Heisenberg replies to Pauli's calculations on hydrogen according to quantum mechanics and makes some remarks on his results.

Heisenberg replies to Pauli's letter. He fully agrees with Pauli's considerations regarding impact processes, which clarify the physical meaning of Born's formalism. He talks about the physical reality of Pauli's p-waves and the indeterminacy relations. Space and time can be applied only to many particles, like temperature and pressure in a gas. He writes about the meaning of the matrix-elements and on the concept of fluctuation of electrical density.

Heisenberg sends Pauli his manuscript, on the whole identical with his long letter. He writes about the postulate character of his quantum mechanical assumption and its similarity with the assumption of the constancy of light velocity.

Heisenberg writes on the difficulties of the phase problem in radiation theory, and on a Hund's paradoxon about optically left- and right-rotating substances and its solution.

Heisenberg writes about Pauli's suggestions for the quantum-theoretical relations between electrical and magnetic field strengths. He writes also about Pauli's criticism of Dirac's paper and discussions with Bohr about his thought experiments.

Heisenberg writes about his discussions with Bohr on the "$\Gamma$-ray-microscope". He makes some remarks on Pauli's electrodynamical considerations, on the Hamiltonian interaction function between radiation and matter and on a paper by Darwin about Heisenberg's and Jordan's formulae.

Heisenberg writes about the Dirac-Jordan theory and Heisenberg's criticism of Bohr's objections.

Heisenberg continues his letter on ferromagnetism.

Heisenberg replies to Pauli's questions about his letter on ferromagnetism: 1) on the magnetic moments of the atom residues, 2) the case of paramagnetism, 3) the calculation of the state-sum.

The letter includes remarks on a paper by Pauli, on a second paper by himself on ferromagnetism for the Sommerfeld-Festschrift and on Dirac's theory.