Heinrich Rudolf Hertz (22 February 1857 – 1 January 1894) was a German physicist who first conclusively proved the existence of electromagnetic waves theorized by James Clerk Maxwell’s electromagnetic theory of light. Hertz proved the theory by engineering instruments to transmit and receive radio pulses using experimental procedures that ruled out all other known wireless phenomena. The scientific unit of frequency – cycles per second – was named the “hertz” in his honor.
Heinrich Rudolf Hertz was born in 1857 in Hamburg, then a sovereign state of the German Confederation, into a prosperous and cultured Hanseatic family. His father Gustav Ferdinand Hertz (originally named David Gustav Hertz) (1827–1914) was a barrister and later a senator. His mother was Anna Elisabeth Pfefferkorn.
Hertz’s paternal grandfather, Heinrich David Hertz (originally named Hertz Hertz) (1797–1862), was a businessman, and his paternal grandmother, Bertha “Betty” Oppenheim, was the daughter of the banker Salomon Oppenheim, Jr. from Cologne.
Hertz’s paternal great-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.
Heinrich Rudolf Hertz’s father and paternal grandparents had converted from Judaism to Christianity in 1834. His mother’s family was a Lutheran pastor’s family.
While studying at the Gelehrtenschule des Johanneums in Hamburg, Heinrich Rudolf Hertz 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 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.
In 1886 Hertz married Elisabeth Doll, the daughter of Dr. Max Doll, a lecturer in geometry at Karlsruhe. They had two daughters: Johanna, born on 20 October 1887 and 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.
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 January 1894. During this time he worked on theoretical on 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.
In 1892, Hertz was diagnosed with an infection (after a bout of severe migraines) and underwent operations to treat the illness. He died of Wegener’s granulomatosis at the age of 36 in Bonn, Germany in 1894, and was buried in the Ohlsdorf Cemetery in Hamburg.
Hertz’s wife, Elisabeth Hertz née Doll (1864–1941), did not remarry. Hertz left two daughters, Johanna (1887–1967) and Mathilde (1891–1975). Hertz’s daughters never married and he has no descendants.
1887 experimental setup of Hertz’s apparatus
During Hertz’s studies in 1879 Helmholtz suggested that Hertz’s doctoral dissertation be on testing Maxwell’s theory of electromagnetism, published in 1865, which predicted the existence of electromagnetic waves moving at the speed of light, and predicted that light itself was just such a wave. 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 insulators, something predicted by Maxwell’s theory. Helmholtz was sure Hertz was the most likely candidate to win it. 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.
After Hertz received his professorship at Karlsruhe he was experimenting with a pair of Reiss spirals in the autumn of 1886 when he noticed that discharging a leyden jar into one of these coils would produce a spark in the other coil. With an idea on how to build an apparatus, Hertz now had a way proceed with the “Berlin Prize” problem of 1879 on proving Maxwell’s theory (although the actual prize had expired uncollected in 1882). He 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 that was not electrically grounded for its operation. This experiment produced and received what are now called radio waves in the ultra high frequency range.
Between 1886 and 1889 Hertz would conduct 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 would send a series of papers to Helmholtz at the Berlin Academy, including papers in 1888 that showed transverse free space electromagnetic waves traveling at a finite speed over a distance. In the apparatus Hertz used, 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 long. Using the ring detector, he recorded how the wave’s 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, polarity and 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. Hertz also described the “Hertzian cone”, a type of wave-front propagation through various media.
Theoretical results from the 1887 experiment
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 (UV) 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.”
Official English translation of Untersuchungen über die Ausbreitung der elektrischen Kraft published in 1893, a year before Hertz’s death.
Hertz’s proof of the existence of airborne electromagnetic waves (referred to as “Hertzian Waves” early on) would lead to experimentation in this new form of electromagnetic radiation and the eventual development of commercial Hertzian wave based wireless telegraphy (radio), audio radio, and later television.
In 1892, Hertz began experimenting and demonstrated that cathode 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. Philipp Lenard, though, did not realize that he was producing X-rays. Hermann von Helmholtz formulated mathematical equations for X-rays. He postulated a dispersion theory before 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.
Legacy and honors
Heinrich Hertz’s nephew Gustav Ludwig Hertz was a Nobel Prize winner, and Gustav’s son Carl Helmut 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, “cycles 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.
Source : Wikipedia