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Owing to the inherent nonlinearity of the equations of motion for a perfect fluid, two or more sound waves passing through a common region will, in general, interact with one another and give rise to scattered waves. In this paper, a source function is obtained for the lowest order scattering process which is quadratic in the primary field variables. This function is rewritten in a form that demonstrates that no scattered waves exist outside the region of interaction of two sound beams intersecting each other at right angles. Furthermore, it is demonstrated that no such scattered waves exist when the two beams intersect at the angle

, where , c, and p stand for the density, sound velocity and pressure, respectively, and the subscript 0 means ambient values of these quantities. The interfering effect of pseudo-sound, induced by radiation pressure, is suggested as an explanation for the results of Ingard and Pridmore-Brown, who have reported recently what they believe to be scattered waves from the interaction region of two sound beams intersecting each other at right angles.

©1957 Acoustical Society of America