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MR. A. E. OXLEY ON THE INFLUENCE OF MOLECULAR 
It appears therefore that these two expressions for the diamagnetic and 
paramagnetic properties are generally applicable and explain the variation of 
susceptibility with temperature in terms of two Curie laws. These laws are exact 
to within the limits of experimental accuracy, and any variation of the magnetic 
property which is apparently not in accordance with them can be attributed to 
variation of the molecular complexity. 
PART II. 
(l) A Theory of the Phenomena found in the above Experimental 
Researches in Terms of the Electron Theory of Magnetism. 
The theory of Lorentz, which postulates no free magnetism, but attributes 
magnetic phenomena to the motion of electric charges, accounts admirably and in a 
simple way for the main characteristics of the Zeeman effect and for the rotation of 
the plane of polarisation in a magnetic field. Each of the latter phenomena appears 
to be closely related to the diamagnetic property of a substance; for Langevin has 
shown that the magnetic moment produced in a molecule by the application of an 
external magnetic field is such as would lead to diamagnetism by a process which is 
compatible with the simple explanation of the Zeeman effect givfin by Lorentz. 
Further, the fact that the magnetic rotation produced by the ferromagnetic elements 
is proportional to the intensity of magnetization, and not simply to the intensity of the 
applied magnetic field, shows that we must take into consideration the magnetic 
property in this case also. 
No theory has yet been devised, however, which is completely consistent with the 
principles of mechanics and the phenomena—optical and electric—of the luminiferous 
medium, and in adopting the theory of Lorentz, we are merely seeking to obtain a 
fuller interpretation, on certain hypotheses, of the experimental facts obtained in 
Part I. But it is evident that whatever theory be adopted with regard to the origin 
of the diamagnetic property, any distortion of the molecular system, such as is 
produced by crystallization, must be accompanied by an adjustment of the magnitude 
of that property. 
To obtain a satisfactory interpretation of the phenomena which have been observed 
in the experiments of Part I., we must take into consideration the forces which the 
systems of rotating electrons in different molecules exert on each other. Lorentz 
has shown that the force exerted on an electron (surrounded by neighbouring systems) 
by an electric force E is not simply eE, where e is the charge on the electron. A term 
e .f{ P) must be added, where P is the electric polarisation of the medium, and the 
function f characterizes the grouping of the molecules for any particular state of the 
substance. The total mechanical force acting on an electron is therefore 
e[E + /(P)]. 
