Ramsden
NAME: Ramsden, Jesse
ACHIEVEMENT(S): Circumferentor
NICKNAME/ALIAS: None
DATE/PLACE OF BIRTH: 6 October 1735, at Halifax, Yorkshire, England
DATE/PLACE/AGE AT DEATH: 5 November 1800, in Brighton, Sussex, England. Aged 65
DISCIPLINE: Instrument-maker
FIELD: Scientific instruments
LANGUAGE: English
PARENTS: Thomas Ramsden and ?
SIBLINGS: ?
SPOUSE: Sarah Dollond, married 1765/6
CHILDREN: John (1768-1841)
EDUCATION: Halifax Free School; mathematics tuition from Rev. Hall, 1747-51
MAJOR WORK: 'Description of an Engine for Dividing Mathematical
Instruments', 1777
LIFE AND TIMES:
Ramsden studied mathematics and other subjects under a private tutor until 1751, when he was apprenticed to a cloth-worker in Halifax. On completion of his apprenticeship in 1755, he moved to London to work as a clerk in a cloth warehouse.
In 1758 he apprenticed himself to a mathematical instrument-maker in Denmark Street, London, and became so good, especially in engraving, that by 1762 he was able to set up in business on his own account in a shop in the Haymarket. His reputation grew quickly, and in either 1765 or 1766 he married Sarah Dollond, youngest daughter of the optician <father-in-law was> Dollond*, receiving as a dowry a share of Dollond's patents for making achromatic lenses.
During the 1760s, Ramsden's great skill won him many important commissions, and he soon became generally regarded as the best instrument-maker of his day. It was during this period that he began to design machines for accurately dividing the circular graduated scales of astronomical instruments.
In 1766 he produced his first dividing machine, which incorporated two important innovations: the use of the "endless" tangent screw (the circumference of the main wheel of the dividing machine having teeth which engaged the threads of this endless screw or worm, and which rotated a smaller telescope circle incised with graduations), and the use of a microscope to find the exact positions of them graduations.
Owing to the unevenness of his tangent screws Ramsden's dividing engine produced only a moderate improvement in accuracy, So he designed an entirely new screw-cutting lathe (with which to produce screws of absolutely constant pitch) completed in 1770. In the lathe a guide screw was placed parallel to a rod to be threaded; a hand crank turned the guide screw, the motion of which was transmitted to a tool holder with a diamond incising head, which then cut a new screw, resulting in a duplicate screw of almost perfect accuracy.
This screw-cutting lathe brought improvements in Ramsden's many different types of precision tools, and in 1797 inspired the English engineer <influenced> Maudslay* to design and construct his own screw-cutting lathe.
In 1774, Ramsden published his first important work, 'Description of a new Universal Equatorial Instrument', describing his design for a new portable telescope mounting, an instrument he had already supplied (in 1770-73) to, among others,<client was> Bute* and <client was> Banks*.
The following year, using his new lathe to cut the screws he needed, he constructed his first great dividing engine, (the “circumferentor”) which reduced the error in circular scales to less than one-half second of arc (as compared to the three seconds of arc of the first machine). For this work he was awarded a grant from the Commissioners of the Board of Longitude, who published his paper detailing this achievement, "Description of an Engine for Dividing Mathematical Instruments" in 1777.
With the increase in business, in 1775 Ramsden transferred his workshop to larger premises in Piccadilly, where his staff increased to about sixty workers and apprentices. A short time after producing his circular dividing engine, Ramsden designed and produced a linear one, which he again described in a paper published by the Commissioners of Longitude as "Description of an Engine for Dividing Straight Lines on Mathematical Instruments" (1779).
During the 1780s, Ramsden supplied many of the observatories of Europe with new achromatic telescopes equipped with accurately divided circles. In particular, he received two special commissions. The first, in 1784, was from <commissioned by> Roy*, who was conducting the trigonometric survey of Great Britain (which was begun by the military and continued by the Board of Ordnance), for a three-foot-diameter <perfected development of> theodolite* and steel measuring chains (completed in 1787).
The second, in 1789, from the astronomer <commissioned by> Piazzi* at the Palermo Observatory for an azimuth instrument with a five-foot-diameter vertical circle and Ramsden's micrometer microscope for reading the graduations.
By 1789 Ramsden had constructed nearly one thousand sextants (the majority for the Royal Navy), as well as theodolites, micrometers, precision balances (for the weighing of metals, particularly money, often with a microscope attached), gasometers (for calculating the density and volume of gases), dilatometers (for measuring the expansion and contraction of metals), barometers, thermometers (for measuring both air and sea temperature), manometers, quadrants, and vertical circles for astronomical observatories,
all using tangent screws (and often microscopes) and all of great accuracy.
He also constructed eyeglasses (1782) with reduced distortion, invented a 'pyrometer' for measuring the expansion of substances when heated, and a 'dynameter' for measuring telescopic powers.
ASSESSMENT: A major figure in the early development of instruments of precision.
EXTRA CONNECTIONS: His work related to that of <work related to> Arago*, <work related to> Frauenhofer*, <work related to> Bessel* and <work related to> CM Hall*.
ONELINER: Jesse Ramsden, great 18th century instrument-maker
BIBLIOGRAPHY:
DSB, DNB, EB
King, Henry C., The History of the Telescope, London: Charles Griffin & Co. Ltd.,1955