Sensitivity of laboratory tests of gravitation beyond the geometrical optics limit

A report is given of a laboratory experiment that reached the sensitivity attained so far in extraterrestrial tests of gravitation beyond the limit of geometrical optics. The sensitivity achieved here in searching for a hypothetical relative change in the velocity of light (deltac/c < approximately 2 x 10-12) seems, however, already near to the presumable maximum for experiments carried out on the earth's surface with static fields. (Auth.)