(translation into English, excerpt) The WORLD of the ATOM, editors H. A. Boorse and L. Motz, Basic Books, Inc. Publishers, New York - London, v.I (1966) 672.
... The discoveries revealed by the observations here given are best explained by assuming that radiation of great penetrating power enters our atmosphere from outside and engenders ionization even in counters lying deep in the atmosphere. The intensity of this radiation appears to vary hourly. Since I found no diminution of this radiation for balloon flights during an eclipse or at night time we can hardly consider the sun as it source.
Measures the dependence of ionization upon altitude.
Conclusive evidence for the cosmic rays.