The first Gregorian reflecting telescope, 1724.
© Science Museum / Science & Society Picture Library
This reflecting telescope by John Hadley (1682-1744) was the first to use the Gregorian optical configuration. The Scottish mathematician, James Gregory, first suggested this optical layout using two concave mirrors in his book 'Optica Promota' in 1663. Yet he was unable to test it due to the difficulty of making mirrors with non-spherical surfaces. Over 50 years later, Hadley succeeded where Gregory had failed, after making a reflecting Newtonian telescope in 1721. He presented his Newtonian Telescope to the Royal Society of London who found it performed favourably against the best telescopes then available. This telescope by contrast remained in the Hadley family until the 19th century when it was given to the University Observatory, Cambridge, who in turn donated it to the Science Museum.