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ROSSE, WILLIAM PARSONS, 3RD EARL

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Originally appearing in Volume V23, Page 745 of the 1911 Encyclopedia Britannica.
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ROSSE, See also:WILLIAM See also:PARSONS, 3RD See also:EARL of (1800—1867), Irish astronomer and See also:telescope constructor, was See also:born at See also:York on the 17th of See also:June ',Boo, a son of the 2nd earl (see above). Until his See also:father's See also:death he was known as See also:Lord Oxmantown. Entered at Trinity See also:College, See also:Dublin, in 1818, he proceeded to Magdalen College, See also:Oxford, in 1821, and in the same See also:year he was returned as M.P. for See also:King's See also:County, a seat which he resigned in 1834. He was Irish representative peer from 1845, See also:president of the See also:British Association in 1843, president of the Royal Society from 1849 to 1854, and See also:chancellor of the university of Dublin from 1862. From 1827 he devoted himself to the improvement of reflecting telescopes; in 1839 he mounted a telescope of 3 ft. See also:aperture at his seat, See also:Birr See also:Castle, Parsonstown; and in See also:February 1845 his celebrated 6-See also:foot reflector was finished. Owing to the See also:famine and the disturbed See also:state of the See also:country, which demanded his See also:attention as a large landowner and See also:lieutenant of King's County (from 1831), the See also:instrument remained unused for nearly three years, but since 1848 it has been in See also:constant use, chiefly for observations of nebulae, for which it was particularly suited on See also:account of its immense See also:optical See also:power, nominally 6000. Lord Rosse died at Monkstown on the 3ist of See also:October 1867. He had four sons. The eldest, See also:Lawrence Parsons, 4th earl of Rosse, and See also:Baron Oxmantown, born on the 17th of See also:November 1840, succeeded to the See also:title on his father's death, and made many investigations on the heavenly bodies, particularly on the See also:radiation of the See also:moon and related See also:physical questions; the youngest, the Hon. See also:Charles Algernon Parsons, born on the 13th of June 1854, is famous for his commercial development of the See also:steam See also:turbine. The first constructor of reflecting telescopes on a large See also:scale, William See also:Herschel, never published anything about his methods of casting and polishing specula, and he does not appear to have been very successful beyond specula of 18 in. See also:diameter, his 4-foot See also:speculum (" the 4o-foot telescope ") having been little used by him (see discussion between See also:Sir J. Herschel and See also:Robinson in The See also:Athenaeum, Nos.

831-36, 1843). Lord Rosse had therefore no help towards his brilliant results. His speculum See also:

metal is composed of four atoms of See also:copper (126.4 parts) and one of See also:tin (58.9 parts), a brilliant alloy, which resists tarnish better than any other See also:compound tried. Chiefly owing to the brittleness of this material, Lord Rosse's first larger specula were composed of a number of thin plates of speculum metal (sixteen for a 3-foot See also:mirror) soldered on the back of a strong but See also:light framework made of a See also:peculiar See also:kind of See also:brass (2.75 of copper to 1 of See also:zinc), which has the same expansion as his speculummetal. In See also:Brewster's See also:Edinburgh See also:Journal of See also:Science for 1828 he described his See also:machine for polishing the speculum, which in all essential points remained unaltered afterwards. It imitates the motions made in polishing a speculum by See also:hand by giving both a rectilinear and a lateral See also:motion to the polisher, while the speculum revolves slowly; by shifting two See also:eccentric pins the course of the polisher can be varied at will from a straight See also:line to an See also:ellipse of very small eccentricity, and a true parabolic figure can thus be obtained. The speculum lies See also:face upwards in a shallow See also:bath of See also:water (to preserve a See also:uniform temperature), and the polisher fits loosely in a See also:ring, so that the rotation of the speculum makes it revolve also, but more slowly. Both the grinding and polishing tools are grooved, to obtain a uniform See also:distribution of the See also:emery used in the grinding See also:process and of the See also:rouge employed in polishing, as also to provide for the lateral expansion of the See also:pitch with which the polisher is coated. In See also:September 1839 a 3-foot speculum was finished and mounted on an altazimuth stand similar to Herschel's; but, though the See also:definition of the images was See also:good (except that the diffraction at the See also:joints of the speculum caused See also:minute rays in the See also:case of a very See also:bright See also:star), and its peculiar See also:skeleton See also:form allowed the speculum to follow atmospheric changes of temperature very quickly, Lord Rosse decided to See also:cast a solid 3-foot speculum. Hitherto it had been See also:felt as a See also:great difficulty in casting specula that the solidification did not begin at one See also:surface and proceed gradually to the other, the See also:common See also:sand See also:mould allowing the edges to cool first, so that the central parts were subject to great straining when their See also:time of cooling came, and in large castings this generally caused cracking. By forming the bottom of the mould of hoop See also:iron placed on edge and closely packed, and the sides of sand, while the See also:top was See also:left open, Lord Rosse overcame this difficulty, and the hoop iron had the further See also:advantage of allowing the See also:gas See also:developed during the cooling to See also:escape, thus preventing the speculum from being full of pores and cavities. This invention secured the success of the casting of a solid 3-foot speculum in 184o, and encouraged Lord Rosse to make a speculum of 6 ft. diameter in 1842.

In the beginning of 1845 this great reflector was mounted and ready for See also:

work. The instrument has a See also:focal length of 54 ft. and the See also:tube is about 7 ft. in diameter; owing to these large dimensions it cannot be pointed to every See also:part of the heavens, but can only be moved a See also:short distance from the See also:meridian and very little to the See also:north of the See also:zenith; these restrictions have, however, hardly been felt, as there is almost at any moment a sufficient number of See also:objects within its reach. From 1848 to 1878 it was but with few interruptions employed for observations of nebulae (see NEBULA) ; and many previously unknown features in these objects were revealed by it, especially the similarity of " See also:annular " and " planetary " nebulae, and the remarkable " See also:spiral " configuration prevailing in many of the brighter nebulae. A See also:special study was made of the nebula of See also:Orion, and the resulting large See also:drawing gives an extremely good See also:representation of this complicated See also:object. (See TELESCOPE.) Lord Rosse gave a detailed account of the experiments which step by step had led to the construction of the 3-foot speculum in the Philosophical Transactions for 184o. In the same publication for 1844 and 185o he communicated short descriptions and drawings of some of the more interesting nebulae, and in the See also:volume for 1861 he published a See also:paper " On the Construction of Specula of 6-ft. Aperture, and a Selection from the Observations of Nebulae made with them," with numerous engravings. The accounts of the observations given in these papers, however, were fragmentary; but in 1879–8o a See also:complete account of them was published by the See also:present earl (" Observations of Nebulae and Clusters of Stars made with the 6-foot and 3-foot Reflectors at Birr Castle from 1848 to 1878 ") in the Scient. Trans. R. Dublin See also:Soc. vol. ii. The drawing of the nebula of Orion was published in the Phil.

Trans. for 1868 See obituary See also:

notice in the Proc. See also:Roy. Soc. (1868), 16, 36, and in the Monthly Notices of Roy. Astr. Soc. vol. 29, p. 123.

End of Article: ROSSE, WILLIAM PARSONS, 3RD EARL

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