Dictionary of National Biography, 1885-1900/Lassell, William

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LASSELL, WILLIAM (1799–1880), astronomer, was born at Bolton in Lancashire on 18 June 1799. At the age of four or five he amused himself by polishing lenses. After his father's death from fever in 1810 he was sent to school at Rochdale for eighteen months, was apprentice from 1814 to 1821 in a merchant's office in Liverpool, and set up in business as a brewer about 1825. In 1820 he began to construct reflecting telescopes, being too poor to buy them. A nine-inch Newtonian erected by him at Starfield, near Liverpool, where he built an observatory in 1840 (Memoirs Royal Astronomical Soc. xii. 265), was virtually the first example of the adaptation to reflectors of the equatoreal plan of mounting. With it he observed the solar eclipse of 8 July 1842 (ib. xv. 91), Faye's, d'Arrest's, Mauvais's second, Vico's first and second comets in 1843–5, following them further than was possible at any public observatory. He desired to possess a larger instrument; but dissatisfied, after inspection, with the methods used by Lord Rosse for grinding specula, he invented a new machine constructed from his design by James Nasmyth [q. v.] With this he ground and polished a speculum of rare perfection, two feet in diameter, and twenty in focal length, and in 1846 mounted it equatoreally at Starfield (ib. xviii. 1). On 10 Oct. 1846 he saw with it the satellite of Neptune (Monthly Notices, vii. 157), and verified the discovery in the following July. On 19 Sept. 1848 he detected, simultaneously with Bond in America, Saturn's eighth satellite (Hyperion) (ib. viii. 195), and was one of the first observers of Saturn's dusky ring, compared by him to a crape veil (ib. xi. 21). For these achievements he received, on 9 Feb. 1849, the gold medal of the Royal Astronomical Society (Memoirs, xviii. 192).

The composition of the Uranian system was first clearly ascertained by Lassell. He discovered on 24 Oct. 1851 the two inner satellites (Ariel and Umbriel), and established later the non-existence of four out of Herschel's six (Monthly Notices, xi. 201, 248, xii. 15, xxxv. 16). The total solar eclipse of 28 July 1851 was observed by him with a two and a half inch Merz refractor at Trollhättan Falls in Sweden, and in the autumn of 1851 he transported his two-foot speculum to Malta, where he observed with it during the ensuing winter. Much of his attention was engaged by the ‘marvellous spectacle’ of the Orion nebula, of which he executed a detailed drawing (Memoirs Royal Astronomical Soc. xxiii. 53). He also made several sketches of Saturn (ib. xxii. 151), and noted for the first time the transparency of its dusky ring (Monthly Notices, xvii. 12). The growth of factories round Starfield compelled him to move his observatory in 1854 to Bradstones, two miles further away from Liverpool. There he observed and depicted Donati's comet, 12 Sept. to 8 Oct. 1858 (Memoirs Royal Astronomical Soc. xxx. 58), and constructed in 1859–60 a reflecting telescope of four feet aperture, thirty-seven focal length, mounted equatoreally at Valetta in Malta towards the close of 1861. The tube of this splendid instrument was of iron lattice-work to avert inequalities of temperature, and the small percentage of arsenic employed in Lassell's earlier specula was omitted from its composition. Assisted by Mr. Marth, he worked with it diligently for three years, and catalogued six hundred new nebulæ, besides carefully describing and drawing nebulæ already known (ib. xxxvi. 1). One, a planetary nebula in Aquarius (Gen. Cat. 4628), showed as 'a sky-blue likeness of Saturn,' of plainly annular structure (Proceedings Royal Soc. xii. 269; Report Brit. Association, 1862, ii. 14), and a large drawing of the Orion nebula, executed by Miss Caroline Lassell under her father's supervision, was by him in 1868 presented to the Royal Society, and was photographically reproduced in 'Knowledge,' 1 May 1889.

After his return from Malta Lassell took a residence near Maidenhead, and set up his two-foot reflector in an observatory there. At Maidenhead Lassell observed a 'black' transit of Jupiter's fourth satellite on 30 Dec. 1871 (Monthly Notices, xxxii. 82), and erected an improved polishing machine, described before the Royal Society on 17 Dec. 1874 (Phil. Trans. clxv. 303). He discussed in 1871 and decided against the reality of alleged changes in the nebula about η Argûs (Monthly Notices, xxxi. 249). He was member of the Royal Astronomical Society from 1839, president 1870–2, and attended its council meetings until his death. He was elected a fellow of the Royal Society in 1849, received a royal medal in 1858, was admitted to membership by the Royal Society of Edinburgh and the Society of Sciences of Upsala, and had an honorary degree of LL.D. conferred upon him by the university of Cambridge in 1874. An affection of the eyes latterly precluded him from observing, and he died peacefully in his sleep at Maidenhead on 5 Oct. 1880, leaving behind him a high reputation for moral worth and practical scientific efficiency. His specula have never been surpassed for perfection and permanence of figure and polish, and he ranks with Sir William Herschel and Lord Rosse among the perfecters of the reflecting telescope. The instrument with which he made most of his discoveries was presented by the Misses Lassell after his death to the Royal Observatory, Greenwich.

[Monthly Notices, xli. 188; Proceedings Royal Soc. xxxi. p. vii; Astronomical Reg. xvii. 284; Nature, xxii. 565 (Huggins); Observatory, iii. 587 (Mrs. Huggins); Times, 7 Oct. 1888; Athenæum, 1880, ii. 469; Ann. Reg. 1880, p. 203; Clerke's Hist. of Astronomy; André et Rayet's L'Astronomie Pratique, i. 114; Astr. Nachrichten, xcviii. 207; Sirius, xiii. 245; Mädler's Geschichte der Himmelskunde, Bd. ii. passim; Royal Society's Cat. of Scientific Papers, vols. iii. viii.]

A. M. C.