  Modern ether-drift experiments look for a preferred frame by measuring the
difference \Delta \nu in the relative frequencies of two cavity-stabilized
lasers, upon local rotations of the apparatus or under the Earth's rotation. If
the small deviations observed in the classical ether-drift experiments were not
mere instrumental artifacts, by replacing the high vacuum in the resonating
cavities with a dielectric gaseous medium (e.g. air), the typical measured
\Delta\nu\sim 1 Hz should increase by orders of magnitude. This prediction is
consistent with the characteristic modulation of a few kHz observed in the
original experiment with He-Ne masers. However, if such enhancement would not
be confirmed by new and more precise data, the existence of a preferred frame
can be definitely ruled out.
