CONSTITUTION AND TEMPERATURE ON MAGNETIC SUSCEPTIBILITY. 
Ill 
molecule and of such modification of that structure as is produced by the mutual 
actions between the molecules. 
Thus stated, the diamagnetic property of a substance depends upon the molecule 
as a whole. The above hypothesis postulates no definite structure of the atom or 
molecule beyond that it is capable of assuming a slightly distorted configuration due 
to the influence of neighbouring atoms or molecules. 
The interpretation of the experimental facts (described in Part I. of this communi¬ 
cation) by means of the electron theory of magnetism will be withheld until the 
results have been discussed from the molecular standpoint. 
PABT I. 
(l) The Measurement of Magnetic Susceptibility at Air Temperature. 
The magnetic potential energy of a body placed in a magnetic field may be written 
W = -kMH 2 
where x is the specific susceptibility of the substance, M the mass of the body, and H 
the intensity of the magnetic field. For a small displacement of the body, 
AY = - x MHdH. 
If the body be so suspended that its displacement causes work to be done on the 
suspended system against a mechanical force, F, acting through a distance, Sr, 
we have 
AY + F . Sr = 0. 
Therefore 
SB. 
F = X MH 
dr 
( 3 ) 
In the present experiments the body, which was spherical, was placed with its 
centre at P (fig. l) with regard to the pole pieces A 
and B. The mechanical forces acting on the body are 
therefore by (3) 
X = xM(H,fAH,ft + HA 1 gf 
( 4 ) 
O 
P 
Yt 
X 
FIG. 
along Ox, with similar expressions for the forces Y 
and Z, acting along 0 y and Oz. If the body were 
truly spherical, with its centre at P, the forces Y and 
Z would be zero. In practice this is never the case, 
and Y and Z, although small, are not zero. Since, however, in these experiments 
* It should be noted that the term involving H x is large in comparison with the terms involving 
H„ and Hr. 
