Heinrich Rudolf Hertz

Heinrich Rudolf Hertz was born in Hamburg in 1857 to a prominent Jewish-turned-Lutheran family — his father was a barrister who later became a senator of the Hanseatic city. He was gifted in languages, in woodwork, and in mathematics; his school reports describe a boy who took everything apart and rebuilt it. He began an engineering course at Dresden and Munich, then switched to physics at the University of Berlin in 1878, where he studied under Gustav Kirchhoff and Hermann von Helmholtz. Helmholtz recognised the talent immediately and set him problems at the research frontier. Hertz took his doctorate in 1880 at twenty-three on electromagnetic induction in rotating conductors, and spent three more years in Berlin as Helmholtz's assistant before moving to a professorship at the Karlsruhe Polytechnic in 1885.

The central work occupied him from 1886 to 1888. The Prussian Academy of Sciences, on Helmholtz's initiative, had offered a prize for the first experimental confirmation of Maxwell's 1865 prediction that accelerating electric charges must radiate transverse electromagnetic waves travelling at the speed of light. Nobody had yet demonstrated it. Hertz designed the apparatus from scratch: an induction coil driven by a battery charged two brass balls separated by a small air gap until the voltage broke down, producing a spark that rang the wire-plus-balls LC circuit at around 50 MHz. A separate loop of wire with a second micro-gap served as the receiver. When the transmitter fired, the receiver produced a faint secondary spark — the first detected radio wave, in the autumn of 1887. Over the following year he measured the wavelength by mapping out standing waves between a wall reflector and the transmitter, computed the propagation speed, and verified it matched Maxwell's c = 1/√(μ₀ε₀). He demonstrated reflection, refraction, and polarisation of the waves — the full set of properties that identified them as electromagnetic. The results were published in *Annalen der Physik* in 1888 and sealed the synthesis.

He moved to a chair at Bonn in 1889 but fell ill soon after. He died in 1894 at thirty-six of what is now recognised as granulomatosis with polyangiitis (formerly Wegener's granulomatosis), an autoimmune disease that attacked his jaw and sinuses and left him in years of pain. In his last year, confined to bed, he prepared *The Principles of Mechanics* for posthumous publication — a reformulation of classical mechanics without force as a primitive concept, that influenced Wittgenstein, Einstein, and the Vienna Circle. The SI unit of frequency, the hertz (Hz), was adopted in his name at the 1930 International Electrotechnical Commission meeting. Marconi, building on Hertz's apparatus, had made a commercial product of transatlantic radio by 1901. Hertz never lived to see it.