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2.1.Energy and Mass Spectrum
During the past few years, using chiefly the photographic plate technique, and to a lesser extent scintillation counters, interesting information has been obtained by balloons close to the top of the atmosphere on the mass energy distribution of the primary particles. This fruitful line of work, which is being ipursued vigorously at Bristol—Dainton et al (1952) and in Rochester-Kaplon et al (1952) is as yet statistically incomplete, but the general form of the results is shown in Figure IV.
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Fig. 1—The minimum energy of charged particles able to reach the earth.
Fig. 2—Proton energies allowed by the earth's magnetic held in the direction 15° east, for various magnetic latitudes.
Fig. 3—Same for 45° west. From Vallarta (1939). Shaded portion represents penumbra.
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Fig. 4—Energy spectra. The limiting energies for vertical incidence corresponding to some geomagnetic latitudes are indicated by broken lines. The parts of the curves referring to energies below the limiting energy for 55° were extrapolated.