The velocity of sound in air

Measurements have been made of the velocity of sound in free air at a frequency of 13500 c/s. A small loudspeaker, connected to an oscillator, emitted sound which, after travelling a distance determined by an accurate screw, was received by a microphone. The input waveform of the transmitter and the output waveform of the receiver were passed through pulse-shaping circuits and displayed together on the screen of a double beam oscillograph. Movement of the transmitter, controlled by rotation of the screw, produced relative motion of the two traces on the oscillograph screen and the wavelength of the sound was determined by measuring the distance between successive positions of the transmitter at which the two trains of pulses coincided on the screen. Corrections were applied for the effects of temperature, humidity and a number of less important factors. The final value for the velocity of sound at a frequency of 13 500 c/s in dry air at a temperature of 273.16° K and a pressure of 1013.2 mb was 331.45 ± 0.04 m/s.