360 
Proceedings of the Royal Society of Edinburgh. [Sess. 
therefore may remain lying tangentially to both atoms. At the same 
time the electrons in the two inner shells will be magnetically attracted 
to each other. It is, however, conceivable that the electrons in one atom 
may be placed so that their north and south poles are reversed, as shown 
in fig. 8. In this case it is evident that the two external electrons are no 
longer stable in the tangential plane, and will tend to swing round a 
common centre into the radial plane of one atom or the other. 
We thus seem to have a possible explanation of why in the case of 
some atoms combination is followed by ionisation, while in the case of 
other atoms no ionisation takes place. 
Let us suppose 
two atoms, as 
shown in 
fig. 8, 
to 
have 
approached 
\N 
s/ 
\n 
s/ 
s\ 
/N 
S\ 
/N 
N 
S 
N 
s 
S 
N 
S 
N 
n/ 
\s 
n / 
\s 
/S 
N\ 
/S 
N\ 
N 
N 
S 
S 
A 
N 
N 
J 
S 
S 
\n 
s/ 
\s 
n / 
s\ 
/N 
N\ 
/S 
N 
S 
s 
N 
S 
N 
N 
s 
n/ 
\s 
s/ 
\N 
/S 
N\ 
/N 
S\ 
Fig. 7. — Combination without ionisation. 
Fig. 8. 
— Combination to be followed by 
ionisation. 
each other, and the two electrons to have swung into a tangential plane ; 
they will now tend to swing on a common centre into a radial plane, with 
a lowering of the magnetic potential energy of the system. They are 
now subjected both to the electrostatic attraction of the nuclei of the 
two atoms and to the magnetic attraction of the two atoms tending to 
draw them into their respective magnetic fields of force. Probably, 
therefore, the question as to which atom will depart with both electrons 
will depend upon the algebraical sum of these electrostatic and magnetic 
attractions. There will be a further lowering of magnetic potential 
energy as the electrons are drawn into the magnetic field of one of the 
atoms (fig. 9). 
We can thus understand how it is that while chlorine in combining 
with potassium ionises, chlorine in combining with oxygen will produce a 
compound and will not ionise ; as we may suppose that in the case of the 
non-metallic elements the electrons are all inserted into the shell with 
