~ 1409 
that they belong to about 65 @ (calculated for solid mercury at Oe C.) 
correspond pretty well to the results obtained in the experiments 
in May 1911 Comm. N°. 1225, July 1911, viz. that a resistance of 
about 40 2 (calculated for solid mercury at 0° C.) becomes 0.084 2 
at the boiling point 4°.25 K. 
8. In these experiments the validity of Onm’s law was confirmed 
above the point where the almost sudden disappearance of the 
resistance begins which was treated in the previous Comm. by one 
measurement at a current strength of 3 and another of 6 milliam- 
peres which within the limits of accuracy gave the same result 
(0.0837 at 3, and 0.0842 at 6 m.A.). In connection with the expe- 
riments in Comm. N°. 1225 July 1911 we may mention that they 
were made with a resistance of a different kind from that’) which 
was used for the experiments in Oct. 1911, viz. the one which 
appears in the Plate of Comm. N°. 123 as 2y, (of about 40 2 
calculated for solid mercury at O° C.). Narrow tubes alternately going 
up and down were connected by expansion heads (as in the Plate 
in Comm. N°. 1245) and connected to platinum leading wires by 
fork-shaped turned down wide pieces’), which can be seen distinctly 
on magnification on the Plate in Comm. N°. 123 (where the resistance 
is shown in the eryostat). 
y. After this digression about the change in the resistance between 
ordinary temperature and the boiling point of helium, let us return 
to the experiments in and below the region of the sudden fall of 
resistance, which as has been said at the beginning of this § were 
made with a mercury resistance with mercury leads, and which 
were treated of in § 3 and fig. 1 of the previous Comm. (Dee. 1911) 
05 
about the resistance at helium temperatures (experiments of Oet. 1911). 
*) This was a ramification of solid mercury threads consisting of a U divided 
at both ends, allowing measurements as well by the method of CaLenpar as by 
the potentiometer method. (Note added in the translation). 
2) In the resistances which were used for the first experiments with mercury, 
the platinum leading in wires were simply sealed into the wider portions of the 
resistance tube at the ends (the expansion heads). When the mercury cannot be 
poured into the tube in vacuo but has to be boiled in the tubes in order that they 
may afterwards be exhausted without any chance of the mercury separating there 
is some fear of platinum amalgam being formed which might penetrate into the 
current circuit. In order to prevent this the wide ends of the tubes are according 
to a suggestion of Mr G. Hoist, made fork-shaped, the prongs which contain the 
sealing place being turned down. In this manner mercury leads may in general 
be replaced by platinum leads without any trouble being experienced with regard 
to the resistance of the current circuit. By a comparison with experiments with 
mercury leads it had been found that the mercury-platinum contacts could be 
allowed in the potential circuit 
