933 
the specific heat and specific volume of water vapour. Calling the 
pressures given by JacoB in K.G./em? p,;, the specific volumes 
. N are . . , 
in m*,K.G. v; and the residual term of the equation of state 
4,706 T | 
EE en hj: R; in dm*/KG. we find: 
a 
/ R; 
Bj Tt 1080 
= 
here v= a 
RD van 
R; de Us : ‘ 
“When ae DSO je draws. funchon. off eeen a 
UZ 
series of straight lines is obtained. From this diagram B and C ean 
be immediately read as a function of the temperature. In this way 
the values were found given in the following table. (p. 934) 
In the first place it will be seen that for water, as for ammonia, 
C is negative, and increases strongly with decreasing temperature. 
It is further clear that it will not be a simple matter to find a 
formula which represents C’ as a function of the temperature, all 
the more that there is nothing to guide us in the choice of the 
correct form of the function. As W. H. Kersom told me that he 
and Miss van Leeuwen had undertaken the deduction of a function 
of the kind required, I thought it advisable to await the result of 
this calculation before venturing upon the calculation of a purely 
empirical formula for myself. 
For the other coefficient, B, there is something to go by: water, 
like ammonia, has a large dielectric constant, which is a tempera- 
ture function. 
We may therefore assume, with P. DeByr'), that the water mole- 
cule has an electric moment. For spherical molecules with an electric 
bipole at the centre, W. H. Krxsom’) has calculated the coefticient 
B as a function of the temperature. [ will therefore compare the 
experimental values with those which Krxsom calculated. For this 
purpose, as suggested in Comm. Leiden Suppl. 25, we will draw F# 
as a function of log hv and log B as function of loy 7’. 
If the curves are shifted until they coincide over a fairly large 
range, we find for instance that loy b= 7,385 — 10 coincides with 
F=0,065 and log 7’ = 2,828 with log hv = 0,358. 
1) P. DeBye. Phys. Zeitschr. (13), 97, 1912. Comp. also J. Kroo. Ann. d, Phys, 
(42), 1383, 1913. 
2) W. H. Kersom. Comm. Leiden Suppl. 240, 
