Excerpt from Electromagnetic Theory and Geometrical Optics I. Introduction. It may seem unnecessary at this late date to discuss the relationship of electromagnetic theory to geometrical Op tics. The content of both fields is well known and everyone knows also that geometrical Optics is the limit for vanishing wave length of electromagnetic theory. Moreover, since Maxwell's theory supersedes the older geometrical optics, presumably, then, geometrical optics could be discarded. The optical industry continues to use it but per haps that is because it is behind the times.