Pauli replies to Ma's letter of 3 May. He makes comparison of Riesz's method with the Lambda-limiting process. He recommands to Ma to work on supra-conductivity.

Pauli discusses Heitler-Wilson and other rules to determine S-matrix. He writes of difficulties with two "test problems": nucleon magnetic moments and Bremsstrahlung.

Pauli has read with great interest Heisenberg's paper on the S-matrix, but as no method is given how to determine it, the work remains purely programatic.

Pauli makes more remarks on Ma's redundant zeros of the S-matrix.

Pauli replies to Ma's letter of 20 July, concerning the validity of a relation by Heisenberg. He reports on the international physics conference in Cambridge, on a discussion there with Powell and Amaldi, and on papers delivered by Wentzel, Møller, Heitler and Pauli.

Pauli talks about Ma's proof of the nonvalidity of Heisenberg's relation. He asks Ma to report to him on papers by Oppenheimer and Bethe at the Amer. Phys. Soc. meeting in New York.

Pauli writes about his decision to remain in Zurich. For the USA he forsees, in about five years, the danger of increasing interference by the military authorities in physical research. As regards Einstein's field equations, he does not believe that the classical field thery can yield any new results. One has to wait for a new generation of young physicists. He also writes of Bertrand Russel's lectures in Zurich.

Pauli mentions the recent results about the magnetic moment of the free neutron and adds a lengthy theoretical comment to this.

Pauli says that Ma's redundant S-matrix zeros invalidates a Heisenberg equation. He writes that he received Heisenberg's papers. He makes travel plans to Stockholm and Copenhagen. He learns the Riesz-Gustafson method.

Pauli writes that Blackett will convey reprints to Heisenberg. He makes progress on the Riesz-Gustafson method.