Electromagnetic waves in media with finite discontinuities

The approach adopted is to write down a wave equation which applies to the medium as a whole. The physical parameters of the medium appear in the coefficients in this equation. It is shown that meaningful solutions can be obtained when the physical parameters possess finite discontinuities. A similar approach was suggested by Brillouin, but was not successfully completed. Some examples are given in which solutions may be obtained by other methods; e.g. using boundary conditions at surfaces of discontinuity.