Victor Francis Hess

Austrian–American physicist (1883–1964)

Hess, the son of a forester, was born at Waldstein in Austria and educated at the University of Graz where he obtained his doctorate in 1906. He worked at the Institute for Radium Research, Vienna, from 1910 to 1920 and then took up an appointment at the University of Graz where he became professor in 1925. In 1931 he set up a cosmic-ray observatory near Innsbruck but in 1938 he was dismissed from all his official positions as he was a Roman Catholic. Leaving Nazi Austria, he emigrated to America where he served as professor of physics at Fordham University, New York, from 1938 to 1956.

In 1911–12 Hess made the fundamental discovery of cosmic rays, as they were later called by Robert Millikan in 1925. For this work he shared the Nobel Prize for physics with Carl Anderson in 1936. The work stemmed from an attempt to explain why gases are always slightly ionized; thus a gold-leaf electroscope, however well insulated it might be, will discharge itself over a period of time. Radiation was clearly coming from somewhere and the most likely source was the Earth itself. To test this, attempts were made to see if the rate of discharge decreased with altitude. But both T. Wulf, who took an electroscope to the top of the Eiffel Tower in 1910, and A. Gockel, who took one up in a balloon in 1912, failed to obtain any clear results.

However when Hess ascended in a balloon to a height of 16,000 feet (4880 m) he found that although the electroscope's rate of discharge decreased initially up to about 2000 feet (610 m), thereafter it increased considerably, being four times faster at 16,000 feet than at sea level. He concluded that his results were best explained by the assumption that a radiation of very great penetrating power enters our atmosphere from above.

He was able to eliminate the Sun as the sole cause for he found that the effect was produced both by day and at night. Further, in 1912, he made a balloon ascent during a total eclipse of the Sun and found that during the period when the Sun was completely obscured there was no significant effect on the rate of discharge. Hess however failed to convince everyone that cosmic rays came from outside the Earth's atmosphere as it could still be argued that the source of the radiation was such atmospheric disturbances as thunderstorms. It was left to Millikan in 1925 finally to refute this objection.

The Austrian-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. de V. 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).

For more information on Victor Francis Hess, visit Britannica.com.

Hess, Victor Francis, 1883–1964, American physicist, b. Austria, Ph.D. Univ. of Graz, 1906. After teaching at the universities of Graz and Innsbruck, he came to the United States in 1938 and was later naturalized. He became professor of physics at Fordham Univ. in 1938. By means of instruments carried aloft in balloons, Hess and others proved that radiation that ionizes the atmosphere is of cosmic origin. For this discovery of cosmic rays he shared with C. D. Anderson the 1936 Nobel Prize in Physics. He attributed (1939) a 27-day cycle of cosmic-ray intensity to the magnetic field of the sun and correlated it with the 27-day period of rotation of the sun. He also worked on devising methods for detecting minute quantities of radioactive substances. His works include Cosmic Radiation and Its Biological Effects (with Jakob Eugster, 1940, 2d ed. 1949).

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