Hertz, Heinrich Rudolf (1857-1894), German physicist, born in Hamburg and educated at the University of Berlin. From 1885 to 1889 he was a Professor of Physics at the technical school in Karlsruhe, and after 1889 a Professor of Physics at the university in Bonn. Hertz clarified and expanded the electromagnetic theory of light which had been proposed by the British physicist James Clerk Maxwell in 1884. Hertz proved that electricity can be transmitted in electromagnetic waves, which travel at the speed of light and which possess many other properties of light. His experiments with these waves led to the development of the wireless telegraph and radio. The unit of frequency, one cycle per second, was renamed the hertz; it is commonly abbreviated Hz.