Victor Francis Hess

The American physicist Victor Francis Hess (1883-1964) shared the Nobel Prize in Physics for his discovery of cosmic rays.

Victor Francis (originally Franz) Hess was born on June 24, 1883, at Schloss Waldstein, Styria. He studied physics at the universities of Graz (1901-1905) and Vienna (1905-1908) and graduated as a doctor of philosophy at Graz in 1906. From 1910 to 1920 Hess was a lecturer at the Institute for Radium Research in the University of Vienna.

In 1900 C. T. R. Wilson proved that air is a slight conductor of electricity. Thereafter it was held that this property of the air was due to ionization by gamma rays emitted by radioactive substances in the air or in the earth. It was known that gamma rays are almost completely absorbed by 300 meters of air. To test the theory, balloon ascents were made between 1909 and 1911. Each showed that the ionization was too great to have been due to gamma rays emitted from the earth. But in each case the instruments were defective. In 1910 Theodore Wulf obtained similar results from readings at the foot and at the top of the Eiffel Tower, which is 300 meters high.

Hess became interested in Wulf's account of his experiment. Hess designed new instruments, and he made two balloon ascents in 1911, seven in 1912, and one in 1913. He showed that, as the height increased, the degree of ionization decreased at first and then rapidly increased. At a height of 5 kilometers it was many times greater than at the earth's surface. He concluded that the phenomenon was due to hitherto unknown rays of high penetration which entered the earth's atmosphere from space. On one ascent, during an almost total eclipse of the sun, the radiation was not diminished. Hess therefore concluded that the rays could not be emitted by the sun. At a later date R. A. Millikan named the radiation discovered by Hess "cosmic rays."

In 1920 Hess was appointed associate professor at Graz. From 1921 to 1923, while on leave of absence, he was director of research at the United States Radium Corporation, New York. In 1925 he became professor of experimental physics at the University of Graz and in 1931 professor of physics at Innsbruck. In 1931 he established an observatory for the study of the diurnal and nocturnal fluctuations of the cosmic rays, at which he had hinted in 1912. In 1938 Hess accepted the chair of physics at Fordham University, New York, and he became a naturalized American citizen in 1944. He died in New York on Dec. 18, 1964.

Hess's discovery encouraged the study of subatomic particles and led to the discovery of the positron by C. D. Anderson. In 1936 Hess shared the Nobel Prize for Physics with Anderson, and he received many other honors.

Further Reading

• There is a biography of Hess in Nobel Lectures, Physics, 1922-1941 (1965), which also includes his Nobel Lecture. For a discussion of his work see N. H. deV. Heathcote, Nobel Prize Winners, Physics, 1901-1950 (1953). For the effects of cosmic rays see F. K. Richtmyer and E. H. Kennard, Introduction to Modern Physics (1950), and S. Glasstone, Sourcebook of Atomic Energy (1958).