Dollond, John and George

Dollond, John and George

(born June 10, 1706, London, Eng.—died Nov. 30, 1761, London) (born Jan. 25, 1774, London—died May 13, 1852, London) British optical scientists. John developed an achromatic (non-colour-distorting) refracting telescope and a practical heliometer (a telescope that measures the Sun's diameter and the angles between celestial bodies). His grandson George worked most of his life for the family firm of instrument makers, inventing various precision instruments used in astronomy, geodesy, and navigation. His micrometer made of rock crystal was used by astronomers; his atmospheric recorder simultaneously measured and recorded on paper tape temperature, atmospheric pressure, wind speed and direction, evaporation, and electrical phenomena.