Kundt's Figures

Series first described by Kundt of Strasburg; produced when air or other gas is thrown into vibration in a gla tube containing a light powder, such as lycopodium or finely divided silica. If such a gla tube, three or four feet long, closed at the ends and filled with air, be held at its middle point and caused to vibrate longitudinally by drawing a wet cloth along it, a series of dust-heaps will be produced in the tube corresponding to the nodal points. These will be the more sharply defined the more closely the wave length in air of the note given by the tube approximates to an aliquot part of the length of the tube. Since the distance between two consecutive heaps represents half the wave length of the given sound in air, and the length of the tube itself represents half the wave length for the same sound in gla , the ratio of the two is the relation of the velocities of sound in air and in gla . If the tube be filled with hydrogen or any other gas, the ratio of the distances between the consecutive dust-heaps under these conditions to those obtained with air is obviously the relation of the velocity in the gas employed to that in air.