Abstract
The prevailing philosophical mood among those physicists today whose interests are mainly in the field of modern atomic theory, is some form of positivism. This is true not only of the leaders in the field of quantum mechanics, as for instance Heisenberg, Jordan, and Dirac, in whose writings on the philosophical aspects of the recent revolutionary advances in physics the positivistic tendency is clearly visible, but also of the rank and file of competent students of the modern quantum theory.