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Heinrich Rudolf Hertz (22 February 1857 – 1 January 1894) was a German physicist who clarified and expanded James Clerk Maxwell’s electromagnetic theory of light, which was first demonstrated by David Edward Hughes using non-rigorous trial and error procedures. Hertz is distinguished from Maxwell and Hughes because he was the first to conclusively prove the existence of electromagnetic waves by engineering instruments to transmit and receive radio pulses using experimental procedures that ruled out all other known wireless phenomena. The scientific unit of frequency – cycles per second – was named the “hertz” in his honor.

While studying at the Gelehrtenschule des Johanneums in Hamburg, Heinrich Rudolf Hertz showed an aptitude for sciences as well as languages, learning Arabic and Sanskrit. He studied sciences and engineering in the German cities of Dresden, Munich and Berlin, where he studied under Gustav R. Kirchhoff and Hermann von Helmholtz.

In 1880, Hertz obtained his PhD from the University of Berlin; and remained for post-doctoral study under Hermann von Helmholtz. In 1883, Hertz took a post as a lecturer in theoretical physics at the University of Kiel. In 1885, Hertz became a full professor at the University of Karlsruhe where he discovered electromagnetic waves.

The most dramatic prediction of Maxwell’s theory of electromagnetism, published in 1865, was the existence of electromagnetic waves moving at the speed of light, and the conclusion that light itself was just such a wave. This challenged experimentalists to generate and detect electromagnetic radiation using some form of electrical apparatus.

The first successful radio transmission was made by David Edward Hughes in 1879, but it would not be conclusively proven to have been electromagnetic waves until the experiments of Heinrich Hertz in 1886. For the Hertz radio wave transmitter, he used a high voltage induction coil, a condenser (capacitor, Leyden jar) and a spark gap—whose poles on either side are formed by spheres of 2 cm radius—to cause a spark discharge between the spark gap’s poles oscillating at a frequency determined by the values of the capacitor and the induction coil.

To prove there really was radiation emitted, it had to be detected. Hertz used a piece of copper wire, 1 mm thick, bent into a circle of a diameter of 7.5 cm, with a small brass sphere on one end, and the other end of the wire was pointed, with the point near the sphere. He bought a screw mechanism so that the point could be moved very close to the sphere in a controlled fashion. This “receiver” was designed so that current oscillating back and forth in the wire would have a natural period close to that of the “transmitter” described above. The presence of oscillating charge in the receiver would be signaled by sparks across the (tiny) gap between the point and the sphere (typically, this gap was hundredths of a millimeter).

In more advanced experiments, Hertz measured the velocity of electromagnetic radiation and found it to be the same as the light’s velocity. 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 obeying the Maxwell equations.

Hertz’s experiments triggered broad interest in radio research that eventually produced commercially successful wireless telegraph, audio radio, and later television.

He died of Wegener’s granulomatosis at the age of 36 in Bonn, Germany in 1894.

In 1930 the International Electrotechnical Commission (IEC) honored Hertz by naming the unit of frequency—one cycle per second—the “hertz”.