© Science Museum / Science & Society Picture Library
This miniature planetary model was made by the London instrument maker, Benjamin Martin (1704-1782). Called an orrery or planetarium, it is a demonstration device to show the motions of the Earth, Moon and planets around the Sun. This example has a bras calendar base with a wooden pedestal stand and six planets (Mercury-Saturn) on rod-arms. Such apparatus became popular during the 17th century, especially after Sir Isaac Newton (1642-1727) published his universal theory of gravity in 1687. To reproduce the motions of the solar system this model uses a hand crank which drives a set of gear wheels. Instead of orbiting in realistic ovals, the planets move in circles. This orrery was probably the novelty piece of a wealthy individual rather a device used by a serious astronomy lecturer.