The measurement of phase and intensity in sonic and ultrasonic fields

A method of recording the phase of a received signal in a system of plane progressive waves in relation to another signal of fixed phase is described, with the primary object of measuring changes in the velocity of sound, hence of the composition, of a mixture of gases. Recent work in ultrasonics is reported in which hot-wires and thermistors have been used for intensity measurements in stationary waves or to measure streaming velocities near a quartz generator, to show the usefulness of these devices.