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



should be able to detect a change of magnetic property when every substance 

 crystallizes. This again implies an enormous value for the local molecular field, even 

 if the change of x produced is so small as to be only on the verge of detection by our 

 present methods, as the first part of 4 shows. 



Among organic compounds aromatic substances show both these effects to an 

 exalted degree and it is from a study of these that the large molecular forcives in 

 diamagnetic crystalline media were first recognized. By the argument of the present 

 section it appears only justifiable to extend these resiilts to diamagnetic crystalline 

 media in general. Such an extension is warranted also by the values of the latent 

 heat. 



(8) ON THE NATURE OF THE MOLECULAR FIELD. 



The large local molecular field which has been recognized in diamagnetic crystalline 

 substances must have its origin in the individual atoms or molecules. In a liquid the 

 effects of these forces at any point within the medium average out to a small 

 resultant effect only as already indicated. When the substance crystallizes the 

 molecules are fixed in definite positions with regard to one another, and the polarization 

 or distortion produced in a molecule owing to the forces exerted by its neighbours is 

 no longer an average value. The modifications of the physical properties of substances 

 at the fusion point readily fall into line with this view. When the substance is 

 vaporized we must still assume that the force quite close up to the molecules is very 

 large and rapidly falls off on account of the compensating action of the other half of 

 the same molecule. If the pressure of the vapour were sufficiently increased so that 

 the local fields overlap, then we should expect that any physical property possessed 

 by the vapour would become modified. Thus HUMPHREYS* has advanced the view 

 that the pressure shift of spectral lines may be due to the co-operation of intense 

 magnetic fields located in neighbouring atoms. The pressure shift can be accounted 

 for if the intra-atomic field, interpreted magnetically, has an intensity of the order 

 10 8 gauss. Further, liiTzf has shown how to deduce the expressions of BALMER and 

 RYDBERG for the representation of spectral series, providing we assume that the 

 electrons are vibrating under an electromagnetic field whose order of intensity is 

 10 8 gauss. For this intensity of the intra-atomic field the frequency of vibration of 

 the electrons corresponds to that of visible light. If in the crystalline structure the 

 surrounding molecules exert a local field of the order 10 7 gauss, the electron in the 

 particular atom we are considering would have its orbit modified by an amount which 

 would account for a few per cent, change in the diamagnetic susceptibility. It is not 

 improbable that the intense intra-atomic fields of RITZ may be identified with the 

 field due to the magneton, the molecular field being the result of their mutual action 



* ' Astrophysical Journal,' vol. 23, p. 232, 1906, and vol. 35, p. 268, 1912. 

 t 'Ann. der Phys.,' vol. 25, p. 660, 1908. 



