On the behaviour of suspended particles in air, and the velocity of sound at super-sonic frequencies

Abstract

In accordance with theory, particles of the size prevailing in ordinary cigarette smoke are found to act as obstacles in air vibrating at supersonic frequencies. This action leads to the formation of figures at the nodes in a resonance tube, from which measurements of the wave-length can be made. These, with a knowledge of the frequency of each piezo-electric crystal used to maintain the oscillations, enable values of the velocity of sound in air to be found at various frequencies in a range from 92.2 to 801.6 kc./sec. The values found show a definite dispersion of sound in this region, contrary to the results of previous experimenters with the Pierce acoustic interferometer. There are two maxima which are attributed to the separate effects of oxygen and nitrogen.