Further Discussion of the Role of Electromagnetic Potentials in the Quantum Theory

In this paper, we present a further discussion of the role of electromagnetic potentials in the quantum theory, aimed at clarifying some of the points made in earlier papers, and indicating some extensions of these earlier ideas. In addition, we go into the problem of subsidiary conditions and questions concerning the full observability of the potentials. In the course of our discussion, we answer certain recent objections of Belinfante and De Witt.