Dyson writes about Baranger's calculation of the relativistic correction to thesecond order lamb-shift. He adds to the letter his ideas about the renormalization programm.

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.

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.