92 MR. A. E. OXLEY. ON THE INFLUENCE OF MOLECULAR 



upon the configuration of the molecule. These latter forces will, in general, be 

 different from the former, and will give rise to a difference of cohesion which accounts 

 for the greater ease of cleavage of crystals in certain directions. [*Her'e, again, we 

 have further proof of the truth of the hypothesis of molecular distortion in crystalline 

 media. It is true that if to a liquid we could apply such an intense field that all its 

 molecules are orientated, that liquid would possess a double refraction equal to that 

 of a crystal, but as long as there is no mutual action between the molecules this 

 doubly refracting medium could show no signs of rigidity and no preference for 

 cleavage along certain planes, t Clearly the process at work in the formation of a 

 crystalline structure is that of a binding force (mutual induction in our case) between 

 two unbalanced parts of two adjacent molecules. All magne-crystallic properties can 

 readily be interpreted in terms of such a mutual effect. It is important to note, 

 however, that unless we recognize the enormous intensity of the local molecular field, 

 which, together with the large local intensity of magnetization in diamagnetic 

 crystals, binds the molecules together and by a mutual induction effect distorts them, 

 we could not account for the rigidity of the crystalline medium, or the extent of its 

 double refraction. It appears that TYNDALL'S explanation! of the deportment of 

 diamagnetic crystals when placed in a magnetic field as due to a mutual action 

 between 'the diamagnetic molecules is sufficient to account qualitatively for the 

 behaviour observed, but it is difficult to see, on TYNDALL'S view of a simple and very 

 minute diamagnetic polarity, where such large forces as those demanded for crystalline 

 media could have their origin. On our view a diamagnetic molecule as a whole 

 possesses a small diamagnetic polarity, an induction effect of the applied field, and the 

 force due to it at a point considerably removed from the molecule is small. But in 

 between a pair of molecules the internal forces are unbalanced, and the intensity of 

 the local field is comparable with that in ferro-magnetic substances. On the other 

 hand, quite close up to the diamagnetic molecule conceived by TYNDALL, the force 

 binding it to a neighbouring molecule is not intense enough to account for the 

 difference of magnetic property in different directions, as Lord KELVIN pointed out. 

 The explanation of magne-crystallic action formulated by TYNDALL (this is the theory 

 of reciprocal molecular induction) accounts qualitatively for the phenomena but 

 certainly fails from a quantitative point of view. The present conception of a 

 diamagnetic molecule surmounts the latter difficulty.] 



As this question of determining the order of intensity of the local forces and local 

 polarizations within diamagnetic crystalline media is of the greatest importance, any 

 additional proof of the correctness of the values assigned to them is valuable. Let us 



therefore try to form some estimate of the magnitude of the term .a' e . P, which 



2/> c 



* [Added November 12, 1914.] 



t Of. the liquid crystalline state. 



I TYNDALL, 'On Diamagnetism and Magne-crystallic Action,' 1870, p. 69. 



