of their life together but Sarah did not accompany him when he moved his workshop (and home). In 1773, Ramsden moved to 199 Piccadilly but Sarah and her son lived at Haymarket at a home belonging to her father's family. At the time of her death on 29 August 1796 she lived at Hercules Buildings, off Westminster Road, Lambeth. She was buried at St Mary's, Lambeth, on 1 September 1796.<ref name=odnb /> In his later years he lived above the workshop with a number of his apprentices.<ref name=mirror>[[#Template:Harvid|Ramsden the optician]]</ref> The Ramsdens had two sons and two daughters with only one, John, living past infancy. John later became a commander in the East India Company's navy.<ref name=odnb />
Ramsden's dividing engine allowed instruments to be made smaller without loss of measurement accuracy. The rights for a portable sextant designed by Ramsden and used for maritime navigation were purchased by the Board of Longitude in 1777 for £300. An additional £315 was paid to allow for its construction details to be used by other craftsmen. He also received charges for servicing of the instruments.<ref name=odnb />
Ramsden was of a genial disposition, but at the same time infuriated his clients with his tardiness in delivering their purchases, particularly of larger commissions. 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.<ref>Template:Harvcolnb describes the argument between Roy and Ramsden.</ref> Many delays could be attributed to Ramsden's quest for perfection, as he continually refined his designs as the slightest shortcomings were revealed.<ref name=mirror/>
Ramsden was elected to the Royal Society in 1786 and to the Royal Society of Edinburgh in (probably) 1798.<ref name="RSE">Template:Cite web</ref> 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. He was buried at St James's Church, Piccadilly on 13 November. His instrument-making business in London was taken over by his foreman, Matthew Berge until his death in 1819. The estate passed on to his son.<ref name=odnb /> Many of Ramsden's apprentices such as William Cary went on to establish their own instrument-making ventures. Others like Edward Troughton incorporated ideas from Ramsden into their own designs.<ref>Template:Cite journal</ref>
Ramsden's instruments
Dividing engines
Ramsden created one of the first high-quality dividing engines. This led to his speciality in dividing circles, which began to supersede the quadrants in observatories towards the end of the 18th century. He published a Description of an Engine for dividing Mathematical Instruments in 1777.Template:Sfn
Other instruments
He also built an early plate electrostatic generator in 1768.
Surveying instruments
In about 1785, Ramsden provided General William Roy a new large theodolite<ref>Template:Harvtxt</ref> 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. This work provided the basis for the subsequent Ordnance Survey of the counties of Britain.
Telescopes
Ramsden is also responsible for the achromatic eyepiece named after him. 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. It had the additional advantage of allowing a greater distance (or eye relief) between the lens and the eye. It thus also allowed sunshades and prisms to be placed before it.<ref>Template:Cite book</ref>
The exit pupil of an eyepiece was once called the Ramsden disc in his honour.
In 1791, he completed the Shuckburgh telescope, an equatorial mounted refracting telescope.<ref name="mcconnell2013">Template:Cite journal</ref><ref name="hingley2013">Template:Cite journal</ref>
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.<ref name="mcconnell2013"/><ref name="chinnici2009">Template:Cite journal</ref><ref>Template:Cite web</ref>
Micrometers
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.Template:Sfn
Honours
Ramsden Rock in Antarctica is named after Jesse Ramsden.
Notes and references
Bibliography
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External links
Template:Copley Medallists 1751–1800 Template:Authority control
- Pages with broken file links
- Wikipedia articles incorporating text from the 1911 Encyclopædia Britannica
- 1735 births
- 1800 deaths
- British scientific instrument makers
- Optical engineers
- Recipients of the Copley Medal
- Fellows of the Royal Society of Edinburgh
- People from Halifax, West Yorkshire
- Fellows of the Royal Society
- Honorary members of the Saint Petersburg Academy of Sciences
- 18th-century British engravers
- English inventors