Geiger‐counter measurements in the upper atmosphere bearing upon the nature of the radiation from solar flares and radio fade‐outs

The intensity of the penetrating radiation at an elevation of 20 km has been measured with a Geiger counter carried at a constant level by a balloon for a continuous interval including times before, during, and after a radio fade‐out. No effect was found, and the precision of the measurement excludes the possibility of an increase of intensity as great as two per cent. Assuming mass‐absorption of the ionizing radiation in a homogeneous atmosphere the limits of the absorption‐coefficient are determined from ( a ) the negative result of the balloon experiment, ( b ) the total ionization required in the region of high collision‐frequency for the absorption of radio energy, and ( c ) the fact that the E ‐ and F ‐layers are not appreciably altered as regards their ion‐density during the fade‐out. The analysis shows that the mass absorption‐coefficient must lie between 0.1 and 25 per gram, or if the solar‐flare radiation is of the nature of X‐rays the wave‐length must lie between 0.1 and 1.5Å.