Hans Christian Ørsted, a Danish natural philosopher, discovers electromagnetism—the relationship between electricity and magnetism—during a lecture demonstration given in April 1820, when Ørsted notices a compass needle deflects from magnetic north when an electric current from a battery is switched on and off, confirming a direct relationship between electricity and magnetism.

His initial interpretation is that magnetic effects radiate from all sides of a wire carrying an electric current, as do light and heat.

Three months later he begins more intensive investigations and soon thereafter publishes his findings, showing that an electric current produces a circular magnetic field as it flows through a wire.

This discovery is not due to mere chance, since Ørsted has been looking for a relation between electricity and magnetism for several years.

The special symmetry of the phenomenon is possibly one of the difficulties that detained the discovery.