,
may be due to a gradual interchange of electrons between the rings, such as is indicated on [p. 45]. Since a ring of
electrons will not be stable the electrons may be arranged in two parallel rings (see [p. 36]). Such a configuration of the inner electrons will act upon the outer electrons in very nearly the same way as a nucleus of charge
. It might therefore be possible that with increase of
another configuration of the same type will be formed outside the first, such as is suggested by the presence of a second period of