CONSTITUTION AND TEMPEEATURE ON MAGNETIC SUSCEPTIBILITY. 259 
As Love points out, the values of these elastic constants for lieryl and topaz are 
remarkable in that they are greater than the corresponding constants in ordinary 
steel. The values of the elastic coefficients for most of the other substances in the 
above table are comparable with the constants for steel, and it is considered that these 
results give very strong evidence in favour of the large intermoleciilar forcive 
operative m diamagnetic crystalline media and confirm the suggestion made in 
Part II., p. 143, that this local forcive is comparable with that in ferro-magnetic media. 
If a crystalline medium be heated, then as long as the crystalline state prevails, 
rotational vibrations of large amplitude are prevented, so that the specific lieat of 
the crystalline medium is lower than that of the supercooled liquid.'^' In the latter 
case, the liquid at low temperatures passes into a rigid gel, and when this is heated, 
the molecules acquire rotational vibrations gradually until finally the ordinary liquid 
state is reached, possessing no appreciable rigidity. It is important to note that the 
molecules are vibrating under a local forcive to which we are ascribing the elastic 
properties of the medium, and therefore the theory is consistent with the theory of 
specific heat developed by Debye, in which the forces which control the thermal 
vibrations of the molecules are identical with those which determine the elastic 
constants of the medium. Madelung and Sutherland have similarly suggested 
that the elastic forces resisting mechanical strain are just those forces which determine 
the infra-red optical vibrations of the atoms m the solid substance. It has been found 
possible to calculate the infra-red frequencies from a knowledge of the mechanical 
properties. In the present researches it has been shown that we can calculate both 
the optical frequenciest and the mechanical stresses from the local molecular forcive. 
Within the core of the atom the local controlling force may be more intense, and 
although such an intense forcive would not be directly operative in determining the 
state of crystallization, yet it might be responsible for determining frequencies on 
the ultra-violet side comparable with X-ray frequencies. (See infra, pp. 273 and 278.) 
(4) The Change of Density on Crystallization Interpreted as a Magneto¬ 
striction Efeect of the Molecular Field. 
If we subject a liquid to a magnetic field, a change of volume occurs to such an 
extent that the internal pressure is reduced by an amount equal to the potential 
energy per unit volume of the magnetic field. This change of internal pressure (see 
Part III., p. 91) is 
+ .(2) 
where 
ki is the susceptibility of the liquid per unit volume, 
X, a constant equal to l/3, 
and 
H, the applied field’intensity. 
* Part III., p. 94. 
t A. E. Oxley, ‘Eoy. Soc. Proc.,’ A, vol. 95, p. 58, 1918, and Part III., p. 84. 
