A considerable number of the general features of cosmic ray phenomena are now understandable on the view that a part of the radiation is made up of electrons and photons which obey the usual laws of radiation.
Theoretical studies have, however, indicated that the expected intensity of the radiation at sea level is larger than would be predicted by this theory and have pointed to the existence of a more penetrating type of radiation.
The presence of such a component in the cosmic radiation has been experimentally demonstrated.
Rossi 1 and his co-workers, Auger and Ehrenfest,2 and Street, Woodward and Stevenson 3 have shown that there are ionizing particles in the cosmic radiation which are capable of penetrating at least a meter of lead, whereas according to the theory no electron of reasonable energy should penetrate through more than approximately 15 centimeters of lead. The conception of two components in the cosmic radiation distinguishable by their penetrating power has been supported for some time by Auger 4 and his coworkers.
Measurements made at sea level show that about 25 per cent. of the particles are absorbed in about IO centimeters of lead. This portion is usually referred to as the soft component.
Another meter of lead reduces the number of particles by about an additional 30 per cent.
This group is called the penetrating component.