will, to a close approximation, act on an electron as a simple nucleus of charge
. For a system consisting of two electrons and a nucleus of charge
, we may therefore assume the existence of a series of stationary states in which the electron most lightly bound moves approximately in the same way as the electron in the stationary states of a hydrogen atom. Such an assumption has already been used in [Part I]. in an attempt to explain the appearance of Rydberg’s constant in the formula for the line-spectrum of any element. We can, however, hardly assume the existence of a stable configuration in which the two electrons have the same angular momentum round the nucleus and move in different orbits, the one outside the other. In such a configuration the electrons would be so near to each other that the deviations from circular orbits would be very great. For the permanent state of a neutral helium atom, we shall therefore adopt the configuration
Since
we see that both electrons in a neutral helium atom are more firmly bound than the electron in a hydrogen atom. Using the values on [p. 38], we get
