Ørsted discovers electromagnetism

Background. Electromagnetism describes the relationship between electricity, magnetism, and optics. Its study reaches back to ancient times, when thinkers sought to explain lightning, static electricity, and the attraction between magnetized pieces of iron ore and compasses. The connection between electricity and magnetism was not widely known until 1820. Ørsted had been searching for this connection since 1818; earlier, in Germany, he had met Johann Wilhelm Ritter, a physicist who believed there was a connection between electricity and magnetism. Ørsted's work eventually gave rise to electrodynamics.

The Discovery. In April 1820, Ørsted observed that an electrical current in a wire caused a nearby compass needle to move. He published his discovery that a compass needle was deflected from magnetic north by a nearby electric current, confirming a direct relationship between electricity and magnetism. This observation was a major step toward a unified concept of energy.

Impact and Recognition. Ørsted's findings stirred research into electrodynamics, influencing André-Marie Ampère's mathematical formulations. For his discovery, the Royal Society of London awarded him the Copley Medal in 1820, and the French Academy granted him 3,000 francs. The CGS unit of magnetic induction, the oersted, is named in his honor.