An experimental investigation of the diffraction correction for a Rayleigh-disc

The torque on a Rayleigh-disc was measured for sound of wavelength sufficiently small to cause diffraction effects. The results of the measurements were used to obtain a diffraction correction to be applied to the conventional König formula for the torque. The correction was found to be in good agreement with theoretical values calculated by Kotani, by King, and by Kawai.

A new derivation of a correction to take account of the finite inertia of the disc is presented. The analysis indicates the reason for the disagreement between two earlier corrections derived by King and by Wood.