Kemmer gives more calculations on the wave equation and makes a comparison with de Broglie's results.

Critical remarks from Kemmer about Bhabha's calculations on the neutretto-meson theory and remarks on the Bremstrahlung of the meson.

Kemmer gives a development of a convenient formalism for the wave equation, different from the usual representation of Dirac's Hamiltonian.

The letter contains some calculations on irreducible group representations.

Kemmer replies to a letter by Pauli. He writes on calculations on the regular representation of the Abel group and about irreducibility of this representation.

Kemmer rejects an assumption made by Pauli.

Continuation of the letters of 8/9 May.

This reply to Pauli's letter is about the irreducibility of the n- group representation.

Continuation of the letter of 8 May, Kemmer makes more remarks about the relation of his representation of the wave equation to de Boglie's.