Hall CM
NAME: Hall, Chester Moor
ACHIEVEMENT(S): Achromatic lens.
NICKNAME/ALIAS: None
DATE/PLACE OF BIRTH: 9 December 1703, at Leigh, Essex, England
DATE/PLACE/AGE AT DEATH: 17 March 1771, in Sutton, Surrey, England. Aged 67
DISCIPLINE: Mathematician and inventor
FIELD: Optics
LANGUAGE: English
PARENTS: Jehu Hall (d. 1728) and Martha Brittridge
SIBLINGS: Martha (elder sister)
SPOUSE: ?
CHILDREN: ?
EDUCATION: Inner Temple, 1724
MAJOR WORK: Achromatic lens.
LIFE AND TIMES:
Chester Moor Hall was born in 1703 at Leigh in Essex, England into a wealthy, landowning family, the only son of Jehu Hall and Martha Brittridge. He studied law and entered the Inner Temple in London in 1724. He eventually inherited estates in Essex.
Hall was also interested in mathematics and science, and during the late 1720s made a study of the human eye which convinced him that it should be possible to find a solution to the problem of chromatic aberration (the failure of a lens to focus all colours in the same plane, resulting in blurring and color distortion) which affected contemporary telescopes.
After experimenting with many different kinds of glass, in 1729 he discovered by trial and error a combination of two lenses of opposite powers which corrected the problem: a strong lens of low-dispersion glass (a convex lens of crown glass) and a weaker lens made of high-dispersion glass (a concave lens made of new lead-containing flint glass).
In 1733, Hall had several of these lenses ground in London and built two or three telescopes with apertures of 2.5 inches (6.5 cm) and focal lengths of 20 inches (50 cm). These were the first truly achromatic refracting telescopes. Hall, who liked his privacy and had no desire for fame, failed to make public his discovery, and news of the invention spread only slowly among London's opticians.
Finally, in 1747, a controversy arose over Newton's statement that chromatic aberration in lenses could not be corrected (owing to his generalization that refraction is always accompanied by dispersion).
In the early 1750s, having heard of Hall's invention (according to the evidence of the instrument-maker <influenced> Ramsden*) in 1750 – the optician <parallel work by> Dollond* developed an achromatic lens made of flint and crown glasses. This "invention" earned him several patents and the Copley Medal of the Royal Society, but the prior discovery of the achromatic lens by Hall was later recognized in a trial (Dollond's right to the invention being contested by yet another inventor, named Champness) of 1766. Although Hall's priority was established, he always remained indifferent to the matter.
ASSESSMENT: His achromatic lens was a major contribution to the development of microscopy, surveying and astronomy.
EXTRA CONNECTIONS: None
ONELINER: CM Hall, inventor of the achromatic lens
BIBLIOGRAPHY:
DNB, EB
King, Henry C., The History of the Telescope, London: Charles Griffin & Company Limited, 1955.