William Rosse

William Parsons, third earl of Rosse, an astronomer and engineer, was president of the Royal Society 1848–54. He built the world’s largest telescope, the six-foot-diameter Leviathan of Parsonstown, which has been restored and can still be seen in the grounds of Birr Castle, Co. Offaly, Ireland, the ancestral home of the Parsons family (now the location of an Irish Historical Science Centre). Its giant speculum, or mirror, is prominently displayed in the Cosmology Hall of London’s Science Museum. Not surpassed in size for 70 years, the telescope made it possible for Rosse to observe and identify for the first time ‘spiral galaxies’ – a discovery described by the astronomer and broadcaster Patrick Moore as ‘one of the turning-points in our understanding of the universe’.