Electromagnetism is the phenomenon of the interaction of electric currents or fields and magnetic fields. Electricity and magnetism were long thought to be separate forces. It was not until the 19th century that it was proved otherwise. In 1905 Albert Einstein’s special theory of relativity established beyond a doubt that both are aspects of one common phenomenon. At a practical level, however, electric and magnetic forces behave quite differently and are described by different equations. Electric forces are produced by electric charges either at rest or in motion. Magnetic forces, on the other hand, are produced only by moving charges and act solely on charges in motion.