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Heinrich Hertz
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Heinrich Hertz

TORIma Academy — Physicist

Heinrich Hertz

Heinrich Hertz

Heinrich Rudolf Hertz ( hurts ; German: [hɛʁts] ; 22 February 1857 – 1 January 1894) was a German physicist who first conclusively proved the existence of the…

Heinrich Rudolf Hertz ( hurts; German: [hɛʁts] ; 22 February 1857 – 1 January 1894) was a German physicist renowned for definitively demonstrating the existence of electromagnetic waves, as theorized by James Clerk Maxwell's equations of electromagnetism.

Heinrich Rudolf Hertz ( hurts; German: [hɛʁts] ; 22 February 1857 – 1 January 1894) was a German physicist who first conclusively proved the existence of the electromagnetic waves proposed by James Clerk Maxwell's equations of electromagnetism.

Biography

Heinrich Rudolf Hertz was born in Hamburg on 22 February 1857, the son of Gustav Ferdinand Hertz, a lawyer and politician, and Anna Elisabeth Pfefferkorn.

During his studies at the Gelehrtenschule des Johanneums in Hamburg, Hertz exhibited proficiency in both scientific disciplines and languages, including Arabic. His higher education in science and engineering took place in Dresden, Munich, and Berlin, where he was mentored by prominent figures such as Gustav Kirchhoff and Hermann von Helmholtz. Hertz earned his Ph.D. from the University of Berlin in 1880, subsequently undertaking three years of postdoctoral research as Helmholtz's assistant. In 1883, he accepted a lectureship in theoretical physics at the University of Kiel, followed by an appointment as a full professor at the University of Karlsruhe in 1885.

In 1886, Hertz married Elisabeth Doll, daughter of Max Doll, a geometry lecturer at Karlsruhe. The couple had two daughters: Johanna, born on 20 October 1887, and Mathilde, born on 14 January 1891, who later distinguished herself as a biologist. It was during this period that Hertz undertook his seminal investigations into electromagnetic waves.

On 3 April 1889, Hertz assumed the role of professor of physics and director of the physics institute at the University of Bonn, a position he maintained until his demise. During his tenure, he focused on theoretical mechanics, with his contributions posthumously published in 1894 as the book Die Prinzipien der Mechanik in neuem Zusammenhange dargestellt (The Principles of Mechanics Presented in a New Form).

Scientific Work

Electromagnetic Waves

In 1864, James Clerk Maxwell, a Scottish mathematical physicist, introduced a comprehensive theory of electromagnetism, subsequently known as Maxwell's equations. This theory posited that interconnected electric and magnetic fields could propagate through space as "electromagnetic waves." Maxwell further hypothesized that light comprised short-wavelength electromagnetic waves; however, experimental verification of this, or the generation and detection of electromagnetic waves at other wavelengths, remained elusive.

In 1879, during Hertz's academic pursuits, Helmholtz proposed that Hertz's doctoral dissertation focus on experimentally validating Maxwell's theory. Concurrently, Helmholtz had established the "Berlin Prize" at the Prussian Academy of Sciences for anyone who could empirically demonstrate an electromagnetic effect in the polarization and depolarization of insulators, a phenomenon predicted by Maxwell's framework. Helmholtz considered Hertz the most probable recipient of this award. However, Hertz initially deemed the experimental challenge too formidable due to the perceived difficulty in constructing the necessary apparatus, opting instead to research electromagnetic induction. Nevertheless, during his tenure at Kiel, Hertz conducted an analysis of Maxwell's equations, affirming their superior validity compared to the then-dominant "action at a distance" theories.

In the autumn of 1886, following his appointment as professor at Karlsruhe, Hertz was conducting experiments with Riess spirals when he observed that discharging a Leyden jar into one coil induced a spark in the other. This observation provided him with a conceptual framework for constructing an apparatus, thereby enabling him to address the 1879 "Berlin Prize" challenge concerning the empirical validation of Maxwell's theory (despite the prize having lapsed unclaimed in 1882). For the radiator, he employed a dipole antenna comprising two collinear one-meter wires, separated by a spark gap at their inner ends, with zinc spheres affixed to the outer ends to provide capacitance. This antenna was energized by approximately 30 kilovolt high-voltage pulses generated by a Ruhmkorff coil. He detected these waves using a resonant single-loop antenna equipped with a micrometer spark gap between its terminals. This pivotal experiment successfully generated and received what are now recognized as very high frequency radio waves.

Hertz conducted a series of experiments between 1886 and 1889, which confirmed that the observed phenomena were attributable to Maxwell's theoretical electromagnetic waves. Beginning in November 1887 with his publication "On Electromagnetic Effects Produced by Electrical Disturbances in Insulators," Hertz submitted multiple papers to Helmholtz at the Berlin Academy. These submissions included 1888 papers demonstrating transverse electromagnetic waves propagating through free space at a finite velocity over a specific distance. Within Hertz's experimental setup, electric and magnetic fields emanated from wires as transverse waves. To generate standing waves, Hertz strategically placed an oscillator approximately 12 meters from a zinc reflecting plate. Each wave measured approximately 4 meters in length. Employing a ring detector, he documented variations in the wave's magnitude and directional components. Hertz successfully measured Maxwell's waves and established that their velocity corresponded to the speed of light. Furthermore, Hertz quantified the electric field intensity, polarization, and reflection properties of these waves. These investigations conclusively demonstrated that both light and these waves constitute forms of electromagnetic radiation, adhering to Maxwell's equations.

Hertz did not fully comprehend the practical implications of his radio wave experiments, remarking that:

It possesses no utility whatsoever... this merely constitutes an experiment validating Maestro Maxwell's theories—we simply possess these enigmatic electromagnetic waves, imperceptible to the unaided eye, yet undeniably present.

When questioned regarding the potential applications of his discoveries, Hertz responded:

Nothing, I suppose.

Hertz's definitive demonstration of airborne electromagnetic waves catalyzed a rapid expansion of experimentation with this novel form of radiation. Initially termed "Hertzian waves," this nomenclature persisted until approximately 1910, when "radio waves" became the standard terminology. Within six years, Guglielmo Marconi initiated the development of a wireless telegraphy system based on radio waves, which subsequently facilitated the widespread adoption of radio communication.

Cathode Rays

In 1883, Hertz attempted to demonstrate the electrical neutrality of cathode rays, observing what he interpreted as a conclusive absence of deflection within an electrostatic field. Nevertheless, as J. J. Thomson elucidated in 1897, Hertz had positioned the deflecting electrodes within a highly conductive region of the tube, which generated a significant screening effect near their surface.

Nine years subsequent to his initial work, Hertz commenced further experimentation, demonstrating that cathode rays possessed the ability to penetrate extremely thin metal foils, such as aluminum. Philipp Lenard, a student of Heinrich Hertz, extended this investigation into the "ray effect." Lenard engineered a modified cathode tube and examined the penetration of various materials by X-rays. However, Lenard remained unaware that he was generating X-rays. Hermann von Helmholtz developed mathematical equations pertaining to X-rays, postulating a dispersion theory prior to Röntgen's discovery and public announcement. This theory was grounded in the electromagnetic theory of light (Wiedmann's Annalen, Vol. XLVIII). Nevertheless, Helmholtz did not conduct experiments with actual X-rays.

Photoelectric Effect

Hertz contributed to the establishment of the photoelectric effect, a phenomenon subsequently elucidated by Albert Einstein, by observing that charged objects discharged more rapidly when exposed to ultraviolet (UV) radiation. In 1887, his observations concerning both the photoelectric effect and the generation and reception of electromagnetic (EM) waves were documented in the journal Annalen der Physik. His receiving apparatus comprised a coil equipped with a spark gap, designed to produce a visible spark upon the detection of EM waves. To enhance the visibility of the spark, Hertz enclosed the setup within a darkened box. He noted that the maximum spark length diminished when the apparatus was contained within the box. A glass panel positioned between the EM wave source and the receiver absorbed UV radiation, which otherwise facilitated electron transfer across the gap. Upon removal of this panel, the spark length increased. Conversely, when quartz was substituted for glass, no reduction in spark length was observed, owing to quartz's transparency to UV radiation. Hertz concluded his multi-month investigation and disseminated his findings. However, he neither pursued further research into this effect nor attempted to provide an explanation for the observed phenomenon.

Contact Mechanics

In 1881 and 1882, Hertz published two seminal articles on what subsequently became known as contact mechanics, establishing a crucial foundation for later theoretical developments in the field. Joseph Valentin Boussinesq provided critically important observations on Hertz's work, thereby solidifying the immense significance of this research in contact mechanics. Hertz's work fundamentally elucidated the behavior of two axi-symmetric objects under load when placed in contact, deriving results based on classical elasticity theory and continuum mechanics. A notable limitation of his theory was the omission of any adhesive forces between the two solids, a factor that becomes increasingly significant as the constituent materials exhibit high elasticity. However, the neglect of adhesion was understandable at the time, given the absence of experimental methods for its detection.

To formulate his theory, Hertz utilized observations of elliptical Newton's rings, which formed when a glass sphere was placed upon a lens, as the basis for postulating an elliptical pressure distribution exerted by the sphere. He subsequently employed the phenomenon of Newton's rings to experimentally validate his theory by calculating the displacement of the sphere into the lens. In 1971, Kenneth L. Johnson, K. Kendall, and A. D. Roberts (JKR) adopted Hertz's theory as a foundational element for calculating theoretical displacement or indentation depth in the presence of adhesion. Hertz's original theory can be derived from their formulation by assuming zero adhesion between the materials. Similarly, in 1975, B. V. Derjaguin, V. M. Muller, and Y. P. Toporov published an alternative theory, known in the research community as the DMT theory, which also recovered Hertz's formulations under the assumption of zero adhesion, albeit using different underlying assumptions. The DMT theory initially proved premature, requiring several revisions before gaining acceptance as another valid material contact theory alongside the JKR theory. Both the DMT and JKR theories constitute the fundamental principles of contact mechanics, serving as the basis for all transition contact models and being applied in material parameter prediction for nanoindentation and atomic force microscopy. These models are central to the field of tribology, leading Duncan Dowson to name Hertz among the 23 "Men of Tribology." Despite preceding his monumental work on electromagnetism, which Hertz himself modestly considered trivial, his research on contact mechanics has been instrumental in advancing the age of nanotechnology.

Hertz also identified the "Hertzian cone," a specific mode of fracture observed in brittle solids, which is induced by the transmission of stress waves.

Meteorology

Hertz maintained a profound interest in meteorology throughout his life, likely stemming from his interactions with Wilhelm von Bezold, who served as his professor during a laboratory course at the Munich Polytechnic in the summer of 1878. While assisting Helmholtz in Berlin, Hertz contributed several minor articles to the field, encompassing research on liquid evaporation, the development of a novel hygrometer, and a graphical method for determining the properties of moist air under adiabatic changes.

Philosophy of science

In the introduction to his 1894 treatise, Principles of Mechanics, Hertz critically examined the various "pictures" or conceptual frameworks employed to represent physics during his era. These included the Newtonian mechanics framework (centered on mass and forces), a second framework (based on energy conservation and Hamilton's principle), and his own proposed framework (uniquely founded on space, time, mass, and the Hertz principle). He evaluated these frameworks based on their 'permissibility,' 'correctness,' and 'appropriateness.' Hertz aimed to eliminate "empty assumptions" and challenged the Newtonian concept of force, particularly the notion of action at a distance. Philosopher Ludwig Wittgenstein, profoundly influenced by Hertz's work, expanded this picture theory into a comprehensive picture theory of language in his 1921 Tractatus Logico-Philosophicus, which subsequently impacted logical positivism. Wittgenstein further referenced Hertz in his Blue and Brown Books.

Death

In 1892, Hertz received a diagnosis of an infection following severe migraines, necessitating surgical intervention. He subsequently succumbed to complications arising from these operations, which aimed to alleviate his condition. A 1997 biography by Albrecht Fölsing, drawing on Hertz's diary and extensive family correspondence, suggests that his illness was likely granulomatosis with polyangiitis, a disease not formally recognized until 45 years later. Hertz passed away on January 1, 1894, in Bonn at the age of 36 and is interred in Hamburg's Ohlsdorf Cemetery.

Elisabeth Hertz (née Doll; 1864–1941), Hertz's wife, remained unmarried after his death. He was survived by his two daughters, Johanna (1887–1967) and Mathilde (1891–1975). As neither daughter married nor had children, Hertz has no direct living descendants.

Persecution under the Third Reich

Despite his family's conversion from Judaism to Lutheranism two decades prior to his birth, Hertz's legacy encountered opposition from the Nazi government in the 1930s, a regime that categorized individuals based on perceived "race" rather than religious adherence.

Hertz's name was systematically expunged from public spaces and academic institutions. Furthermore, efforts were made to rename the frequency unit, hertz, which was established in his honor, to Hermann von Helmholtz, while retaining the symbol (Hz).

His family also faced persecution due to their classification as non-Aryan. Mathilde, Hertz's youngest daughter, was dismissed from her lectureship at Berlin University following the Nazi ascent to power. Within a few years, she, her sister, and their mother emigrated from Germany and established residence in England.

Legacy and Honors

Heinrich Hertz's nephew, Gustav Ludwig Hertz, was a recipient of the Nobel Prize, and Gustav's son, Carl Helmut Hertz, is credited with inventing medical ultrasonography. His daughter, Mathilde Carmen Hertz, achieved recognition as a biologist and comparative psychologist. Furthermore, Hertz's grandnephew, Hermann Gerhard Hertz, a professor at the University of Karlsruhe, pioneered NMR-spectroscopy and published Hertz's laboratory notes in 1995.

The International Electrotechnical Commission established the SI unit hertz (Hz) in 1930 to honor Hertz, defining it as the unit for frequency, which quantifies the number of repetitions of an event per second. The Conférence générale des poids et mesures (CGPM) formally adopted this unit in 1960, thereby officially superseding the earlier designation, "cycles per second" (cps).

The Heinrich-Hertz Institute for Oscillation Research was established in Berlin in 1928. This institution is currently recognized as the Fraunhofer Institute for Telecommunications, Heinrich Hertz Institute, HHI.

In 1969, East Germany issued a commemorative Heinrich Hertz memorial medal.

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

The Submillimeter Radio Telescope, located at Mt. Graham, Arizona, and completed in 1992, bears his name.

The Hertz crater, situated on the Moon's far side just beyond the eastern limb, is named in his honor.

On his birthday in 2012, Google commemorated Hertz by featuring a Google doodle, inspired by his life's work, on its homepage.

Works

Books