To determine the standing longitudinal waves in column of air and velocity of sound in air. It comprises a glass tube approx 1.2 mtr. length and 34 mm diameter. There is a tightly fitting but adjustable piston on a 390 mm long rod at one end of the glass tube. A loose fitting piston attached to a 1.2 mtr. long sounding rod at the other end of the glass tube. Fitted on a wooden base board.