Local and extensive penetrating cosmic ray showers

Penetrating cosmic ray showers are observed with an anticoincidence method which indicates whether or not each shower is associated with an extensive air shower. Those not associated with extensive showers (local penetrating showers) are found to show a transition effect which is mass-proportional, while the others (extensive penetrating showers) show a transition effect which is strongly Z-dependent, and is very like the Rossi transition effect of cascade showers. It is concluded that these are two completely independent types of penetrating showers, the local showers being groups of mesons produced in absorbers near the apparatus by single fast primary nucleons, and the extensive penetrating showers being large cascade showers containing penetrating particles. This separation is shown to accord well with previous observations.