Terrestrial globe, 1855-1860.
© Science Museum / Science & Society Picture Library
This apparatus demonstrates the precesion of the equinoxes due to the wobble of the Earth's axis of rotation. The axis of the spinning Earth is remarkably stable but does preces very slightly, taking 25,800 years for each circular wobble. This precesion is largely caused by the gravitational pull of the Sun and Moon on the Earth's equatorial bulge. This globe was once the property of the English astronomer, Sir William Huggins (1824-1910).