ហេនរីច ហឺត

**ហែងរីហ ហឺត** () (២២ កុម្ភៈ ១៨៥៧ – ១ មករា ១៨៩៤) ជារូបវិទូសញ្ជាតិអាឡឺម៉ង់ដែលបានបកស្រាយ និងបន្លាយពង្រីកបន្ថែមលើទ្រឺស្ដីអេឡិចត្រូម៉ាញ៉េទិចនៃពន្លឺ ដែលបានរកឃើញមុខដំបូងដោយ  ម៉ាកស្វែល។ គាត់ជាមនុស្សទីមួយដែលបានរកឃើញរលកសញ្ញាវិទ្យុក្នុងឆ្នាំ១៨៨៨។  គាត់ក៏បានបកស្រាយនិងពន្យល់ថា ពន្លឺគឺជារលកសញ្ញាអេឡិចត្រូម៉ាញ៉េទិច។ ដូច្នេះហើយទើប ខ្នាតនៃប្រេកង់ (ហឺត / Hz) យកតាមឈ្មោះរបស់គ្នា។

## ជីវប្រវត្តិ
### ឆ្នាំដំបូងៗ
ហឺតចាប់កំណើតនៅរដ្ឋហាំបួក (Hamburg) ដែលជាអតីតរដ្ឋឯករាជមួយ​នៅក្នុងសហព័ន្ធអាល្លឺមង់ ទៅក្នុងគ្រួសារមួយមានវណ្ណៈខ្ពស់ មានទ្រព្វសម្បត្តិស្ដុកស្ដម្ភ​និងកំរិតវប្បធម៌ខ្ពស់។ ឪពុករបស់គាត់ឈ្មោះ ហ្គាស្តាវ ហ្វែរឌីណាន់ ហឺត (Gustav Ferdinand Hertz) ជាអ្នកនិពន្ធសៀវភៅ​និងក្រោយមកក្លាយជាសមាជិកសភាជាតិ។  His mother was the former Anna Elisabeth Pfefferkorn. His paternal grandfather David Wolff Hertz (1757–1822), fourth son of Benjamin Wolff Hertz, moved to Hamburg in 1793 where he made his living as a jeweller. He and his wife Schöne Hertz (1760–1834) were buried in the former Jewish cemetery in Ottensen. Their first son Wolff Hertz (1790–1859), was chairman of the Jewish community. His brother Hertz Hertz (1797–1862) was a respected businessman. He was married to Betty Oppenheim, the daughter of the banker Salomon Oppenheim, from Cologne. Hertz converted from Judaism to Christianity and took the name Heinrich David Hertz.

While studying at the Gelehrtenschule des Johanneums in Hamburg, he 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 clearly successful attempt was made by Heinrich Hertz in 1886. For his 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&nbsp;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&nbsp;mm thick, bent into a circle of a diameter of 7.5&nbsp;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 would soon trigger the invention of the wireless telegraph, radio, and later television.  In 1930 the International Electrotechnical Commission (IEC) recognized his work by naming the unit of frequency—one cycle per second—the "hertz". 

### Meteorology
He always had a deep interest in meteorology probably derived from his contacts with Wilhelm von Bezold (who was Hertz's professor in a laboratory course at the Munich Polytechnic in the summer of 1878). Hertz, however, did not contribute much to the field himself except some early articles as an assistant to Helmholtz in Berlin, including research on the evaporation of liquids, a new kind of hygrometer, and a graphical means of determining the properties of moist air when subjected to adiabatic changes.

### Contact mechanics
]]

In 1886–1889, Hertz published two articles on what was to become known as the field of contact mechanics. Hertz is well known for his contributions to the field of electrodynamics (*see below*); however, most papers that look into the fundamental nature of contact cite his two papers as a source for some important ideas. 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 loading, he obtained results based upon the classical theory of elasticity and continuum mechanics. The most significant failure 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 in that age as there were no experimental methods of testing for it.

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 which the sphere has into the lens. K. 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 their landmark article "Surface energy and contact of elastic solids" published in 1971 in the Proceedings of the Royal Society (A324, 1558, 301–313). 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 rather 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. So Hertz's research from his days as a lecturer, preceding his great work on electromagnetism, which he himself considered with his characteristic soberness to be trivial, has come down to the age of nanotechnology.

### Electromagnetic research
In 1886, Hertz developed the **Hertz antenna** receiver. This is a set of terminals which is not electrically grounded for its operation. He also developed a transmitting type of dipole antenna, which was a center-fed driven element for transmitting UHF radio waves. These antennas are the simplest practical antennas from a theoretical point of view.

In 1887, Hertz experimented with radio waves in his laboratory. These actions followed Michelson's 1881 experiment (precursor to the 1887 Michelson–Morley experiment), which did not detect the existence of aether drift.  Hertz altered Maxwell's equations to take this view into account for electromagnetism. Hertz used a Ruhmkorff coil-driven spark gap and one meter wire pair as a radiator. Capacity spheres were present at the ends for circuit resonance adjustments. His receiver, a precursor to the dipole antenna, was a simple half-wave dipole antenna for shortwaves.  Hertz published his work in a book titled: *Electric waves: being researches on the propagation of electric action with finite velocity through space*.

Through experimentation, he proved that transverse free space electromagnetic waves can travel over some distance. This had been predicted by James Clerk Maxwell and Michael Faraday. With his apparatus configuration, the electric and magnetic fields would radiate away from the wires as transverse waves. Hertz had positioned the oscillator about 12 meters from a zinc reflecting plate to produce standing waves. Each wave was about 4 meters. Using the ring detector, he recorded how the magnitude and wave's component direction vary. Hertz measured Maxwell's waves and demonstrated that the velocity of radio waves was equal to the velocity of light. The electric field intensity and polarity was also measured by Hertz. (Hertz, 1887, 1888).

The Hertzian cone was first described by Hertz as a type of wave-front propagation through various media. His experiments expanded the field of electromagnetic transmission and his apparatus was developed further by others in the radio. Hertz also found that radio waves could be transmitted through different types of materials, and were reflected by others, leading in the distant future to radar.

Hertz helped establish the photoelectric effect (which was later explained by Albert Einstein) when he noticed that a charged object loses its charge more readily when illuminated by ultraviolet light. 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 ultraviolet radiation that assisted the electrons 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.

Hertz did not realize the practical importance of his experiments. He stated that,
: "''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 ramifications of his discoveries, Hertz replied,
: "*Nothing, I guess''."

Hertz's wife, Elizabeth Hertz (maiden name: Elizabeth Doll), did not remarry. Heinrich Hertz left two daughters, Joanna and Mathilde. Subsequently, all three women left Germany in the 1930s and went to England, after the rise of Adolf Hitler. Charles Susskind interviewed Mathilde Hertz in the 1960s and he later published a book on Heinrich Hertz. Heinrich Hertz's daughters never married and he does not have any descendants, according to the book by Susskind.

### Legacy and honors
His nephew Gustav Ludwig Hertz was a Nobel Prize winner, and Gustav's son Carl Hellmuth Hertz invented medical ultrasonography.

The SI unit *hertz* (Hz) was established in his honor by the IEC in 1930 for frequency, an expression of the number of times that a repeated event occurs per second. It was adopted by the CGPM (Conférence générale des poids et mesures) in 1960, officially replacing the previous name, the "cycle per second" (cps).

In 1969 (East Germany), a Heinrich Hertz memorial medal 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*".

A crater that lies on the far side of the Moon, just behind the eastern limb, is named in his honor. The Hertz market for radio electronics products in Nizhny Novgorod, Russia, is named after him.  The Heinrich-Hertz-Turm radio telecommunication tower in Hamburg is named after the city's famous son.

Hertz is honored by Japan with a membership in the Order of the Sacred Treasure, which has multiple layers of honor for prominent people, including scientists.

Heinrich Hertz has been honored by a number of countries around the world in their postage issues, and in post-World War II times has appeared on various German stamp issues as well.

On his birthday in 2012, Google honored Hertz with a Google doodle inspired by his life's work on its home page.

### Nazi revisionism
Although Hertz would not have considered himself Jewish, his "Jewish" portrait was removed by the Nazis from its prominent position of honor in Hamburg's City Hall (*Rathaus*) because of his partly "Jewish ancestry."  Hertz was a Lutheran; and although his father’s family had been Jewish, his father had converted to Catholicism before marrying. The painting has since been returned to public display.

## មើលផងដែរ
;People
* Jagadish Chandra Bose
* Berend Wilhelm Feddersen
* Hans Christian Ørsted
* David Edward Hughes
* Reginald Fessenden
* Guglielmo Marconi
* Nikola Tesla
* Wilhelm Röntgen

;Lists and histories
* Electromagnetism timeline
* Timeline of mechanics and physics
* List of people on stamps of Germany
* List of physicists
* Radio history
* Outline of physics
* Wireless telegraphy

;Electromagnetic radiation
* Microwave

;Other
* List of German inventors and discoverers

## កំនត់ចំណាំ
## ឯកសារយោង
* Hertz, H.R. "Ueber sehr schnelle electrische Schwingungen", *Annalen der Physik*, vol. 267, no. 7, p.&nbsp;421-448, May 1887. (WILEY InterScience)
* 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. (WILEY InterScience)
* 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. (WILEY InterScience)
* Hertz, H.R. "Ueber die Ausbreitungsgeschwindigkeit der electrodynamischen Wirkungen", *Annalen der Physik*, vol. 270, no. 7, p.&nbsp;551-569, May, 1888. (WILEY InterScience)
* Hertz, H.R. (1893). *Electric waves: being researches on the propagation of electric action with finite velocity through space* (translated by David Evans Jones). Ithica, New York: Cornell University Library.  10-ISBN 1-429-74036-1; 13-ISBN 978-1-429-74036-4
* 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).
* IEEE (Institute of Electrical and Electronics Engineers) Global History Network, IEEE History Center: ["Heinrich Hertz" (retrieved 27 Jan 2007)](http://www.ieeeghn.org/wiki/index.php/Heinrich_Hertz_(1857-1894)) 
*  Jenkins, John D. "The Discovery of Radio Waves - 1888; Heinrich Rudolf Hertz (1847-1894)" (retrieved 27 Jan 2008)
* Koertge, Noretta. (2007). *Dictionary of Scientific Biography.* New York: Thomson-Gale.     10-ISBN 0-684-31320-0; 13-ISBN 978-0-684-31320-7
* Naughton, Russell. "Heinrich Rudolph (alt: Rudolf) Hertz, Dr : 1857 - 1894" (retrieved 27 Jan 2008) 
* Roberge, Pierre R. "Heinrich Rudolph Hertz, 1857-1894" (retrieved 27 Jan 2008) 
* Robertson, Struan. "Buildings Integral to the Former Life and/or Persecution of Jews in Hamburg" (retrieved 27 Jan 2008) 
* Robertson, Struan. "Heinrich Hertz, 1857-1894" (retrieved 27 Jan 2007) 

## អានបន្ថែម
* Appleyard, Rollo. (1930). *Pioneers of Electrical Communication*". London: Macmillan and Company. [reprinted by Ayer Company Publishers, Manchester, New Hampshire: 10-ISBN 0836-90156-8; 13-ISBN 978-0-836-90156-6 (cloth)]
* Baird, Davis, R.I.G. Hughes, and Alfred Nordmann, eds. (1998). 'Heinrich Hertz: Classical Physicist, Modern Philosopher.* New York: Springer-Verlag.  10-ISBN 0-792-34653-X; 13-ISBN  978-0-792-34653-1
* Bodanis, David.  (2006). *Electric Universe: How Electricity Switched on the Modern World.*  New York: Three Rivers Press.  10-ISBN 0-307-33598-4; 13-ISBN 978-0-307-33598-2
* Buchwald, Jed Z. (1994). *The Creation of Scientific Effects : Heinrich Hertz and Electric Waves.* Chicago : University of Chicago Press. 10-ISBN 0-226-07887-6; 13-ISBN 978-0-226-07887-8 (cloth)  10-ISBN 0-226-07888-4; 13-ISBN 978-0-226-07888-5 (paper)
* 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). 10-ISBN 0-879-42710-8; 13-ISBN 978-0-879-42710-8
* [Lodge, Oliver Joseph. (1900). *Signalling Across Space without Wires by Electric Waves: Being a Description of the work of Heinrich(https://km.wikipedia.org/wiki/Heinrich) Hertz and his Successors.*]  [reprinted by Arno Press, New York, 1974. 10-ISBN 0-405-06051-3
* Maugis, Daniel. (2000). *Contact, Adhesion and Rupture of Elastic Solids.* New York: Springer-Verlag. 10-ISBN 3-540-66113-1; 13-ISBN 978-3-54066113-9]
* Susskind, Charles. (1995).*Heinrich Hertz :a Short Life.* San Francisco: San Francisco Press.   10-ISBN 0-911-30274-3; 13-ISBN 978-0-911-30274-5

## តំណភ្ជាប់ខាងក្រៅ
*
* Hertzian radiation - better known as radio waves: what it is and how it happens 
* *Encyclopædia Britannica'' (1911): Hertz biography