Källén replies to two letters and questions about dipole ghosts. He talks about his own work.

Källén replies to Pauli's last letter. The normal pertubation theory cannot be used in the case mentioned by Pauli.

Enz writes about a student's diploma work and about a discussion he had with R Jost on "associated production" of $\mu$ -mesons.

Einstein sends his contribution on the subject of complementarity for the periodical Dialectica. Einstein writes about the new progress he made in the extension of the gravitation equation. Alas he was not yet able to obtain a strong and free of any singularities field equation for interesting physical cases. Einstein looks forward to seeing Pauli and his wife in an expected visit. He ends his letter on some remarks on American politics.

Clusius refers to quotations on atoms made by several figures from the late 19th century. He quotes Marignac.

Budini has not yet reached a satisfactory result as regards the orthogonality of the eigen-solutions of an equation connected with the regular representation of the homogeneous Lorentz group.

Budini thanks Pauli for his letter. He is now convinced that the eigen-functions in question are not orthogonal to each other.