Heinrich Hertz (February 22, 1857 – January 1, 1894) was a German physicist. He clarified and expanded the electromagnetic theory of light that had been put forth by Maxwell. He was the first to prove the existence of electromagnetic waves by engineering instruments to transmit and receive radio pulses.
Hertz measured the velocity of electromagnetic radiation and found it to be the same as the velocity of the light. He also showed that the nature of radio waves’ reflection and refraction was the same as those of light, and established beyond any doubt that light is a form of electromagnetic radiation.
Hertz's experiments would soon trigger the invention of the wireless telegraph, radio, and later television.
In recognition of his work, the unit of frequency — one cycle per second — is named the "hertz".