in Diamagnetic Substances. 451 
where a,’ is the constant of the molecular field of the diamagnetic 
‘substance, J is the aggregate of the local intensities of magnet- 
ization per unit volume, and p is the density of the substance. 
This is analogous to the case of ferro-magnetism, given by Weiss%*, 
where the magnetic energy term is 
N/2 
gp css per gram. 
N is the constant of the ferro-magnetic field, / the saturation 
intensity of magnetization and D the density of the substance. 
If, as the diamagnetic crystalline substance is heated, the 
‘molecules perform rotational vibrations under the influence of 
the intense local forces, more heat must be supplied for a given 
rise of temperature than would be necessary if the molecules did 
‘not rotate. The corresponding increase of specific heat is given 
by the term 
where J is the mechanical equivalent of the calorie. 
: The molecular field, by which we may interpret the forces 
within the crystalline structure, is a,J, and is of the order of 
magnitude of the ferro-magnetic field of Weiss (10’ gauss). Hence, 
as in the case of ferro-magnetic substances, we may expect that 
the above term will form an appreciable fraction of the specific 
heat. Moreover, the expression (2) passes through a maximum 
in the neighbourhood of the fusion point. 
In so far as we can test the above experimentally, there seems 
_to be evidence in favour of the additional specific heat represented 
by (2). For sodiwm+ and mercury} there is a decided maximum 
of the specific heat in the neighbourhood of the fusion point such 
as (2) demands. A large number of substances have been in- 
vestigated by Nernst and Lindemann§, and they found that in 
general the specific heat is abnormally high as the fusion point 
is approached. 
This work will be continued in a future paper. 
if all the contained elementary systems are independent. Let n be the number of 
molecules per c.c., then we may write $Z|i||h|=4nih. h corresponds to the 
molecular field in terro-magnetism. If we write ni=I and h=a,’.JI, we find that 
LTD 
a 
the energy associated with one c.c. of the substance is eles 
2 
* Journ. de Phys., Sér. tv. vol. 7, p. 249, 1908. 
+ Kzer Griffiths, Proc. Roy. Soc., vol. 89 A, p. 561, 1914. 
+ The values for mercury were taken from the Tables of Physical Constants 
published by the Société Francaise de Physique, 1913, p. 305. 
§ La Théorie du Rayonnement et les Quanta, Paris, 1912. 
