Testing Newton’s Law in the Megget Water Reservoir

Summary

Gravity was measured at seven levels inside a submerged tower in Megget Water Reservoir, Scotland, in an experiment to test the inverse square law of gravitation over length scales from decimetres to tens of kilometres. The effects of Earth rotation, the global mass distribution, natural topography and man-made structures must be predicted at points outside the solid Earth, in order that that part of the measured attraction which is due to water in the reservoir can be separately identified. This attraction can be related to the Newtonian gravitational constant because, unlike natural rock masses, the density of water can be reliably predicted. This paper describes techniques aiming to determine all necessary corrections with a differential accuracy of 5 nm.s^-2 over a 50 m vertical interval in order to exploit the 10 nm.s^-2 accuracy available from LaCoste & Romberg gravity meters.