Pauli sends Heisenberg his calculations on the hole theory. He thinks the whole derivations are cogent, in spite of the starting point which differs completely from Dirac's. He makes some remarks on the neutrino problem. He believes, like De Broglie, that a photon consists of a neutrino plus a neutrino hole.

Pauli writes of his calculations with Weisskopf of polarization effects in changing fields.

Pauli sends Heisenberg his calculation on the quantization of the Klein-Gordon equation and explains the results.

Pauli writes of his intention to publish with Weisskopf on the quantization of the relativistic scalar wave equation, and with Bose on statistics. He comments on Heisenberg's ideas about a future unified field theory.

Pauli is disappointed with Heisenberg's letter on nuclear physics. The indefiniteness of the go-functions in Heisenberg's and Majorana's nuclear theory is unsatisfactory.

Pauli agrees with Heisenberg about V Neumann's paper. He also believes in the significance of a universal length.

Pauli agrees with Heisenberg's suggestion (letter of 2nd February) for the modification of his theory, and adds some remarks on this.

Pauli comments on a paper by Heisenberg about nuclear forces and its relation to the Yukawa-theory.

Pauli makes two remarks concerning Heisenberg's letter of 5 April about nuclear forces.

Pauli talks about the question of Beta-spectra. The literature gives ample evidence against Heisenberg's hypothesis.