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HALL, CHESTER MOOR (1703–1771), inventor of the achromatic telescope, was born at Leigh in Essex, and was baptised in the parish church on 9 Dec. 1703. He was the only son of Jehu Hall by his wife Martha, daughter and coheiress of Richard Brittridge of New House, Sutton, Essex. The Halls were originally from Stepney, but settled at Leigh on inheriting by successive marriages the properties of the Moors and of the Chesters of Leigh. Jehu Hall removed to Brentwood, and there died in 1728. Chester Moor Hall was admitted a student of the Inner Temple on 5 Oct. 1724, and was made a bencher in 1763. He resided at New Hall, Sutton, where he died on 17 March 1771, aged 67. His elder sister, Martha Hall, erected a marble monument to him in the church of Sutton, of which he was patron. The inscription describes him as 'a judicious lawyer, an able mathematician, a polite scholar, a sincere friend, and a magistrate of the strictest integrity.' He was an extensive landowner in Essex, and is frequently designated as 'Moor of Moor Hall.' His library was sold in 1772.

A writer in the 'Gentleman's Magazine' states that Hall obtained, from a study of the human eye, the conviction that achromatic lenses were possible, and discovered in 1729, after various experiments, two kinds of glass of dispersion sufficiently different to enable him to realise his idea. He accordingly constructed, about 1733, several telescopes, subsequently pronounced by experts to be truly achromatic. Their excellence was shown by their bearing, with apertures of two and a half, focal lengths of twenty inches. One was on sale with Ayscough of Ludgate Hill in 1754: another was in 1790 in the possession of the Rev. Mr. Smith of Charlotte Street; some were stated by Sir John Herschel and Professor Barlow to have been in existence about 1827. Hall proved his indifference to claims of priority by taking no part in the trial of Dollond v. Champness in 1766, although probably in London [see Dollond, John], Some of the workmen whom he had employed, having furnished them with the radii of curvature and added finishing touches, gave evidence, and his invention of the achromatic telescope in 1733 was regarded by Lord Mansfield as fully proved. The obscurity in which it was allowed to remain is inexplicable. Hall's autograph, presented by Mr. R. B. Prosser in 1886 to the Royal Astronomical Society, was ordered to be framed and suspended in the council room.

[Ranyard, Astronomical Register, xix. 194; Monthly Notices, xlvi. 460; Wackerbarth, ib. xxviii. 202; Gent. Mag. 1766 p. 102, 1771 p. 143, 1 790 pt. ii. p. 890; Morant's Hist, of Essex, i. 254; Observatory, ix. 177; Brewster's Edinburgh Encyclopaedia, i. pt. i. p. 105; Encycl. Metropolitana, iii. .408 (Barlow), iv. 411 (Herschel); Nichols's Lit. Anecd. iii. 669.]

A. M. C.