Heisenberg replies to Pauli's letter. He is now satisfied with the state of the theory of holes. There are two problems. The first is what kind of Schrödinger equation characterizes the theory of holes and what are at any moment the expectation values for current and charge-density. The second problem is what are the expectation values for the energy-density. He discusses the solutions for both problems. If Pauli agrees, he would like to publish the theory of holes in the present form. He is grateful for Pauli's criticism of his attempts to solve the self-energy question.

Addition to the last letter of the 24 October 1934 (heisenberg_0205).

Pauli is interested in Heisenberg's new calculations on the hole theory and on the problem of magnetic nuclear moments.

Heisenberg talks of more progress about e$^{2}$(h.c.). He also writes of a solution of the Schrödinger equation in the present theory of holes by a power-series of e$^{2}$(h.c.).

Pauli writes about the necessity for continuation of his leave from Zürich. He writes about the possibilities for non-American physicists to get jobs in the U.S.A., because many Americans are busy with defense work. He writes about his paper with Dancoff on strong coupling in the pseudo-scalar meson theory and about his correspondance with Dirac on his efforts to remove divergences in quantum electrodynamics. He comments on Scherrer's attitude to theoretical physics.

Pauli replies to some points in Heisenberg's letters (18th April 1947 and 20th June 1947). The idea of an analytical continuation of the S-matrix is a failure. He is scepticalabout future theories, especially as the problem of the dimensionless constant e2/(n.c) is not solved. He doesn't believe in the existence of a universal length. He does not believe either in the mathematical existence of a convergent quantum electrodynamics with arbitrary e2/(n.c). He writes of his impending visit to Sweden and Copenhagen.

Pauli gives his opinion on the present situation of quantum electrodynamics.

Pauli writes about longitudinal photons. The principle of "renormalization" of charge and mass works satisfactorily only in special interactions. Another question: will it be necessary to modify the space-time concept for small dimensions?