A Cloud-Chamber Study of Extensive Air Showers at 3260 Meters Elevation

The penetrating particles in extensive air showers have been observed in a cloud chamber under 6 inches of lead at an elevation of 3260 meters. If a group of air showers is selected in such a way that their cores mostly land between 4 and 24 meters from the chamber, the penetrating particles are seen to consist mainly of $\mu$-mesons which have been produced in the air above the apparatus. If a group of air showers is selected so that their cores are mostly $\mu$-mesons and in addition there is evidence for local production of penetrating particles in mixed showers and high energy nuclear disintegrations produced by both neutral and ionizing penetrating particles. Thus we have evidence that high energy neutral particles and highly interacting ionizing particles make up an appreciable portion of the penetrating particles in the cores of air showers. There are more cascades of energy >${10}^8$ ev under the lead shield than can be accounted for by the radiation and knock-on processes of the observed number of mesons.