On the ‘‘bubble grapes’’ induced by a sound field

A suggestion is advanced that the stable bubble clusters observed by Marston et al. [Bubble Dynamics and Interface Phenomena, edited by J. R. Blake et al. (Kluwer Academic, Dordrecht, 1994), pp. 343–353] in an ultrasonic field are due to the radiative interaction forces of the bubbles, which change from attraction to repulsion when the distances between the bubbles become comparable with their sizes. This reversal is predicted by a theory developed in a previous paper by the authors [Phys. Fluids 7, 1923–1930 (1995)].