Heisenberg believes that Pauli's proof of the infinity of eigenvalues is not cogent.

Heisenberg reports on the results of his investigation on the mathematical properties of Pauli's lattice world. He believes that further investigation on this model is worthwhile.

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

Heisenberg agrees now with Pauli that their model does not lead to the existence of showers, and cites qualitative arguments for this conjecture. He also writes about recent experimental results in nuclear physics.

The letter contains more remarks on the same model.

Pauli aknowledges receipt of Kemmer's manuscript. He asks him to look into the latest American papers on nuclear forces.

Heisenberg comments on Bhabha's and Heitler's paper which leads to agreement with Heisenberg's data about cross-section for genuine showers. There is a difference between Bhabha's and Heisenberg's conception regarding cosmic radiation at great depths. He writes on an experiment deciding between both conceptions: measurement of electron energies at great depths.

Heisenberg revokes his former statement about the relativistic invariance of the cut-off-method.

Heisenberg has received Fierz's paper and agrees.

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