Orrery

Orrery, a working model of any system of heavenly bodies. Various spheres would, for instance, represent the planets, and these would be geared up together in such a way that they could move around a model sun in the same directions as do actual planets. Their velocities too would all be the same fraction of the actual velocities, so that their motions with respect to each other would be the same as the movements we view in the celestial sphere. The Earl of Orrery, in 1745, paid for the construction of the first one (designed by a clockmaker, George Graham), hence the name.