Heisenberg says that in his new mechanics, the geometrical concept of orbit has no sense, as orbits are not observables.

Pauli's interpretation of intercombination lines and the application of his model to several cases (Zeeman-effect). He expresses hope for the progress of physics through Heisenberg's mechanics.

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

Heisenberg writes about Bohr's optimism as regards Goudsmit's theory and gives some additional comments on it.

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

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 writes about the Lorentz transform of the magnetic moment. He suggests a non-relativistic example of Thomas term.

Heisenberg writes about the connection of the singulet-triplet distance with Pauli's exclusion principle.