Double-barrelled air pump, late 18th century.
© Science Museum / Science & Society Picture Library
This example of a table air pump has two bras cylinders. The pistons are operated by turning the handle in one direction. The rising piston sucks air from a vesel placed on the pump plate; the one being lowered expels air from its cylinder to the open air. When the two pistons had travelled to the ends of the cylinders, the handle was turned in the opposite direction to continue the proces. This pump was made by George Adams or his son George Adams the Younger, both of whom were instrument makers to the king.