Gustav Hertz Biography

Gustav Hertz's greatest fame came early in his career as the result of his collaboration with James Franck , a colleague at the University of Berlin. Hertz and Franck studied the energy changes that take place when an electron strikes an atom. Their results provided important confirmation of the Bohr theory of the atom, a theory announced only shortly before Hertz and Franck conducted their experiments. In recognition of their work, the Nobel Prize in physics was awarded jointly to Hertz and Franck in 1925.

Hertz was born in Hamburg, Germany, on July 22, 1887. His mother was Auguste Arning, and his father was Gustav Hertz, an attorney. Hertz was the nephew of the famous Heinrich Rudolf Hertz , who carried out a number of important studies on electromagnetic waves in the 1880s, and for whom the unit of frequency is now named.

Hertz received his secondary education at the Johanneum Realgymnasium in Hamburg. Between 1906 and 1911, he studied mathematics and physics at the universities of Göttingen, Munich, and Berlin. He eventually decided to concentrate on a career in experimental physics . In 1911, he earned a Ph.D. from the University of Berlin for his study of the infrared absorption spectrum of carbon dioxide.

A position as research assistant at the physical institute of the University of Berlin was offered to Hertz in 1913. When he began work at the institute, Hertz met Franck, and the two decided to collaborate on their research. The first project they undertook involved a study of the emission of electrons from a metal surface when bombarded by a stream of electrons. This type of research can be traced to studies of the photoelectric effect , the emission of electrons from a metal surface that has been exposed to light energy. In 1902, German physicist Philipp E. A. Lenard carried out some experiments on this effect. Three years later, Albert Einstein provided a theoretical explanation of Lenard's results and of the photoelectric effect in general. Hertz and Franck attempted to determine the properties of electrons emitted from a metal surface bombarded by electrons rather than by light.

In their experiment, Hertz and Franck accelerated electrons from a hot tungsten wire by means of a positively charged metal gauze placed a few centimeters from the wire. The electrons were forced to pass through an atmosphere of mercury vapor. A second positively charged wire gauze was then arranged so as to detect electrons that had collided with mercury atoms and lost energy. The experiment consisted of gradually increasing the charge on the metal gauze and tracking the loss of energy for electrons reaching the detector screen. Hertz and Franck found that this loss of energy was negligible until the potential difference reached 4.9 volts. At that point, the electron current reaching the detector dropped nearly to zero.

For some months, Hertz and Franck were not able to interpret their results. They thought that 4.9 volts might represent the ionization potential of mercury, the energy needed to remove a single electron from a mercury atom. In fact, the correct explanation for their results was already available in Niels Bohr's recently announced quantum model of the atom. Hertz and Franck eventually realized that the 4.9-volt result they observed corresponded to the transition between the first two electron energy levels (K to L) in the mercury atom. In fact, that numerical value precisely matched the energy difference that Bohr had predicted in his theory. As such, the Hertz-Franck results provided one of the first pieces of experimental confirmation for Bohr's revolutionary new theory. In recognition of this achievement, Hertz and Franck were jointly awarded the 1925 Nobel Prize in physics.

Less than a year after completing his momentous experiments, Hertz was inducted into the German army. He was seriously wounded at the battlefront in 1915 and spent more than a year in recuperation. After the war, he returned to Berlin, where he worked for three years as an unsalaried lecturer (privatdozent). He married Ellen Dihlmann in 1919, with whom he had two sons, Hellmuth and Johannes. In 1943, two years after Dihlmann died, Hertz was married a second time, to Charlotte Jollasse.

In 1920, Hertz accepted an offer of employment at the Philips Incandescent Lamp Works in Eindhoven, Netherlands. Philips was one of the first corporations to maintain a basic research laboratory. After five years at Philips, Hertz returned to Germany in October 1925 as professor of physics and director of the physical institute at the University of Halle. He remained there for three years before returning once more to Berlin. There, he became professor of physics at the Charlottenburg Technical University.

With the rise of National Socialism (the Nazi party), Hertz faced yet another career change. Unwilling to sign an oath of loyalty to the new government, he was forced to resign his post at the Technical University. Surprisingly, he was offered and accepted a job with the Siemens and Halske Company in Berlin in 1934. He remained in that job until the end of World War II, at which time he moved to the Soviet Union. He told friends that he hoped to be able to make a contribution to Soviet physics. That hope was not realized, however, since he and his German colleagues were assigned to a segregated community in Sukhumi on the Black Sea, where they worked on atomic energy, radar, and supersonics projects in isolation from Soviet scientists. At the conclusion of his -year commitment to the Soviet government, Hertz returned to East Germany, where he became director of the physics institute at Karl Marx University in Leipzig. He retired from that position in 1961 and returned to Berlin, where he died on October 30, 1975.