  A new ether-drift experiment in D\"usseldorf is currently measuring the
relative frequency shift of two cryogenic optical resonators upon active
rotations of the apparatus. I point out that the observed fractional amplitude
of the sidereal variations of the signal in February, C_sid \sim (11 \pm 2)
10^{-16}, is entirely consistent with the expectations based on Miller's
observations in the same epoch of the year. This leads to predict that, with
future data collected in August-September, the observed sidereal variations
should increase by \sim + 70 %, i.e. up to C_sid \sim (19\pm 2) 10^{-16}
retaining the present normalization. This would represent clean experimental
evidence for the existence of a preferred frame.
