250 
MAJOR A. E. OXLEY ON THE INFLUENCE OF MOLECULAR 
susceptibility of matter in hulh depends upon a transition from the liquid to the 
crystalline state. When thus considering diamagnetic matter in hulk, the large local 
forcive which has been shown to hind the molecules of the crystalline structure 
together need not he considered, since for matter in hulh its effects are cut out by the 
mutual compensation of molecular fbrcives. It is only when we enquire into the 
molecular structure of the crystalline medium, or to changes in this structure, that we 
pass to the inner limit where the principles of Larmor and Cauchy for the fluid state 
no longer apply. Larmor remarks : “ The result of the integration still however gave 
us a valid estimate of the effect of the material system as a whole, when we bore in 
mind that the infinite or rather undetermined term entering at the inner limit really 
represents the part of the result which depends solely upon the local molecular 
configuration ; a part whose actual magnitude coidd he determined only when that 
configuration is exactly assigned or known ” (loc. cit., p. 125). 
It is with this “ infinite or rather undetermined term.which depends 
solely upon the local molecular configuration ” that these researches are mainly 
concerned. It lias been called the local molecular field of the crystalline medium 
(Part III., p. 83). 
(2) On the Energy and Ultimate Tensile Strength Associated with 
Crystalline Media or Gels. 
The large intrinsic potential energy associated with a crystalline medium has been 
discussed in para. 5, Part III., pp. 90-95. It now remains for us to examine the 
accompanying stresses to see how far the elastic properties of material media may be 
interpreted in terms of these intrinsic forcives. Consider first the case of a liquid 
which is gradually cooled in liquid air so that it passes into a glass-hard transparent 
gel when it arrives at the temperature of the liquid air. 
It has been suggested (Part III., p. 81) that the appearance of rigidity in the gel 
is due to an interlocking of the irregulaily shaped molecules (arranged at random) 
whose thermal agitation is sufficiently reduced. On account of this random orientation 
of the interlocked molecules the gel will he Isotropic. At such a low temperature, 
also, the molecular motions will he highly constrained so that a particular molecule 
will present practically the same aspect to the surrounding molecides over a long 
period. If this is the case, then the local molecular forcive between this and a 
neighhouring molecule will act in a definite direction and will not be rapidly changing 
its direction as would he the case with the same molecides at a considerably higher 
temperature (in the ordinary liquid state). It is clear therefore that between the 
molecules of the gel at low temperature we shall have a large local forcive in operation, 
due to the interaction of the magnetic systems or revolving electrons within each 
molecule, but the direction of the action of this forcive between any pair of molecules 
will he one of random distribution, as we pass from pair to pair of molecules, although 
at any given point it is fixed in direction. 
