The total energies involved in cosmic radiation are so large, individually and collectively, that however they are generated the process or processes involved certainly are basic to the total structure of the universe. Moreover, since some of the hypotheses suggest experimental tests, the speculation on the origin of cosmic radiation has been extremely beneficial to the progress of physics. The speculations exhibit an exciting variety and give full play to imaginative thinking which, nevertheless, must be limited by experimental facts and by reasonable conjectures based on experimental facts.

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