Prospects for cosmic ray physics around 1015 eV

Knowledge of the chemical composition of primary cosmic ray nuclei is a prerequisite to understanding the origin, acceleration and propagation of the cosmic rays. Details of composition up to 100 GeV/nucleon have been studied extensively for many years, and the subject is a mature one in this low energy region. At much higher energies the flux becomes so low that the primaries cannot be studied directly, but can be observed only through their secondary cascades in the atmosphere. In the air shower energy region from 1014 to 1020 eV the subject of cosmic ray composition is therefore still in its infancy. New air shower experiments now operating promise to give qualitatively new data on longitudinal development of individual, large showers (1017-1020 eV). New colliding beam experiments will soon give direct information on hadron-hadron collisions at energies equivalent to 1014-1015 eV in the lab, which will enable significant progress in interpreting existing data on small showers and others atmospheric cascade experiments. We review the situation, with emphasis on energies around 1015 eV