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Heinrich Rudolf Hertz (February 22, 1857 - January 1, 1894), was the German physicist and mechanician for whom the hertz, the SI unit, is named. In 1888, he was the first to demonstrate the existence of electromagnetic radiation by building apparatus to produce UHF radio waves.

Biography

Early years

Hertz was born in Hamburg, Germany, to Gustav Ferdinand Hertz, whose father converted from Judaism to Lutheranism and married into a Lutheran family, and Anna Elisabeth Pfefferkorn, herself a Lutheran. His father was an advisor in Hamburg, his mother the daughter of a doctor. While going to school at the University of 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. He was a student of Gustav R. Kirchhoff and Hermann von Helmholtz. He obtained his PhD in 1880, and remained a pupil of Helmholtz until 1883 when he took a post as a lecturer in theoretical physics at the University of Kiel. In 1885 he became a full professor at the University of Karlsruhe where he discovered electromagnetic waves.

Meteorology

Hertz had always had a deep interest in meteorology probably derived from his contacts with Willhelm von Bezold (he 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 for 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. J. F. Mulligan and H. G. Hertz, "On the energy balance of the Earth", American Journal of Physics, vol. 65, pp 36-45

Electromagnetic research

Hertz helped establish the photoelectric effect (which was later explained by others) 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, whereupon a spark would be seen upon detection of EM waves. He placed the apparatus in a darkened box in order to see the spark better; he observed, however, 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. Earlier in 1886, Hertz developed a dipole antenna. This antenna is a center-fed driven element for transmitting or receiving radio frequency energy. 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 the 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.

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 traverse waves. Hertz had positioned the oscillator about 12 meters from a zinc reflecting plate to produce standing waves. Each wave was about four meters. 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.

The Hertzian cone was first described by Hertz as a type of wave-front propagation through various media. His experiments help expand the field of electromagnetism transmission and his apparatus was developed further by others in the history of radio. Hertz also found that radio waves could be transmitted through different types of materials, and were reflected by others. This was key to radar and was investigated and exploited later by others. Hertz did not understand the practical importance of his experiments. He stated that,

"It's of no use whatsoeverthis 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." Eugenii Katz, "[http://chem.ch.huji.ac.il/~eugeniik/history/hertz.htm Heinrich Rudolf Hertz ". Biographies of Famous Electrochemists and Physicists Contributed to Understanding of Electricity, Biosensors & Bioelectronics.
Asked about the ramifications of his discoveries, Hertz replied,
"Nothing, I guess." Katz, "Heinrich Rudolf Hertz ".
His discoveries would later be more fully understood by others and be part of the new "wireless age". In bulk, Hertz' experiment explain reflection, refraction, polarization, interference, and velocity of electric waves.

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.

Death and afterwards

In 1892, a bone malignancy was diagnosed (after a bout of severe migraines) and Hertz underwent some operations to correct the illness. He died of blood poisoning at the age of 37 in Bonn, Germany. 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, a measurement of the number of times that a repeated event occurs per unit of time (also called "cycles per sec" (cps)). In 1969 (East Germany), there was cast a Heinrich Hertz memorial medal. 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". It was adopted by the CGPM (Conférence générale des poids et mesures) in 1960. A crater that lies on the far side of the Moon, just behind the eastern limb, is named in his honor.

See also

People

Lists and histories

Electromagnetic radiation

Other


Further reading

  • Appleyard, Rollo, "Pioneers of electrical communication". London, Macmillan and co., limited, 1930. LCCN 30011090 //r87 ( ed. memoirs were published in Electrical communication.)
  • Buchwald, Jed Z., "The creation of scientific effects : Heinrich Hertz and electric waves". Chicago : University of Chicago Press, c1994. ISBN 0226078876 (alk. paper) ISBN 0226078884 (pbk.; alk. paper) LCCN 93041783
  • Susskind, Charles, "Heinrich Hertz : a short life". San Francisco, CA : San Francisco Press, c1995. ISBN 0911302743
  • Lodge, Oliver, "The work of Hertz and his successors : being a description of signalling across space without wires by electric waves, "The Electrician" series. Signalling without wires. London : "The Electrician" Printing and Pub. Co., *, 2nd ed.
  • Bryant, John H., "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 : Institute of Electrical and Electronics Engineers ; Piscataway, NJ : IEEE Service Center, Single Publication Sales Dept. *, c1988. ISBN 0879427108 LCCN 88176362 (ed. 1988 IEEE/MTT-S Hertz Centennial Celebration exhibition at the 1988 MTT-S International Microwave Symposium)
  • Baird, Davis. (ed.), Hughes, R. I. G. (ed.), and Nordmann, Alfred, (ed.), "Heinrich Hertz : classical physicist, modern philosopher". Boston studies in the philosophy of science. v. 198, Dordrecht ; Boston : Kluwer Academic Publishers, c1998. ISBN 079234653X (hardcover; alk. paper) LCCN 97023406
  • Ducretet, E., "La télégraphie hertzienne sans fils : expériences de Henri Hertz" (Tr., Hertzian telegraphy without wire: experiments of Henri Hertz). Guise (Aisne) : s.n., 1898 (Baré)

References, external links, and other articles

Citations

Websites

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