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{{Infobox scientist
| name = Heinrich Hertz
| birth_date = {{birth date|1857|2|22|df=y}}
| birth_place = Hamburg, German Confederation
| death_date = {{death date and age|1894|1|1|1857|2|22|df=y}}
| death_place = Bonn, German Empire
| nationality = German
| fields = Physics, Electromagnetism, Mechanics
| workplaces = University of Kiel; Karlsruhe Polytechnic; University of Bonn
| known_for = Detection of electromagnetic waves, the photoelectric effect, the Maxwell-Hertz equations
}}

'''Heinrich Rudolf Hertz''' (22 February 1857 – 1 January 1894) was a German physicist who produced and detected electromagnetic waves in the laboratory, proving [[James Clerk Maxwell|Maxwell]]'s theory, and who died at 36 with a large part of his programme unfinished.

Hertz was a student of [[Hermann von Helmholtz|Helmholtz]] in Berlin, and it was Helmholtz who set him the problem of testing Maxwell's theory against its Continental rivals. At Karlsruhe between 1886 and 1889 Hertz built a spark-gap oscillator and a simple loop receiver, generated waves of roughly metre wavelength, and demonstrated in turn their reflection, refraction, polarisation, diffraction and interference. By setting up standing waves against a metal sheet he measured their wavelength and, with the known oscillator frequency, their speed — finding it equal to that of light. Light and radio waves were shown to be the same thing.

In 1887, while working on the spark gaps, Hertz noticed that ultraviolet light falling on the electrodes made the spark easier to produce. He reported the observation carefully and did not pursue it. It was the discovery of the '''photoelectric effect''', whose explanation eighteen years later won Einstein the Nobel Prize.

Hertz also gave Maxwell's theory the form in which it was taught for a generation. Working in parallel with [[Oliver Heaviside]], he reduced Maxwell's twenty-odd quaternion equations to the compact vector set long known as the Maxwell–Hertz equations. His verdict on what the theory ''was'' has been quoted ever since: "Maxwell's theory is Maxwell's system of equations."

His posthumous ''Die Prinzipien der Mechanik in neuem Zusammenhange dargestellt'' (1894) attempted to rebuild mechanics without the concept of force, using only mass, space, time and hidden constraints — an axiomatic project admired by Wittgenstein and by Einstein. The SI unit of frequency is named for him.

==Hertzian invariant electrodynamics==

The part of Hertz's work that matters most on this wiki is the least known. Maxwell's equations are not invariant under the Galilean transformation. Hertz showed that they can be made so by a single substitution: replace every partial time derivative with the total or convective derivative. The result is a Galilean-invariant covering theory of Maxwell's electrodynamics, reducing to Maxwell's when the convective velocity vanishes.

The physical cost, as understood at the time, was that the convective term implied complete dragging of the medium by moving matter — which appeared to be excluded by stellar aberration and by Fizeau's moving-water experiment. Hertz died before he could give the velocity parameter an interpretation, and the theory was set aside. Lorentz's approach, and then special relativity, took the field instead.

==On this wiki==

Hertz is not treated here as an opponent of Maxwell but as the author of an abandoned alternative to Lorentz and Einstein; see [[:Category:Electrodynamics]] and [[:Category:Relativity]].

* [[Thomas E Phipps]] is the central figure. "[[On Hertz's Invariant Form of Maxwell's Equations]]" (''[[Physics Essays]]'', 1993) gives an explicit invariance proof and argues that, had the result been recognised, it could have furnished the key to unifying electrodynamics with Newtonian mechanics and to explaining the [[Michelson-Morley Experiment|Michelson–Morley]] null result nearly two decades before Minkowski. Phipps developed this into what he called '''neo-Hertzian''' electrodynamics: "[[Neo-Hertzian Wave Equation and Aberration]]" (''[[Galilean Electrodynamics]]'', 1994) replaces frame time with detector proper time and gives an account of aberration on a three-vector rather than four-vector basis; see also "[[Hertz' Equations of Electrodynamics]]" (1997) and "[[Force in Hertzian Electrodynamics]]" (2010). His book ''Old Physics for New'' collects the programme.
* [[Constantin I Mocanu]] extends Maxwell–Hertz electrodynamics to relativistic velocities and non-inertial frames in "[[Hertz's Relativity: A Complimentary Theory to Einstein's SR]]" (''Galilean Electrodynamics'', 1995) and "[[Hertz's Speciasl Relativity and Physical Reality|Hertz's Special Relativity and Physical Reality]]" (1994), arguing for a two-sided theory in which Einstein's relativity covers inertial motion and Hertz's covers non-inertial.
* [[Domina Eberle Spencer]] places Hertz among the Continental tradition in "[[The Electrodynamics of Gauss, Neumann, and Hertz]]".

A separate and quite distinct thread uses "non-Hertzian" to mean longitudinal or scalar electromagnetic waves in the [[Nikola Tesla|Tesla]] tradition, largely under [[:Category:New Energy]] — for example [[Robert W Bass]]'s "[[Self-Sustained Non-Hertzian Longitudinal Wave Oscillations as Rigorous Solutions of Maxwell's Equations for Electromagnetic Radiation]]" (1984) and [[Elizabeth A Rauscher]]'s "[[Electromagnetic Phenomena in Complex Geometries and Nonlinear Phenomena, and Non-Hertzian Waves]]" (1983). These concern waves Hertz did not produce rather than his theory, and should not be confused with neo-Hertzian electrodynamics.

'''A caution for editors.''' The Franck–Hertz experiment, discussed here in [[Johann Marinsek]]'s "[[Physics H: Franck-Hertz Experiment Not a Verification of the Existence of Definite Energy Quanta]]" (2008), is the work of Gustav Ludwig Hertz — Heinrich's nephew — not of Heinrich Hertz.

==See also==

* [[James Clerk Maxwell]]
* [[Hermann von Helmholtz]]
* [[Oliver Heaviside]]
* [[Thomas E Phipps]]
* [[Maxwell's Equations]]
* [[Michelson-Morley Experiment]]

[[Category:Scientist|Hertz Heinrich]]
[[Category:Electromagnetism]]
[[Category:Electrodynamics]]
[[Category:Light]]

Heinrich Hertz - Revision history

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