About the character of the 'knee' at E ≅ 3 x 1015 eV in the energy spectrum and the mass composition of primary cosmic rays in the energy range 1015-1017 eV

The method of rescaling from the muon-multiplicity spectrum to the extensive-air-shower spectrum as a function of the total muon number nμ is presented. The method allows a direct comparison of data obtained in different experiments with muon groups. A direct comparison of data at nμ > 1800 and nμ = 75-660 has been performed. The data in the region nμ = 75-3500 agree better with the assumption that the slope change in the energy spectrum of primary cosmic rays occurs approximately at the same energy per nucleus, Ec ≅ 3 x 1015 eV, and the mass composition in the energy range 1015-1017 eV is close to that observed at 1014 eV