Heinrich Rudolph Hertz, a German physicist, discovered the existence of electromagnetic waves in 1887. This was a result of his expansion of James Clerk Maxwell's mathematical "Electromagnetic Theory of Light," published in 1873. The international unit of frequency, one cycle per second, is named in his honor.
Hertz engineered the oscillator used to prove Maxwell's theory. The oscillator – two brass knobs connected by induction coils – created tiny sparks that jumped between the knobs when it was turned on.
He designed a circular receiving wire, also with two knobs separated by a gap, and placed it away from his oscillator. Hertz powered the oscillator, and it generated a spark that traveled the distance to the receiver, thus proving the existence of electromagnetic waves.