This pump, made by William Cary, is mounted on a wooden baseboard and fitted with two brass barrels whose pistons carry racks and are operated by means of a crank-and-pinion mechanism. A pair of small brass pillars supports the wooden pediment housing the mechanism. The bell-jar rests on a plate: the flow of air between the bell-jar and the barrels is controlled by a tap at the base of the barrels. Next to the bell-jar plate is a smaller plate that was used to evacuate an upright glass cylinder. This typical English portable air pump had evolved by c. 1760.