Abstract
An inquiry is made into the fundamental mode of origin of the allowed cone of cosmic radiation introduced by Lemaitre and Vallarta. Two kinds of allowed cone are distinguished. One of these, that discussed by Lemaitre and Vallarta, postulates the presence of an impenetrable earth; for it all forbidden directions are due to the earth's shadow effect. The second type of allowed cone, applicable in the first approximation to such problems as that of the sun's magnetic field, does not postulate the presence of an impenetrable earth; for it all forbidden directions are associated with bounded charged particle orbits. The general topological features of each of these kinds of allowed cone, and their relationship to one another, are described.

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