Physics. — “On the calculation of the molecular quadrupole-moments 
from the equation of state.” By Prof. W. H. Kersom. (Com- 
munication N°. 9 from the Laboratory of Physics and Physical 
Chemistry of the Veterinary College at Utrecht). (Communicated 
by Prof. H. KAMERLINGH ONNEs). 
(Communicated at the meeting of September 24, 1921). 
§ 1. Introduction. When the potential in the field of the electric 
charges in a rotational symmetric homopolar molecule is developed 
in a series of powers of r~!, the first term may be regarded as 
being due to a zonal quadrupole. 
As far as is evident from the investigation of the equation of 
state especially for hydrogen, the molecular attraction in diatomic 
homopolar gases may be regarded to a first approximation as due 
to such a quadrupolar term in the field of force of the molecule, 
at least for a high temperature and in a diluted gaseous state. That 
finally an attraction results must be ascribed to two causes: 1st that 
two molecules when approaching each other will try to direct 
each other in such a way that attracting forces arise between them, 
and 2nd that in two approaching molecules the charges are displaced 
by their mutual influence thus that this gives rise to an attraction. 
As far as this Drsiue') and the author’) agree. Their opinions 
1), P. Depie. Physik. ZS. 22, p. 302, 1921. Very interesting is the application 
made by Depise of these considerations to monatomic gases, where the mutually 
directing influence of the molecules mentioned under 1st becomes zero, so that only 
the attraction due to the polarisation of the molecules mentioned under 2nd remains. 
See for this also F. Zwicky, Physik. ZS. 22, p. 449, 1921. As to this, we may 
remark however the following. The application of the above to a quadrupole 
term in the field of the monatomic molecules gives us a mean value of the 
potential energy of two such molecules proportional with r—§ (a dipole term would 
give r—6), while on tbe contrary the observations for argon are more in favour 
of r—t or r-5 (hydrogen below the BoyLr-point 7-4), see Leiden Suppl. N°. 26 
§ 3, these Proceedings October 1912, p. 643. 
2) Comm. N°. 6), these Proc. Vol. XXIII, NO. 6, 1920. Physik. ZS. 22, p. 129, 
1921. 
