electrons in the atom shall be bound in each succeeding element in an orbit of the same principal quantum number as that possessed by the particular electron, when it first appeared. It is readily seen that this is no longer the case for the
th electron. With increasing nuclear charge and the consequent decrease in the difference between the fields of force inside and outside the region of the orbits of the first
bound electrons, the dimensions of those parts of a
orbit which fall outside will approach more and more to the dimensions of a
-quantum orbit calculated on the assumption that the interaction between the electrons in the atom may be neglected. With increasing atomic number a point will therefore be reached where a