Geophysics and the law of gravity

Geophysical measurements of the gravitational constant and a recent reexamination of experiments performed early in the century on the equivalence of inertial and gravitational mass may have provided either observational clues to the unification of gravity with electroweak and strong nuclear forces or an indication of a new, previously unrecognized force. The evidence is still less than completely conclusive but it has now become difficult to find explanations of the geophysical observations other than non-Newtonian gravity. We also point to the requirements of the next generation of experiments. These include measurements of gravity or gravity gradient in the deep ocean and high above it and Von Eötvös-type experiments in steep terrain to test the possibility that a postulated short-range (100 to 1000 m) component of gravity depends upon fundamental particle count rather than mass.