has the same signification as in [Part II.], and
denotes the component, perpendicular to the plane of the ring, of the force due to the nuclei, which acts upon one of the electrons in the ring when it has suffered a small displacement
perpendicular to the plane of the ring. As for the systems considered in [Part II.], the displacements can be imagined to be produced by the effect of extraneous forces acting upon the electrons in direction parallel to the axis of the system.
For a system of two nuclei each of charge
and with a ring of
electrons, we find