Heisenberg replies to Pauli's and Weisskopf's letters about the self-energy of the photon.

Pauli is disappointed with Heisenberg's letter on nuclear physics. The indefiniteness of the go-functions in Heisenberg's and Majorana's nuclear theory is unsatisfactory.

Heisenberg writes in order to proceed with electrodynamics. One has to know the consequences of the present formalism. He asks for Pauli's opinion.

Heisenberg writes on Bohr's forthcoming reply to Einstein's thought experiment (screen and two diaphragms) concerning causality and quantum theory. He talks of his own plans for a paper on nuclear physics.

Reply from Pauli to letters by Klein, especially about five-dimensional formalism.

Pauli makes a comparison of Klein's theory with his relevant lecture given in Paris.

Pauli says that he does not agree with Kronig's prejudice against the USA. He makes comments on Kronig's work in connection with Jordan's neutrino theory.

Heisenberg does not agree with Pauli about the identical situation of quantum electrodynamics and Fermi's theory, because the latter contains a universal constant of nature. He says that for high energies one has to expect completely different results. He writes that is the shower-formation is as an important consequence of Fermi's theory.

Heisenberg agrees with Pauli that the mathematical problems should be approached by a limiting process from the lattice-world. He gives some suggestion for a Hamiltonian scalar theory. He talks about a common trip to Copenhagen.