450 Mr Oxley, On an Application of the Molecular Field f 
On an Application of the Molecular Field wn Diamagneme 
Substances. By A. E. Ox ey, B.A., Coutts Trotter Student, 
Trinity College. 
[Read 23 February 1914. | | 
It is well known how Nernst and Lindemann* have extended 
the formula, given by Einstein, for the variation of the specific! 
heat of substances with temperature. Although the new formula} 
expresses the experimental results with moderate degree of ac-| 
curacy, yet, in the neighbourhood of the fusion point, there is an | 
abnormally large departure, the experimental value of the specific 
heat being always greater than the calculated value. The 
empirical expansion term, aS? (a, coefficient of expansion; S$, 
absolute temperature), used by Lindemann does not satisfactorily | 
account for the discrepancy f. 
Later Debyet has modified the Planck-Kinstein theory and | 
given a relation between the thermal properties and the claema) 
constants of a substance. 
In a crystalline substance we must regard the molecules as. 
subjected to large local forces which hold the molecules in position | 
in the crystalline structure, and if at the higher temperatures. 
the molecules begin to vibrate under the control of these forces, 
then we should expect the experimental value of the specific heat 
to be greater than that calculated on Debye’s theory. : 
It has been shown|| that we may interpret the forces which | 
hold.the molecules in position in a diamagnetic crystalline strue- ‘ 
ture, magnetically, and if we do so the magnetic energy associated | 
with one gramme of the substance may be written {] j 
4 i 
ee 
{ 
* Sitz. d. preuss. Akad. d. Wiss., p. 347, 1911. é ‘| 
+ See the memoirs by Nernst and Einstein, La Théorie du Rayonnement et les f 
Quanta, Paris, 1912; particularly p. 272. i 
+ Ann. der Phys., iv. vol. 39, p. 789, 1912. 4 
§ See Jeans, Phil. Mag., v1. vol. 17, p. 771, 1909. I am indebted to Mr Hzer | 
Griffiths for pointing out the work of Jeans in this connection. q 
| A. BE. Oxley, Phil. Trans. Roy. Soc., 1914 (Unpublished). 
4] On the electron theory of magnetism developed by Langevin, a diamagnetic 
molecule has no initial magnetic moment and the resultant force due to it will be | 
negligibly small except at points whose distances from the molecule are comparable 
with molecular dimensions. l 
If i be the local magnetic moment between any two molecules and h the local | 
intensity of the magnetic field, then the magnetic energy associated with one ¢.¢. | 
of the substance is | 
4>/a|| Al, | 
Ba 
