1416 
evenly distributed through the metal. It might also be that the pure 
metal in the particular condition in which it comes below 4°.19 K. 
and in which the atoms perhaps form one whole together, does not 
possess any resistance at all, but that somewhere (§ 11) in the thread 
through some peculiarity a section is sufficiently heated by great 
current density, to bring the temperature of the thread locally up 
to the vanishing point. In either way an ordinary resistance could 
be formed somewhere, which, when the strength of current is 
further increased, gives rise to an accelerated heat evolution and an 
increased development of resistance. 
§ 5. Further investigation of the potential difference phenomena, 
in particular at temperatures slightly below the vanishing point. It was 
considered desirable in the first place, to investigate the influence 
of the thickness of the thread upon the temperature, at which the 
fall of resistance occurs, and also upon the more or less sudden 
disappearance of the resistance. 
The resistance apparatus with which 
the experiments (Jan. 1912) for this 
ob Qe O&, |%,4 purpose were made differed from those 
~ of Dee. 1911 only in this, that in the 
two pairs of mercury threads which 
serve for the measurement of the 
resistance of the mercury (two current 
leads and two potential threads) the 
pieces that were above helium tempe- 
rature were replaced by copper wire, 
in this way that the mercury legs 
were cut off and sealed up, and in the 
sealed up ends, as in the resistances 
of Oct. 1911, platinum wires were 
sealed in, which were in their turn 
joined to copper leads *). During the 
experiments all these contacts were 
immersed in liquid helium, compare 
Vig. 3. fig. 3. This change was made since 
tj The wires were made comparatively fine, to prevent the liquid helium from 
evaporating too quickly from the conduction of heat. Besides the condition of heat 
from above the absorption of radiated heat by the metal in the transparent 
apparatus was avoided. Later on, when the various circumstances conld be better 
surveyed, leads were constructed which could carry a strong current without 
causing too much evaporation, 
