1410 
At 4°.20 K. we find ourselves in the higher part of the almost 
sudden change. In the case that we are now about to treat it had 
almost become complete. With a current of 7.1 m.A. it was a con- 
siderable time before the condition became stable. When this had 
taken place, the resistance of Hy, Hg, was found to be 0.000746 2°). 
At a further cooling of the mercury to 4°.19° K. with the same 
strength of current the result was only Hg,Hy, < 1410 2. 
d. At 4°19 K. we come into the lower part of the region with 
which this Comm. deals in particular. The strength of the current 
had to be increased to 14 m.A. to give a perceptible potential difference 
at the ends of the resistance but even then it remained doubtful. It 
became distinct at a current strength of 0.02 amp. and was then 
2.510-5 V. At 0.023 amp. it became 5.10 V, and at 0.0288 amp. 
16 AO ENE 
When the mereury thread was cooled by helium which evaporated 
at a mercury pressure of 40 cm. that is at about 3°.65 K., with a 
strength of current of 0.49 amp. there was no potential difference 
to be observed at the extremities, the current had to be increased 
to the threshold value of 0.72 amp. to make the potential difference 
observable. 
e. The highest limit of the value which the residual resistance 
can have in the case of the lowest temperature, is therefore in 
these last experiments again considerably reduced by the application 
of stronger currents, viz. in this case (38°.65 K.) to 10~° of the 
resistance at O° C. (calculated for solid mercury) while in Comm. 
N°. 1226 June 1911 at 3° K. it could only be put at < 107. 
§ 3. Appearance of the same potential phenomena in a revised 
arrangement of the experiment. The appearance of the peculiar pheno- 
mena immediately above the “threshold value” of the current, gave 
rise to the question whether the just established limit would not 
have to be put lower when it should be possible to avoid the dis- 
turbanees, which might still exist, and perhaps showed themselves 
in the above mentioned phenomena. The most obvious thing in the 
first place was to prevent the possibility with great current density 
of heat, developed in places in the main circuit where the temperature 
is higher, penetrating to the resistance that is being measured. By 
this, from both ends, the thread would be brought over part of 
1) Here and in the following we speak repeatedly of resistance, without wishing 
to give it beforehand any other meaning than: calculated by Oum’s law from the 
strength of current and the potential difference observed. 
