Precision Cosmic-Ray Measurements up to Within a Percent or Two of the Top of the Atmosphere

Self-recording, constant pressure, argon-filled electroscopes sent into the stratosphere by sounding balloons at San Antonio, Texas, mag. lat. 39°N, yielded accurate readings of cosmicray intensities up to an altitude 98.3 percent of the way to the top of the atmosphere, where the pressure is but 12.9 mm of Hg. The ionization within these electroscopes passes through a definite maximum at 47.6 mm of Hg and falls 22 percent in rising to where the pressure is 12.9 mm of Hg. These results, combined with similar accurate measurements on the variation of cosmic-ray intensities as a function of latitude, both at sea level and at altitudes of 22,000 feet, indicate (1) that atmospheric cosmic-ray ionization is not produced in appreciable amount by incoming protons, and (2) that the Oppenheimer-Bethe-Heitler law of nuclear absorption is not valid for incoming electrons of a few billion $e$-volts of energy.