Pauli repays a loan.

Pauli talks about spectral terms for oxygen. He finds support for Landé-Heisenberg "branching rule" and "Heisenberg's theory". He comments Kronig's formulas. He makes personal remarks on Lenz.

Heisenberg writes more about the polarization of Stark effect components, about Heisenberg's new quantum mechanics, about the principle of the use of "observables"and about the equations for the harmonic and anharmonic oscillators.

Heisenberg replies to Pauli's calculations on hydrogen according to quantum mechanics and makes some remarks on his results.

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 says that Goudsmit told him about Thomas' calculations, and this confirms his ideas about the definition of the moment of the electron. Pauli gives some consideration to the implications of the model of the rotating

Pauli admits that his objections against Thomas' Theory of fine-structure are not valid, (i.e. that thte concept of spin has to be accepted).

Pauli writes about his calculations of the Balmerline intensities with the help of Schrödinger's calculus.