CONSTITUTION AND TEMPERATURE ON MAGNETIC SUSCEPTIBILITY. 
143 
oppositely rotating systems of electrons. A diamagnetic molecule, on Langevin’s 
theory, has no initial magnetic moment but there can be complete compensation of the 
electro-magnetic forces due to the spinning electrons only at points considerably 
removed from the molecule. Although these forces are compensated at an external 
point, and the magnetic property observed corresponds to diamagnetism, yet between 
the molecules the forces will be large and the local intensity of magnetization may 
be comparable with that of ferro-magnetic substances.* It is interesting that the 
value of a c ', which defines the crystal structure of a diamagnetic substance, should be 
at least of as high an order of magnitude as the constant N of the ferro-magnetic 
field. It is probable that these large values of the coefficients of the molecular fields 
are the origin of the stability and rigidity of crystal structure in general. 
Since we may interpret the effect of the surrounding molecules by means of the 
term aP, it follows that if from any cause the polarisation P suffers a reversal of sign, 
then the sign of AH. will change, i.e., the variation of x on crystallization will 
correspond to the abnormal cases referred to in Part I. The mechanism by which 
this reversal of 0x is brought about may be attributed to a directive influence of the 
substituent (or other dissymmetry of the complex molecule) which will produce an 
electric polarisation effect of opposite kind in a neighbouring nucleus, according to the 
direction of the force between the substituent and the nucleus. 
The liquid state will be more diamagnetic than the crystalline state if AH./H, is 
negative, i.e., if the process of crystallization involves a small reduction of the self- 
induction of the electron orbits. This corresponds to the majority of cases investigated 
in Part I. 
In the above theory no account has been taken of the small reaction forces! which 
will arise from the production of the diamagnetic moment AM„. Since, however, x 
(and therefore AM.) does not vary by more than a few per cent, as the substance 
passes from the liquid to the crystal state, these small reaction effects will appear in 
both states approximately to the same extent and therefore the value of 3x will not 
be affected on their account. 
• Summary of Conclusions. 
The experimental results described in Part I. have established an almost complete 
parallelism between the dependence of diamagnetic and ferro-magnetic susceptibilities 
upon molecular constitution. The molecular changes are of the same nature and the 
only difference between the two classes of magnetic phenomena lies in the character 
of the magnetic property possessed by the molecules and by which the variation of 
molecular complexity is disclosed. 
* See Note added, p. 145. 
t Langevin, ‘Ann. de Chim. et de Phys.,’ VIII., vol. 5, p. 88, 1905, concludes that such effects would 
not produce an appreciable change in the magnitude of \. 
