Iv. On the acoustic shadow of a sphere

In my book on the ‘Theory of Sound,’ 328, I have discussed the effect upon a source of sound of a rigid sphere whose surface is close to the source. The question turns upon the relative magnitudes of the wave-length (λ) and the radius (c) of the sphere. If kc he smal, where k = 2π/λ, the presence of the sphere has but little effect upon the sound to be perceived at a distance.