Precision gravity gradiometers and precision differential gravimeters are described. The instruments possess a gaseous medium comprised of molecules that scatter light from typically a laser light source. These molecules may be large molecular scattering structures that include assemblages of tungsten atoms surrounded by fluorine atoms that strongly scatter light. Measurements of variations in the density of the gaseous medium in a gravitational field are used to determine the gravity gradient. Great sensitivity exceeding 1 part in 10.sup.10 are obtained that may be used to measure gravity in a variety of environments. Measurements may be performed in a borehole in the earth and on the earth's surface. The precision gravity gradiometer may be used in a laboratory as a test instrument having the required sensitivity to test certain fundamental laws of physics.