1408 
quickly and methodically on the day of experiment. Modifications 
of the experiments in connection with what one observes, must usually 
be postponed to another day on which experiments with liquid helium 
could be made. Very likely in consequence of some delay caused by the 
careful and difficult preparation of the resistances, the helium appa- 
ratus would have been taken into use for something else. And when 
we could go on with the experiment again, the resistance sometimes 
became useless (e.g. § 3) because in the freezing the fine mercury 
thread separated, and all our preparations were labour thrown away. 
Under these circumstances the detection and elimination of the 
causes of unexpected and misleading disturbances took up a great 
deal of time. 
§ 2. Confirmation of the sudden disappearance of the resistance 
at 4°19 K. and first observations concerning the potential phenomena 
at low temperature. The first experiments which showed the pheno- 
mena to be discussed were made in October 1911, with the resistance 
described in the previous Comm. (N°. 124c). 
a. Before discussing them let us consider for a moment the 
measurements which were made with this resistance at 4°.23K. and 
add something to what we said about them in the previous Comm. *). 
In the measurements which we are considering we could take ad- 
vaniage*) of the presence of Hg, to measure the portions between 
Hg, and Hg, and between Hy, and Hg, separately and afterwards the 
two in series. The result was Hy, Hg,=0.05182, Hy,Hg,=0.06172, 
together 0.1135 Q. This gave a necessary check on the determination 
of the twoin series Hg,Hg, = 0.1142 2°*). These values, considering 
1) For a survey of the observations concerning mercury at the lowest temp. in 
three figs. with rising scale the reader is referred to Rapport du Comité Solvay, 
Nov. 1911, fig. 11, 12 and 13 (in which read 13 for 12, and 12 for 13, Leiden 
Comm. Suppl. N° 29). 
2) The measurements with a view to which the tube Hg; was added (see Plate I 
in Comm. N°. 124c) were not made then, but postponed till later. (See § 5. 
They were to enable us to judge of the dependence on the section. 
3) The resistance at the boiling point of hydrogen was 3.27 2. A further Comm, 
will refer to the difference of the ratio of the values at 273° K. and 20° K. to 
those in previous measurements, which is here of no consequence and is due to 
different ways in which the mercury freezes. In the experiments described here 
similar differences were constantly found. 
It should be mentioned that the glass was tested at all temperatures for its 
insulation and also that when the potential difference at the terminals was found 
to be zero, it was always ascertained that the resistance of the galvanometer 
circuit which served to measure the P. D. had not changed materially. 
