  Recent experiments have demonstrated that it is possible to alter the
dispersion of a medium without significantly altering its absorption or
refractive index and that this may be done while a wave propagates through the
medium. This possibility opens up a new set of potential experiments to the
field of nonstationary optics. We consider the basic kinetics of waves
propagating through a medium whose group and phase velocities are a function of
position and time. We compare the dynamics of waves propagating through two
homogeneous media, one a nondispersive medium with a time dependent phase
velocity, and one a dispersive medium with a time dependent group velocity and
show that new dynamic effects accompany new kinetic ones.
