Physics. — “The cohesion forces in the theory of VAN DER Waars”’. 
By Prof. W. H. Kersom. (Communication N°. 65 from the 
Laboratory of Physics and Physical Chemistry of the Veteri- 
nary College at Utrecht). Communicated by Prof. KAMERLINGH 
ONNES). 
(Communicated at the meeting of November 27, 1920). 
§ 1. (Introduction. Desise') has recently shown in an important 
paper on the cohesion forces in the theory of vaN DER Waats that 
these may be explained in this way that one molecule in the field 
of neighbouring molecules obtains a bipole moment, and that because 
of this bipole moment it is attracted by the inducing molecule. 
DeBije considered especially those gases the molecules of which 
possess no spontaneous bipole moment. In the calculation he assumed 
that the field of the molecules could be treated in first approximation 
as that of a quadrupole. Evidently neighbouring molecules will influence 
their mutual direction in such a way that the cases of attraction 
are more frequent than those of repulsion. In a preliminary orientating 
calculation the mean mutual attraction of the molecules due to their 
own quadrupole moment was neglected. In fact, this will be allowed, 
as was already remarked by Desig, for sufficiently high temperatures. 
Then this mean attraction vanishes namely as the heat movement 
hinders the directing influences of the molecules mutually. 
On the other hand we have shown (Comm. Leiden Suppl. N°. 39a) °) 
that the molecular attraction in hydrogen, at least as far as to the 
second virial coefficient, may be explained by the circumstance that 
those molecules possess a quadrupole moment, while a contribution 
to the attraction due to the mobility of theelectrons in the molecules 
was neglected. In fact, Derije remarks rightly that in the calculation 
of the molecular attraction we shall have to attend to the attraction 
of the molecules mutually because of their quadrupole moments as 
well as to that especially treated by DeBie and due to the polarisa- 
bility of the molecules in an electric field. 
In this paper we shall discuss principally the influence of the 
1) P. Dezije, Physik. Z.S. 21 (1920), p. 178. 
*) These Proceedings, vol. 18, p. 636, See also W. H. KEEsom and Miss C. 
VAN LEEUWEN, these Proceedings, Vol. XVIII, NO, p. 1568. 
