A Study of Time-Variations in Cosmic-Ray Intensity at High Altitudes

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Abstract
Twelve balloon flights with a recording cosmic-ray ionization chamber apparatus have been carried out at Chicago between October, 1938 and November, 1939. The results show marked changes in cosmic-ray intensity during this period, the maximum variation observed being about fourteen percent for the peak value of the ionization pressure curve. The changes follow in general the "world-wide" variations of cosmic rays observed at ground stations but when the high altitude results are somewhat arbitrarily corrected for such "world-wide" variations certain residual changes remain. These residual variations show a maximum in the early spring of 1939, then a sudden drop of about eight percent and lower values during the early summer with increasing values again in the autumn. Whether this represents a true seasonal effect can be determined only by further experiments. Though there is some indication that the variations are related to magnetic changes, the agreement with the theory of Vallarta and Godart is not quantitatively good.