Hans Oersted had discovered the magnetic effect of a current, but Faraday grasped the fact that a conductor at rest and a steady magnetic field do not interact and that to get an induced current either the conductor or the field has to move. On August 29, 1831, Faraday discovered electromagnetic induction.
During the next 10 years, Faraday explored and expanded the field of electricity. In 1834, he announced his famous two laws of electrolysis. Briefly, they state that for any given amount of electrical force in an electrochemical cell, chemical substances are released at the electrodes in the ratio of their chemical equivalents. He also invented the voltammeter, a device for measuring electrical charges, which was the first step toward the later standardization of electrical quantities.
Faraday continued to work in his laboratory, but his health began to deteriorate and he had to stop work entirely in 1841. Almost miraculously, however, his health later improved and he resumed work in 1844. He began a search for an interaction between magnetism and light and in 1845 turned his attention from electrostatics to electromagnetism. He discovered that an intense magnetic field could rotate the plane of polarized light, a phenomenon known today as the Faraday effect. In conjunction with these experiments, he showed that all matter conducts the magnetic line of force.
Objects that were good conductors he called paramagnetics, while those that conducted the force poorly he named diamagnetics. Thus, the energy of a magnet is in the space around it, not in the magnet itself. This is the fundamental idea of the field theory.
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