Dollond, John
NAME:
Dollond, John
ACHIEVEMENTS:
The first person to publicize and develop commercially the achromatic telescope he independently invented
NICKNAME/ALIAS:
None
DATE AND PLACE OF BIRTH:
10 June 1706, London, England
DATE AND PLACE OF DEATH AND AGE AT DEATH:
30 November 1761, London, England. Aged 55
DISCIPLINE:
Optician
FIELD:
Optics
LANGUAGE:
English
PARENTS:
Father: name???
Mother: name???
SIBLINGS:
Names?
SPOUSE:
Name?
CHILDREN:
2 sons: Peter, John
3 daughters: names?
EDUCATION:
Unknown
MAJOR WORK:
“A Letter from Mr John Dollond to Mr James Short, FRS, concerning an Improvement of Refracting Telescopes” (1753)
“An Account of some Experiments concerning the different Refrangibility of Light” (1758)
LIFE AND TIMES:
Dollond was the son of French Protestants who had fled persecution in France and settled in Spitalfields, London where the government had set up a refugee settlement for the manufacture of silk weaving.
In his youth, Dollond made sundials and set himself mathematical problems. He became a silk weaver but in what spare time he could find he studied mathematics, astronomy and optics, Latin and Greek. His eldest son Peter followed him into the silk weaving trade but was no more enamored of it than his father.
He eventually left and became an optical instrument maker. He was so successful that in 1752 John Dollond joined him in the business. His first project was to improve the combination of lenses in refracting telescopes and he succeeded in producing improved telescopes with five lenses. He wrote a description of his work to the Royal Society and his letter was read to the society in March 1753 and printed in the “Philosophical Transactions”.
Dollond then improved Savery’s* micrometer (heliometer - an instrument for measuring the sun’s diameter and the angles between celestial bodies) for the telescope. Dollond did this by using only one lens cut into two halves, one of which moved laterally across the other. This meant that the micrometer could be applied to the refracting telescope.
The improvements Dollond made to the refracting telescope enabled astronomers to make much more precise observations. He was now highly regarded among the scientific community.
He corresponded with the Swiss mathematician Euler*, in particular about the views of Newton* on the divergence of prismatic colors in refraction. Newton wrote that “all refracting substances diverged the prismatic colors in a constant proportion to their mean refraction,” on the basis of which he concluded that refraction could not be produced without color and that the refracting telescope could not therefore be improved. Euler believed that refraction in very small angles could be obtained without color. Dollond defended Newton but then he decided, in 1757, to repeat Newton’s experiment for himself.
In June 1758 he discovered “the difference in the dispersion of the colors of light, when the mean rays are equally refracted by different mediums”. From this he drew the conclusion that the lenses of refracting telescopes were “capable of being made without the image formed by them being affected by the different refrangibility of the rays of light”.
Dollond’s work brought him the Copley medal from the Royal Society. The telescopes Dollond made on the basis of his findings were named achromatic because they were free of prismatic colors. They were fitted to Hadley’s sextant and were a valuable navigational aid.
In 1761 Dollond was elected a Fellow of the Royal Society and appointed royal optician (to George III). He patented his invention but it was challenged by a group of London optical instrument makers after his death.
In 1766 Peter Dollond won his right to the patent when a court decided that Hall* had not publicized or developed commercially the achromatic lens combination he had invented some twenty odd years before Dollond.
Dollond’s became one of the two leading optical firms in Britain. They were considered the best opticians in Europe and their pre-eminence lasted until the work of the German optician made German optics supreme in first quarter of nineteenth century.
ASSESSMENT: Dollond was the first to publish a description of an achromatic (non-color producing) lens and the first to develop the achromatic lens commercially.
EXTRA CONNECTIONS: Daughter married Ramsden*
ONELINER: John Dollond, major British optical manufacturer
BIBLIOGRAPHY:
Kelly, John, The Life of John Dollond FRS, Inventor of the Achromatic Telescope, M Thiselton, London, 1808