  More recently, Feigel has considered the quantum vacuum contribution to the
momentum of electromagnetic media. However, in Feigel's treatment he did not
take into account the relativistic transformation of the optical constants
(electric permittivity and magnetic permeability) of moving media. Here it is
shown that the effect arising from such a transformation will also provide a
quantum vacuum contribution to the velocity of media, in addition to the one
derived by Feigel himself.
