Heinrich Hertz - first to detect radio waves in 1887 by causing a spark to leap across a gap that generated electromagnetic waves - built oscillator and resonator by 1893.
[b. Hamburg, Germany, February 22, 1857, d. Bonn, Germany, January 1, 1894]

The equations for electromagnetism that James Clerk Maxwell developed from 1856 to 1873 showed that an electromagnetic wave is caused by the oscillation of an electric charge and propagates at the speed of light. Maxwell speculated (correctly) that light is an electromagnetic wave and that other forms of radiation have shorter or longer wavelengths. Hertz set out to create an electromagnetic wave with an apparatus that developed an oscillating spark. In 1888 he produced, detected, and identified what we now call radio waves. Hertz also observed that his device made better sparks when exposed to ultraviolet radiation, a result of the photoelectric phenomenon caused by energetic photons knocking electrons off a metal surface.

A young man in his teens happened to read the article while he was vacationing in the Alps. For him, Hertz's discovery gave him an idea: why not use the waves set off by Hertz's spark oscillator for signaling? Guglielmo Marconi was that young man. He rushed back home to Italy to give the idea a try.

When Hertz died in Bonn, Germany, in 1894, Sir Oliver Lodge gave Hertz credit for accomplishing what the great English physicists of the time were unable to do. It was not hard to give Hertz credit. Not only had he established the validity of Maxwell's theorems, he had done so with a winning modesty. "He was a noble man," said one eulogist in 1894, "who had the singular good fortune to find many admirers, but none to hate or envy him; those who came into personal contact with him were struck by his modesty and charmed by his amiability. He was a true friend to his friends, a respected teacher to his students, who had begun to gather around him in large numbers, some of the coming from great distances; and to his family a loving husband and father."

Frequency is expressed in hertz (Hz); a frequency of 1 Hz means that there is 1 cycle or oscillation per second. The unit is named in honor of the German physicist Heinrich Rudolf Hertz, who first demonstrated the nature of electromagnetic wave propagation.