Some problems in the interpretation of underground cosmic-ray data

Further data from observations made in a coal-mine are reported. The 20% discrepancy between the intensity at moderate depths underground and that deduced from the sea-level muon spectrum, already indicated by other work, has been confirmed. The possibilities of modifying the spectrum or the ionization-loss expression are discussed.Observations of the angular distribution strengthen the view that the exponent is rather higher than expected. This appears to imply that the K/π ratio must be quite high for muons of a few hundred GeV.The various reports of pairs and groups of muons at different depths underground are reviewed. Regarded as a cosmic-ray component muon pairs are less strongly attenuated underground than any other phenomenon (except neutrinos). The experimental results are discussed in terms of Greisen's semiempirical expression for the intensity of muons in extensive air showers.