  We extend the method of Huygens' construction in a uniformly moving optical
medium [Am. J. Phys. 72, 934 (2004)] to the case when the medium is dispersive
in its rest frame of reference. The first-order Huygens' construction analysis
of the light drag in a transversely moving dispersive slab is in agreement with
the results of the experiment by Jones (1975) and with the Player-Rogers
formula for the downstream deflection of the beam. The derivation purports that
the original Huygens' principle remains valid in non-stationary situations if
it is modified to include the relativistic effects on the secondary wavelets
caused by the motion of the medium.
