Fierz replies to a question put by Pauli in his letter, about causality and quantum electrodynamics.

Fierz gives some additions to his previous letter and makes some connections with Kant's categories.

In this letter, Fierz makes a reference to a passage in Molière's "Les Femmes savantes".

Fierz gives some calculations on the problem of form factors.

Fierz criticizes earlier work by Pauli and Fierz on the H-theorem, published in: Zeitschrift für Physik: 106 (1973), 572. He suggests some improvements in entropy as measured by macroscopic observer.

Pauli writes about his intention to write an essay on space, time and God in Newton's writings.

Fierz thanks Pauli for the offprint of a paper on gravitational waves. It seems to follow from it that the statement about non-existence of gravitational radiation is unjustified.

Fierz gives the conclusions of his letters about the Lorentz group and makes general observations about the problem.