Rosse, William Parsons, 3d earl of (rôs) [key], 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.