Prehistory - The electron, the proton and X-rays.- Prehistory - Radioactivity.- Cosmic rays - The antefacts.- The discovery - Victor F. Hess and the balloon flights.- The confirmation - Robert Millikan and the "birth cry" of the borning atoms.- A turning point - Things are not as they look.- The earth magnetic field and the geomagnetic effects.- The positive electron.- The electromagnetic showers.- The muon.- The discovery of the π-meson, nuclear...