Recent experiments on plasma heating and confinement in a multiple-mirror magnetic device GOL-3 demonstrate substantial improvement in comparison with the previous results obtained in a uniform magnetic field. The observed confinement time, which is of the order of a millisecond, is determined chiefly by the longitudinal losses while the transverse ones seem to be irrelevant. Simple estimates of the latter reveal, however, that the cross-field thermal losses are presently only marginally small and, therefore, may become important in future experiments.