Fierz gives Pauli his calculation on $\Box$ G-H.

Fierz replies to a letter written by Pauli, on gravitational waves and on form factors.

Fierz writes about the results of his calculations on the unitary Lorentz-transformations.

Fierz defends his position that entropy is the "measure of information" obtained by an observer. He examines information obtained in classical theory from observation of changing macrostate; in quantum theory from observation of microstate that is then generalized to a macrostate. He claims entropy exists only with observation.

Fierz summarizes findings on entropy and observation in 5 "theses".

Fierz writes on the significance of the "causal function Dc" in quantum electrodynamics.

Fierz makes some additions to his letter of the 15th May 1951.

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

Fierz makes some critical remarks on a paper sent to him by Pauli written by Heisenberg, in particular on a discussion of the S-matrix.

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