“…Further, one must increase the numerator by SO",', to allow for the effect of the neutral rr-mesons, which will of course contribute to star production, if reabsorbed, but will not leave visible meson tracks. The figure of 50% comes from the known ratio of the photoproduction cross sections for charged and neutral mesons (Silverman andStearns 1952, Steinberger andBishop 1952), and also from cosmic-ray data (Carlson, Hooper and King 1950). The results of this calculation are given in table 5.…”