Delivery of the Rosse six-foot mirror, Science Museum, June 1914.
© Science Museum / Science & Society Picture Library
Built by William Parsons, Third Earl of Rosse (1800-1867), between 1842-1845, the four-tonne metal mirror was part of the Great Rosse Telescope, which stood at Parsonstown, now Birr in the Republic of Ireland. Known as the 'Leviathan of Parsonstown', the telescope had a tube 15m long suspended between masive masonry walls. It was the largest telescope in the world for 75 years, only being superseded by the 100 inch reflector at Mount Wilson, California in 1917. Rosse used this great telescope to try and determine the nature of nebulae - misty patches in the sky. He was the first to discover that some had spiral forms, now known to be remote and massive islands of stars like our own Milky Way Galaxy.