Orrery

an astronomical contrivance. The name was given by Richard Steele to one constructed for the Earl of Orrery from plans drawn by a George Graham, who invented it. It is known also as a planetarium. The principal planets and the moon were represented by spheres affixed to wires. The wires are inserted in disks of metal which may be caused to revolve by cogwork so as to represent the motions of the planets and moon about the sun. The spheres used are necessarily so out of proportion to the actual relative sizes of the heavenly bodies that the orrery is to be regarded as an astronomical toy, rather than a valuable means of geographical instruction. See Planets