proof for the existence of displacement currents, but it is obvious from reading his book that he considered both displacement
currents and the implications of their existence as fact. Experimental proof of the existence of electromagnetic waves at
frequencies well below those of light came only in 1888, when the young Heinrich Hertz5 showed through his famous
experiments that an electromagnetic disturbance travels through air and can be received at a distance. This was almost 10
years after Maxwell died and 15 years after he wrote the Treatise. Some of the most important implications of displacement
currents and of Maxwell’s equations in general are as follows:
(1) Interdependence of the electric and magnetic fields.
(2) The existence of electromagnetic waves.
(3) Finite speed of propagation of electromagnetic waves.
(4) Propagation in free space is at the speed of light, and light itself is an electromagnetic wave.