  The definition of the photon in the vacuum of general relativity provided by
Kermack et al. and by Synge is extended to nondispersive, nonhomogeneous,
isotropic dielectrics in arbitrary motion by Hamiltonian methods that rely on
Gordon's effective metric. By these methods the old dilemma, whether the
momentum-energy vector of the photon in dielectrics is timelike or spacelike in
character, is shown to reappear under a novel guise.
