ESSENTIAL FEATURES OF THE TORSION BALANCE
Whenever the gravitational field is warped or distorted, the values of gravity at neighboring points on the surface of the earth differ both in magnitude and direction.
Thus, if two small masses at different elevations are supported at opposite ends of a beam which is suspended by a torsion wire, the equipotential surfaces passing through the two small masses will not be parallel and the magnitudes of the force of gravity acting on the two masses wili not be the same.
The non-parallelism of the two equipotential surfaces through the two masses and the difference in the forces of gravity acting on the masses create a rotational torque which acts on the suspended system. The torsion balance is an instrument for measuring this rotational torque. In principle, the torsion balance is simple.
However, due to the extreme precision of measurement required, it is a complex and highly refined instrument.
A schematic representation of an Eötvös Torsion Balance
