Everything about Heinrich Hertz totally explained
Heinrich Rudolf Hertz was a German physicist, born in Hamburg, and educated at the University of Berlin. From 1885 to 1889 he was a professor of physics at the technical school in Karlsruhe and after 1889 a professor of physics at the University in Bonn. Hertz clarified and expanded the electromagnetic theory of light that had been put forth by the British physicist James Clerk Maxwell in 1884.
Biography
Early years
Hertz was born in
Hamburg,
Germany, into a prosperous and cultured
Hanseatic family. His father, Gustav Ferdinand Hertz, was a barrister and later a senator. His mother was the former Anna Elisabeth Pfefferkorn. He had three younger brothers and one younger sister.
While studying at the
gymnasium 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, 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 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.
Meteorology
Hertz had always had a deep interest in
meteorology probably derived from his contacts with
Wilhelm von Bezold (he was Hertz's professor in a laboratory course at the
Munich Polytechnic in the summer of 1878). Hertz, however, didn't contribute much to the field himself except for some early article 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 1881–1882, 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. 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 adhesion.
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
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, 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 doesn't absorb UV radiation. Hertz concluded his months of investigation and reported the results obtained. He didn't 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 the
Hertz antenna receiver. This is a set of terminals that isn't electrically grounded for its operation. He also developed a transmitting type of
dipole antenna, which was a center-fed driven element for transmission
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 didn't 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. 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
history of 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 didn't realise 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 can't see with the naked eye. But they're 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". In bulk, Hertz' experiments 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, didn't 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 didn't work with actual X-rays.
Death at age 36
In
1892, an infection was diagnosed (after a bout of severe
migraines) and Hertz underwent some operations to correct the illness. He died of
Wegener's granulomatosis at the age of 36 in
Bonn, Germany in
1894.
His wife, Elizabeth Hertz (maiden name: Elizabeth Doll) didn't marry again. Heinrich Hertz left two daughters, Joanna and Mathilde. Subsequently, all three women left Germany in the 1930s 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 so he doesn't have any descendants, according to the book by Susskind.
Legacy
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 1964.
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 radioelectronics 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.
Nazi revisionism
Although Hertz wouldn't 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 what was construed as having been "
Jewish ancestry." Hertz was a Lutheran; and although his father’s family had been Jewish, his father had been converted to Catholicism before marrying. One additional fact gives this historical moment a poignant clarity. By this point in German history, Hertz himself had been dead for 26 years. The painting has since been returned to public display.
Honors
Hertz was honored by Japan with the
Order of the Sacred Treasure.
Further Information
Get more info on 'Heinrich Hertz'.
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