The Barker lever is a pneumatic system which multiplies the force of a finger on the key of a tracker pipe organ. It employs the wind pressure of the organ to inflate small bellows called "pneumatics" to overcome the resistance of the pallets (valves) in the organ's wind-chest . This lever allowed for the development of larger, more powerful organs still responsive to the human hand. These larger organs first flourished in France, e.g., the organ produced by Cavaillé-Coll at St. Sulpice.