William Parsons 3d earl of Rosse

William Parsons Rosse, 3d earl of , 1800-1867, British astronomer and constructor of telescopes. He served as member of Parliament for King's Co., Ireland (1821-34), Irish representative peer (from 1845), president of the British Association (1843), president of the Royal Society (1849-54), and chancellor of the Univ. of Dublin (from 1862). His greatest interest was the construction of specula of large size for reflecting telescopes; he overcame defects caused by warping and cracking of surfaces in the cooling process and counteracted to a considerable degree other defects. His great reflecting telescope, with a speculum 6 ft (1.8 m) in diameter, the largest up to that time, was mounted in his park at Parsonstown (now Birr), Ireland, in 1845. For many years it was chiefly devoted to the study of the nebulae. Some nebulae that had eluded Sir William Herschel were resolved into groups of stars, many binary and triple stars were discovered, and the moon was more completely described.

Parsons, William (1800–67), 3rd earl of Rosse, astronomer and politician. Born in York, he was brought up at the ancestral home in Birr, Co. Offaly. After Trinity College, Dublin, and Oxford (where he excelled in mathematics) he entered Parliament as member for King's County (Offaly) (1821–34); from 1831 he was lord lieutenant of King's County, and in 1841 entered the House of Lords. His intellectual passion was astronomy, particularly the design of large telescopes in which regard he expanded on the work of William Herschel. In 1842 he constructed at Birr the famous 72‐inch telescope (‘Leviathan’) with which he made many important observations, principally of nebulae.

David Sturdy