Untangling Ohm’s Apparatus
In the early nineteenth century a series of surprising revelations changed how natural philosophers understood electricity. Fierce debates raged between adherents to a chemical theory of the battery, and followers of Volta who saw the contact between two different metals as the source of electrical power. Meanwhile Ørsted’s discovery of electromagnetic effects inspired theories of electrical fields and led to the discovery of thermoelectricity. In the midst of these debates the mathematically talented Georg Simon Ohm found himself teaching at a progressive college in Cologne, equipped with an unusually well stocked ‘Cabinet’ of scientific apparatus. This paper will describe the key features of Ohm’s torsion balance, exploring the theoretical background that underpinned the different component parts of the apparatus. The development of the balance drew on the theories of the day, and its design betrays Ohm’s own theoretical leanings. The now famous law that Ohm produced using his torsion balance was first published in 1826, but failed to gain recognition in Germany for well over a decade. By positioning Ohm’s work in the midst of the wide ranging debates about theory and methodology in electrical science, this paper aims to offer some reasons for the slow uptake of Ohm’s law.