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The paper describes measurements of the ratio of μ-mesons to electrons as a function of shower size and barometric pressure for showers containing about 5 × 105 particles at sea level. Measurements on the change of rate with atmospheric pressure and temperature are also described, and it is shown how, on the assumption that all showers suffer the same attenuation, these measurements yield the attenuation lengths of electrons and μ-mesons. At each stage, the measurements are compared with the results of other experiments, and finally with various theories of the nucleon cascade. It is shown that none of the theories fits the data wall, and that one may suspect the assumption of similar attenuation for all showers. Possible mechanisms giving rise to a distribution of attenuation lengths ere briefly discussed, and a case made for an experimental investigation of this point.

An apparatus suitable for measuring the mean lifetimes of negatively-charged muons brought to rest in targets of Z < 30 is described. Measurements made on iron and copper yield mean lifetimes of (204±14) × 10-8 sec and (157±20) × 10-9 sec respectively.