Heinrich Rudolf Hertz was born on 22 February 1857 inHamburg, the son ofGustav Ferdinand Hertz, a lawyer and politician, and Anna Elisabeth Pfefferkorn.[6][7]
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 andMathilde, born on 14 January 1891, who went on to become a notable biologist. During this time Hertz conducted his landmark research into electromagnetic waves.[9]
Hertz took a position of Professor of Physics and Director of the Physics Institute at theUniversity of Bonn on 3 April 1889, a position he held until his death. During this time he worked ontheoretical mechanics with his work published in the bookDie Prinzipien der Mechanik in neuem Zusammenhange dargestellt (The Principles of Mechanics Presented in a New Form), published posthumously in 1894.[10]
In 1892, Hertz was diagnosed with an infection (after a bout of severemigraines) 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.[11] He died on 1 January 1894 inBonn, aged 36, and is buried in theOhlsdorf Cemetery in Hamburg.[12][13][14]
Hertz's wife, Elisabeth Hertz (née Doll; 1864–1941), did not remarry. He was survived by his daughters, Johanna (1887–1967) and Mathilde (1891–1975).[15] Neither ever married or had children, hence Hertz has no living descendants.[16]
Hertz's 1887 apparatus for generating and detecting radio waves: aspark-gap transmitter(left) consisting of adipole antenna with a spark gap(S) powered by high voltage pulses from aRuhmkorff coil(T), and a receiver(right) consisting of a loop antenna and spark gap.
One of Hertz's radio wave receivers: a loop antenna with an adjustablespark micrometer(bottom).[17]
In 1864 Scottish mathematical physicistJames Clerk Maxwell proposed a comprehensive theory of electromagnetism, now calledMaxwell's equations. Maxwell's theory predicted that coupledelectric andmagnetic fields 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.[18]
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 thePrussian Academy of Sciences for anyone who could experimentally prove an electromagnetic effect in the polarization and depolarization ofinsulators, something predicted by Maxwell's theory.[19][20] Helmholtz was sure Hertz was the most likely candidate to win it.[20] Not seeing any way to build an apparatus to experimentally test this, Hertz thought it was too difficult, and worked onelectromagnetic 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.[21]
In the autumn of 1886, after Hertz received his professorship at Karlsruhe, he was experimenting with a pair ofRiess spirals when he noticed that discharging aLeyden 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).[22][23] He used adipole antenna consisting of two collinear one-meter wires with a spark gap between their inner ends, and zinc spheres attached to the outer ends forcapacitance, as a radiator. The antenna was excited by pulses of high voltage of about 30kilovolts applied between the two sides from aRuhmkorff coil. He received the waves with a resonant single-loop antenna with amicrometer spark gap between the ends. This experiment produced and received what are now calledradio waves in thevery high frequency range.
Hertz's first radio transmitter: acapacitance loadeddipole resonator consisting of a pair of one meter copper wires with a 7.5 mm spark gap between them, ending in 30 cm zinc spheres.[17] When aninduction coil applied a high voltage between the two sides, sparks across the spark gap createdstanding waves of radio frequency current in the wires, which radiatedradio waves. Thefrequency 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 transversefree spaceelectromagnetic waves traveling at a finite speed over a distance.[23][24] In the apparatus Hertz used, the electric and magnetic fields radiated away from the wires astransverse waves. Hertz had positioned theoscillator about 12 meters from azinc reflecting plate to producestanding waves. Each wave was about 4 meters long.[citation needed] Using the ring detector, he recorded how the wave'smagnitude and component direction varied. Hertz measured Maxwell's waves and demonstrated that thevelocity of these waves was equal to the velocity of light. Theelectric field intensity,polarization andreflection 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.[25]
Hertz's directional spark transmitter(center), ahalf-wave dipole antenna made of two 13 cm brass rods with spark gap at center(closeup left) powered by aRuhmkorff coil, on focal line of a 1.2 m x 2 m cylindrical sheet metalparabolic reflector.[26] It radiated a beam of 66 cm waves with frequency of about 450 MHz. Receiver(right) is similar parabolic dipole antenna withmicrometer spark gap.
Hertz's demonstration ofpolarization 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.[26]
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).[26]
Demonstration ofrefraction: radio waves bend when passing through aprism made ofpitch, similarly to light waves when passing through a glass prism.[26]
Hertz's plot ofstanding waves created when radio waves are reflected from a sheet of metal
Hertz did not realize the practical importance of hisradio wave experiments. He stated that,[27][28][29]
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.
Asked about the applications of his discoveries, Hertz replied,[27]
Nothing, I guess
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 yearsGuglielmo Marconi began developing a radio wave basedwireless telegraphy system,[30] leading to the wide use of radio communication.
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, asJ. 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.[31]
Nine years later Hertz began experimenting and demonstrated thatcathode rays could penetrate very thin metal foil (such as aluminium).Philipp Lenard, a student of Heinrich Hertz, further researched this "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 beforeRöntgen 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.[32]
Hertz helped establish thephotoelectric effect (which was later explained byAlbert Einstein) when he noticed that acharged object loses its charge more readily when illuminated byultraviolet radiation (UV). In 1887, he made observations of the photoelectric effect and of the production and reception of electromagnetic (EM) waves, published in the journalAnnalen der Physik. His receiver consisted of a coil with aspark 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 theelectrons 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, asquartz 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.[33]
Memorial of Heinrich Hertz on the campus of theKarlsruhe Institute of Technology, which translates asAt this site, Heinrich Hertz discovered electromagnetic waves in the years 1885–1889
In 1881 and 1882, Hertz published two articles[34][35][36] on what was to become known as the field ofcontact 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 twoaxi-symmetric objects placed in contact will behave underloading, he obtained results based upon the classical theory ofelasticity andcontinuum mechanics. The most significant flaw of his theory was the neglect of any nature ofadhesion 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.[37]
To develop his theory Hertz used his observation of ellipticalNewton's rings formed upon placing a glass sphere upon a lens as the basis of assuming that the pressure exerted by the sphere follows anelliptical distribution. He used the formation of Newton's rings again while validating his theory with experiments in calculating thedisplacement 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 orindentation depth in the presence of adhesion in 1971.[38] 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,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 innanoindentation andatomic force microscopy. These models are central to the field oftribology and he was named as one of the 23 "Men of Tribology" byDuncan Dowson.[39] Despite preceding his great work on electromagnetism (which he himself considered with his characteristic soberness to be trivial[27]), Hertz's research on contact mechanics has facilitated the age ofnanotechnology.
Hertz also described the "Hertzian cone", a type offracture mode in brittle solids caused by the transmission of stress waves.[40]
Hertz always had a deep interest inmeteorology, probably derived from his contacts withWilhelm 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 theevaporation of liquids,[41] a new kind ofhygrometer, and a graphical means of determining the properties of moist air when subjected toadiabatic changes.[42]
Because Hertz's family converted from Judaism to Lutheranism two decades before his birth, his legacy ran afoul of theNazi government in the 1930s, a regime that classified people by "race" instead of religious affiliation.[45][46]
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) afterHermann von Helmholtz instead, keeping the symbol (Hz) unchanged.[46]
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.[47]
The SI unithertz (Hz) was established in his honor by theInternational Electrotechnical Commission in 1930 forfrequency, an expression of the number of times that a repeated event occurs per second.[49] It was adopted by theCGPM (Conférence générale des poids et mesures) in 1960, officially replacing the previous name, "cycles per second" (cps).[50]
In 1969, inEast Germany, a Heinrich Hertz memorial medal[51] was cast.
TheIEEE 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".
Hertz, H.R. "Ueber sehr schnelle electrische Schwingungen",Annalen der Physik, vol. 267, no. 7, p. 421–448, May 1887doi: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. 983–1000, June 1887doi: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. 155–170, March 1888doi:10.1002/andp.18882700510
Hertz, H.R. "Ueber die Ausbreitungsgeschwindigkeit der electrodynamischen Wirkungen",Annalen der Physik, vol. 270, no. 7, p. 551–569, May 1888doi:10.1002/andp.18882700708
Hertz, H. R.(1899)The Principles of Mechanics Presented in a New Form, London, Macmillan, with an introduction byHermann von Helmholtz (English translation ofDie Prinzipien der Mechanik in neuem Zusammenhange dargestellt, Leipzig, posthumously published in 1894).
^Krech, Eva-Maria; Stock, Eberhard; Hirschfeld, Ursula; Anders, Lutz Christian (2009).Deutsches Aussprachewörterbuch [German Pronunciation Dictionary] (in German). Berlin: Walter de Gruyter. pp. 575, 580.ISBN978-3-11-018202-6.
^Kleiner, Stefan; Knöbl, Ralf (2015) [First published 1962].Das Aussprachewörterbuch [The Pronunciation Dictionary] (in German) (7th ed.). Berlin: Dudenverlag. p. 440.ISBN978-3-411-04067-4.
^O'Connor, J.J.; Robertson, E.F. (November 1997)."James Clerk Maxwell". School of Mathematical and Computational Sciences University of St Andrews.Archived from the original on 5 November 2021. Retrieved19 June 2021.
^abBaird, Davis, Hughes, R.I.G. and Nordmann, Alfred eds. (1998).Heinrich Hertz: Classical Physicist, Modern Philosopher. New York:Springer-Verlag.ISBN0-7923-4653-X. p. 49
^Heilbron, John L. (2005)The Oxford Guide to the History of Physics and Astronomy. Oxford University Press.ISBN0195171985. p. 148
^Baird, Davis, Hughes, R.I.G. and Nordmann, Alfred eds. (1998).Heinrich Hertz: Classical Physicist, Modern Philosopher. New York:Springer-Verlag.ISBN0-7923-4653-X. p. 53
^abHuurdeman, Anton A. (2003)The Worldwide History of Telecommunications. Wiley.ISBN0471205052. p. 202
^abc"Heinrich Rudolph Hertz".History. Institute of Chemistry, Hebrew Univ. of Jerusalem website. 2004. Archived from the original on 25 September 2009. Retrieved6 March 2018.{{cite web}}: CS1 maint: bot: original URL status unknown (link)
^Capri, Anton Z. (2007)Quips, quotes, and quanta: an anecdotal history of physics. World Scientific.ISBN9812709207. p 93.
^MacRakies K. 1993.Surviving the Swastika: Scientific Research in Nazi Germany. New York, USA: Oxford University Press
^Hertz, H.G.; Doncel, M.G. (1995). "Heinrich Hertz's Laboratory Notes of 1887".Archive for History of Exact Sciences.49 (3):197–270.doi:10.1007/bf00376092.S2CID121101068.
Appleyard, Rollo. (1930).Pioneers of Electrical Communication". London:Macmillan and Company. reprinted by Ayer Company Publishers, Manchester, New Hampshire:ISBN0-8369-0156-8
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).ISBN0-87942-710-8
Buchwald, Jed Z. (December 2011) [September 1994],The Creation of Scientific Effects: Heinrich Hertz and Electric Waves, University of Chicago Press, p. 45,ISBN9780226078915
