Orthotomic systems of rays in inhomogeneous isotropic media.

The behavior of orthotomic systems of rays, rays associated with a system of wavefronts, is analyzed from the point of view of classical geometrical optics. The rays themselves are described in terms of the ray equation derived from Fermat's principle. A condition for an aggregate of rays to comprise an orthotomic system is found. Some consequences of this condition on the geometric properties of wave-fronts are found. The resemblance of some of these to the Maxwell equations is noted.