Hertz, Heinrich Rudolf (1857–1894)
Heinrich Hertz was born into a well-to-do German family in Hamburg on February 22, 1857. He was an exceptionally talented student, doing equally well in the humanities and sciences. He read extensively, tried his hand at sculpting, and even built scientific apparatus on a lathe at home. After a year of military service, Hertz studied structural engineering in Munich, but gave it up for physics when he realized he had the ability to contribute something substantial to that field. At the age of 20 he wrote to his parents: "... I would rather be a great scientific investigator than a great engineer, but I would rather be a second-rate engineer than a second-rate investigator."
In 1878 Hertz enrolled at the University of Berlin to study under Hermann von Helmholtz, the leading German physicist of the time. He obtained his degree magna cum laude in 1880 with a theoretical dissertation on the electromagnetic induction of currents in conducting spheres rotating in a magnetic field. He remained at the Berlin Physics Institute as assistant to Helmholtz until 1883; during these years he published fifteen research papers on a great variety of topics in physics.
In 1883 Hertz was appointed Privatdozent for mathematical physics at Kiel, and after two years became a full professor at the Technische Hochschule in Karlsruhe. In 1889 Hertz left Karlsruhe to assume his last academic post as Professor of Physics at the Friedrich-Wilhelm University in Bonn. Five years later, following a long period of declining health and many painful operations, Heinrich Hertz died in Bonn of blood poisoning on January 1, 1894, a few months before his thirty-seventh birthday.
After Hertz's death Helmholtz paid tribute to his former student as a "consummate physicist," who uniquely combined mathematical ability, theoretical insight, and experimental skill. These qualities enabled Hertz to make many important contributions to physics, of which only those relating more directly to energy are outlined below.
Hertz's most direct involvement with all aspects of the energy question was the research he did to prepare his inaugural lecture to the faculty at the Technische Hochschulein Karlsruhe, delivered on April 20, 1885 and entitled: "On the Energy Balance of the Earth." The manuscript for this lecture has only recently been found and published in both German and English. Although written more than a century ago, this impressive document records both Hertz's insightful view of the Earth's energy situation at that time and his remarkably good order-of-magnitude estimates of the energy sources then known to be available to the Earth.
The most important contribution Hertz made in this inaugural lecture was his prediction, based on his estimates of the energy sources available, that ultimately the Earth was completely dependent on the Sun for the light and heat it needed to support life. Of course, this picture would change after Henri Becquerel discovered radioactivity in 1896, and thus introduced the nuclear age of physics.
The research that brought Hertz undying fame as a physicist was that on electromagnetic waves, performed in 1886–1889 in Karlsruhe. By his elegant experiments he confirmed the theoretical prediction of James Clerk Maxwell that electromagnetic waves in what are now called the microwave and radiowave regions of the spectrum travel through a vacuum at the speed of light. He also demonstrated that microwaves of 66-cm wavelength exhibit the same properties of reflection, refraction, interference and polarization as do light waves. Hertz's research also provided conclusive evidence that electromagnetic energy cannot be transmitted from place to place instantaneously, but only at a finite velocity, that of light. Hertz never considered the possibility of using electromagnetic waves for wireless communication over long distances. His sole interest was in understanding the world about him — "the intellectual mastery of nature," in the words of Helmholtz.
In the course of his research on electromagnetic waves Hertz discovered the photoelectric effect. He showed that for the metals he used as targets, incident radiation in the ultraviolet was required to release negative charges from the metal. Research by Philipp Lenard, Wilhelm Hallwachs, J. J. Thomson, and other physicists finally led Albert Einstein to his famous 1905 equation for the photoelectric effect, which includes the idea that electromagnetic energy is "quantized" in units of hν, where h is Planck's constant and ν is the frequency of the "bundle of energy" or "photon." Einstein's equation is simply a conservation-of-energy equation, stating that the energy of the incident photon (hν) is used partially to provide the energy needed to extract the negative particle (electron) from the metal, with the rest of the photon's energy going into the kinetic energy of the extracted electron. Hertz's discovery of the photoelectric effect in 1887 therefore led eventually to Einstein's energy-conservation equation for submicroscopic systems.
Hertz's last piece of experimental work was done when his health was deteriorating and he was devoting most of his research time to intensive theoretical work on the logical foundations of mechanics. In 1892 in his laboratory in Bonn, he discovered that cathode rays could pass through thin metallic foils. He published a short paper on the subject, but did not pursue the matter further. Instead he handed his apparatus and his ideas over to Philipp Lenard (1862–1947), his assistant in Bonn. Lenard pushed Hertz's suggested research so far that Lenard received the Nobel Prize in Physics in 1905 "for his work on cathode rays."
During his brief life Hertz moved back and forth with extraordinary ease and great dedication between intense theoretical study at his desk and equally demanding experimental work in his laboratory. As Robert S. Cohen wrote of Hertz in 1956, "His like is rare enough within science ... but his fusion of theory and experiment with a creative interest in philosophical and logical foundations [as revealed particularly in his Principles of Mechanics] is nearly unique."
Bibliography
Fölsing, A. (1997). Heinrich Hertz. Eine Biographie. Hamburg: Hoffmann und Campe.
Hertz, H. G. and Mulligan, J. F., eds. (1998). "Der Energiehaushalt der Erde," von Heinrich Hertz, Fridericiana (Zeitschrift der Universität Karlsruhe), Heft 54:3–15.
McCormmach, R. (1972). "Hertz, Heinrich Rudolf." In Dictionary of Scientific Biography, ed. Charles Coulston Gillispie, Vol. 6, 340–350. New York: Scribner.
Mulligan, J. F., ed. (1994). Heinrich Rudolf Hertz: A Collection of Articles and Addresses; with an Introductory Biography by the editor. New York: Garland.
Mulligan, J. F., and Hertz, H. Gerhard. (1997). "An Unpublished Lecture by Heinrich Hertz: 'On the Energy Balance of the Earth.'" American Journal of Physics 65: 36–45.
Planck, M. (1894). Heinrich Rudolf Hertz: A Memorial Address. English translation in Heinrich Rudolf Hertz: A Collection of Articles and Addresses (1994), ed. J. F. Mulligan, pp. 383–403. New York: Garland.
Susskind, C. (1995). Heinrich Hertz. A Short Life. San Francisco: San Francisco Press, Inc.
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