1129 
permissible for the explanation of the molecular attraction in the 
equation of state. In this paper it will be shown that very probably 
the answer to the above question must be in the negative. 
§ 2. Introductory considerations. 
When in the gaseous state two oxygen molecules come so near 
to each other that there arise mutual forces between them, these 
forces will generally form a couple, so that the molecules have 
a directing influence on each other. When we take the statistical 
mean and when we treat the electric field of the molecule to the 
first approximation as that of a quadrupole, it is due to this direc- 
ting action that there remains an attraction between the molecules, 
which becomes manifest in the equation of state as the attraction 
term introduced by van per WaAALs. *) 
When we desire to investigate what influence this directing 
action will have on the susceptibility, we must take into consi- 
deration the relative position of the electric quadrupolar axis and the 
magnetie dipolar axis in the oxygen molecules. In doing this we shall 
assume these two axes to have a fixed position in the molecule. 
Then we may distinguish the following three cases: 
a. the magnetic dipolar axis coincides with the quadrupolar 
axis; 6. the magnetic dipolar axis is perpendicular to the quadru- 
‚polar axis and c. they form an arbitrary angle with each other. 
In this paper only the two extreme cases viz. a and 6 will be treated. 
First we shall consider case a viz. where magnetic axis and 
quadrupolar axis coincide. This assumption would seem the more 
preferable, for all our considerations in this paper will be based 
on the validity of the laws of equipartition; and in that case only 
assumption « gives the right value for the specific heat in the 
gaseous state. 
First we shall investigate the influence on the susceptibility of 
the mutual directing action, which the molecules also exert on 
each other because of their quadrupolar forces, when the gas is 
placed in a magnetic field. We may then imagine, that by these 
attracting actions all molecules would be 
8 anited to form double molecules as has been 
represented in fig. 1 viz. that one of the two 
electric poles of one molecule lies against the 
7 equator of the other molecule (either one 
Heet magnetic axis, or both may also have direc- 
tions opposite to those indicated in the figure). 
1) Comp. W. H. KeEsom. Comm. No. 65. These Proceedings 23, p. 943. 
73 
Proceedings Royal Acad. Amsterdam. Vol. XXIII. 
