Bohr thanks Bohr for his letter of the 25th September.

Pauli makes some objections to Thomas' derivation of the missing factor in magnetic interaction of the spinning electron. He is opposed to its publication.

Pauli describes the theoretical tasks if the spinning electron is correct. He criticizes Thomas' relativistic derivation, published in: Nature : 117 (1926), 514.

Pauli capitulates to Bohr and Thomas and suggests some improvements in Thomas' manuscript. He also plans to visit Copenhagen. At the end of the letter Pauli writes to Kramers.

Pauli suggests postponing his visit to Copenhagen. He talks about his work on quantum electrodynamics and makes a criticism of Klein's paper in the Zs. f. Phys. Pauli thinks that Klein is not ready to see the use of multidimensional spaces as an inherent part of the approach of quantum phenomena.

This letter is a reply to Bohr's letter of the 15th July. Pauli writes about Jordan's manuscript. He criticises its last paragraph where Jordan does not distinguish between the particles (de Broglie field) and the electromagnetic field. He talks about Jordan's and his own work on radiation electrodynamics in the absence of charged particles. He also writes about a paper by de Broglie in the Journ. de Phys. which attempts to harmonize between dualism of waves and corpuscles on the one hand and complete determinism of physical events on the other hand.

Pauli hopes to get Bohr's new manuscript. He talks about the use of half-integer K-values for a description of penetrating electron orbits. He doubts that these methods could lead to a real explanation of the atomic structure.

Pauli writes against Bohr, Kramers and Slater's paper. He mentions his talk with Einstein about the paper and gives Einstein's main arguments against it, in particular his belief in the strict validity of energy-momentum conservation for elementary processes. Pauli gives his own arguments against Bohr's assumption.

Pauli sends Bohr a manuscript of an unpublished work. He writes about his new interest in quantum theory and his idea to explain the anomalous Zeeman-effect through relativistic considerations. His hypothesis is that the doublet-structure of alkali spectra is alone a property of the valency-electron. He talks about the necessity for a correct formulation of the correspondence principle for atoms with more than one electron and about the necessity for a modification of the classical kinematic concept of motion.

Pauli thanks Bohr for the days he spent in Copenhagen.