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RAMSDEN, JESSE (1735–1800), optician and mechanician, was born at Salterhebble, a suburb of Halifax in Yorkshire, where his father, Thomas Ramsden, kept an inn. He was baptised, according to the parish register, on 3 Nov. 1735, and seems to have been born on 6 Oct. previously. Having attended the free school at Halifax for three years, he was sent at the age of twelve to his uncle at Craven in the North Riding, and there studied mathematics under the Rev. Mr. Hall. Four years later his father bound him apprentice to a clothworker in Halifax, and, having served his full time, he repaired in 1755 to London, and became clerk in a cloth warehouse. In 1758 he entered as apprentice the workshop in Denmark Street, Strand, of a mathematical instrument maker named Burton, and gained such skill in engraving that the best artists employed him in that capacity on his setting up independently about 1762. His reputation and experience rapidly increased. He married, in 1765 or 1766, Sarah, youngest daughter of John Dollond, F.R.S. [q. v.], receiving as her portion a share in her father's patent for making achromatic lenses, and opened a shop in the Haymarket, transferred about 1775 to Piccadilly.

His inventive genius quickly displayed itself. He took out a patent for, and in May 1774 published a description of, a ‘New Universal Equatoreal,’ reprinted with additions in 1791, the original stock having been accidentally destroyed by fire. Instruments of the kind had already been furnished by him in 1770–3 to Lord Bute, Sir J. Banks, and Mr. McKenzie. George III had one at Richmond; and the largest equatoreal then extant was completed by him for Sir George Shuckburgh in 1793 (Phil. Trans. lxxxiii. 75, plate ix; also described by Pearson in Rees's Cyclopædia, and by Vince in his Treatise on Practical Astronomy). The clockwork movement given to a ‘heliostat’ by Ramsden, mounted in President Saron's observatory in Champagne, was so accurate that Von Zach once followed Sirius with it during twelve hours (Berl. Astr. Jahrbuch, 1799, p. 115).

Ramsden published in 1777, by order of the commissioners of longitude, a ‘Description of an Engine for dividing Mathematical Instruments.’ In a preface by Maskelyne, it is stated that he received 315l. from the government by way of premium for this important invention, and 300l. for his property in it. The ‘Description’ was translated into French by Lalande in 1790. A ‘Description of an Engine for dividing Straight Lines on Mathematical Instruments’ was issued by Ramsden in 1779. On 25 March of the same year he laid before the Royal Society a ‘Description of two new Micrometers’ on the double-image principle, one by reflection, the other by refraction (Phil. Trans. lxix. 419); and on 19 Dec. 1782 a paper on ‘A New Construction of Eyeglasses,’ by which the aberrations of colour and sphericity were much diminished (ib. lxxiii. 94). Before 1789 he had constructed nearly a thousand sextants, greatly improved from Hadley's design; he made a new instrument of the theodolite; devised novel methods for illuminating the wires of transits and determining their collimation errors; invented a ‘pyrometer’ for measuring the expansion of substances through heat; a ‘dynameter’ for ascertaining telescopic powers; and was the first to apply ‘reading-off microscopes’ to circular instruments. His most famous work was a five-foot vertical circle, turned out in 1789 with admirable perfection under Piazzi's personal supervision for the Palermo observatory. Its high qualities rendered inevitable the substitution of entire circles for quadrants and sectors, a reform consistently advocated by Ramsden. From observations made with it, Piazzi constructed his great star-catalogue, and he described it in detail with illustrative plates in ‘Della Specola di Palermo’ (i. 15). A similar but larger instrument was built by Ramsden for the Dublin observatory.

A fine zenith-sector, constructed for the measurement of the British arc, was finished by his successor Berge in 1803. Placed for safety in the Tower, it perished in the fire of 1841. William Pearson [q. v.] described and figured it in his ‘Practical Astronomy’ (ii. 533–46). A theodolite four feet in diameter, carrying telescopes of three feet focus, was delivered by Ramsden in 1787 for use in General Roy's survey. It was eventually presented by George III to the Royal Society. The delay of three years in completing it caused great inconvenience (Phil. Trans. lxxx. 111), but the artist's genius disdained time restrictions (Zach, Monat. Correspondenz, vii. 251). On one occasion he attended at Buckingham House precisely, he supposed, at the time named in the royal mandate. The king remarked that he was punctual as to the day and hour, while late by a whole year.

He was elected a member of the Royal Society on 12 Jan. 1786, and of the Imperial Academy of St. Petersburg in 1794. The Copley medal was bestowed upon him in 1795 for his ‘various inventions and improvements in philosophical instruments.’ Among the first were an electrical machine, barometer, manometer, assay-balance, and level. A duplicate of his dividing-engine was said to have been introduced by President Saron into France, concealed in the pedestal of a table. He became acquainted with Von Zach in 1783; the Dukes of Marlborough and Richmond frequently entertained him; and Piazzi expressed veneration for his memory, and showed his portrait to an English traveller in 1813 (Hughes, Travels in Greece and Sicily, i. 131).

After some years of declining health, Ramsden went to Brighton to recruit, and there died on 5 Nov. 1800, aged 65. Delambre styled him ‘le plus grand de tous les artistes.’ The demand from all parts of Europe for his incomparable instruments was greater than could be satisfied by the constant labour of sixty workmen; yet they were considerably cheaper than those by other makers. His life was one of extreme frugality. He ate and slept little and studied much. His favourite scientific authors were Euler and Bouguer, and in advanced years he learned French enough to read Boileau and Molière. Most of his evenings were spent drawing plans by the kitchen fire, a cat on one side, a mug of porter and plate of bread and butter on the other, while some apprentices sat round, and he whistled or sang. After explaining a design to a workman, he would say, ‘Now, see, man, let us try to find fault with it,’ and intelligent suggestions generally led to amendments. But if a completed instrument fell short of his ideal, it was invariably rejected or destroyed, with the exclamation, ‘Bobs, man! this won't do; we must have at it again.’ In consequence of this disregard of gain, he left but a small fortune, mostly divided by will among his workmen. A portrait of him by Robert Home (d. 1836?) [q. v.], engraved by Jones in 1791, was given by Sir Everard Home to the Royal Society. The Palermo circle occupies the background; Ramsden appears clad in a fur coat, introduced by the artist to commemorate an order lately executed for the Emperor of Russia, greatly, however, to the disgust of his sitter, who said that he had never worn such a thing in his life. In person, Ramsden was, according to Dutens, ‘above the middle size, slender, but extremely well made, and to a late period of life, possessed of great activity. His countenance was a faithful index of his mind, full of intelligence and sweetness. His forehead was open and high, with a very projecting and expressive brow. His eyes were dark hazel, sparkling with animation.’ He had a musical voice, a manner so affable as to conciliate universal good will, an upright and benevolent character. He left one son, John Ramsden (1768–1841), a captain in the East India Company's mercantile marine.

[Original communication by the Rev. L. Dutens in Aikin's General Biography; Letter written by Piazzi from London, 1 Sept. 1788, in Journal des Sçavans, 1788 p. 744, 1789 p. 572; Hutton's Mathematical Dict. 1815; Kitchiner's Practical Observations on Telescopes, pp. 85, 87, 90; Weld's Descriptive Catalogue of Portraits, p. 57; Weld's History of the Royal Society, ii. 187; Gent. Mag. 1800, pt. ii. p. 1116; European Mag. xv. 91; Lalande's Bibl. Astr. p. 556; Poggendorff's Biogr. Lit. Handwörterbuch; Grant's Hist. of Astronomy, pp. 149, 490; Thomson's Hist. of the Royal Society; Wolf's Geschichte der Astronomie, pp. 514, 562, 570; Mädler's Geschichte der Himmelskunde, ii. 348; Marie's Histoire des Sciences, ix. 66; Montucla's Hist. des Mathématiques, iv. 343; Penny Cyclopædia; Notes and Queries, vol. x. ser. vi. pp. 67, 156; Holroyd's Collectanea Bradfordiana, p. 104; Pearson's Practical Astronomy, ii. passim (descriptions of instruments); Watt's Bibl. Brit. under John Ramsden; Bromley's Cat. of Engraved Portraits.]

A. M. C.