We appreciate Dr. NieminenÕs reference to the pioneering calculation of Waterman, which was unknown to us. To our reading, his proof that a rotationally symmetric object does not couple different azimuthal modes in scattering is certainly a good, different explanation of our point of view, which we stated as a physically reasoned theorem.
However, Waterman uses (Eq. 9) an expansion in regular wave functions. Bodies with edges (i.e., all real bodies) will have non-analytic surface currents in the edge vicinity, and WatermanÕs result may not be true there. This is precisely where we find, in our exact calculations, that the coupling of wave to body is largest.
This illustrates the virtue of a physical argument; Waterman does not venture a physical explanation of his results, and indeed does not discuss conveying angular momentum to objects; his concern is scattering. We invoked instead the averaging of the J Â B force over the geometry, including sharp edges. This may be more appealing, intuitive a picture.
NieminenÕs generalization to dielectrics, considering symmetries, seems correct and shows the usefulness of this approach.