Källén talks about Thirring's work on quantum electrodynamics.

Ever since Pauli and his wife gave the Bohrs the great pleasure of coming to Bohr's birthday, it has been on Bohr's mind to write to Pauli to say how much their friendship has meant to him during the many years, and how thankful he was again to feel how well they understand each other. Not least when one has come so far in years and has to seek the greatest joy in following the younger generations' progress, all the kindness shown to him was a very great encouragement. It was sad to hear about the death of Pauli's elderly father, and they are all sorry for the loss of Placzek and Weyl. Under these conditions Pauli's and his wife's visit to Princeton will be a great encouragement to all of them, not least for Oppenheimer, of whom they are often thinking. Bohr mentions some questions about the invitation to Lindau, he says that he and his wife plan to go there in the summer. It should be a special joy if Pauli and his wife also came.

Källén enumerates various points of Heisenberg's theory, with which he does not agree.

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.