944 
molecular attraction on the equation of state, confining ourselves to 
the second virial coefficient. 
Now we may ask which of the two mentioned contributions to 
the attraction will have the greatest influence on the second virial 
coefficient at the temperatures for which the measurements on the 
equation of state were made. It will appear that for these tempera- 
tures the influence of the molecular attraction in B is principally 
due to the spontaneous quadrupole moments of the molecules. 
§ 2. Preliminary orientation. For shortness sake we shall denote 
by the name ‘quadrupole attraction” the contribution to the attraction 
due to the spontaneous quadrupole moments and by the name 
“induced attraction” the part due to the forces exerted by the qua- 
drupoles on the bipoles that are induced in the molecules. In the 
same way we shall speak of “quadrupole terms’ for the terms in 
the second virial coefficient due to the quadrupole attraction and 
of “induced terms” for those caused by the induced attraction. 
Between them this important difference exists, that at high tem- 
peratures the quadrupole terms become proportional to 7-2, 
while the induced terms become proportional to 7. 
This comes to the same as saying that the Van per W aars attrac- 
tion force in the case of quadrupole attraction becomes proportional 
to 7-1, whereas in the case of induced attraction they become constant. 
Now it has been shown already (Leiden Suppl. N°. 39a. See Fig. 
2 there and comp. also Leiden Suppl. N°. 39c § 3) that for hydrogen 
the second virial coefficient behaves more in agreement with the 
hypothesis of quadrupole attraction than with that a, = const., as 
would be demanded for high temperatures because of the induced 
attraction. Therefore we may evidently expect that at least for 
hydrogen, the quadrupole terms prevail. 
We may compare the values derived by Denise for the quadrupole mo- 
ment under the assumption that for high temperatures the induced attrac- 
tion has only to be considered, with the quadrupole moment found in 
Leiden Suppl. N°. 39a for hydrogen. This comparison is in agreement 
with the above conclusion. For hydrogen Dusise finds (table I 1.c.) 3,20 X 
10-26, while in the Leiden Suppl. N°. 39a a quadrupole moment of 
2,03 > 10-2 has been shown to give already a quadrupole attrac- 
tion sufficient to explain the experimentally found equation of state. 
The first of the quadrupole terms being proportional to the fourth 
power of the quadrupole moment, the quadrupole moments of 
Draijer would therefore give a quadrupole attraction that would be 
far too great. 
