Schweydar-Bamberg Types of Eotvos Torsion Balance

Abstract

The general principle of the torsion balance is explained and the development of the automatic recording type is briefly described. Details on the large model Schweydar-Bamberg are given. Also a small model of this type has been developed by adopting a new shape of the balance beam. Future possibilities in the construction of small torsion balances are discussed. A list of references is appended. Principle of torsion balance: For his gravitational researches Baron Roland von Eotvos designed an instrument which made it possible to observe gravitational data with an accuracy previously unobtainable, namely, the torsion balance. The principle of this instrument, that is, a horizontal bar loaded at its ends by two weights and suspended from a thin wire, thus reflecting very small horizontal attractions, was already known at that time, since Cavendish had used it for the determination of the gravitational constant, and Coulomb for electric and magnetic investigations. Eotvos was the first who made the torsion balance suitable especially for the solution of practical geological problems by changing the design of the torsion balance already known. He suspended one of the loading masses below the horizontal part of the beam. This improvement enabled him not only to measure horizontal directing forces, as was possible with the first type, but also the alteration of gravity in horizontal direction, the so-called of gravity. A deflection of such a balance with two weights in different levels is produced by irregularities in the subsoil, since the directions of attractions of such masses are different at the two weights, thus causing a small horizontal component. Naturally there occur no differences in those directions of attractions over the c nter of heavy masses in the subsoil, but they reach their highest amount over the edges, meaning that the greatest deflection is produced where the gradient of gravity is the largest. The described balance system is inclosed in a triple casing in order to protect it against air currents and temperature changes. Generally two balances by the side of each other are used in the same instrument. The deflections of the two beams are observed either visually in three azimuths, or the instrument is moved automatically in these three positions, taking records photographically after the balances have come to rest.