The coincidence experiments of Bothe-Kolhörster, Rossi and others, considered in the light of various alternative interpretations, show the existence of penetrating, electrically charged particles which are either primary cosmic rays or are secondaries of primaries that are absorbed high in the atmosphere. The shower-producing radiation, which seems to consist of photons, must, in view of the marked latitude effect to which it is subject, be produced by some electrically charged primary rays, which are provisionally identified as electrons.
The variation of cosmic-ray-intensity with latitude is shown to increase from about 16 per cent at sea-level to a ratio of 40-fold between 55° and 20° at very high altitudes. Extrapolation to the top of the atmosphere near the poles and the equator would indicate a ratio greater than 100: 1, which would imply that less than 1 per cent of the unfiltered primary cosmic rays are electrically neutral. In conjunction with the coincidence experiments, this means that the primary rays responsible for cosmic-ray effects are nearly all electrically charged particles.
A method of analysing these electrically charged rays is described and applied to typical ionization data for different altitudes at various latitudes. The method consists in (1) calculating the effective minimum energy of various types of particles admitted through the earth's field at different magnetic latitudes; (ii) determining the minimum ranges in air of the particles corresponding to these minimum energies; and (iii) analyzing the data relating the altitude with ionization and thus obtaining experimental range-minima that can be compared with the calculated values. The balloon experiments show two such range-minima, A and B, at higher and lower altitudes respectively. Their ranges progress with changing latitude approximately in the manner that the theory predicts. A third range-group C appears on analysis of the curve showing the latitude effect for sea-level. Using the best available information regarding magnetic latitudes and the relation between energy and range, these range-groups are identified respectively as alpha particles, electrons and protons. Comparison with directional experiments indicates that the electron group probably consists of about equal parts of positrons and negatrons.
The possible errors involved in applying this analysis are of such magnitude as to leave the identification of the range-groups questionable. Comparison with other data is on the whole however confirmatory, except for the failure to find proton tracks in Wilson photographs of cosmic rays. For this a possible explanation is offered.