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     The Greeks knew the magnetic properties of the mineral lodestone (magnetite) as early as 600 B.C. Thales Miletus (640 - 540 B.C.), an early Greek mathematician and astronomer, was aware of the properties of attraction and repulsion of lodestone with like pieces of lodestone. He too knew if an electrostatic effect called the amber effect, that is, the attraction of bits of straw to an amber rod that had been rubbed with wool. The laws of electricity and magnetism were closely studied by James Clerk Maxwell (1831 1879), a Scottish physicist. Maxwell wondered why the physical laws were not symmetric when expresses in mathematical form. By applying the concept of symmetry, he found an additional law, which completed the equations of electromagnetism in 1865. Maxwell studied these equations and discovered that, according to the equation, light is made up of electromagnetic waves. The theoretical fact that electromagnetic waves of radio frequency are likely led to experiments in which radio waves were generated and detected. This discovery opened up a new era of wireless communication and in due time brought us commercial radio and television and a host of other devices. Many of these practical developments will be described in this section.


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