102 
THE QUANTUM [vii. 5 
both in connection with successive elements forming a sequence 
and as regards the family relationships of analogous elements. 
We may emphasize his conclusion that the magnetic character 
istics of the ions in the first transition series may be brought 
into relation with the spectra of these elements, though the 
correlation is at present by no means complete.* Hund f has 
treated the question of the ionic magnetic moments of the rare 
earths, and has shown how the magnetic constants may be com 
puted from the quantum numbers of the electron orbits, employ 
ing Heisenberg’s principles to find the probable ground terms 
of the ions. 
“ The survey of the periodic table shows that the magnetic 
properties of atoms, so far as they are known, fall into line with 
the chemical and spectroscopic properties, being generally 
capable of correlation in terms of the general quantum theory 
of atomic structure” (Stoner). 
5. Magnetism and Chemical Combination 
In the electronic theory of magnetism developed by Langevin J 
the electrons are assumed to revolve in individual orbits, thus 
producing average effects similar to those of ordinary current 
circuits. Speaking of the electrons responsible for the magnetic 
properties of the molecule, he says (loc. cit., p. 122) : 
“ These are perhaps the very same electrons, situated in the 
outer part of the system, forming the molecule, that play a part 
in chemical actions, where we know that electrons equal in 
number to the valence come into action.” 
It should be observed that Langevin does not specify that 
the chemical forces due to his electrons are magnetic in nature. 
Such an idea was at least suggested in the work of Weiss § on 
the magneton, for he asks : “ What is the role of magnetic 
phenomena in chemical combination ? Are chemical forces 
magnetic in nature ? Are the valences, indeed, referable in 
some way to magnetons ? ” A. L. Parson || identified the electron 
with the magneton, and showed that many of the facts of 
chemistry receive an explanation by means of this assumption, 
special stress being laid on the stability of the group of eight 
magnetons. Parson was the first to point out the remarkable 
parallelism between chemical and magnetic unsaturation. 
* Stoner has pointed out the difficulties that arise in dealing with 
these ions in a paper on “ Magnetism and Molecular Structure,” Phil. 
Mag., vol. 3, p. 342, 1927. 
t Hund, Zeits. f. Physik, vol. 33, p. 855, 1925. 
X Langevin, Ann. de Chim. et de Phys., vol. 5, pp. 70-127, 1905. 
§ Weiss, Journal de Physique, [5] 1, pp. 900, 965, 1911. 
|| Parson, Smithsonian Misc. Coll., vol. 65, no. 11, 1915.