Pauli gives some suggestions for changing a few points in the formulation.

Pauli finds a discrepancy between certain equations in Heisenberg's letter and certain group relations.

Pauli announces that he is forced, because of differences of opinion, to give up the plan of a joint publication with Heisenberg on the isospin group in the theory of elementary particles.

Pauli replies to Heisenberg's letter of 13 April. He criticizes his pressing for a premature publication of the work. He is now convinced that some of the field equations have nothing to do with the real nature of the elementary particles. Possibly, at the present stage of quantized field-theories and on the level of special relativity, a theory of elementary particles is impossible without ad hoc assumptions.

Pauli hopes to come to Copenhagen and to discuss radiation problems. He has now to write a Handbuch article for Springer on the problem of closed shells. He believes in a definite value of momentum of the atom in a stationary state, if this momentum is conceived as a dynamical (not kinematical) quantity. He writes also about the theory of multiplet intensities in an electric field, Ornstein's sum-rules, Kramer's dispersion theory and about the so-called Smekal-jumps (frequency of the external field goes to zero).

Pauli writes that he will not come to Debye's conference in Leipzig. He explains the meaning of some sentences in his Handbuch-article, especially those related to discontinuity created by observation. He explains what he means by second quantization. He asks Heisenberg's view on the uncertainity relations for field strengths.

Pauli sends copies of two papers with Casimir on scattering of Gamma-rays by bound electrons. He says that he believes again in the validity of the energy law in the case of Beta-disintegration, because very penetrative particles are emitted in this process.

Pauli makes some remarks on Dirac's theory of holes. He does not believe in it, because he thinks that the laws of nature are asymetrical with regard to positive and negative electricity.

This letter contains Pauli's additions to Heisenberg's last letter. He talks about Ehrenfest's suicide and suggests the edition of a memorial issue of "Naturwissenschaften".

Pauli gives some calculations and makes some critical remarks on some of Heisenberg's results.