This paper describes a method for determiningγfor gases by measuring the velocity of sound in a closed resonance tube with fixed ends. Air, nitrogen, helium, carbon dioxide, normal hydrogen, and parahydrogen were studied at temperatures between 77°K and 373°K. Inexpensive ceramic transistor radio earphones were used as both exciter and detector. The exciter was driven by a variable frequency audio oscillator in the range 50–3000 cps and the output voltage of the detector was amplified and observed on an oscilloscope. The measured values ofγare accurate to about 1%. This accuracy, and the simplicity of the experiment, combine to offer a good experiment for the undergraduate laboratory.