No. 50: Mar-Apr 1987
Well publicized lately has been the modern reanalysis of the old Eotvos balance experiments. Some think they show the presence of that famous "fifth force" which is supposed, according to some theories, to modify Newton's Law of Gravitation, and become measurable at distances of about 100 to 1000 meters. The Eotvos results may also be explicable in terms of laboratory air currents. But the fifth force may be showing up in geophysical experiments.
"One of the most comprehensive geophysical experiments so far has been conducted by Frank Stacey at University of Queensland in Brisbane, Australia, and his colleagues. Working in two metal mines, the researchers have measured a gravitational constant that is 0.7 percent greater than that measured in the laboratory -- suggesting the presence of a fifth force."
(Weisburd, Stefi; "Geophysics on the Fifth Force's Trail," Science News, 131: 6, 1987.)