Fluctuations of Cosmic-Ray Ionization

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Abstract
The cosmic-ray ionization in air contained at a pressure of 157.5 atmospheres in the 13.8 liter steel chamber surrounded by the 5.5-6 ft. water shield as previously described, was measured at four-hour intervals during a period of fifteen consecutive days, April 6-20, 1932. Controlled laboratory conditions and compensation features of the measuring equipment contributed to the constancy of measured ionization values. By means of recording instruments, simultaneous records of the atmospheric potential gradient, the atmospheric temperature, the barometric pressure, and the relative humidity were also secured. It was determined that a decrease of 2.1 percent in the cosmic-ray ionization corresponded to an increase of 1 cm in the barometric column. No correlation was established between the ionization and the atmospheric potential gradient, the atmospheric temperature, or the absolute humidity. There appeared to be no regular diurnal variation of the ionization either before or after the application of corrections for variations in barometric pressure. When deviations from the average of the ionization values corresponding to a particular time of day were regarded as statistical fluctuations, the average probable error so calculated was 0.21 percent. The greatest difference between the grand average and the average ionization for a particular time of day was only about one-third of one percent, less than twice the probable error. It seems very likely that the fluctuations observed were of a statistical nature.