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.

Pauli sends Heisenberg his calculations on the hole theory. He thinks the whole derivations are cogent, in spite of the starting point which differs completely from Dirac's. He makes some remarks on the neutrino problem. He believes, like De Broglie, that a photon consists of a neutrino plus a neutrino hole.

Pauli makes some theoretical remarks about the connection between self-energy difficulties and the existence of the electric charge.

Pauli writes of his calculations with Weisskopf of polarization effects in changing fields.

Pauli comments on a manuscript by Heisenberg. The important progress lies in the recognition of the fact that all infinities are created by the field quantization. Mathematically things are satisfactory, but physically, no experimental consequences can be expected, because the neglect of the radiation-reaction forces is not legitimate. He remarks on coherent scattered radiation and on Weisskopf's and Delbrück's work on it. He writes of his thoughts on the significance of e$^{2}/(h.c) and of the concept of charge and its conservation.

Pauli sends Heisenberg his calculation on the quantization of the Klein-Gordon equation and explains the results.

Pauli writes of his intention to publish with Weisskopf on the quantization of the relativistic scalar wave equation, and with Bose on statistics. He comments on Heisenberg's ideas about a future unified field theory.