Pauli letter collection: letter to Niels Bohr

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.