Electromagnetic waves In 1864, Scottish mathematical physicist
James Clerk Maxwell proposed a comprehensive theory of electromagnetism, now called
Maxwell's equations. Maxwell's theory predicted that coupled
electric and
magnetic fields could travel through space as an "
electromagnetic wave". Maxwell proposed that light consisted of electromagnetic waves of short wavelength, but no one had been able to prove this, or generate or detect electromagnetic waves of other wavelengths. During Hertz's studies in 1879, Helmholtz suggested that Hertz's doctoral dissertation be on testing Maxwell's theory. 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. In the autumn of 1886, after Hertz received his professorship at Karlsruhe, he was experimenting with a pair of
Riess spirals when he noticed that discharging a
Leyden jar into one of these coils produced a spark in the other coil. With an idea on how to build an apparatus, Hertz now had a way to 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
dipole antenna consisting of two collinear one-meter wires with a spark gap between their inner ends, and zinc spheres attached to the outer ends for
capacitance, as a radiator. The antenna was excited by pulses of high voltage of about 30
kilovolts applied between the two sides from a
Ruhmkorff coil. He received the waves with a resonant single-
loop antenna with a
micrometer spark gap between the ends. This experiment produced and received what are now called
radio waves in the
very high frequency range.
dipole resonator consisting of a pair of one-meter copper wires with a 7.5 mm spark gap between them, ending in 30 cm zinc spheres. In the apparatus Hertz used, the electric and magnetic fields radiated 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,
polarization, and
reflection of the waves were also measured by Hertz. These experiments established that light and these waves were both forms of electromagnetic radiation obeying the Maxwell equations. Hertz did not realize the practical importance of his
radio wave 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 applications of his discoveries, Hertz replied, leading to the wide use of radio communication.
Cathode rays In 1883, he tried to prove that the cathode rays are electrically neutral and got what he interpreted as a confident absence of deflection in an electrostatic field. However, as
J. J. Thomson explained in 1897, Hertz placed the deflecting electrodes in a highly-conductive area of the tube, resulting in a strong screening effect close to their surface. Nine years later, 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. However, Lenard 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.
Photoelectric effect 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 radiation (UV). 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 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.
Contact mechanics , which translates as
At this site, Heinrich Hertz discovered electromagnetic waves in the years 1885–1889 In 1881 and 1882, Hertz published two articles on what was to become known as the field of
contact mechanics, which proved to be an important basis for later theories in the field.
Joseph Valentin Boussinesq published some critically important observations on Hertz's work, nevertheless establishing this work on contact mechanics as 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 flaw 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 at the time, however, as there were no experimental methods of testing for it. 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.
Kenneth 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 1971. 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 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. These models are central to the field of
tribology and he was named as one of the 23 "Men of Tribology" by
Duncan Dowson. Despite preceding his great work on electromagnetism (which he himself considered with his characteristic soberness to be trivial
Meteorology Hertz always had a deep interest in
meteorology, probably derived from his contacts with
Wilhelm von Bezold (who was his professor in a laboratory course at the Munich Polytechnic in the summer of 1878). As an assistant to Helmholtz in Berlin, he contributed a few minor articles in the field, 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.
Philosophy of science In the introduction of his 1894 book
Principles of Mechanics, Hertz discusses the different "pictures" used to represent physics in his time including the picture of
Newtonian mechanics (based on mass and forces), a second picture (based on
conservation of energy and
Hamilton's principle) and his own picture (based uniquely on space, time, mass and the
Hertz principle), comparing them in terms of 'permissibility', 'correctness' and 'appropriateness'. Hertz wanted to remove "empty assumptions" and argue against the Newtonian concept of
force and against
action at a distance. ==Death==