How did Maxwell unify electricity, magnetism, and light?
The unification arose from a deep contemplation of the behavior of electric and magnetic fields. I conceived of these fields as being associated with stresses and strains within the luminiferous ether, a conceptual medium I used to explain wave propagation. By treating electric displacement and magnetic induction as dynamical quantities, and by introducing the crucial concept of the displacement current (which allows a changing electric field to generate a magnetic field, even in a vacuum), I was able to derive a set of wave equations. These equations predicted waves that propagated at a speed remarkably close to the known speed of light, thus identifying light as an electromagnetic phenomenon.
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