|MadSci Network: Physics|
J. C. Maxwell derived the equations of electricity and magnetism, which are thus called Maxwell's Equations in his honor. By manipulating these equations he showed that there should exist electromagnetic waves which propagate in free space. The velocity at which these waves travel is determined by the equations, and it turned out to be essentially equal (within the accuracy of the measurements) to the speed of light, which had already been measured.
"We can scarcely avoid the inference," said Maxwell, "that light consists in the transverse undulations of the same medium which is the cause of electric and magnetic phenomena."
If you are interested in more details, I recommend reading volume 2 of "The Feynman Lectures on Physics", by R. P. Feynman, R. B. Leighton and M. Sands.
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