Cosmic-ray transparency for a medium-latitude observatory

The access of cosmic-ray particles to a medium-latitude observatory is analysed fromresults coming fromthe numerical solution of the charged-particle motion in the geomagnetic field. Evaluations are performed mainly for the Lomnicky Stit neutron monitor location (LS: 2634 m a.s.l., geographic coordinates 49.20æ N, 20.22æ E), but some results for the Antarctic Laboratory for Cosmic Rays (LARC:40 ma.s.l, 62.20æ S and 301.04æ E) are also given. Particular attention is paid to the variability of the magnetospheric screening appearing when the external magnetic field is added to the internal one.