Hans Oersted was the Danish physicist who in 1820 discovered that an electric current produces a magnetic effect (we would now say that the current produces a magnetic field). At the University of Copenhagen, after completing a PhD on Kantian philosophy and having travelled extensively in Europe, Oersted began to investigate electromagnetism, predicting (on philosophical grounds) that the magnetic effect produced by a current-carrying conductor would act in a transverse direction to the current flow. He conducted the crucial experiment in 1820 using a battery, a wire and a compass: with the compass placed under the wire, he noticed that the compass needle moved slightly when the circuit was completed. He first tried this during a lecture, although the students attending were not impressed because the effect was barely observable. He investigated the effect more fully, finding that the magnetic field was circular around the current carrying wire. This discovery of a clear connection between electricity and magnetism paved the way for the work of Ampère and Faraday, and led to the development of the galvanometer, in which Oersted was also involved.
Copyright 1997, The Open University