In the 1880s Heinrich Hertz discovered that a spark jumping between two pieces of metal emits a flash of light—rapidly oscillating electromagnetic waves—which can be picked up by an antenna.

In the late 1880s, German physicist Heinrich Hertz tested Maxwell's theory. He succeeded in producing electromagnetic waves, and confirmed Maxwell's prediction about their speed. Not long after ...

All forms of electromagnetic ... the crest of one wave to the crest of the next wave), by frequency (the number of wave cycles that pass by in a given period, measured in Hertz, which stands ...