(1874-1957) Bavarian Theoretician and Experimentalist, Atomic Physicist
Johannes Stark is famous for his discovery of what is now known as the Stark effect, the division of spectral lines in an electric field, work that was recognized by the 1919 Nobel Prize in physics.
Stark was born in Schikenhof, Bavaria, on April 15, 1874. His father, a landowner, sent the boy to secondary schools in Bayreuth and Regensburg. Stark then went on to the University of Munich, where he studied physics, mathematics, chemistry, and crystallography. He wrote his dissertation on the phenomenon of Newton’s rings in a dim medium, and received his Ph.D. in 1897. For the next three years, he worked as a research assistant at the Physics Institute at the University of Munich.
In 1900, Stark moved to the University of Gottingen to work as an unsalaried lecturer. However, two years later, his fortunes changed when he predicted that the high-velocity canal rays (positively charged ions produced in a cathode ray tube) should exhibit the Doppler effect (an apparent change in the frequency of a wave motion, caused by relative motion between the source and the observer). In 1905, he confirmed this prediction by demonstrating the frequency shift in hydrogen canal rays. On the basis of this work, he was made a professor at the Technische Hochschule in Hanover, in 1906 and, three years later, obtained a similar position at the Technische Hochschule in Aachen, where he remained until 1917.
More than a decade earlier, pieter zeeman had demonstrated that a division of the spectral lines emitted by atoms can be caused by the influence of a magnetic field, the so-called Zeeman effect. Stark built on this work by demonstrating that the same division of spectral lines can be produced by the influence of an electric field. His technique was to photograph the spectrum emitted by canal rays, consisting of hydrogen and helium atoms, as they passed through a strong electric field. The electric field caused the electrons in the radiating atoms to change position relative to the nucleus and distorted the electron orbital motion. Since light is emitted when an excited electron moves from a higher- to a lower-energy orbit, distortion of the orbits also distorts the emitted light, which manifests itself as division of the spectral lines. Stark announced his discovery of this spectral phenomenon, now known as the Stark effect, in 1913.
In that same year, Stark made yet another important contribution when he generalized the photoelectric law proposed by albert einstein in 1906. This principle, now called the Stark-Einstein law, states that each molecule involved in a photochemical reaction absorbs only one quantum of the radiation that causes the reaction.
Stark went on to become professor of physics at the University of Greifswald. His discovery of the Stark effect garnered him the 1919 Nobel Prize in physics, and he used his prize money to set up his own laboratory. Surprisingly, at this high point in his career, he made a detour into the world of commerce, attempting to set up a porcelain factory in northern Germany. The German economy was depressed, however, and Stark was forced to abandon his venture and return to the world of science.
Stark married Luise Uepler, with whom he had five children. The later part of his scientific career was marred by his involvement in the rabid anti-Semitism sweeping Germany, which led him to join the Nazi Party in 1930. He became an important figure in German physics, serving as president of both the Reich Physical-Technical Institute and the German Research Association, from 1933 to 1939, when a conflict with government authorities caused him to resign. After World War II, he was sentenced, for his Nazi activities, by a German denazification court, to four years in a labor camp.
A prolific writer, Stark published more than 300 scientific papers, as well as books on electricity, elementary radiation, and electrical spec-troscopic analysis of chemical atoms. He founded the Jahrbuch der Radioaktivitat und Elec-tronik (Yearbook of radioactivity and electronics), which he edited from 1904 to 1913. In his final years, he worked in his private laboratory on his country estate near Traunstein, West Germany, studying the effect of light deflection in an inhomogeneous electric field. He died on June 21, 1957, in Traunstein.
The discovery of the Stark effect, together with the Zeeman effect, provided support for the quantum mechanical model of the atom and acted as an experimental template against which the development of quantum mechanics in general, and the evolution of the Bohr model of the atom, could be refined and advanced.
