Pauli is ready to contribute to the Festschrift for Sommerfeld. In connection with experiments in the U.S.A. on the shift of S-terms in the H-atom he has returned to quantum electrodynamics.

Pauli criticizes certain passages in Heisenberg's manuscript of the Dialectica-article, and asks to correct them. He writes about the "fundamental length" in quantum theory. The problem is not how to introduce such a length, but how to get rid of the multitude of lengths (Compton-length for each particle) in the present theory.

Pauli cannot come to Geneva, but would like to hear Heisenberg's opinion on non-local interaction and hear about biological literature.

Pauli asks about quantized field theory. He makes some remarks on Heisenberg's article for the Bohr-Festschrift, and on Einstein idea of physical reality: "the isolated observer". More about "incomplete descriptions" in physics.

Pauli talks about a paper by Kita who found an error in Heisenberg's calculations. Pauli doubts that Heisenberg's S-matrix can remain unitary.

Pauli replies to Heisenberg's letter of 10 December. He writes on clarifications of the differences in their respective views on the necessary presuppositions for a quantized field theory. He has a short discussion of quantum-electrodynamics and the Lee model.

Pauli talks on further calculations about dipole-ghosts. He asks about Eta-matrix.

Pauli talks about analysis of the defects of Heisenberg's approach and of some errors in his conclusions.

Pauli replies to Heisenberg's letter of 20 February.

Pauli acknowledges the letter of the 27 February and is ready to continue the discussion.