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Jesse Ramsden was born near Halifax, Yorkshire, England,on October 6, 1735, the son of an innkeeper. He attended a free school in Halifax from 1744 to 1747, after which he was sent to live with an uncle in the North Riding of Yorkshire, where he spent four years studying mathematics. Apprenticed to a cloth maker in 1751, Ramsden spent about four years in that trade before apprenticing himself to a maker of mathematics instruments. He quickly excelled in this profession, and within four years he had opened his own instrument making shop in London.
One of Ramsden's neighbors was John Dollond, a fellow of the Royal Society and a skilled designer of optical instruments, from whom he learned much about optical instruments. He also met Sarah Dollond, John Dollond's daughter, and they were married on August 16, 1766. Of their two sons and two daughters, only one son, John, survived to adulthood. Marriage gave Ramsden a share in the patent that John Dollond had taken out on his most famous invention, the achromatic lens.
Meanwhile, Ramsden quickly gained a reputation as the best designer and manufacturer of mathematical, astronomical, surveying, and navigational instruments in England, and even built instruments for King George III. That reputation grew even more after Ramsden invented the dividing engine, a device that enabled him to mechanically produce incredibly accurate instrument scales, in 1766; an improved version of the engine, developed in 1775, led to Ramsden being awarded £300 by the longitude commissioners.
Ramsden's dividing engine
Ramsden also made significant improvements to the design of theodolites and transits (surveying instruments), and invented a pyrometer to quantify thermal expansion and a device for determining telescopic powers. Using what he learned from Dollond, he designed a unique eyepiece for reflecting telescopes. The Ramsden eyepiece, a name it still carries today, reduces blurring of the image caused by chromatic aberrations and is still used in telescopes.
In addition to his work with instruments, Ramsden also built and designed one of the first electrostatic generators. The electricity produced by Ramsden generators was sometimes used in medical treatments of the day, especially in cases of paralysis, muscle spasms, and heart problems. The machines were also utilized to charge Leyden jars.
Ramsden was elected to Royal Society in 1786, and was awarded the Copley Medal in 1795. He died in Brighton on November 5, 1800. His contributions to optics and astronomical instruments were memorialized by the naming of a Moon crater in his honor.
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This page was last updated on June 22, 2017.