Known for his collaborations with fellow colleague James Franck at the University of Berlin, German scientist Gustav Hertz (1887-1975) achieved fame and success early in life when he and Franck documented the changes in energy that occur when an electron strikes an atom. The information the two men discovered confirmed the quantum theory put forth by physicist Neils Bohr regarding the amount of energy that can be absorbed by an atom. For their work Hertz and Franck received the Nobel Prize in Physics in 1925. Hertz was also involved in some of the Soviet Union's early research into atomic energy.
Hertz was born on July 27, 1887, in Hamburg, Germany to Auguste Arning and Gustav Hertz, an attorney. His uncle, Heinrich Rudolf Hertz, had studied electromagnetic waves in the 1880s and he is the man for whom the unit of frequency is now named. Hertz first attended the Johanneum Realgymnasium in Hamburg, and after graduating in 1906 he began his college education at the University of Göttingen, majoring in mathematics and physics. He later transferred to the University of Münich and eventually ended up at the University of Berlin where he completed his education. During his studies Hertz developed an interest in the field of experimental physics and ultimately finished his studies in this field. In 1911, he graduated from the University of Berlin with a Ph.D., his doctorate studies focusing on the infrared absorption spectrum of carbon dioxide with relation to pressure and partial pressure.
Bombarded Metal with Electrons
In 1913 Hertz was offered the position of research assistant at the University of Berlin's Physical Institute. It was at this post that he first met Franck. Interested in the same questions of experimental physics, the two men decided to pursue their research collaboratively. The first assignment they resolved to concentrate on involved bombarding a metal surface with a stream of electrons and then studying the emission of electrons from the metal, thereby determining the effect the impact of electrons had on atoms. They were especially interested in the changes this bombardment would have on the atomic energy level. This kind of research was similar to past studies of the photoelectric effect, which occurs when a metal surface is exposed to light energy and is measured through the emission of electrons from the metal surface. A study of the photoelectric effect was undertaken in 1902 by German physicist Philipp E. A. von Lenard, and a short time later Albert Einstein figured out a theory to explain von Lenard's data and the photoelectric effect in general. Taking this kind of experiment one step further, Hertz and Franck attempted to glean the make-up of electrons given off by a metal surface when it was bombarded by electrons instead of light.
Hertz and Franck sped up electrons by heating up a wire by means of a positively charged metal gauze placed a short distance from the wire. They forced the electrons to pass through a vapor of mercury and then placed a second wire gauze to catch the electrons that had not bumped into the mercury atoms and had therefore not lost their energy; the electrons that had lost their energy would not hit the second gauze, but would be motionless. They discovered that the loss of energy was negligible at the temperature they started from and so they increased the charge on the metal gauze and continued to track the loss of energy for electrons reaching the screen. They still measured little loss of energy as they slowly increased the voltage. The measurements remained relatively constant until they reached 4.9 volts. At that point, the electron current reaching the detector plunged almost to zero.
For a while, Hertz and Franck were at a loss as to how to interpret their results. They soon found, however, that Bohr's recently announced theory on the quantum model of the atom fit their research perfectly. Hertz and Franck came to the realization that the 4.9 volt result they observed matched up with the change between the first two electron energy levels in the mercury atom. In fact, the number 4.9 matched exactly the energy difference Bohr had predicted in his theory. The results of Hertz and Franck's experiments offered up one of the first pieces of experimental confirmation for Bohr's revolutionary new theory. This research "demonstrated the quantitative relations between the series of spectra lines and the energy losses of electrons in collision with atoms corresponding to the stationary energy states of the atoms," according to Hertz's biography posted on the Nobel Prize Website. Bohr's theory, for which the physicist had won the Nobel Prize in 1922, was an early model of the structure of the atom that has since become common knowledge. In this model the electrons traveled around a nucleus in numerous orbits which could be determined by the theory of quantum conditions. A quantum is the smallest amount by which certain physical quantities can change, especially concerned with electromagnetic radiation. It is the way in which scientists can examine and understand movement at the atomic level.
Awarded the Nobel Prize for Physics
Shortly after his groundbreaking experiment was completed, Hertz was drafted into the German army; the year was now 1914 and World War I had begun. He was gravely wounded in battle in 1915, and his wound was so severe that his recuperation took over a year. At the end of World War I Hertz moved back to Berlin where, in 1917, he was offered a position as a lecturer, or privatdozent. While this proved a good position from which to gain experience, the position was, unfortunately, unpaid.
In 1919 Hertz married Ellen Dihlmann. The couple eventually had two sons, Hellmuth and Johannes, and both boys eventually became involved in physics. Hellmuth Hertz became a professor at the Technical College in Lund, and Johannes Hertz went on to work at the Institute for Optics and Spectroscopy at the German Academy of Sciences in Berlin. Fortunately for Hertz and his growing family, in 1920 he was offered a position at the Philips Incandescent Lamp Works in Eindhoven, Netherlands, and he and his family moved to the Netherlands where they stayed for five years. The Philips Incandescent Lamp Works was one of the first major corporations to establish and run a full-time research laboratory. His new employment allowed Hertz freedom to continue with his research work.
In 1925 Hertz and his family again returned to Germany, where Hertz had been offered the position of professor of physics at the University of Hale. He also took over as the director of the Physical Institute at that university. In that same year, in recognition of his earlier work with Franck, the two men were jointly awarded the 1925 Nobel Prize for Physics for their work with atomic energy.
Hertz stayed at the University of Hale for three years before he once again moved back to Berlin. In 1928 he became a professor of physics at the Charlottenburg Technical University. He was also entrusted with the task of rebuilding the school's Physics Institute, a job that required much of his time. Still, Hertz also continued his work in physics, and discovered a method of separating neon isotopes using a diffusion cascade.
Moved to Soviet Union
In the 1930s National Socialism gained strength in Germany through the growth of the Nazi Party. Hertz did not approve of the fascism that was the backbone of the Nazi party and he was unwilling to pledge his allegiance to this new government. Because of this, Nazi officials forced him to resign from his position at the Charlottenburg Technical University. Despite his refusal to back the Nazi party, however, and much to his surprise, Hertz was offered a position at the Siemens and Halske Company in Berlin in 1935. He remained at that position, continuing his research, throughout World War II. Tragically, his wife Ellen died in 1941, and two years later he remarried, to Charlotte Jollasse. At the close of World War II, with the German economy now in ruins, things became increasingly turbulent in Germany, and in 1945 Hertz and his family moved to the Soviet Union.
Although Hertz had hoped to contribute to Soviet physics, he and other German colleagues who had fled Germany with him were not allowed to participate to any great extent in government-sponsored science programs. Swept up in the fervor of communism, the Soviets moved these German scientists to a remote area in Sukhumi near the Black Sea that was separated from the rest of the country. More significantly, for Hertz, was the fact that Sukhumi was far removed from the Soviet scientists he had hoped to work with. However, because he had made a commitment to work in the Soviet Union for ten years, he stayed in the Soviet Union, working on supersonics, radar, and continuing his research into atomic energy. Although he was seemingly hidden away, Hertz's work did not go unnoticed. In 1951 he won the Stalin Prize for his work on atomic energy. Hertz stayed in the Soviet Union until he finished his term of employment in 1954. After living briefly in East Germany, he was offered and accepted the position of director at the Karl Marx University's Physics Institute, located in Leipzig, Germany.
Hertz retired from Karl Marx University in 1961, at which time he was made professor emeritus. He returned for the last time to his former home in what still then East Berlin, and died there on October 30, 1975.
Throughout his life Hertz published papers detailing the research he had done, and his work furthered the work of others in the study of atomic energy. He also published frequently with other scientists, including Franck and other colleagues he worked with along the way. His papers run the gamut from the quantitative exchange of energy between electrons and atoms to the measurement of ionization potentials. He also authored some papers concerning the separation of isotopes. Hertz was a member of several prestigious scientific organizations, including the German Academy of Sciences in Berlin, and the Göttingen Academy of Sciences. In addition to receiving the Max Planck Medal from the German Physical Society, he was also named an honorary member of the Hungarian Academy of Sciences, a member of the Czechoslovakian Academy of Sciences, and was a foreign member of the Academy of Sciences of the USSR.
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Gustav Hertz–Biography, Nobel Prize Website,http://nobelprize.org/physics/laureates/1925/hertz-bio.html (April 5, 2005).
HERTZ, GUSTAV (1887–1975), German physicist and Nobel Prize winner, son of a Jewish father. Born in Hamburg, he became an assistant in the Physical Institute at Berlin in 1913. He was severely wounded in World War i, and subsequently worked at Eindhoven in the Netherlands. In 1925 he became professor of physics and director of the Physical Institute at Halle, and in 1928 at the Technische Hochschule. He resigned "for political reasons" in 1934, and became director of the Siemens Research Laboratory ii. He remained in Germany throughout World War ii and subsequently became professor of physics at the University of Leipzig in the German Democratic Republic. He and James *Franck were awarded jointly the Nobel Prize for physics in 1925 for their discovery of the laws governing impact between an electron and an atom. Hertz converted to Christianity. He was a nephew of Heinrich Rudolph Hertz (1857–1894), the discoverer of electromagnetic waves, who was the son of a baptized Jewish father and a Christian mother.
N.H. Heathcote, Nobel Prize Winners in Physics (1953), 230–48.
[J. Edwin Holmstrom]