These three letters are about progress in Pauli's work on the He-model and some technical questions concerning his coming to Copenhagen.

Pauli asks about the possibility of visiting Copenhagen during his vacation. He says that he met Heisenberg in Copenhagen. He talks about his own work on heat conduction in solids.

Pauli talks about Bohr's paper on the statistical interpretation of quantum results which has its origin in the decision between observed object and measuring instrument. Critical remarks are made on the paper, but Pauli is still very positive about Bohr's conception, especially his view that the stationary states are as real as the particles themselves.

Pauli sends Bohr a short summary of his calculations on the H-atom using the "Göttinger" quantum mechanics. He writes about the difficulty of the excluded pendulum orbits (R=0), about the great progress made by Heisenberg on quantum mechanics and on Heisenberg's theory which may actually not not suffice to explain the two-term system of He. He also talks about other problems that are still open, like the time-dependent processes.

Pauli is glad about the changes Bohr made in his manuscript, in particular about his explanation of complementarity. He looks forward to meeting him in Hamburg.

Pauli asks if the last proofs of Bohr's paper are completed; if so, he would like to come to Copenhagen for some talks.

Pauli thanks Einstein for the proofs of his paper (written by Einstein with Ehrenfest) concerning the elementary processes in which several quanta are simultaneously absorbed or emitted. Pauli shows that there exists an analogue for such processes in classical theory.

Pauli writes about mathematical contributions to the quantum-mechanical calculus.

Pauli discusses the question of a degenerated gas and compares statistics of Bose-Einstein with that of Fermi-Dirac. Another part of the letter deals with scattering which Pauli does not yet understand.

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).