The interaction between two fermions of charge ${\epsilon }_{\mathrm{I}}$ and ${\epsilon }_{\mathrm{II}}$ and intrinsic magnetic moment ${\mu }_{\mathrm{I}}$ and ${\mu }_{\mathrm{II}}$ is described by a sixteen-component wave equation of the Breit type. The method of reduction of two-particle wave equations, as given in two previous papers by Chraplyvy, is used to convert this equation to an approximate four-component Pauli equation. A simple perturbation calculation is used to determine the contribution of the intrinsic magnetic moments to the fine and hyperfine structure of hydrogen and positronium.

• Received 12 November 1954

DOI:https://doi.org/10.1103/PhysRev.99.317