270 
MAJOR A. E. OXLEY ON THE INFLUENCE OF MOLECULAR 
In a diamagnetic crystalline medium, as the temperature is raised, the local positive 
susceptibility will obey a similar law, the temperature of fusion now corresponding to 
the critical temperature in the ferro-magnetic case. Although locally the relation 
between susceptibility and temperature is the same in the two cases, the effect passes 
unnoticed in the diamagnetic case because the molecule has a total zero magnetic 
moment. Nevertheless, the effect of temperature acts in its two antagonistic ways in 
diamagnetic as well as in ferro-magnetic media. When the temperature is above the 
melting point, the rotational energy of the molecules annuls the local forcive (liquid 
state), when it is very low the molecules become interlocked and cannot readjust 
themselves in a space lattice (gel state). There is an intermediate region of 
temperature where opportunity is offered for the tendency of self-orientation under 
the mutual local forcives to display itself, and over this range crystallization may 
take place. This intermediate temperature range deffnes the closed region of stability 
of the crystalline form on the pressure temperature diagram of equilibrium of the 
crystalline and amorphous states (see p. 263). 
A discussion as to how far we may regard it as proved that the local molecular tield 
in crystalline media is of magnetic nature was given in para. 8, of Part III. The 
conclusion reached was that the molecular field is certainly in part magnetic. It is 
possible to bring forward further evidence of the truth of this deduction. In some 
noteworthy researches* published by Tyndall, as long ago as 1870, it was shown that 
magnetic properties of crystalline media bear a close relation to molecular aggregation. 
About 100 different crystals were examined and from the deportment of these, when 
subjected to a magnetic field, Tyndall found that “if the arrangement of the 
component particles of any body be such as to present different degrees of proximity 
in different directions, then the line of closest proximity, other circumstances being 
equal, will l)e that chosen by the respective forces for the exhibition of their greatest 
energy. If the mass be magnetic this line will stand axial, if diamagnetic, 
equatorial. ”t 
The exactness of the dependence of magnetic deportment on the position of cleavage 
planes is remarkably shown in these experiments. Whatever the crystal examined, it 
was found that the magnetic deportment disclosed accurate information of the planes 
of cleavage. Tyndall describes the results of his important experiments in such 
elegant language that it may be permissible to quote some of them at length. Thus 
he continues ;—“ From this point of view, the deportment of the two classes of crystals 
represented by Iceland spar and carbonate of iron, presents no difficulty. This 
crystalline form is the same, and as to the arrangement of the particles, what is true 
of one will be true of the other. Supposing then, the line of closest proximity to 
coincide with the optic axis; this line, according to the principle expressed, will stand 
axial or equatorial, according as the mass is magnetic or diamagnetic, w'hich is 
* ‘ On Diamagnetism and Magnecrystallic Action,’ 1870, 
t Loc . cit ., j). 23. 
