Bohr thanks Pauli for his congratulations on his 65th birthday. He writes about the double role of a human being as an observer and as an actor in the theatre of life. He also speaks of the preparation of an article on free will and life, and of a book based on his Grifford lecture.

Bohr does not agree with Pauli's and Heisenberg's criticism of Thomas' work in: Nature : 117 (1926), pp. 514. He discusses the problem in detail and asks for further comments from Pauli.

Bohr will pass through Hamburg together with Klein on their way to Holland. He hopes that Pauli will join him on his way back to Copenhagen.

Bohr has heard that Pauli developed new thoughts on the mystic of relativity in the atom theory and is asking for some developments.

Bohr discusses Goudsmit and Uhlenbeck's work published in: Nature : 117 (1926), pp.264. Thomas has explained the missing factor of 2 by calculating the relativistic motion in: Nature : 117 (1926), pp.514. Thomas' note is enclosed.

Bohr comments on a book by A Pauly (1905) on "Darwinism and Lamarchism". Bohr gives his attitude to the great progress in biology and psychology made in recent time, in the light of the results of atomic physics as regards the description of phenomene.

Källén thanks Pauli for an offprint of a paper by Pauli that is helpful for his calculations on the Lee model. He writes on the question of the unitary of the S-matrix in this model.

Møller and Kristensen thank Pauli for his instructive letter. They answer the question he asked and give some details of their form factor theory.