Victor Francis Hess was born on June 24, 1883, in Waldstein Castle, near Peggau, in Steiermark, Austria. His father was a royal forester in the service of Prince Öttinger-Wallerstein. Hess completed his education in Graz, Austria. He attended secondary school from 1893 to 1901 and then enrolled as an undergraduate at the University of Graz from 1901 to 1905. He continued on as a graduate student in physics and received his Ph.D. in 1910. For approximately a decade after earning his doctorate, Hess investigated various aspects of the radioactivity of radium while working as a staff member at the Institute of Radium Research of the Viennese Academy of Sciences.
Between 1911 and 1913, Hess performed the pioneering research that allowed him to eventually share the 1936 Nobel Prize in physics. Before Hess began his work, other scientists had used electroscopes (an early nuclear radiation detection instrument) to compare the level of ionizing radiation in high places, such as the top of the Eiffel Tower, or during relatively low altitude balloon ascents into the atmosphere. These early studies (performed between 1909 and 1910) provided a vague, but interesting, indication that the level of ionizing radiation at higher altitudes might actually be greater than the level detected on Earth’s surface. Yet the indefinite, somewhat conflicting, readings really puzzled scientists. They expected the observed radiation levels to simply decrease as some function of altitude when they operated their radiation detectors farther away from Earth’s surface and the sources of natural radioactivity within the planet’s crust. Scientists had not anticipated the possible existence of very energetic nuclear particles arriving from outer space.
Hess attacked the physical mystery first by making considerable improvements in his radiation detection instrumentation and then by personally taking his improved instruments on a number of daring balloon ascents to heights up to 5.3 kilometers in 1911 and 1912. To investigate solar influence, he made these dangerous balloon flights both during the daytime and at night, when the operations were much more hazardous. The results were similar, as they were in 1912 when he made a set of balloon flight measurements during a total solar eclipse. His careful, systematic measurements revealed that there was indeed a decrease in ionization up to an altitude of about 1 kilometer, but beyond that height the level of ionizing radiation increased considerably. In fact, he found that at an altitude of 5 kilometers, the detected ionizing radiation had twice the intensity of that measured at sea level.
Hess completed analysis of his measurements in 1913 and published his results in the Proceedings of the Viennese Academy of Sciences. He concluded that there was an extremely penetrating radiation, an “ultra radiation,” entering Earth’s atmosphere from outer space. Hess had discovered “cosmic rays”—the term later coined in 1925 by the American physicist Robert Milikan (1868–1953).
Cosmic rays are very energetic nuclear particles that arrive at Earth from all over the galaxy. Scientists all over the world began using Hess’s discovery to turn Earth’s atmosphere into a giant natural laboratory. Prior to the development of high-energy particle accelerators, the study of cosmic ray interactions with the atoms of the atmosphere opened the door to many new discoveries in high-energy nuclear physics.
In 1919, Hess received the Lieben Prize from the Viennese Academy of Sciences for his discovery of ultra radiation (cosmic rays). The following year, he received an appointment as a professor of experimental physics at the University of Graz. From 1921 to 1923, he took a brief leave of absence from his position at the university to work in the United States, first as director of the research laboratory of the United States Radium Company in New Jersey and then as a consultant to the Bureau of Mines of the U.S. Department of the Interior in Washington, D.C.
In 1923, Hess returned to Austria and resumed his position as physics professor at the University of Graz. He moved to the University of Innsbruck in 1931 and became director of its newly established Institute of Radiology. As part of his activities at Innsbruck, he also founded a research station on Mount Hafelekar (at an altitude of 2.3 kilometers) to continue to observe and study cosmic rays. In 1932, the Carl Zeiss Institute in Jena awarded him the Abbe Memorial Prize and the Abbe Medal. That same year, Hess became a corresponding member of the Academy of Sciences in Vienna.
The greatest acknowledgement of the importance of his pioneering research came in 1936, when Hess shared that year’s Nobel Prize in physics for his discovery of cosmic rays. The other recipient was a young American physicist, Carl D. Anderson (1905–1991). Anderson had discovered the positron using cosmic ray interactions. As Anderson’s work indicates, when a primary cosmic ray particle hits the nucleus of an atmospheric atom, the result is an enormous number of interesting secondary particles. In the 1920s and 1930s, careful study of these so-called cosmic ray “showers” of secondary particles provided nuclear scientists an early opportunity to examine very energetic nuclear reactions.
In 1938, the Nazis came to power in Austria, and Hess, a Roman Catholic with a Jewish wife, was immediately dismissed from his university position. The couple fled to the United States by way of Switzerland. Later that year, Hess accepted a position at Fordham University in New York City as a professor of physics. He became an American citizen in 1944 and retired from Fordham University in 1956.
Hess wrote over 60 technical papers and published several books, including: The Electrical Conductivity of the Atmosphere and Its Causes (1928) and The Ionization Balance of the Atmosphere (1933). He died on December 17, 1964, in Mount Vernon, New York. Hess’s discovery of opened a new area within nuclear physics and provided scientists with an important new source of very energetic nuclear particles that led to many other breakthroughs in physics in the 1920s, the 1930s, and beyond.
ALBERT EINSTEIN (1879 – 1955)
