  The symmetry of vacuum is characterized by the Lorentz group with the
parameter $c$. Physical space inside the homogeneous optical medium should be
described by the Lorentz group with the parameter $c/n$, where $n$ is the
refractive index of the medium. Violation of a one-parameter phenomenological
symmetry in the discrete medium, such as gas, creates the opportunity for the
experimental detecting the motion of the optical medium relative to
luminiferous aether.
