Cosmic rays consist of subatomic particles which have high energy (those not from our own sun) due to their high velocities. Victor Franz Hess (1883-1964) showed in 1911 that the ionization of the Earth's atmosphere increases with altitude. Hess made ten ascents in balloons with detectors over 1911-12. He reached altitudes of 5000 meters. He came to the conclusion that a powerful radiation entered Earth's atmosphere and then diminished as it progressed toward the ground. This radiation he called "cosmic rays".

Bruno Rossi (1905-) demonstrated how penetrating cosmic rays were. At first thought to be gamma radiation it was proved in the 1920's that cosmic rays are actually high energy particles and are a constant "cosmic rain" falling onto the Earth. It was also discovered that the intensity of the radiation was dependent on latitude. This finding indicated that the particles which make up cosmic rays are electrically...