Resistance to the Discovery of Electromagnetism: Ørsted and the Symmetry of the Magnetic Field

In 1820 Ørsted found that an electric current produced a rotating magnetic effect. The symmetry properties of the new phenomenon were unexpected and acted as a hindrance to the discovery of the phenomenon. Ørsted could not anticipate the geometrical properties of the effect, but according to some authors he claimed he anticipated the rotational symmetry of the phenomenon. This paper offers a new interpretation of the discovery of electromagnetism compatible with Ørsted’s own accounts. On the day of his famous lecture experiment Ørsted replaced his first “longitudinal effect ” hypothesis by a second “transversal effect ” hypothesis that assumed the magnetic effect to have a cylindrical symmetry around the wire. This paper proposes a reconstruction of Ørsted’s lecture experiments, inferred from the expected behaviour of a competent physicist who intended to check the second hypothesis. This reconstruction explains why Ørsted described the observed effect of his early experiment as “irregular”. 1