Experimental searches for gravitational effects outside of general relativity

A certain class of experiments - those seeking to evaluate dG/dt, G(r) and matter creation at exceedingly high sensitivity - provide one way to pursue the possible incompleteness of General Relativity acknowledged by Einstein. The status of these searches is summarized in the first part of this paper. The second part takes up the basic properties of precision macroscopic rotors and their potential use in four gravitational experiments of the class we are considering. Several active and several other possible experiments are described which use the method of the ''protected rotor'' as a means of achieving cosmological rotor decay times and ultra high Q. Finally, details of two experimental designs are presented, along with the present status of this research. (Auth.)