  Relationship between the speed of gravity c_g and the speed of light c_e in
the bi-metric theory of gravity is discussed. We reveal that the speed of light
is a function of the speed of gravity which is a primary fundamental constant.
Thus, experimental measurement of relativistic bending of light propagating in
time-dependent gravitational field directly compares the speed of gravity
versus the speed of light and tests if there is any aether associated with the
gravitational field considered as a transparent `medium' with the constant
refraction index.
