Skip to main content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.


The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Measurement of the ratio of the speed of sound to the speed of light



James B. Mehl, Michael R. Moldover


Measurements of the resonance frequencies of the acoustic modes and of the microwave modes of a single cavity can determine u/c, the ratio of the speed of sound of a gas to the speed of light. Such measurements with a monatomic gas would determine the thermodynamic temperature T with unprecedented accuracy. By judicious choices of cavity geometry and resonance modes, u /c can be measured to part-per-million accuracy using cavities whose geometry is known only to parts per thousand. These techniques can also be applied to measurements of the universal gas constant R. A measurement of 8 would also require an accurate determination of the average atomic mass of the monatomic gas.
Physical Review A
Created October 1, 1986, Updated November 10, 2018