This model was made by George Adams, instrument maker to King George III. The black and white ball represents the Moon, the central ivory ball represents the Earth, and the other two balls represent the water on each side of the Earth. The weights imitate the gravitational pull of the Moon. When the base was spun around the central hole at a certain speed, the Earth ball hung vertically, and it was seen that the 'water' rose on each side of the Earth.
© Science Museum / Science & Society Picture Library