The dynamic theory of electromagnetic wave propagation in a composite medium is considered. With reference to cermet topology, we study the multiple scattering by a regular array of metallic spheres dispersed in a dielectric host. By analogy with the electronic problem, we can reveal the interplay between the geometric structure effects and the effects of the scattering potential. This is the main advantage of our treatment as compared to the work of Lamb, Wood, and Ashcroft <article>[Phys. Rev. B 21, 2248 (1980)]</article> which is based on the use of logarithmic derivatives. The secular equation of our formalism, which is very manageable, is well suited to study the role of different multipole corrections and to test the approximations of model dielectric functions.