Victor Hess (1883-1964). Computer illustration of the Austrian physicist and discoverer of cosmic rays Victor Francis Hess ascending in a hot air balloon during a solar eclipse to measure cosmic radiation (cosmic rays). In 1911-12 Hess made 10 balloon ascents to determine the source of radiation in the atmosphere. On 7th August 1912 he rose to a height of over 5000 metres and found that the intensity of the radiation increases rapidly with altitude. This proved that the radiation comes from outside earth. This balloon flight during a solar eclipse showed no reduction in radiation, ruling out the sun as the source. This work led to his being awarded the 1936 Nobel Prize in physics, which he shared with Carl Anderson.