Built by William Parsons, Third Earl of Rose (1800-1867), between 1842-1845, the four-tonne metal mirror was part of the Great Rose Telescope. 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 It was the largest telescope in the world for 75 years, only being superseded by the 100 inch reflector at Mount Wilson, California in 1917. Rose 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 masive islands of stars - galaxies like our own Milky Way.
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