Cosmic-ray intensities in the stratosphere

Three flights which reached altitudes, according to official weather bureau records, corresponding to the barometric pressures 79 mm, 32 mm, and 16 mm of mercury respectively are reported. In two of these flights dependable electrometer readings down to pressures of 88 mm and 61 mm, respectively, are obtained. These flights enable a weighted mean ionization-altitude curve to be obtained down to a pressure of 61 mm or 92 percent of the way to the top of the atmosphere. The same shape of the ionization-altitude curve is obtained from both flights and also from the flights made by Regener and by Piccard. This shape is concave downward at the top, i.e., it shows a decreasing absorption coefficient as the top is approached. This indicates non-ionizing primary entering rays not yet wholly in equilibrium with their secondary particle rays. The absolute values of the ionization found in each of these two flights and on Regener's flight are in agreement within the limits of observational uncertainty.