Möller and Kristensen reply to Pauli's question about the polarization of the vacuum by an external meson field.

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

Kottler writes about the Christoffel symbols.

Kottler writes about the expressions for the velocity 4-vector, for the Christoffelsymbols, the pseudotensors and the differential operators of special velocity.

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

Klein writes about his discussion with Sommerfeld on the use of Einstein's notation "Lorentz, Amsterdam Verlag, 1916" and about Klein's inability to work on relativity for a year, and his receipt of Pauli's manuscript.

Klein's editorial remarks on Pauli's relativity article : notation, use of Lorentz group and clarity.

Historical remarks from Klein about Poincaré's note in "Comptes Rendus 146" and in "the origins of relativity".

Klein's reply to Pauli's letter of 4 May, and detailed comments on several passages in the encyclopedia.

Klein's further remarks and suggestions about the encyclopedia article.