Editing Heinrich Hertz

{{Short description|German physicist (1857–1894)}}
{{Use dmy dates|date=April 2021}}
{{Infobox scientist
| name              = Heinrich Hertz
| image             = HEINRICH HERTZ.JPG
| caption           = Hertz, {{Circa|1890}}
| birth_name        = Heinrich Rudolf Hertz
| birth_date        = {{Birth date|1857|02|22|df=yes}}
| birth_place       = [[Hamburg]], [[German Confederation]]
| death_date        = {{Death date and age|1894|01|01|1857|02|22|df=yes}}
| death_place       = [[Bonn]], [[Kingdom of Prussia]], [[German Empire]]
| resting_place     = [[Ohlsdorf Cemetery]], Hamburg
| education         = [[Johanneum Gymnasium]]
| alma_mater        = {{Plain list|
* [[Technical University of Munich|Technische Hochschule Munich]]
* [[University of Berlin]] ([[PhD]])
}}
| known_for         = {{Plain list|
* Founding [[contact mechanics]] (1881)
* Work on [[cathode ray]]s <br/> (1883, 1892)
* Discovering [[radio wave]]s (1886)
* Discovering the [[photoelectric effect]] (1887)
* Inventing the [[parabolic antenna]] (1888){{cn|date=May 2025}}
}}
| spouse            = {{Marriage|Elisabeth Doll|1886}}
| children          = 2, including [[Mathilde Carmen Hertz|Mathilde]]
| father            = [[Gustav Ferdinand Hertz]]
| relatives         = [[Gustav Ludwig Hertz]] (nephew)
| awards            = {{Plain list|
* [[Matteucci Medal]] (1888)
* [[Rumford Medal]] (1890){{cn|date=May 2025}}
}}
| fields            = {{Plain list|
* [[Electromagnetism]]
* [[Mechanics]]
}}
| work_institutions = {{Plain list|
* University of Berlin <br/> (1880–1883)
* [[University of Kiel]] <br/> (1883–1885)
* [[Technische Hochschule Karlsruhe]] (1885–1889)
* [[University of Bonn]] <br/> (1889–1894)
}}
| thesis_title      = Über die Induction in rotirenden Kugeln (On induction in rotating spheres)
| thesis_url        = https://edoc.hu-berlin.de/items/9d46acc4-ef7e-4c02-92b9-117ed13019dc
| thesis_year       = 1880
| doctoral_advisor  = [[Hermann von Helmholtz]]
| academic_advisors = {{Plain list|
* [[Gustav Kirchhoff]] 
* [[Wilhelm von Bezold]] 
}}
| notable_students  = [[Philipp Lenard]] 
| signature         = Autograph of Heinrich Hertz.png
}}

'''Heinrich Rudolf Hertz''' ({{IPAc-en|h|ɜː|t|s}};<ref>{{Cite web|title=HERTZ Definition & Meaning|url=https://www.dictionary.com/browse/hertz|website=[[Dictionary.com]]}}</ref> {{IPA|de|hɛʁts|lang|De-Hertz.ogg}};<ref>{{Cite book |last1=Krech |first1=Eva-Maria |url=https://books.google.com/books?id=E-1tr_oVkW4C&q=deutsches+ausspracheworterbuch |title=Deutsches Aussprachewörterbuch |last2=Stock |first2=Eberhard |last3=Hirschfeld |first3=Ursula |last4=Anders |first4=Lutz Christian |publisher=Walter de Gruyter |year=2009 |isbn=978-3-11-018202-6 |location=Berlin |pages=575, 580 |language=de |trans-title=German Pronunciation Dictionary}}</ref><ref>{{Cite book | url=https://books.google.com/books?id=T6vWCgAAQBAJ |title=Das Aussprachewörterbuch |last1=Kleiner |first1=Stefan |last2=Knöbl |first2=Ralf |publisher=Dudenverlag |year=2015 |isbn=978-3-411-04067-4 |edition=7th |location=Berlin |page=440 |language=de |trans-title=The Pronunciation Dictionary |orig-year=First published 1962}}</ref> 22 February 1857 – 1 January 1894) was a German [[physicist]] who first conclusively proved the existence of the [[electromagnetic waves]] predicted by [[James Clerk Maxwell]]'s [[Maxwell's equations|equations of electromagnetism]].

==Biography==
Heinrich Rudolf Hertz was born in 1857 in [[Hamburg]], then a sovereign state of the [[German Confederation]], into a prosperous and cultured [[Hanseatic (class)|Hanseatic]] family. His father was [[Gustav Ferdinand Hertz]].<ref name="st-andrews">{{Cite web |title=Biography: Heinrich Rudolf Hertz |url=http://www-history.mcs.st-andrews.ac.uk/Biographies/Hertz_Heinrich.html |access-date=2 February 2013 |publisher=MacTutor History of Mathematics archive}}</ref> His mother was Anna Elisabeth Pfefferkorn.<ref>[[#JB11|Buchwald 2011]], p. 45</ref>

While studying at the [[Gelehrtenschule des Johanneums]] in Hamburg, Hertz showed an aptitude for sciences as well as languages, learning [[Arabic]]. He studied sciences and engineering in the German cities of [[Dresden]], [[Technical University of Munich|Munich]] and [[Humboldt University of Berlin|Berlin]], where he studied under [[Gustav R. Kirchhoff]] and [[Hermann von Helmholtz]]. In 1880, Hertz obtained his PhD from the [[University of Berlin]], and for the next three years remained for post-doctoral study under Helmholtz, serving as his assistant. 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]].<ref>[[#JB11|Buchwald 2011]], pp. 51-65</ref>

In 1886, Hertz married Elisabeth Doll, the daughter of Max Doll, a lecturer in geometry at Karlsruhe. They had two daughters: Johanna, born on 20 October 1887 and [[Mathilde Carmen Hertz|Mathilde]], born on 14 January 1891, who went on to become a notable biologist. During this time Hertz conducted his landmark research into electromagnetic waves.<ref>[[#JB11|Buchwald 2011]], p. 218</ref>

Hertz took a position of Professor of Physics and Director of the Physics Institute in [[Bonn]] on 3 April 1889, a position he held until his death. During this time he worked on [[analytical mechanics|theoretical mechanics]] with his work published in the book ''Die Prinzipien der Mechanik in neuem Zusammenhange dargestellt'' (''The Principles of Mechanics Presented in a New Form''), published posthumously in 1894.<ref>
Stathis Psillos, Philosophy of Science A-Z, Edinburgh University Press · 2007, page 107</ref>

==Death==
In 1892, Hertz was diagnosed with an infection (after a bout of severe [[migraines]]) and underwent operations to treat the illness. He died due to complications after surgery which had attempted to cure his condition. Some consider his ailment to have been caused by a malignant bone condition.<ref>{{Cite web |last=Robertson, O'Connor |title=Heinrich Rudolf Hertz |url=https://mathshistory.st-andrews.ac.uk/Biographies/Hertz_Heinrich/ |access-date=20 October 2020 |website=MacTutor |publisher=University of Saint Andrews, Scotland}}</ref> He died at the age of 36 in [[Bonn]], Germany, in 1894, and was buried in the [[Ohlsdorf Cemetery]] in Hamburg.<ref name="Friedhof_Hamburg">[http://www.friedhof-hamburg.de/ohlsdorf/prominente/h/ Hamburger Friedhöfe » Ohlsdorf » Prominente]. Friedhof-hamburg.de. Retrieved 22 August 2014.</ref><ref name="Map_of_Cemetery_Ohlsdorf">[https://web.archive.org/web/20120131202611/http://www.friedhof-hamburg.de/fileadmin/Dateien/pdf/ohlsdorf/plan_ohlsdorf_A4.pdf Plan Ohlsdorfer Friedhof (Map of Ohlsdorf Cemetery)]. friedhof-hamburg.de.</ref><ref name="IEEE_Did_you_know">IEEE Institute, [http://theinstitute.ieee.org/technology-focus/technology-history/did-you-know-historical-facts-that-are-not-true Did You Know? Historical ‘Facts’ That Are Not True] {{webarchive|url=https://web.archive.org/web/20140110200549/http://theinstitute.ieee.org/technology-focus/technology-history/did-you-know-historical-facts-that-are-not-true |date=10 January 2014 }}</ref><!-- Note: [[Ohlsdorf Cemetery]] is not the same as [[Ohlsdorf Jewish Cemetery]]. Heinrich Hertz is buried at Q24, 53-58. The map shows that this is located in the middle of the Ohlsdorf Cemetery. The Ohlsdorf Jewish Cemetery is located about a kilometer southwest of the Ohlsdorf Cemetery. -->

Hertz's wife<!-- married in 1886 -->, Elisabeth Hertz (''[[née]]'' Doll; 1864–1941), did not remarry. He was survived by his daughters, Johanna (1887–1967) and Mathilde (1891–1975).<ref>{{Cite news |date=March 26, 1938 |title=Pope Gives Cash To Aid Family of Jew Scientist |url=https://www.newspapers.com/article/chicago-tribune-pope-gives-cash-to-aid-f/168246203/ |access-date=2025-03-18 |work=Chicago Tribune |pages=7 |via=[[Newspapers.com]]}}</ref> Neither ever married or had children, hence Hertz has no living descendants.<ref name="Susskind_1995">Susskind, Charles. (1995). ''Heinrich Hertz: A Short Life.'' San Francisco: San Francisco Press. {{ISBN|0-911302-74-3}}</ref>

==Scientific work==
===Electromagnetic waves===
{{multiple image
| align = right
| direction = horizontal
| header   =
| image1   = Hertz transmitter and receiver - English.svg
| caption1 = Hertz's 1887 apparatus for generating and detecting radio waves: a [[spark-gap transmitter]] ''(left)'' consisting of a [[dipole antenna]] with a spark gap ''(S)'' powered by high voltage pulses from a [[Ruhmkorff coil]] ''(T)'', and a receiver ''(right)'' consisting of a loop antenna and spark gap.
| width1   = 300
| image2   = Hertz micrometer resonator.png
| caption2 = One of Hertz's radio wave receivers: a loop antenna with an adjustable [[spark micrometer]] ''(bottom)''.<ref name="Appleyard">{{Cite journal |last=Appleyard |first=Rollo |date=October 1927 |title=Pioneers of Electrical Communication part 5 – Heinrich Rudolph Hertz |url=http://www.americanradiohistory.com/Archive-ITT/20s/ITT-Vol-06-1927-02.pdf |journal=Electrical Communication |location=New York |publisher=International Standard Electric Corp. |volume=6 |issue=2 |pages=63–77 |access-date=19 December 2015}}The two images shown are p. 66, fig. 3 and p. 70 fig. 9</ref>
| width2   = 131
| footer   =
}}

In 1864 Scottish mathematical physicist [[James Clerk Maxwell]] proposed a comprehensive theory of electromagnetism, now called [[Maxwell's equations]].  Maxwell's theory predicted that coupled [[electric field|electric]] and [[magnetic field]]s could travel through space as an "[[electromagnetic wave]]".  Maxwell proposed that light consisted of electromagnetic waves of short wavelength, but no one had been able to prove this, or generate or detect electromagnetic waves of other wavelengths.<ref name="mactutor">{{cite web |url=https://mathshistory.st-andrews.ac.uk/Biographies/Maxwell/ |title=James Clerk Maxwell |last1=O'Connor |first1=J.J. |last2=Robertson |first2=E.F. |date=November 1997 |publisher=School of Mathematical and Computational Sciences University of St Andrews |access-date=19 June 2021 |archive-date=5 November 2021 |archive-url=https://web.archive.org/web/20211105081645/https://mathshistory.st-andrews.ac.uk/Biographies/Maxwell/ |url-status=live }}</ref>

During Hertz's studies in 1879 Helmholtz suggested that Hertz's doctoral dissertation be on testing Maxwell's theory. Helmholtz had also proposed the "Berlin Prize" problem that year at the [[Prussian Academy of Sciences]] for anyone who could experimentally prove an electromagnetic effect in the polarization and depolarization of [[electrical insulator|insulators]], something predicted by Maxwell's theory.<ref>[http://www.nndb.com/people/419/000072203/ Heinrich Hertz]. nndb.com. Retrieved 22 August 2014.</ref><ref name="autogenerated49">Baird, Davis, Hughes, R.I.G. and Nordmann, Alfred eds. (1998). ''Heinrich Hertz: Classical Physicist, Modern Philosopher.'' New York: [[Springer-Verlag]]. {{ISBN|0-7923-4653-X}}. p. 49</ref> Helmholtz was sure Hertz was the most likely candidate to win it.<ref name="autogenerated49" /> Not seeing any way to build an apparatus to experimentally test this, Hertz thought it was too difficult, and worked on [[electromagnetic induction]] instead. Hertz did produce an analysis of Maxwell's equations during his time at Kiel, showing they did have more validity than the then prevalent "[[action at a distance]]" theories.<ref>Heilbron, John L. (2005) ''The Oxford Guide to the History of Physics and Astronomy''. Oxford University Press. {{ISBN|0195171985}}. p. 148</ref>

In the autumn of 1886, after Hertz received his professorship at Karlsruhe, he was experimenting with a pair of [[Riess spiral]]s  when he noticed that discharging a [[Leyden jar]] into one of these coils produced a spark in the other coil. With an idea on how to build an apparatus, Hertz now had a way to proceed with the "Berlin Prize" problem of 1879 on proving Maxwell's theory (although the actual prize had expired uncollected in 1882).<ref>Baird, Davis, Hughes, R.I.G. and Nordmann, Alfred eds. (1998). ''Heinrich Hertz: Classical Physicist, Modern Philosopher.'' New York: [[Springer-Verlag]]. {{ISBN|0-7923-4653-X}}. p. 53</ref><ref name="h202">Huurdeman, Anton A. (2003) ''The Worldwide History of Telecommunications''. Wiley. {{ISBN|0471205052}}. p. 202</ref> He used a [[dipole antenna]] consisting of two collinear one-meter wires with a spark gap between their inner ends, and zinc spheres attached to the outer ends for [[capacitance]], as a radiator.  The antenna was excited by pulses of high voltage of about 30 [[volt|kilovolts]] applied between the two sides from a [[Induction coil|Ruhmkorff coil]].  He received the waves with a resonant single-[[loop antenna]] with a [[spark micrometer|micrometer spark gap]] between the ends. This experiment produced and received what are now called [[radio wave]]s in the [[very high frequency]] range.

[[File:Hertz first oscillator.png|thumb|upright=3|center|Hertz's first radio transmitter: a [[loaded dipole|capacitance loaded]] [[dipole antenna|dipole resonator]] consisting of a pair of one meter copper wires with a 7.5&nbsp;mm spark gap between them, ending in 30 cm zinc spheres.<ref name="Appleyard" /> When an [[induction coil]] applied a high voltage between the two sides, sparks across the spark gap created [[standing wave]]s of radio frequency current in the wires, which radiated [[radio wave]]s. The [[frequency]] of the waves was roughly 50 MHz, about that used in modern television transmitters.]]

Between 1886 and 1889 Hertz conducted a series of experiments that would prove the effects he was observing were results of Maxwell's predicted electromagnetic waves. Starting in November 1887 with his paper "On Electromagnetic Effects Produced by Electrical Disturbances in Insulators", Hertz sent a series of papers to Helmholtz at the Berlin Academy, including papers in 1888 that showed transverse [[free space]] [[electromagnetic wave]]s traveling at a finite speed over a distance.<ref name=h202/><ref>{{Cite web |title=The most important Experiments – The most important Experiments and their Publication between 1886 and 1889 |url=http://www.hhi.fraunhofer.de/fraunhofer-hhi-the-institute/about-us/history-of-hhi/the-most-important-experiments.html |access-date=19 February 2016 |publisher=Fraunhofer Heinrich Hertz Institute}}</ref> In the apparatus Hertz used, the electric and magnetic fields radiated away from the wires as [[transverse waves]]. Hertz had positioned the [[oscillator]] about 12 meters from a [[zinc]] reflecting plate to produce [[standing wave]]s. Each wave was about 4 meters long.{{citation needed|date=March 2020}} Using the ring detector, he recorded how the wave's [[amplitude|magnitude]] and component direction varied. Hertz measured Maxwell's waves and demonstrated that the [[velocity]] of these waves was equal to the velocity of light. The [[electric field intensity]], [[polarization (waves)|polarization]] and [[Reflection (electrical)|reflection]] of the waves were also measured by Hertz. These experiments established that light and these waves were both a form of electromagnetic radiation obeying the Maxwell equations.<ref>[[#JB11|Buchwald 2011]], pp. 77-91</ref>

{{multiple image
| align = center
| direction = horizontal
| header   =
| image1   = Hertz radio wave experiments - parabolic antennas.png
| caption1 = Hertz's directional spark transmitter ''(center)'', a [[half-wave dipole]] antenna made of two 13 cm brass rods with spark gap at center ''(closeup left)'' powered by a [[Ruhmkorff coil]], on focal line of a 1.2 m x 2 m cylindrical sheet metal [[parabolic reflector]].<ref name="Pierce">{{Cite book |last=Pierce |first=George Washington |url=https://play.google.com/books/reader?id=yRZDAAAAIAAJ&printsec=frontcover&output=reader&hl=en&pg=GBS.PA51 |title=Principles of Wireless Telegraphy |date=1910 |publisher=McGraw-Hill Book Co. |location=New York |pages=51–55}}</ref> It radiated a beam of 66 cm waves with frequency of about 450&nbsp;MHz.  Receiver ''(right)'' is similar parabolic dipole antenna with [[Spark micrometer|micrometer spark gap]].
| width1   = 254
| image2   = Hertz radio wave experiments - crossed polarization.png
| caption2 = Hertz's demonstration of [[polarization (antenna)|polarization]] of radio waves: the receiver does not respond when antennas are perpendicular as shown, but as receiver is rotated the received signal grows stronger (as shown by length of sparks) until it reaches a maximum when dipoles are parallel.<ref name="Pierce" />
| width2   = 231
| footer   =
}}
{{multiple image
| align = center
| direction = horizontal
| header   =
| image1   = Hertz radio wave experiments - polarization filter.png
| caption1 = Another demonstration of polarization: waves pass through polarizing filter to the receiver only when the wires are perpendicular to dipoles ''(A)'', not when parallel ''(B)''.<ref name="Pierce" />
| width1   = 200
| image2   = Hertz radio wave experiments - refraction.png
| caption2 = Demonstration of [[refraction]]: radio waves bend when passing through a [[Prism (optics)|prism]] made of [[pitch (resin)|pitch]], similarly to light waves when passing through a glass prism.<ref name="Pierce" />
| width2   = 230
| image3   = TransverseEMwave.PNG
| caption3 = Hertz' plot of [[standing wave]]s created when radio waves are reflected from a sheet of metal
| width3   = 170
| footer   =
}}
{{clear}}
Hertz did not realize the practical importance of his [[radio wave]] experiments. He stated that,<ref name="UnivOfJerusalem">{{Cite web |date=2004 |title=Heinrich Rudolph Hertz |url=http://chem.ch.huji.ac.il/history/hertz.htm |url-status=bot: unknown |archive-url=https://web.archive.org/web/20090925102542/http://chem.ch.huji.ac.il/history/hertz.htm |archive-date=25 September 2009 |access-date=6 March 2018 |website=History |publisher=Institute of Chemistry, Hebrew Univ. of Jerusalem website |df=dmy-all}}</ref><ref>Capri, Anton Z. (2007) ''Quips, quotes, and quanta: an anecdotal history of physics''. World Scientific. {{ISBN|9812709207}}. p 93.</ref><ref name="Norton">{{Cite book |last=Norton |first=Andrew |url=https://books.google.com/books?id=XRRMxjr24pwC&q=nothing&pg=PA83 |title=Dynamic Fields and Waves |date=2000 |publisher=CRC Press |isbn=0750307196 |pages=83}}</ref>

<blockquote>It's of no use whatsoever ... this is just an experiment that proves Maestro Maxwell was right—we just have these mysterious electromagnetic waves that we cannot see with the naked eye. But they are there.</blockquote>

Asked about the applications of his discoveries, Hertz replied,<ref name="UnivOfJerusalem" /><ref name="Hertz1893">{{Cite book |last=Heinrich Hertz |url=https://archive.org/details/electricwavesbe00hertgoog |title=Electric Waves: Being Researches on the Propagation of Electric Action with Finite Velocity Through Space |publisher=Dover Publications |year=1893 |isbn=1-4297-4036-1}}</ref>

<blockquote>Nothing, I guess</blockquote>

Hertz's proof of the existence of airborne electromagnetic waves led to an explosion of experimentation with this new form of electromagnetic radiation, which was called "Hertzian waves" until around 1910 when the term "[[radio waves]]" became current.  Within 6 years [[Guglielmo Marconi]] began developing a radio wave based [[wireless telegraphy]] system,<ref>
[https://ewh.ieee.org/reg/7/millennium/radio/radio_differences.html John S. Belrose, Fessenden and Marconi: Their Differing Technologies and Transatlantic Experiments During the First Decade of this Century, International Conference on 100 Years of Radio -- 5-7 September 1995, ieee.org</ref> leading to the wide use of radio communication.

=== Cathode rays ===
In 1883, he tried to prove that the cathode rays are electrically neutral and got what he interpreted as a confident absence of deflection in electrostatic field. However, as [[J. J. Thomson]] explained in 1897, Hertz placed the deflecting electrodes in a highly-conductive area of the tube, resulting in a strong screening effect close to their surface.<ref>{{Cite journal |last=Thomson |first=George |date=1970 |title=An Unfortunate Experiment: Hertz and the Nature of Cathode Rays |url=https://www.jstor.org/stable/530878 |journal=Notes and Records of the Royal Society of London |volume=25 |issue=2 |pages=237–242 |doi=10.1098/rsnr.1970.0032 |jstor=530878 |issn=0035-9149|url-access=subscription }}</ref>

Nine years later Hertz began experimenting and demonstrated that [[cathode ray]]s could penetrate very thin metal foil (such as aluminium). [[Philipp Lenard]], a student of Heinrich Hertz, further researched this "[[X-rays|ray effect]]". He developed a version of the cathode tube and studied the penetration by X-rays of various materials. However, Lenard did not realize that he was producing X-rays. Hermann von Helmholtz formulated mathematical equations for X-rays. He postulated a dispersion theory before [[Wilhelm Conrad Röntgen|Röntgen]] made his discovery and announcement. It was formed on the basis of the electromagnetic theory of light (''Wiedmann's Annalen'', Vol. XLVIII). However, he did not work with actual X-rays.<ref>[[#JB11|Buchwald 2011]], pp. 151-153</ref>

=== Photoelectric effect ===
Hertz helped establish the [[photoelectric effect]] (which was later explained by [[Albert Einstein]]) when he noticed that a [[electric charge|charged]] object loses its charge more readily when illuminated by [[ultraviolet radiation]] (UV). In 1887, he made observations of the photoelectric effect and of the production and reception of electromagnetic (EM) waves, published in the journal ''[[Annalen der Physik]]''. His receiver consisted of a coil with a [[spark gap]], whereby a spark would be seen upon detection of EM waves. He placed the apparatus in a darkened box to see the spark better. He observed that the maximum spark length was reduced when in the box. A glass panel placed between the source of EM waves and the receiver absorbed UV that assisted the [[electron]]s in jumping across the gap. When removed, the spark length would increase. He observed no decrease in spark length when he substituted quartz for glass, as [[quartz]] does not absorb UV radiation. Hertz concluded his months of investigation and reported the results obtained. He did not further pursue investigation of this effect, nor did he make any attempt at explaining how the observed phenomenon was brought about.<ref>[[#JB11|Buchwald 2011]], p. 244</ref>

===Contact mechanics===
{{Main|Contact mechanics}}
[[Image:Büste von Heinrich Hertz in Karlsruhe.jpg|thumb|Memorial of Heinrich Hertz on the campus of the [[Karlsruhe Institute of Technology]], which translates as ''At this site, Heinrich Hertz discovered electromagnetic waves in the years 1885–1889'']]

In 1881 and 1882, Hertz published two articles<ref>{{Cite journal |last=Hertz, Heinrich |year=1882 |title=Ueber die Berührung fester elastischer Körper |url=https://www.degruyter.com/document/doi/10.1515/crll.1882.92.156/html |journal=Journal für die reine und angewandte Mathematik |volume=1882 |issue=92 |pages=156–171 |doi=10.1515/crll.1882.92.156 |s2cid=123604617|url-access=subscription }}</ref><ref>{{Cite journal |last=Hertz |first=Heinrich |date=1882 |title=Über die Berührung fester elastischer Körper und über die Härte |url=https://d-nb.info/1138446343/34 |journal=Verhandlungen des Vereins zur Beförderung des Gewerbefleißes |volume=1882 |pages=449–463 |access-date=9 February 2022}}</ref><ref>{{Cite book |last=Hertz |first=Heinrich |url=https://books.google.com/books?id=0wM1AQAAMAAJ |title=Miscellaneous Papers |date=1986 |publisher=Macmillan and Co, Ltd. |location=London |pages=146–183 |access-date=13 February 2022}}</ref> on what was to become known as the field of [[contact mechanics]], which proved to be an important basis for later theories in the field. [[Joseph Valentin Boussinesq]] published some critically important observations on Hertz's work, nevertheless establishing this work on contact mechanics to be of immense importance. His work basically summarises how two [[axi-symmetric]] objects placed in contact will behave under [[Structural load|loading]], he obtained results based upon the classical theory of [[elasticity (physics)|elasticity]] and [[continuum mechanics]]. The most significant flaw of his theory was the neglect of any nature of [[adhesion]] between the two solids, which proves to be important as the materials composing the solids start to assume high elasticity. It was natural to neglect adhesion at the time, however, as there were no experimental methods of testing for it.<ref>[https://www.researchgate.net/publication/282260101_Understanding_the_tip-sample_contact_An_overview_of_contact_mechanics_at_the_nanoscale Tevis D. B. Jacobs, C. M. Mate, Kevin T. Turner, Robert W Carpick, Understanding the tip-sample contact: An overview of contact mechanics at the nanoscale, November 2013]</ref>

To develop his theory Hertz used his observation of elliptical [[Newton's rings]] formed upon placing a glass sphere upon a lens as the basis of assuming that the pressure exerted by the sphere follows an [[elliptical distribution]]. He used the formation of Newton's rings again while validating his theory with experiments in calculating the [[displacement (fluid)|displacement]] which the sphere has into the lens. [[Kenneth L. Johnson]], K. Kendall and A. D. Roberts (JKR) used this theory as a basis while calculating the theoretical displacement or ''indentation depth'' in the presence of adhesion in 1971.<ref>{{Cite journal |last1=Johnson, K. L. |last2=Kendall, K. |last3=Roberts, A. D. |year=1971 |title=Surface energy and contact of elastic solids |url=http://www.ewp.rpi.edu/hartford/~ernesto/F2012/FWM/Papers/Johnson-Kendall-Roberts-1971.pdf |journal=Proceedings of the Royal Society A |volume=324 |issue=1558 |pages=301–313 |bibcode=1971RSPSA.324..301J |doi=10.1098/rspa.1971.0141 |doi-access=free |s2cid=137730057}}</ref> Hertz's theory is recovered from their formulation if the adhesion of the materials is assumed to be zero. Similar to this theory, however using different assumptions, [[Boris Derjaguin|B. V. Derjaguin]], V. M. Muller and Y. P. Toporov published another theory in 1975, which came to be known as the DMT theory in the research community, which also recovered Hertz's formulations under the assumption of zero adhesion. This DMT theory proved to be premature and needed several revisions before it came to be accepted as another material contact theory in addition to the JKR theory. Both the DMT and the JKR theories form the basis of contact mechanics upon which all transition contact models are based and used in material parameter prediction in [[nanoindentation]] and [[atomic force microscopy]]. These models are central to the field of [[tribology]] and he was named as one of the 23 "Men of Tribology" by [[Duncan Dowson]].<ref>{{Cite journal |last=Dowson |first=Duncan |date=1 April 1979 |title=Men of Tribology: Heinrich Rudolph Hertz (1857–1894) and Richard Stribeck (1861–1950) |url=https://asmedigitalcollection.asme.org/tribology/article/101/2/115/419215/Men-of-Tribology-Heinrich-Rudolph-Hertz-1857-1894 |journal=Journal of Lubrication Technology |language=en |volume=101 |issue=2 |pages=115–119 |doi=10.1115/1.3453287 |issn=0022-2305 |doi-access=|url-access=subscription }}</ref> Despite preceding his great work on electromagnetism (which he himself considered with his characteristic soberness to be trivial<ref name="UnivOfJerusalem"/>), Hertz's research on contact mechanics has facilitated the age of [[nanotechnology]].

Hertz also described the "[[Hertzian cone]]", a type of [[fracture mechanics|fracture mode]] in brittle solids caused by the transmission of stress waves.<ref>[https://docs.lib.purdue.edu/dissertations/AAI1510251/ "Purdue University - Study on Hertzian cone crack"]</ref>

===Meteorology===
Hertz always had a deep interest in [[meteorology]], probably derived from his contacts with [[Wilhelm von Bezold]] (who was his professor in a laboratory course at the Munich Polytechnic in the summer of 1878).  As an assistant to Helmholtz in [[Berlin]], he contributed a few minor articles in the field, including research on the [[evaporation]] of liquids,<ref>{{Cite journal |last=Hertz |first=H. |date=1882 |title=Ueber die Verdunstung der Flüssigkeiten, insbesondere des Quecksilbers, im luftleeren Raume |url=https://onlinelibrary.wiley.com/doi/abs/10.1002/andp.18822531002 |journal=Annalen der Physik |language=en |volume=253 |issue=10 |pages=177–193 |bibcode=1882AnP...253..177H |doi=10.1002/andp.18822531002 |issn=1521-3889}}</ref> a new kind of [[hygrometer]], and a graphical means of determining the properties of moist air when subjected to [[adiabatic]] changes.<ref>{{Cite journal |last1=Mulligan, J. F. |last2=Hertz, H. G. |year=1997 |title=An unpublished lecture by Heinrich Hertz: "On the energy balance of the Earth" |journal=American Journal of Physics |volume=65 |issue=1 |pages=36–45 |bibcode=1997AmJPh..65...36M |doi=10.1119/1.18565|doi-access=free }}</ref>

=== Philosophy of science ===
In the introduction of his 1894 book ''Principles of Mechanics'', Hertz discusses the different "pictures" used to represent physics in his time including the picture of [[Newtonian mechanics]] (based on mass and forces), a second picture (based on [[conservation of energy]] and [[Hamilton's principle]]) and his own picture (based uniquely on space, time, mass and the [[Hertz principle of least curvature|Hertz principle]]), comparing them in terms of  'permissibility', 'correctness' and 'appropriateness'.<ref name=":0">{{Citation |last=Barker |first=Peter |title=Hertz, Heinrich Rudolf (1857–94) |date=2016 |url=https://www.rep.routledge.com/articles/biographical/hertz-heinrich-rudolf-1857-94/v-1 |encyclopedia=Routledge Encyclopedia of Philosophy |access-date=2023-08-24 |edition=1 |place=London |publisher=Routledge |doi=10.4324/9780415249126-q046-1 |isbn=978-0-415-25069-6|url-access=subscription }}</ref> Hertz wanted to remove "empty assumptions" and argue against the Newtonian concept of [[force]] and against [[action at a distance]].<ref name=":0" /> Philosopher [[Ludwig Wittgenstein]] inspired by Hertz's work, extended his picture theory into a [[picture theory of language]] in his 1921 ''[[Tractatus Logico-Philosophicus]]'' which influenced [[logical positivism]]''.''<ref name=":0" /> Wittgenstein also quotes him in the ''[[Blue and Brown Books]]''.<ref>{{cite book |last1=Fielding |first1=James Matthew |title=The Movement of Thought: Wittgenstein on Time, Change and History |date=2023 |publisher=Springer International Publishing |page=219}}</ref>

==Third Reich treatment==
Because Hertz's family converted from Judaism to Lutheranism two decades before his birth, his legacy ran afoul of the [[Nazism|Nazi]] government in the 1930s, a regime that classified people by "race" instead of religious affiliation.<ref name="DSB340">Koertge, Noretta. (2007). ''Dictionary of Scientific Biography''. New York: [[Thomson-Gale]]. {{ISBN|0-684-31320-0}}. Vol. 6, p. 340.</ref><ref name="Wolff_2008">Wolff, Stefan L. (2008-01-04) [http://www.juedische-allgemeine.de/article/view/id/1394 ''Juden wider Willen – Wie es den Nachkommen des Physikers Heinrich Hertz im NS-Wissenschaftsbetrieb erging'']. Jüdische Allgemeine.<!-- Since there are several authors named Stefan Wolff, the author of the above mentioned article is this one: http://www.deutsches-museum.de/forschung/wissenschaftl-mitarbeiter/dr-stefan-wolff/ --></ref>

Hertz's name was removed from streets and institutions and there was even a movement to rename the frequency unit named in his honor (hertz) after [[Hermann von Helmholtz]] instead, keeping the symbol (Hz) unchanged.<ref name="Wolff_2008"/>

His family was also persecuted for their non-Aryan status. Hertz's youngest daughter, Mathilde, lost a lectureship at Berlin University after the Nazis came to power and within a few years she, her sister, and their mother left Germany and settled in England.<ref name="macrakies">MacRakies K. 1993. ''Surviving the Swastika: Scientific Research in Nazi Germany.'' New York, USA: Oxford University Press</ref>

==Legacy and honors==
[[File:Heinrich Hertz Deutsche-200-1Kcs.jpg|thumb|right|Heinrich Hertz]]

Heinrich Hertz's nephew, [[Gustav Ludwig Hertz]] was a Nobel Prize winner, and Gustav's son [[Carl Helmut Hertz]] invented [[medical ultrasonography]]. His daughter [[Mathilde Carmen Hertz]] was a well-known biologist and comparative psychologist. Hertz's grandnephew Hermann Gerhard Hertz, professor at the [[University of Karlsruhe]], was a pioneer of NMR-spectroscopy and in 1995 published Hertz's laboratory notes.<ref>{{Cite journal |last1=Hertz |first1=H.G. |last2=Doncel |first2=M.G. |year=1995 |title=Heinrich Hertz's Laboratory Notes of 1887 |journal=Archive for History of Exact Sciences |volume=49 |issue=3 |pages=197–270 |doi=10.1007/bf00376092 |s2cid=121101068}}</ref>

The SI unit ''[[hertz]]'' (Hz) was established in his honor by the [[International Electrotechnical Commission]] in 1930 for [[frequency]], an expression of the number of times that a repeated event occurs per second.<ref name="hertzunit">{{cite web | url = http://www.iec.ch/about/history/overview/ | title = IEC History | archive-url = https://web.archive.org/web/20130519144600/http://www.iec.ch/about/history/overview/ |archive-date=19 May 2013 | publisher = Iec.ch }}</ref> It was adopted by the [[CGPM]] (Conférence générale des poids et mesures) in 1960, officially replacing the previous name, "[[cycles per second]]" (cps).<ref>Brian Taylor, H. Gustav Mueller, Fitting and Dispensing Hearing Aids, Plural Publishing, Incorporated · 2020, page 29</ref>

In 1928 the [[Fraunhofer Institute for Telecommunications|Heinrich-Hertz Institute for Oscillation Research]] was founded in Berlin. Today known as the ''Fraunhofer Institute for Telecommunications, Heinrich Hertz Institute, HHI''.

In 1969, in [[East Germany]], a Heinrich Hertz memorial medal<ref>[http://highfields-arc.co.uk/biogs/hrhertz.htm Heinrich Rudolf Hertz] {{webarchive|url=https://web.archive.org/web/20130603182619/http://highfields-arc.co.uk/biogs/hrhertz.htm |date=3 June 2013 }}. Highfields-arc.co.uk. Retrieved 22 August 2014.</ref> was cast.

The [[IEEE Heinrich Hertz Medal]], established in 1987, is "''for outstanding achievements in Hertzian waves ''[...]'' presented annually to an individual for achievements which are theoretical or experimental in nature''".

The [[Heinrich Hertz Submillimeter Telescope|Submillimeter Radio Telescope]] at Mt. Graham, Arizona, constructed in 1992 is named after him.

A [[Impact crater|crater]] that lies on the [[Far side (Moon)|far side]] of the [[Moon]], just behind the eastern limb, is the [[Hertz (crater)|Hertz crater]], named in his honor.

On his birthday in 2012, Google honored Hertz with a [[Google doodle]], inspired by his life's work, on its home page.<ref>{{Cite web |last=Albanesius |first=Chloe |date=22 February 2012 |title=Google Doodle Honors Heinrich Hertz, Electromagnetic Wave Pioneer |url=https://www.pcmag.com/article2/0,2817,2400529,00.asp |access-date=22 February 2012 |website=PC Magazine}}</ref><ref>[https://doodles.google/doodle/heinrich-rudolf-hertzs-155th-birthday/ Heinrich Rudolf Hertz's 155th Birthday]. Google (22 February 2012). Retrieved 22 August 2014.</ref>

==Works==
===Books===
* {{Cite book |title=Ueber<!-- sic! --> die Induction in rotirenden Kugeln |publisher= Gustav Schade |year=1880 |location=Berlin |language=de}}
* {{Cite book |url=https://gutenberg.beic.it/webclient/DeliveryManager?pid=11925721 |title=Die Prinzipien der Mechanik in neuem Zusammenhange dargestellt |publisher=Johann Ambrosius Barth |year=1894 |location=Leipzig |language=de}}
* {{Cite book |url=https://gutenberg.beic.it/webclient/DeliveryManager?pid=11924476 |title=Schriften vermischten Inhalts |publisher=Johann Ambrosius Barth |year=1895 |location=Leipzig |language=de}}

<gallery>
Hertz1880.jpg|''Ueber<!-- sic! --> die Induction in rotirenden Kugeln'', 1880
Hertz, Heinrich – Schriften vermischten Inhalts, 1895 – BEIC 11924476.jpg|''Schriften vermischten Inhalts'', 1895
</gallery>

===Articles===
{{refbegin|30em}}
* Hertz, H.R. "Ueber sehr schnelle electrische Schwingungen", ''Annalen der Physik'', vol. 267, no. 7, p.&nbsp;421–448, May 1887 {{doi|10.1002/andp.18872670707}}
* Hertz, H.R. "Ueber einen Einfluss des ultravioletten Lichtes auf die electrische Entladung", ''Annalen der Physik'', vol. 267, no. 8, p.&nbsp;983–1000, June 1887 {{doi|10.1002/andp.18872670827}} 
* Hertz, H.R. "Ueber die Einwirkung einer geradlinigen electrischen Schwingung auf eine benachbarte Strombahn", ''Annalen der Physik'', vol. 270, no. 5, p.&nbsp;155–170, March 1888 {{doi|10.1002/andp.18882700510}} 
* Hertz, H.R. "Ueber die Ausbreitungsgeschwindigkeit der electrodynamischen Wirkungen", ''Annalen der Physik'', vol. 270, no. 7, p.&nbsp;551–569, May 1888 {{doi|10.1002/andp.18882700708}} 
* Hertz, H. R.(1899) ''The Principles of Mechanics Presented in a New Form'', London, Macmillan, with an introduction by [[Hermann von Helmholtz]] (English translation of ''Die Prinzipien der Mechanik in neuem Zusammenhange dargestellt'', Leipzig, posthumously published in 1894).
{{refend}}

==See also==
'''Lists and histories'''
{{Div col}}
* [[Fraunhofer Institute for Telecommunications]], Heinrich Hertz Institute
* [[History of radio]]
* [[Invention of radio]]
* [[List of physicists]]
* [[Outline of physics]]
* [[Timeline of atomic and subatomic physics|Timeline of mechanics and physics]]
* [[Timeline of electromagnetism and classical optics|Electromagnetism timeline]]
* [[Wireless telegraphy]]
{{Div col end}}

'''Electromagnetic radiation'''
* [[Microwave]]

'''Other'''
* [[List of German inventors and discoverers]]

==References==
{{reflist}}

==Further reading==
{{refbegin|30em}}
* Appleyard, Rollo. (1930). ''Pioneers of Electrical Communication''". London: [[Macmillan and Company]]. reprinted by Ayer Company Publishers, Manchester, New Hampshire: {{ISBN|0-8369-0156-8}}
* Bodanis, David. (2006). ''Electric Universe: How Electricity Switched on the Modern World.'' New York: [[Three Rivers Press]]. {{ISBN|0-307-33598-4}}
* Bryant, John H. (1988). ''Heinrich Hertz, the Beginning of Microwaves: Discovery of Electromagnetic Waves and Opening of the Electromagnetic Spectrum by Heinrich Hertz in the Years 1886–1892.'' New York: IEEE (Institute of Electrical and Electronics Engineers). {{ISBN|0-87942-710-8}}
* {{citation | first = Jed Z. | last = Buchwald | author-link = Jed Buchwald | title = The Creation of Scientific Effects: Heinrich Hertz and Electric Waves | publisher = University of Chicago Press | orig-date = September 1994 | date = December 2011 | page = 45 | isbn = 9780226078915 | ref = JB11 }}
* Jenkins, John D. [http://www.sparkmuseum.com/BOOK_HERTZ.HTM "The Discovery of Radio Waves – 1888; Heinrich Rudolf Hertz (1847–1894)" (retrieved 27 Jan 2008)]
* {{citation | url = https://babel.hathitrust.org/cgi/pt?id=uiug.30112112082133&seq=11 | last = Lodge | first = Oliver Joseph | date = 1897 | title = Signaling Across Space without Wires by Electric Waves: Being a Description of the work of Hertz and his Successors | publisher = "The Electrician" Printing and Pub. Co. | location = London }}
* Maugis, Daniel. (2000). ''Contact, Adhesion and Rupture of Elastic Solids.'' New York: Springer-Verlag. {{ISBN|3-540-66113-1}}
* Naughton, Russell. [https://webarchive.nla.gov.au/awa/20040302130000/http://pandora.nla.gov.au/pan/13071/20040303-0000/www.acmi.net.au/AIC/HERTZ_BIO.html "Heinrich Rudolph (alt: Rudolf) Hertz, Dr : 1857 – 1894" (retrieved 27 Jan 2008)]{{cbignore|bot=medic}}
* Roberge, Pierre R. [http://www.corrosion-doctors.org/Biographies/HertzBio.htm "Heinrich Rudolph Hertz, 1857–1894" (retrieved 27 Jan 2008)]
* Susskind, Charles. (1995). ''Heinrich Hertz: A Short Life.'' San Francisco: San Francisco Press. {{ISBN|0-911302-74-3}}
{{refend}}

==External links==
{{Commons category|Heinrich Rudolf Hertz}}
{{wikiquote}}
* {{Cite EB1911|wstitle=Hertz, Heinrich Rudolf |volume= 13 | pages = 400&ndash;401  |short= 1}}
* {{PM20|FID=pe/007711}}

{{Scientists whose names are used as SI units}}
{{Authority control}}

{{DEFAULTSORT:Hertz, Heinrich Rudolf}}
[[Category:Heinrich Hertz| ]]
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