Hertz , Heinrich Rudolf

(1857–1894) German physicist

Hertz came from a prosperous and cultured Hamburg family. In 1875 he went to Frankfurt to gain practical experience in engineering and after a year of military service (1876–77) spent a year at the University of Munich. He had decided on an academic and scientific career rather than one in engineering, and in 1878 chose to continue his studies at the University of Berlin under Hermann von Helmholtz. Hertz obtained his PhD in 1880 and continued as Helmholtz's assistant for a further three years. He then went to work at the University of Kiel. In 1885 he was appointed professor of physics at Karlsruhe Technical College and in 1889 became professor of physics at the University of Bonn. His tragic early death from blood poisoning occurred after several years of poor health and cut short a brilliant career.

Hertz's early work at Berlin was diverse but included several pieces of research into electrical phenomena and equipment. With no laboratory facilities at Kiel he had considered more theoretical aspects of physics and had become more interested in the recent work of James Clerk Maxwell on electromagnetic theory. Helmholtz had suggested an experimental investigation of the theory to Hertz in 1879 but it was not until 1885 in Karlsruhe that Hertz found the equipment needed for what became his most famous experiments. In 1888 he succeeded in producing electromagnetic waves using an electric circuit; the circuit contained a metal rod that had a small gap at its midpoint, and when sparks crossed this gap violent oscillations of high frequency were set up in the rod. Hertz proved that these waves were transmitted through air by detecting them with another similar circuit some distance away. He also showed that like light waves they were reflected and refracted and, most important, that they traveled at the same speed as light but had a much longer wavelength. These waves, originally called Hertzian waves but now known as radio waves, conclusively confirmed Maxwell's prediction on the existence of electromagnetic waves, both in the form of light and radio waves.

Once at Bonn Hertz continued his analysis of Maxwell's theory, publishing two papers in 1890. His experimental and theoretical work put the field of electrodynamics on a much firmer footing. It should also be noted that in 1887 he inadvertently discovered the photoelectric effect whereby ultraviolet radiation releases electrons from the surface of a metal. Although realizing its significance he left others to investigate and explain it.

Hertz's results produced enormous activity among scientists but he died before seeing Guglielmo Marconi make his discovery of radio waves a practical means of communication. In his honor the unit of frequency is now called the hertz.