Page:Dictionary of National Biography volume 15.djvu/204

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to the king, but his enjoyment of these honours was of brief duration. While engaged, on 30 Nov. 1761, in an intense and prolonged study of Clairaut's treatise on the motions of the moon, he was struck with apoplexy, and died in a few hours, aged 55. He left two sons and three daughters, one of whom married his celebrated apprentice, Jesse Ramsden. The only authentic account of his life was written by the husband of one of his granddaughters, Dr. John Kelly, rector of Copford, Essex, who thus described him: ‘In his appearance he was grave, and the strong lines of his face were marked with deep thought and reflection; but in his intercourse with his family and friends he was cheerful and affectionate; and his language and sentiments are distinctly remembered as always making a strong impression on the minds of those with whom he conversed. His memory was extraordinarily retentive, and amidst the variety of his reading he could recollect and quote the most important passages of every book which he had at any time perused.’

[Kelly's Life of John Dollond, privately printed, substantially reproduced in Phil. Mag. xviii 47 (1804), and in Phil. Trans. Abridg. x. 341 (Hutton), 1809; Haag's La France Protestante (2nd ed.), v. 433; Gallery of Portraits, iii. 12, with engraving by Posselwhite from a portrait of Dollond in the Royal Observatory; Gent. Mag. 1820, p. 90; Hutton's Phil. and Math. Dict.; Grant's Hist. of Phys. Astronomy, p. 531; Bailly's Hist. de l'Astr. Moderne, iii. 116; Montucla's Hist. des Math. iii. 448; Whewell's Hist. of Inductive Sciences (3rd ed.), ii. 213, 289; Brewster's Edinb. Cyclopædia, art. ‘Telescopes;’ H. Servus's Gesch. des Fernrohrs, p. 77 (Berlin, 1886); G. Fischer on Heliometer, Sirius, xvii. 176; Watt's Bibl. Brit.]

A. M. C.

DOLLOND, PETER (1730–1820), optician, eldest son of John Dollond [q. v.], was born in London in 1730. He was brought up to his father's trade of silk-weaving, which for some years they carried on together at Spitalfields. But Peter had higher aspirations. He had learnt much on optical subjects from intercourse with his father, and conceived the project of setting up business as an optician under his guidance. In 1750 he accordingly took a shop for the purpose near the Strand, whence he removed, two or three years later, to the well-known premises in St. Paul's Churchyard. Unexpected fame, patronage, and success rewarded the venture. From 1752 to 1761 he enjoyed his father's active co-operation; he admitted his brother, John Dollond, to partnership in 1766; and replaced him, after his death on 6 Nov. 1804, with his nephew, George Dollond [q. v.] He himself retired from business in 1819.

Dollond worthily continued his father's great work of developing the capabilities of the refracting telescope. Yet he was no mathematician, and obtained his results by assiduous trials and the cunning of his eye and hand. John Bernoulli, who visited him and inspected his workshops in 1769, has left on record his astonishment at the scanty theoretical knowledge possessed by so distinguished an artist (Lettres Astronomiques, 1771, p. 66).

His triple achromatic object-glasses were described in ‘An Account of an Improvement made by Mr. Peter Dollond in his new Telescopes: in a Letter to James Short, F.R.S.,’ read before the Royal Society on 7 Feb. 1765 (Phil. Trans. lv. 54). The great advantage of this combination (consisting of two convex crown lenses with one double-concave of flint) was that it greatly reduced the spherical error, and hence admitted of increased apertures. Dollond accordingly constructed two telescopes on this principle, one five, the other (purchased for the Royal Observatory) three and a half feet in focal length, both of 33/4 inches aperture and of excellent performance; and was hindered from a further advance in the same direction only by the difficulty of procuring suitable pieces of glass. The improvement was universally recognised and accepted.

‘A Letter describing some Additions and Alterations made to Hadley's Quadrant, to render it more serviceable at Sea,’ addressed by him to Maskelyne, was communicated to the Royal Society on 29 March 1772 (ib. lxii. 95). The aim proposed and secured was to bring the back-observation into use by ameliorating the adjustments. His ‘Account of an Apparatus applied to the Equatorial Instrument for correcting the Errors arising from the Refraction in Altitude’ was imparted to the same body by Maskelyne on 4 March 1779 (ib. lxix. 332). By the application in front of the object-glass, and the regulated movements of a concave and a convex lens, a displacement of the image, it was shown, could be produced equal and contrary to that by atmospheric refraction.

In 1789 Dollond published ‘Some Account of the Discovery made by the late Mr. John Dollond, F.R.S., which led to the grand Improvement of Refracting Telescopes, in order to correct some Misrepresentations, in Foreign Publications, of that Discovery.’ Although read before the Royal Society, it was, by the decision of the council, excluded from the ‘Philosophical Transactions,’ and was accordingly circulated in a separate form by the author. It contained a temperate and lucid narrative of the steps by which the