Masses in the Theory of Relativity

TheFermi, E. great conceptual importance of the theory of relativity, as a contribution to a deeper understanding of the relations between space and time, and the lively and often impassioned discussions to which it has consequently given rise even outside strictly scientific circles, have perhaps somewhat distracted attention from another of its results which, though less dramatic and, let us admit it, less paradoxical, has nevertheless consequences no less noteworthy in physics, and whose interest is probably destined to grow in the subsequent development of science.