Elsasser gives further explanations of the principle which forms the central idea of his book and he explains why it differs from the second law.

About Wolfgang Pauli's death.

Ivanenko writes of a letter he received from Heisenberg about his participation in the non-linear spinor theory of matter. He mentions some papers published by himself and his associates dealing with non-linear theories.

Klein's writes about his and Hilbert's view that the specific significance of Einstein's theory is to be found in its physical conception, but that its precise formulation is a purely mathematical problem. He makes further comments about relativity.

Klein writes about the paginated proofs of the article and gives more suggestions.

Kottler writes about some suggestions of Pauli as regards the treatment of relativistic line elements.

Kottler thanks Pauli for his letter and his readiness to deal with his work on relativity.