To-day one investigates primary cosmic rays, before they have started to interact with the material of the Earth’s atmosphere, by use of balloons, rockets and artificial satellites. They include protons, α-particles and heavy nuclei. By means of tracks in photographic emulsions, one can determine their charge-number Z and then one finds the following abundance-distribution compared with ordinary stellar material of population I. The table gives log N referred to hydrogen = 12, where N is the relative number of atoms.