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Hess, Victor Francis

sun ground cosmic balloon

(1883–1964) Austrian–US physicist: discovered cosmic rays.

Son of a forester, Hess was educated at Graz, receiving his doctorate in 1906. He worked on radioactivity at Vienna until 1920, and afterwards at Graz, New Jersey and Innsbruck. In 1931 he set up a cosmic ray observatory on the Hafelekar mountain. When the Nazis occupied Austria in 1938 Hess was dismissed, as his wife was Jewish, and he became professor of physics at Fordham University, New York City.

In 1910 T Wulf measured the background radioactivity of the atmosphere at the top of the 300 m Eiffel Tower with a simple electroscope and showed that it was greater than at ground level, indicating that it came from an extraterrestrial source; but the results were not conclusive. A Gockel in 1912 also used the rate of discharge of a gold-leaf electroscope to measure the radioactive ionization of the air, this time from a balloon; again the results were inconclusive. However in 1911–12 Hess made 10 balloon flights and showed that the ionization is four times greater at 5000 m than at ground level. Night ascents and an ascent during an eclipse of the Sun in 1912 showed that the radiation could not be from the Sun in 1925 named these high-energy particles ‘cosmic rays’. Their study led to discoveries of the positron and muon and discovery of the pi-meson. Hess shared the 1936 Nobel Prize for physics with Anderson.

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