Fletcher, Neville H.2020-10-160002-9505http://hdl.handle.net/1885/212550The common assumption that the speed of sound in a gas is determined by the adiabatic compressibility because the pressure variations are so rapid that no heat flow can take place is shown to be incorrect. The criterion for applicability of the adiabatic assumption in a free wave is rather that the frequency be lower than a certain very high limit. The propagation of sound in tubes is also discussed and it is shown that the frequency must, in addition, lie above a certain low limit if the adiabatic assumption is to be valid.application/pdfen-AU© 1974 American Association of Physics Teachers197410.1119/1.1987757