Recent Evidence Concerning the Sidereal Anisotropy in the Charged Primary Cosmic Radiation

Significant evidence for a bi-directional sidereal anisotropy has been obtained from observations with meson telescopes at depths in the vicinity of 40 metres water equivalent (m.w.e.) underground. The anisotropy is of the type which should occur when charged particles which were formerly isotropic stream equally in both directions along a magnetic field, if there is a tendency for pitch angles to become reduced (the pitch angle being the angle between the particle trajectory and the direction of the field). If the magnetic moments of the particles are adiabatically invariant, changes in the magnetic field, both with position and time, could be responsible for the anisotropy.