Heisenberg has sent copy of his Solvay-report also to Bohr. He writes about his trip to the USA.

Heisenberg continues his letter on ferromagnetism.

Heisenberg replies to Pauli's questions about his letter on ferromagnetism: 1) on the magnetic moments of the atom residues, 2) the case of paramagnetism, 3) the calculation of the state-sum.

Heisenberg asks questions about the theory of holes.

Heisenberg writes about Pauli's objections to his exchange-relations.

Heisenberg revokes his remarks made in the last letter.

Heisenberg gives new calculations about the theory of holes. He writes about the gauge-invariance of certain expressions, about the problem of self-energy. he talks on the necessity for theories with infinite degrees of freedom and a quadratic wave equation should be possible in the case of absence of external fields.

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.

Heisenberg gives a few corrections to the last letter.

Heisenberg sends a manuscript describing the present situation of the theory of holes. He expresses the hope that the way from this theory to the explanation of $^{2}$/(h.c) will be short.