Ehrenfest discusses the disappearance of the "zeroth-order spectrum" for X-ray diffraction in liquids (Zernike-Prins, in: Z. Phys. : 41 (1972), pp.190). He asks Pauli to calculate it.

Ehrenfest discusses in a joking language the results of some of his investigations in the light of Pauli's exclusion principle.

Dyson writes about the renormailzed field theory and on Pauli's problem of "ghosts".

Dyson explains why the symmetrical treatment of the radiation field gives the right answer in Schwinger's theory. The letter contains information about experimental results of Powell on fast Pi-mesons and a discussion of the question longitudinal photons.

The letter contains Dyson's reply to Pauli's letter about the convergence problem, meson theories and renormalization and series expansion.

In this letter Dyson criticizes Heisenberg's use of the "Hilbert space II" as an alternative to renormalization.

Dyson writes about the renormalization method in quantum electrodynamics, especially on the renormalization of the Heisenberg operators.

Dyson sends more details about the renormalization method.

Dürr's original letter was accompagnied by a copy of the preprint "Isospin group in the theory of elementary particles" by Heisenberg and Pauli. He added some remarks to the document.

Dürr clarifies certain points in his note concerning his remarks to Heisenberg's and Pauli's preprint.