Thomas Wright's Machina Coelestis, or the Great Orrery, 1730.
© Science Museum / Science & Society Picture Library
Engraved by T. Vandergucht after C. Lempriere. According to Dr Johnson, an orrery is 'an instrument which by many complicated movements represents the revolution of the heavenly bodies.' The instrument takes its name from Charles Boyle, the fourth Earl of Orrery, who was one of the first to own one. Thomas Wright was King George II's instrument maker and was responsible for designing a new base plate in the form of concentric rings, each bearing a planet. The Tropic of Cancer and the Arctic Circle are represented by the semi-circular arches over the top of the base, as is the 'moveable horizen', which is hinged to allow for motion.