ROSSE, rds, William Parsons, 3d EARL OF, British astronomer: b. York, 17 June 1800; d. Monkstown, Ireland, Oct. 1867. He was educated at Dublin and at Magdalen College, Oxford, where he was graduated in 1822. He was member of Parliament for King's County from 1823 to 1834, and succeeded his father in the earldom in 1841. In 1845 he was elected a representative peer of Ireland, but took little interest in 'politics. During the stormy dis cussions on the first reform bill he was occupied with the construction of his first famous reflect ing telescope, the speculum of which had a diam eter of three feet, and was soon superseded by one of double the size. The two great de fects which had hitherto baffled opticians in constructing large reflecting mirrors were spher ical aberration and absorption of light by spec ula, and in the casting of those of large size there arose the apparent impossibility of pre venting cracking and warping of the surface on cooling. Even the proper admixture of the
metals for the reflector had to be ascertained by numerous and costly experiments. At last, however, a gigantic speculum, weighing three tons, was turned out without warp or flaw and was then polished and mounted on a telescope 52 feet in length in Lord Rosse's park at Par sonstown, at a cost of $150,000; The sphere of celestial observation was immensely widened by an instrument so powerful; nebular which had defied Herschel's telescope were resolved into stars and new nebulous mist was revealed to the observation. The construction of the tele scope, effected under the earl's direction and superintendence, is fully described in the 'Phil osophical Transactions of the Royal Society, of which body he was president,