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JONES, THOMAS (1775–1852), optician, was born on 24 June 1775. In 1789 he entered the establishment of Jesse Ramsden (1735–1800), optician in Piccadilly, London. Subsequently he carried on business on his own account, first at 21 Oxenden Street and afterwards in Rupert Street, and soon attained a high reputation for his skill in constructing astronomical instruments of the larger class, many of which he was commissioned to supply for the principal observatories of Great Britain and the colonies (see a list of the most important in Monthly Notices, xiii. 112). He assisted, in conjunction with Dr. George Pearson, Edward Troughton, Captain W. H. Smyth, and others, in the formation of the Astronomical Society in 1820. On 4 June 1835 he was elected a fellow of the Royal Society. He died on 29 July 1852.

Descriptions of the following instruments invented or improved by Jones have been published: 1. ‘The Englefield Improved Side Transit Instrument,’ for obtaining time with accuracy, Tilloch's ‘Phil. Mag.’ vol. xliii., and separately London, 8vo, 1814. 2. ‘The Sectograph, principally intended for the purpose of dividing right lines into equal parts … dividing angles,’ &c., ‘Phil. Mag.’ vol. xlii., and separately London, 1814, 8vo. 3. An improved hygrometer, ‘Phil. Trans.’ 20 Feb. 1825, vol. cxvi. pt. ii. pp. 53–4. 4. A double eye-piece, ‘Monthly Notices of the Roy. Astron. Soc.’ xii. 95–6. Jones was also the author of ‘A Companion to the Mountain Barometer, consisting of Tables, &c., together with a Description and Use of the most improved Mountain Barometers,’ London, 1817, 8vo; 2nd edit. (? 1820).

W. & S. Jones was the title of another well-known firm of opticians and mathematical instrument makers in Holborn, London, in the early years of this century. The chiefs, William and Samuel Jones, were sons of John Jones, himself an optician of some note, and were at one time employed in the business of George Adams the younger [q. v.] The elder partner, William Jones (1763–1831), received some instruction from Benjamin Martin, and gave lessons in astronomy and mathematics. He was intimate with Priestley, Hutton, Maskelyne, and other well-known men of science, and was a fellow of the Astronomical Society. He published descriptions of a new portable orrery (1782), geometrical and graphical essays, giving a description of mathematical instruments (1798; 4th edit. 1813), and ‘Lectures on Electricity,’ 1800. He also edited and revised a reissue of George Adams's works on natural philosophy (1799 and 1812); wrote many scientific articles in Rees's ‘Encyclopædia’ and the ‘Encyclopædia Britannica,’ and criticised Dr. Wollaston's invention of ‘ periscopic spectacles’ in Nicholson's ‘Journal,’ vols. vii. viii. He retired to Brighton late in life, and died there on 17 Feb. 1831. He left to his surviving brother, Samuel, a valuable mathematical library (Gent. Mag. 1831, pt. i. p. 275; Dict. of Living Authors, 1816; Watt, Bibl. Brit.)

[Monthly Notices of the Royal Astronomical Society, xiii. 112; Imperial Dict. of Universal Biography, iii. 51.]

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