Electrons in Equilibrium with the Penetrating Component of Cosmic Rays in Lead at 10,000 Feet and at Sea Level

The number of electrons ($N$) in equilibrium with the penetrating component of the cosmic rays in lead at 10,000 ft. and at sea level has been measured with Wilson cloud chambers containing lead plates. The value for $N$ obtained at 10,000 ft. is 7.4±0.2 percent, at sea level 6.8±0.6 percent. Comparison is made with values for $N$ calculated from the equations of Bhabha and Tamm and Belenky with a mesotron mass of 200 m and Blackett's cosmic-ray spectrum. If the loss of low energy electrons as a result of scattering in the lead is taken into account, the calculated values for $N$ are only slightly larger than the experimental values. If the calculated values for $N$ are assumed to be correct, the present results provide additional evidence that protons constitute only a small fraction of the cosmic-ray particles in the lower atmosphere.