  Radiation pressure on a flat mirror submerged in a transparent liquid,
depends not only on the refractive index n of the liquid, but also on the phase
angle psi_0 of the Fresnel reflection coefficient of the mirror, which could be
anywhere between 0^{\circ} and 180^{\circ}. Depending on the value of psi_0,
the momentum per incident photon picked up by the mirror covers the range
between the Abraham and Minkowski values, i.e., the interval
(2\hbarw_0/nc,2n\hbarw_0/c). Here \hbar is the reduced Planck constant, w_0 is
the frequency of the incident photon, and c is the speed of light in vacuum. We
argue that a simple experimental setup involving a dielectric slab of
refractive index n, a vibrating mirror placed a short distance behind the slab,
a collimated, monochromatic light beam illuminating the mirror through the
slab, and an interferometer to measure the phase of the reflected beam, is all
that is needed to deduce the precise magnitude of the radiation pressure on a
submerged mirror. In the proposed experiment, the transparent slab plays the
role of the submerging liquid (even though it remains detached from the mirror
at all times), and the adjustable gap between the mirror and the slab simulates
the variable phase-angle psi_0. The phase of the reflected beam, measured as a
function of time during one oscillation period of the mirror, then provides the
information needed to determine the gap-dependence of the reflected beam's
Doppler shift and, consequently, the radiation pressure experienced by the
mirror.
