Great Rosse telescope, Birr Castle, Ireland, 1880.
© Science Museum / Science & Society Picture Library
One of two photographs showing views of the Great Rosse reflecting telescope, taken by Lieutenant Colonel Harry J Watson (who can just be seen, seated on the ladder) whilst he was posted to nearby Newbridge. Constructed in Parsonstown (now Birr) in Ireland by William Parsons, the Third Earl of Rosse (1800-1867), it was soon known as the 'Leviathan of Parsonstown'. The reflecting telescope used a six foot metal mirror weighing four tons. This was mounted in a 15 m tube slung by chains between massive masonry walls. Rosse used his great instrument 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 massive islands of stars like our own Milky Way Galaxy.