Given the way we seem to have continually ignored the ripple, one could be excused for thinking it nothing but a noisy nuisance. It is certainly ubiquitous, as seen in Fig. 3.4 for Qext(β), in Fig. 6.4 for Qabs(β), in Fig. 6.6 for Qpr(β), and in Figs. 3.6 and 6.16 for backscattering. Far from being a nuisance, however, the ripple reflects a great deal of additional physics taking place within the transparent sphere, and at this point requires much closer scrutiny. Unless clearly stated otherwise we shall consider n to be real.

What is it that needs to be explained about the ripple? First and foremost, we should like to understand clearly the origin of the sharp, almost chaoticlooking peaks in these cross sections, not only mathematically, but also physically. In addition, the ripple structure appears to oscillate about the slowly varying background of Eq. (6.3), as seen in Fig. 6.1b. Why is this?

Ultimately the ripple must be linked to the behavior of the electromagnetic fields produced by the encounter of the incident plane wave with the sphere. What processes are taking place in terms of these fields that might lead to the ripple structure? Physics beyond the scattering mechanism emerges here, in the fields internal to the sphere, and a major goal in this chapter will be to explicate these phenomena.