  We show that the mean phase of waves propagating all the way from the far
side of the Sun to the front side, as measured by seismic holography, varies
with time. The change is highly anticorrelated with solar cycle activity and is
consistent with other recent results on the variation of the seismic radius of
the Sun. The phase change that we observe corresponds to a few kilometers
difference in the seismic solar radius from solar maximum to solar minimum in
agreement with inferrences from global helioseismology studies.
