Large orrery with eight-day clock by Charles Butcher, 1733.

This planetary model was made by Charles Butcher of Bedford, for Lord Trevor, the Baron of Bromham. Later acquired by Stephen Demainbray, it was used by him in his public lectures on natural philosophy. Called an orrery, the working model illustrates the motions of the Earth, Moon and planets around the Sun. To reproduce the motions of the solar system, the model is fitted with an eight-day clock. This would show the planetary motions in real time, or if disengaged the model could be moved more rapidly using a hand crank. Such devices became popular during 17th century especially after Sir Isaac Newton published his universal theory of gravity.