Addition to the letter of the 27 January 1934.

Pauli makes some remarks on Dirac's theory, on the mass of the neutron and on the negative protons.

Pauli replies to Heisenberg's letter concerning e$^{2}$. He gives an outline of how far a future theory will have to differ from the present one in order to avoid infinities.

Pauli writes on the basis of his Princeton experience to suggest a new approach to problems like that dealt with in Fermi's theory.

Pauli replies to Heisenberg's letter of 26th November. He writes about consideration of the possibility of introducing the lattice method for the solution of the impact problem.

Pauli makes some remarks on Heisenberg's latest results, especially properties of the Hamilton-function. He gives some comments on nuclear theory, especially the role of the neutrino-field for nuclear forces.

Pauli makes a short report about his research program and about pair creation.

Pauli comments on recent work on cosmic rays (Bhabha and Heitler), and on the experimental confirmation of Bethe-Heitler's brems-formula for fast electrons. He talks on the quantization of waves.

Pauli congratulates Heisenberg on his engagement.

Pauli makes further remarks about the necessity of a universal length.