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 is on vacation in Arosa with Harald. He hopes to see Pauli when coming through Hamburg on their return and will talk about Pauli's planned visit to Copenhagen. Bohr has sent an entirely new manuscript to Berlin for "Naturwissenschaften : 16 (1928), pp.245".

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.

Ehrenfest is looking forward to see Pauli in Leiden. he mentions some papers by Heisenberg, Hund and on group theory, on which he wants to ask Pauli several questions.

Ehrenfest sends a short note in which he expresses his doubts as to the separability of the operator-function M representing the spin interaction of the two He-electron.