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Two entirely different suggestions have been advanced in the literature as to where the cosmic rays originate. The first suggestion is that cosmic rays are of local origin (upper earth atmosphere, our own planetary system, etc.). The other suggestion is that cosmic rays are produced or have been produced throughout the universe, or even more specifically, throughout interstellar or intergalactic spaces. This latter view has especially been advanced by R. A. Millikan.
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F. Zwicky (1933) studied this question.
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