  It is shown that Extensive Air Shower (EAS) longitudinal development has a
critical point where an equilibrium between the main hadronic component and the
secondary electromagnetic one exhibits a brake. This results in a change of
slope in quasi-power law function $N_{e}(Eo)$. The latter leads to a knee in
the EAS size spectrum at primary energy of about 100 TeV/nucleon. Many
``strange'' experimental results can be successfully explained in the frames of
current approach.
