Glass tube for demonstrating standing sound waves and calculating wavelengths of sound using cork powder in a method devised by Kundt. Cork powder is spread evenly throughout the tube by means of a filler chute. Then a sound source, e.g. a whistle or a 1700 Hz tuning fork or the speaker below is used to excite the powder into a regular pattern of nodes and antinodes. The effective length of the tube can be altered by means of a piston. Length: 600mm, external diameter: 20mm, internal diameter: 17mm. Supplied with tube, funnel, plunger, filler chute, whistle and bottle of cork powder.