Jesse Ramsden | |
|---|---|
 Mezzotint by J. Jones, 1790, after Robert Home. This, the only portrait of Ramsden shows him with the dividing engine in front of him and a great circle made for thePalermo Astronomical Observatory behind him. Ramsden never wore fur coats but the artist added it because the painting commemorated an order from theEmpress of Russia that Ramsden had worked on. | |
| Born | (1735-10-06)6 October 1735 Salterhebble, Yorkshire, UK |
| Died | 5 November 1800(1800-11-05) (aged 65) Brighton, Sussex |
| Known for | Dividing engine Ramsden eyepiece Surveying instruments Optical telescopes |
| Awards | Copley Medal (1795) |
| Scientific career | |
| Fields | astronomical optics |
Jesse RamsdenFRSFRSE (6 October 1735 – 5 November 1800) was a British mathematician,astronomical and scientific instrument maker. His reputation was built on the engraving and design ofdividing 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 theBritish Empire and outside. An achromatic eyepiece that he invented for telescopes and microscopes continues to be known as the Ramsden eyepiece.
Ramsden was born atSalterhebble,Halifax,West Riding of Yorkshire, England[1] the son of Thomas Ramsden, an innkeeper and his wife Abigail née Flather.[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 theNorth 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 amathematical instrument maker[2] and he proved so proficient that he was able to set up his own business only four years later.[3] 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.[4][1]
In 1765, Ramsden married Sarah Dollond, daughter ofJohn Dollond, the famous maker of high quality lenses and optical instruments. Ramsden received a share in Dollond's patent achromatic lens as dowry.[1] 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 atSt Mary's, Lambeth, on 1 September 1796.[1] In his later years he lived above the workshop with a number of his apprentices.[5] 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.[1]
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 theBoard 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.[1]
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 providingWilliam Roy with the theodolite for theAnglo-French Survey (1784–1790) provoked a public row within the portals of theRoyal Society and in itsPhilosophical Transactions.[6] Many delays could be attributed to Ramsden's quest for perfection, as he continually refined his designs as the slightest shortcomings were revealed.[5]
Ramsden was elected to the Royal Society in 1786 and to theRoyal Society of Edinburgh in (probably) 1798.[7]TheCopley 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 toBrighton on the south coast to try to benefit from its better climate; he died there on 5 November 1800. He was buried atSt 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.[1] Many of Ramsden's apprentices such asWilliam Cary went on to establish their own instrument-making ventures. Others likeEdward Troughton incorporated ideas from Ramsden into their own designs.[8]
Ramsden created one of the first high-qualitydividing 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 aDescription of an Engine for dividing Mathematical Instruments in 1777.[3]
He also built an early plateelectrostatic generator in 1768.
In about 1785, Ramsden provided GeneralWilliam Roy anew large theodolite[9] which was used for the measurement of the latitude and longitude separations of London (Greenwich) and Paris and later for thePrincipal Triangulation of Great Britain. This work provided the basis for the subsequentOrdnance Survey of the counties of Britain.
Ramsden is also responsible for theachromaticeyepiece 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.[10]
Theexit pupil of an eyepiece was once called theRamsden disc in his honour.
In 1791, he completed theShuckburgh telescope, anequatorial mountedrefracting telescope.[11][12]
His most celebrated work was a 5-feet vertical circle, which was finished in 1789 and was used byGiuseppe Piazzi at thePalermo Astronomical Observatory in constructing his catalogue of stars and in the discovery of thedwarf planetCeres 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 theDuc 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.[3]
Ramsden Rock inAntarctica is named after Jesse Ramsden.
This article incorporates text from a publication now in thepublic domain: Chisholm, Hugh, ed. (1911). "Ramsden, Jesse".Encyclopædia Britannica. Vol. 22 (11th ed.). Cambridge University Press. p. 880.
Media related toJesse Ramsden at Wikimedia Commons