  We use a relativistic argument to define an effective photon that travels
through a transparent (non-absorbing) nondispersive dielectric medium of index
of refraction $n$. If $p$ is the momentum of the photon in a vacuum, then the
momentum of an effective photon inside the medium may be of the form $p_{\rm
eff}=pn^\alpha$ and still reproduce the observed transverse relativistic drift
when the medium is in motion. We employ an energy argument to determine the
value of the exponent to be $\alpha =-1$, so that the effective photon momentum
is $p_{\rm eff}=p/n$, which is the Abraham momentum.
