Current use of Eötvös Torsion Balance, the tidal effect

In the 20th century, many torsion balance measurements had been carried out around the world. The measurements still provide a good opportunity to detect the lateral underground mass inhomogeneities and the geological fault structures using the so called edge effects in gravity gradients. Usually, the horizontal gradients were used for geophysical prospecting, but the curvature gradients measured by torsion balance remained unused. However, curvature gradients are instrumental data in geodesy, using these gradients, precise deflections of the vertical can be calculated by interpolation and the fine structure of the potential surfaces of the Earth can be derived. Based on the horizontal and the curvature gradients of gravity, the full Eötvös tensor (including the vertical gradients) can be derived by the 3D inversion method. Application of torsion balance is also important in physics. Lorand Eötvös and his colleagues Dezső Pekár and Jenő Fekete executed a series of measurements (EPF experiment) from 1906 till 1908 to validate the equivalence of gravitational and inertial mass. Repeating this experiment by using a 90 years old, high precision torsion balance, but under better conditions with and applying the current modern technology for enhancing the precision, exposing and filtering out tiny environmental disturbances and barely perceptible flaws in instruments is a big challenge today..