Maxwell’s equations tell us what light is. Maxwell realizes that his equations predict that Faraday’s lines can tremble and undulate, just like the waves of the sea. He computes the speed at which the undulations of Faraday’s lines move, and the result turns out to be . . . the same as for light! Why? Maxwell understands: because light is nothing other than this rapid trembling of Faraday’s lines! Not only have Faraday and Maxwell figured out how electricity and magnetism work, but with the same stroke, as a collateral effect, they have figured out what light is.
