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THE QUANTUM [ix. 2 
hexagon, is of the same order of magnitude for an element as 
for a polar compound. These results certainly suggest that the 
electrons occupy, or oscillate about, positions of equilibrium in 
the atomic lattice. 
This view forms the basis of the theory developed by Borelius * 
to account for the electric properties of the metals, a theory 
which leads to results in good agreement with experiment. On 
the ground of simplicity there is much to be said for the supposition 
that the electrons concerned in fixing the space lattice of the 
metallic crystal are either stationary or execute small oscillations, 
and if this be correct, it is natural to assume that in a gaseous 
molecule also those electrons which play the part of chemical 
bonds occupy more or less fixed positions with regard to the 
atomic cores. 
The question suggests itself whether it is possible to construct 
a static model of an atom in which all the negative electrons are 
in fixed positions with reference to the positive part of the atom. 
Historically, the atomic models of Kelvin and J. J. Thomson 
in which the positive electricity is a spherical volume distribution 
are of great importance, but when we employ the model of the 
nuclear atom the conditions for statical equilibrium cannot be 
satisfied in so simple a manner. 
An interesting attempt to construct an atomic model on 
mechanistic principles was made in 1915 by A. L. Parson,f who 
supposed the electron endowed with a magnetic moment. A 
prominent feature of this theory is the group of 8 magnetons, 
which forms a system of low magnetic energy, and therefore of 
considerable stability. In the hydrogen molecule two shared 
magnetons are regarded as forming the chemical bond between 
two like atoms. 
2. The Static Models of Lewis and Langmuir 
A most interesting attempt to assign a definite spatial con 
figuration to the electronic system of atoms and molecules has 
been made by G. N. Lewis, and his work has been extended by 
Langmuir. The facts of stereochemistry make it clear that an 
arrangement in three dimensions is required. 
The inert gases are the most stable of the elements. We infer 
that in these the electron configurations are the most stable 
possible, and are “ complete ” ; in other elements the groupings 
are incomplete, and the activity of such elements is attributed 
* Borelius, Phil. Mag., voi. 40, p. 746, 1920. 
t A. L. Parson, Smithsonian Miscellaneous Collections, voi. 65, No. 11, 
1915.