Magnetism and the quantum theory

The results of the modern form of the quantum theory are reviewed in relation to the explanation which they afford of magnetic phenomena. Reference is made to the magnetic moment of the spinning electron which appears to play an important part in the new quantum mechanics, and to the explanation of the molecular field of Weiss as originating in the quantum interaction between electrons. The necessity for taking into account the principle of relativity is emphasized in connection with the possible structure of the electromagnetic field: the quantum theory may demand four-dimensional tubes of force in space-time. Heisenberg's principle of indeterminacy is briefly discussed.