Torsion balance with photographic recording, main unit with wooden case, serial no. 20420, L. Oertling Ltd., London, UK, 1925. Used for geophysical prospecting through gravitational methods, the instrument is based on a design by Hungarian physicist Loránd Eötvös. It is believed to have been purchased in 1927 for field trials in Britain by the Geological Survey, and modified by the National Physical Laboratory the following year. In 1931 it was transferred to the newly-founded department of applied geophysics at Imperial College, forming part of their suite of apparatus for practical education in applied geophysics.

This torsion balance measures gravity by observing two forces—gravitational acceleration and the inertial force of earth’s rotation—acting on a pair of weights suspended from a wire, with observations made using a photographic recording system. Subtle variations in these forces can indicate underground structures and mineral deposits.

In many nations during and after WW1, geophysical prospecting was an active area of research, driven especially by the shift from coal energy to oil. Versions of Eötvös’s torsion balance were manufactured by several makers, including his collaborator Ferdinand Süss (ScM object 1920-809 is an example). At the time, L. Oertling Ltd. was the only British maker of this instrument design; the firm made 12 in total between 1923 and 1925, of which ten used photographic observation. The Oertling instrument was not considered a success. Following their field trials, Geological Survey staff concluded that it had been put on the market too hastily; the photographic results were not reliable and visual readings were only possible at night.

In the inter-war period, geophysical prospecting was seen to be crucial for the exploitation of resources in Britain’s imperial territories, and the perception of German dominance in this field—as for many areas of scientific and technological work—was a crucial concern.

For more information see:

Katharine Anderson (2019) 'An "experimental" instrument: testing the torsion balance in Britain, Canada and Australia', Annals of Science, 76:1, 58-86, DOI: 10.1080/00033790.2019.1578897

Barry J. Oliver (2020) Ludwig Oertling, balance maker: the man, his company and its products