The logarithmic part of the Lamb shift in hydrogen is related to the usual infrared divergence and can be obtained immediately from the corresponding radiative correction to the Coulomb scattering amplitude. By a simple generalization of Welton’s arguments we get one of the recoil contributions. To complete the recoil calculation one has to include an elementary iteration of the Thomson amplitude. In this way we derive also the logarithmic part of the Lamb‐shift operator in positronium and many‐electron atoms.

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