Heinrich Hertz

Heinrich Rudolf Hertz
"I do not think that the wireless waves I have discovered will have any practical application."
Born	February 22, 1857 Hamburg, Germany
Died	January 1, 1894 Bonn, Germany
Residence	Germany
Nationality	German
Field	Physicist and Electronic Engineer
Institutions	University of Kiel University of Karlsruhe University of Bonn
Alma mater	University of Munich University of Berlin
Academic advisor	Hermann von Helmholtz
Known for	Electromagnetic radiation

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

Biography

Early years

Heinrich Rudolf Hertz was born in Hamburg, Germany on February 22, 1857, the oldest of five children of Gustav Ferdinand Hertz and Anna Elisabeth Pfefferkorn. Hertz's paternal grandfather converted from Judaism to Lutheranism and married into a Lutheran family. His father was an attorney who belonged to the Hamburg senate, his mother the daughter of a doctor. Both Hertz's father and mother were Lutheran.

In his youth, Hertz showed an advanced aptitude for mathematics, and took extra geometry lessons on Sundays. He was always ranked first in his class. He also had a strong affinity for languages, quickly learning Latin, Greek, Arabic and Sanskrit. At the same time, he showed a facility for the practical in drawing, sculpture and handicraft. To combine these interests, he at first pursued a career in engineering construction.

University training

In 1875 Hertz spent a year in a construction department in Frankfort. He then attended the polytechnic in Dresden, and was particularly fond of the mathematical lectures given there, but also took a keen interest in history and philosphy. After only a semester in Dresden, he joined the military and spent one year in active duty. In 1877 he enrolled at the polytechnic in Munich, changing his major to physics. During this time, encouraged by his teachers, he studied the original works of famous physicists such as Isaac Newton, Gottfried Leibnitz, Joseph Lagrange and Pierre-Simon Laplace.

Hertz was dissatisfied with the level of physics education in Munich, so he moved to Berlin. There, he studied in the laboratory of Hermann von Helmholtz, and won a prize for the investigation of inertia in electric currents. Hertz was able to show that the intertia of a current was small or nonexistent, this result dovetailing with theoretical research Helmholtz was doing on electromagnetic theory. During this period, he attended lectures by Gustave Kirchhoff on mechanics. Although he would become famous for his electrical researches, Hertz's works on mechanics were also substantial.

In 1779, he considered, but turned down, a proposal by Helmholtz to determine the existence of an electric current in a dieletric, the insulating material between two conductors used to store electric charge. James Clerk Maxwell had predicted the existence of such currents. Hertz convinced Helmholtz that the study would take longer than it was worth.

Hertz obtained his PhD in 1880, and continued to work in Helmholtz's laboratory until 1883. As an assistant to Helmholtz in Berlin, Hertz submitted memoirs 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.

He also published articles on what was to become known as the field of contact mechanics. Hertz analyzed the mechanical deformations of two colliding elastic spheres, and from this arrived at a new definition of hardness he hoped would be of some use to mineralogists.

In 1883, Hertz accepted 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.

Photoelectric effect

In 1886, Hertz began a series of experiments to clarify some of the theoretical predictions of Maxwell's electromagnetic theory. At this time, he discovered the utility of a spark gap, and realized that its regular effects would enable him to investigate the questions left unanswered when he turned down Helmholtz's research idea. While undertaking these experiments, he noticed what was at first an unwanted side effect: that a spark gap discharged more easily when another spark gap from the opposite side of the room was activated. Hertz traced this effect to the presence of ultraviolet light waves generated from the second spark gap, which, when it reached the first, promoted current flow, thus making the discharge easier. This phenomenon was later called the photoelectric effect, and became the topic of a famous paper by Albert Einstein that won him a Nobel Prize. After solving this problem, Hertz returned to the original purpose of his research.

Electromagnetic waves

Hertz wanted to show that the speed of electromagnetic waves was finite in air and in a vacuum, thus concluding that air and dielectric insulators act in the same manner. He at first noticed that he obtained a much greater reaction at his second spark gap than the normal laws of the propagation of force, which generally predict a diminished action with distance, would allow. He realized that he was producing electromagnetic waves that retain their power of action over longer distances. Not only was he able to produce and detect these waves, but he also determined their properties, such as reflection and refraction. His results, which he published in 1887, were quickly accepted by the scientific community. His work, when publicized by others such as Oliver Lodge and George Fitzgerald, who were working in the same field, effectively launched an all-out effort to use the pheomena for the purposes of communication, resulting in the invention of radio in the next decade. One of Hertz's students, Philipp Lenard, continued Hertz's electrical researches.

After his work on electromagnetic waves, Hertz turned to one of his original fields of interest, mechanics. He wrote an important work that attempted to remove ambiguity and confusion in the various presentations up to that time.

In 1892, an infection 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 36 in Bonn, Germany.

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

Discoveries

In 1887, Hertz made observations of the photoelectric effect and of the production and reception of electromagnetic waves, published in the journal Annalen der Physik. His receiver consisted of a coil with a spark gap, whereupon a spark would flash in the presence of electromagnetic 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 the waves and the receiver absorbed ultraviolet radiation that was strengthening the spark.

1887 experimental setup of Hertz's apparatus.

When removed, the spark length would increase. He observed no decrease in spark length when he substituted quartz for glass. Hertz concluded that ultraviolet light somehow increased the conductivity of the intervening air, and submitted a memoir on the subject. He did not further pursue investigation of this effect, since it was not the main focus of his research at the time, nor did he make any attempt at explaining how the observed phenomenon was brought about. His experiments did, however, generate a tremendous amount of interest among scientists.

Radio waves

In 1887, Hertz experimented with radio waves in his laboratory. Hertz used a Ruhmkorff coil-driven spark gap and one meter wire pair as a radiator. Metallic spheres were present at the ends to adjust the electrical properties of the circuit. His receiver was not much more than a curved wire with a spark gap.

Through experimentation, he proved that electromagnetic waves can travel over some distance through the air. 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 waves. Hertz had positioned the oscillator about 12 meters from a zinc reflecting plate to produce standing waves, similar to the way a musical note is produced by sound waves reverberating in a tube of a set length. Each wave was about four meters long. Using the ring detector, he recorded how the magnitude and direction of the waves varied. Hertz failed, however, to conclusively measure the speed of the waves. At first he thought the speed was infinite; another series of measurements showed a large discrepancy between the velocity of waves in a wire and through air. Later investigators resolved these differences, and showed that the waves move at the speed of light.

X-Rays

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 of various materials which were later called X-rays.

Legacy

Like many of the scientists of his time, Hertz did not understand the wide-ranging applications of his production and detection of electromagnetic radiation. His original purpose was to demonstrate certain principles contained in Maxwell's theory. Had not others been working in the same field, such as Lodge and Fitzgerald, his work and its applications might not have been well understood.

Of his discovery, he said:

"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."

His discoveries would later be more fully understood by others and be part of the new "wireless age."

It took more practical people like Nikola Testla, Guglielmo Marconi, and, perhaps, Oliver Lodge, to understand the practical advantage of using the waves to send messages over long distances. Hertz did not live long enough to see the blossoming of the new technology based on his discoveries.

Honors

Hertz's autograph

The hertz (Hz) was established in Hertz's honor 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 theoretical achievements. A crater that lies on the far side of the Moon, just behind the eastern limb, is named in his honor.

See also

People Hans Christian Ørsted David Edward Hughes Reginald Aubrey Fessenden Guglielmo Marconi Gustav Ludwig Hertz Hermann von Helmholtz James Clerk Maxwell Nikola Tesla Wilhelm Röntgen Lists and histories Electromagnetism timeline Timeline of mechanics and physics List of physicists Radio history Wireless telegraphy List of people on stamps of Germany List of physics topics

Electromagnetic radiation Microwave Luminiferous aether Other University of Bonn University of Karlsruhe Radio

References

ISBN links support NWE through referral fees

• Buchwald, Jed Z. 1994. The Creation of Scientific Effects: Heinrich Hertz and Electric Waves. Chicago: University of Chicago Press. ISBN 0226078876
• Dahl, P.F. 1997. Flash of the Cathode Rays: A History of J.J. Thomson's Electron. Bristol: Institute of Physics Pub. ISBN 0750304537
• Lützen, Jesper. 2005. Mechanistic Images In Geometric Form: Heinrich Hertz's Principles of Mechanics. New York: Oxford University Press. 50-62. ISBN 0198567375
• Appleyard, Rollo, "Pioneers of electrical communication." London, Macmillan and co., limited, 1930. LCCN 30011090 //r87 ( ed. memoirs were published in Electrical communication.)
• Bodanis, David. Electric Universe: How Electricity Switched on the Modern World. New York: Three Rivers Press, 2005. ISBN 0-307-33598-4
• Buchwald, Jed Z., "The creation of scientific effects : Heinrich Hertz and electric waves." Chicago : University of Chicago Press, c1994. ISBN 0-226-07887-6 (alk. paper) ISBN 0-226-07888-4 (pbk.; alk. paper) LCCN 93041783
• Susskind, Charles, "Heinrich Hertz : a short life." San Francisco, CA : San Francisco Press, c1995. ISBN 0-911302-74-3
• 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., [1897?], 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. [distributor], c1988. ISBN 0-87942-710-8 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 0-7923-4653-X (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)
• Maugis, D., "Contact, Adhesion and Rupture of Elastic Solids." ISBN 3-540-66113-1, (Springer-Verlag)

External links

• Kim Breitfelder (Program Manager) and Mike Geselowitz, (Director), "Heinrich Hertz." IEEE History Center, IEEE 2006.
• John D. Jenkins, "The Discovery of Radio Waves - 1888; Heinrich Rudolf Hertz (1847-1894)." sparkmuseum.com.
• Francesco Errante, "Hertzian Radiation, (better known as radio-waves) : what it is and how it happens." Radiondistics.com.
• Russell Naughton, "Heinrich Rudolph (alt: Rudolf) Hertz, Dr : 1857 - 1894." Adventures in CyberSound.
• "Heinrich Rudolf Hertz." Institute of Experimental Physics, University of Debrecen.
• Wilhelm Mosel, "Buildings Integral to the Former Life and/or Persecution of Jews in Hamburg - Eimsbüttel/Rotherbaum." Deutsch-Jüdische Gesellschaft, Hamburg.
• "Heinrich Hertz." The First Electronic Church of America.
• "Heinrich Rudolph Hertz (1857 - 1894)." Corrosion-doctors.org.
• Struan Robertson, "Heinrich Hertz (1857 - 1894)." uni-hamburg.de. (ed. Hertz' portrait in the Hamburg City Hall.)
• Electric waves: being researches on the propagation of electric action with finite velocity through space by Heinrich Rudolph Hertz. Cornell University Library Historical Monographs Collection. {Reprinted by} Cornell University Library Digital Collections

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