The experimental confirmation of the Hemholtz, Kirchhoff theory for the propagation of long waves in pipes has been subject to some doubt. This theory is complicated both by viscous drag and the irreversibility consequent to the transition from adiabatic to isothermal processes. An experimental method has been devised which eliminates the effects of thermodynamic irreversibility and permits a direct determination of the viscous effects. The Kirchhoff equations are recast in a form which, together with the analogy of the propagation of sound in pipes with the electric long line, permits a ready comparison of experimental results with the theory.

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