The Effect of Retardation on the Interaction of Two Electrons

An approximate wave-equation (6) is set up which takes into account terms of the order ${\left(\frac{v}{c}\right)}^2$ in the interaction of two electrons. This equation (6) is reduced to a form (48) which can be interpreted in terms of electronic spins. Disregarding the effect of retardation the two electrons are described by formula (10). This is reduced to a form (36) which can also be described in terms of spins. It is shown that the retarded equation (48) differs from the non-retarded (36) by terms which affect the fine structur of orthohelium and which have not been known so far.