(b Bolton, Lancashire, England, 18 June 1799; d.. Maidenhead, Berkshire, England, 5 October 1880),
Lassell served a seven years’ apprenticeship with a merchant at Liverpool and then became a brewer. About 1820 he began to construct reflecting telescopes and in 1840 installed a nine-inch Newtonian instrument in a private observatory bear Liverpool.
Lassell was the first to design and use machines for surfacing mirrors of speculum metal in which the movement of the polisher closely imitated the circular motion used in polishing by hand. He was also the first to apply Fraunhofer’s equatorial mounting to large reflecting telescopes. He mounted both the nine-inch telescope and a fine twenty-four-inch Newtonian, completed in 1846, in that way. With the latter he discovered Neptune’s larger satellite, Triton, in 1846; detected Hyperion, the eighth satellite of Saturn (seen simultaneously by W. C. Bond at Harvard College Observatory) in 1848; and confirmed the existence of two satellites of Uranus, Ariel and Umbriel, in 1851.
In 1852 Lassell took the twenty-four-inch telescope to Valletta, Malta, where he expected that the climate would enable him to improve and extend his observational work. He then found that an even larger instrument was desirable, and in 1860 he completed a forty-eight-inch Newtonian telescope supported on a fork-type equatorial mounting. With this instrument, assisted by A. Marth, he searched unsuccessfully for new satellites, discovered 600 new nebulae, and monographed several others.
Upon his return to England in 1864, Lassell settled at Maidenhead, Berkshire. There he resumed his experiments with surfacing machines and constructed an improved form for polishing forty-eight-inch disks. Even so, he did not erect the forty-eight-inch telescope at Maidenhead but relied on the twenty-four-inch until failing eyesight forced him to abandon his studies.
Lassell became a fellow of the Royal Astronomical Society in 1839, received its gold medal in 1849, and was elected its president in 1870. He was elected a fellow of the Royal Society in 1849 and received the Royal Medal in 1858. He was an honorary member of the Royal Society of Edinburgh and the Royal Society of Sciences at Uppsala and held an honorary LL.D. conferred by the University of Cambridge.
I. Original Works. For descriptions of machines for polishing specula, see Monthly Notices of the Royal Astronomical Society,8 (1848), 197; 9 (1849), 29; 13 (1853), 43; and Philosophical Transactions of the Royal Society,165 (1875), 303; Lassell’s telescopes are described in Memoirs of the Royal Astronomical Society: the nine-inch reflector, 12 (1842), 265-272; the twenty-four-inch reflector, 18 (1850), 1-25; and the forty-eight-inch reflector, 35 (1866), 1-4. For an account of the Malta observations, see Mem-oirs of te Royal Astronomical Society, 35 (1866), 33-35.
II. Secondary Literature. Obituary notices include W. Huggins, in Proceedings of the Royal Society,31 (1880-1881), vii–x; and M. L. Huggins, in Observatory,3 (1880), 587-590. Lassell’s activities in telescope-making are discussed in H. C. King, The History of the Telescope (London, 1955), pp. 218-224.
H. C. King
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