JOHN

See also:

• JOHN DOLLOND (1706—1761)

DOLLOND (1706—1761)  , English optician, was the son of a Huguenot refugee, a silk-weaver at Spitalfields; London, where he was born on the loth of June 1706 . He followed his father's trade, but found time to acquire a knowledge of Latin, Greek, mathematics, physics, anatomy and other subjects . In 1752 he abandoned silk-weaving and joined his eldest son, Peter Dollond (1730-1820), who in 1750 had started in business as a maker of optical instruments . His reputation grew rapidly, and in 1761 he was appointed optician to the king . In 1758 he published an " Account of some experiments concerning the different refrangibility of light " (Phil . Trans., 1758), describing the experiments that led him to the achievement with which his name is specially associated, the discovery of a means of constructing achromatic lenses by the combination of crown and flint glasses . Leonhard Euler in 1747 had suggested that achromatism might be obtained by the combination of glass and water lenses . Relying on statements made by Sir Isaac Newton, Dollond disputed this possibility (Phil . Trans., 1753), but subsequently, after the Swedish physicist, Samuel Klingenstjerna (1698—1765), had pointed out that Newton's law of dispersion did not harmonize with certain observed facts, he began experiments to settle the question . Early in 1757 he succeeded in producing refraction without colour by the aid of glass and water lenses, and a few months later he made a successful attempt to get the same result by a combination of glasses of different qualities (see TELESCOPE) . For this achievement the Royal Society awarded him the Copley medal in 1758, and three years later elected him one of its fellows . Dollond also published two papers on apparatus for measuring small angles (Phil .

Trans., 1753, 1754) . He died in London, of

apoplexy, on the 3oth of November 1761 . An account of his life, privately printed, was written by the Rev . John Kelly (1750-1809), the Manx scholar, who married one of his granddaughters .