originally Viktor Franz. In 1912 he began to investigate the recently discovered ionization of the atmosphere. In a series of balloon ascents, he used electroscopes to show that radiation was always present above 150 m, and increased steadily with altitude. Its intensity did not depend on the time of day or night, and so could not come from the Sun—it had to be of cosmic origin. Hess’s discovery of these cosmic rays was not recognized until after World War I; for it he shared the 1936 Nobel Prize in Physics.