935 
The dimensions of the molecule, correspond, therefore, as regards 
the order of magnitude, with those determined in other ways. 
For liquid water DerBye has calculated the electric moment, and 
gives m,—=5,7.10-!" es. units. The correspondence is not altogether 
what might be desired. | have therefore recalculated the electric 
moment from the measurements made by BARDEKER ‘), who deter- 
‘mined the electric constant for water vapour and for ammonia. 
For water vapour the range of temperatures examined is very small, 
so that not much reliance was be put on the conclusions to be drawn. 
According to DeBrr, the following formula applies to the dielectric 
constant 
dame? N 
where a aay ate *). MN represents the number of molecules in 
1 em?*., & Prank’s constant 1,346. 10-16 erg. 
The first term «, is due to the quasi-elastic electrons, the second 
to the bipoles. | have calculated the first from the index of refraction 
for which I took n =1,000255 for water, and n = 1,000377 *) for 
ammonia. These values apply, it is true, to the visible spectrum, 
but the uncertainty introduced by this cannot be great, as «, itself 
is small. In the following table the calculated values of (€ — €) Seg 
QO 
will be found. The factor 9 
o 
NS 0 
the same number of molecules. 
The last column in the above table shows that for that part of 
the dielectric constant which is due to the bipoles, the same law 
holds as given by Curie for the magnetic susceptibility, at least in the 
case of ammonia. The correspondence is not so good for water. 
At the same time, in order to be able to continue the calculation, | 
have assumed that the law applied to water also’), using the mean 
constant in the calculation. In this way we find for the electric 
is introduced so as always to work with 
1) K. BAzDEKER Z. f. phys. Chem. (36), 305, 1901. 
2) See P. LANGEVIN. Ann. Chim. Phys. (5), 70, 1905. 
3) Recueil de Constantes Physiques. 
4) Whether deviations actually occur in water, as in magnetic substances, must 
be settled by further experiments. 
Further, the question arises, why the value of the electric moment calculated 
for water vapour deviates from that calculated by Derye for the liquid. [ thought 
the deviation might be accounted for by the fact that Derye has assumed in his 
