648 The Philippine Journal of Science 1921 
able to each nucleus and electron in the compound A — B — C, 
and therefore any shift of any of the electrons in the compound, 
or of nucleus A or B, will cause a slight displacement of the 
position of equilibrium of the electron in question. For calcu- 
lating the direction and relative amount of such displacement 
we may tentatively apply the ordinary laws of electrostatics, 
but only to the mutual repulsion of electrons. 
When an electron is shared by two shells, as an electron shared 
by C and D in the compound A — B — C — D — E — F, it is con- 
J)/jfa/2ce J^ro/n nuclei C 
— > 
Fig. 2. Composition of forces of restitution acting on a shared electron. 
venient to consider its constraint to be the resultant of two 
single constraints of the nature just described. One of these 
originates in A — B — C — , and the other in — D — E — F. The 
composition of two single constraints is shown in fig. 2. 
Shell boundary. — It is convenient to consider that, when an 
electron is moved beyond the point where its constraint toward 
the nucleus reaches a maximum, it is dissociated and no longer 
inside the shell. Accordingly the points of maximum radial 
single constraint constitute a dissociation boundary. This boun- 
dary <}bviously has meaning only in reference to a certain 
specified electron or pair of electrons. For certain purposes 
there seems to be an advantage in extending the idea to a shell 
