Magnetism and electricity are not separate phenomena; they are the related manifestations of an underlying electromagnetic force. Experiments in the early 19th century by, among others, Hans Orsted (in Denmark), Andr-Marie Ampre (in France), and Michael Faraday (in England) revealed the intimate connection between electricity and magnetism and how the one can give rise to the other. The results of these experiments were synthesized in the 1850s by the Scottish physicist James Clerk Maxwell in his electromagnetic theory. Maxwell's theory predicted the existence of electromagnetic waves--undulations in intertwined electric and magnetic fields, traveling with the velocity of light.

The final steps in synthesizing electricity and magnetism into one coherent theory were made by Maxwell. He was deeply influenced by Faraday's work, having begun his study of the phenomena by translating Faraday's experimental findings into mathematics. (Faraday was self-taught and had never mastered mathematics.) In 1856 Maxwell developed the theory that the energy of the electromagnetic field is in the space around the conductors as well as in the conductors themselves. By 1864 he had formulated his own electromagnetic theory of light, predicting that both light and radio waves are electric and magnetic phenomena. While Faraday had discovered that changes in magnetic fields produce electric fields, Maxwell added the converse: changes in electric fields produce magnetic fields even in the absence of electric currents. Maxwell predicted that electromagnetic disturbances traveling through empty space have electric and magnetic fields at right angles to each other and that both fields are perpendicular to the direction of the wave. He concluded that the waves move at a uniform speed equal to the speed of light and that light is one form of electromagnetic wave. Their elegance notwithstanding, Maxwell's radical ideas were accepted by few outside England until 1886, when the German physicist Heinrich Hertz verified the existence of electromagnetic waves traveling at the speed of light; the waves he discovered are known now as radio waves.

Excerpt from the Encyclopedia Britannica without permission.