1429 
thought of § 4 and taking into account the heat motion which takes 
the electrons now to the inside and then to the surface of the 
conductor, a pushing forward of the electrons in the galvanic current 
through a super-conductor without performance of work seems only 
possible, when its surface only comes into contact with an insulator, 
which reflects the electrons with perfect elasticity. If the electrons 
can hit against the atoms (or more accurately the vibrators) of an 
ordinary conductor, they will of course give off work in this collision. 
Thus a thread of super-conducting mercury, if an ordinary conducting 
particle were present anywhere in the current path, could show 
resistance at that spot, even although the particle did not entirely 
bar the section which was otherwise free from resistance. 
These considerations lead to the following experiment. A steel 
capillary tube, supplied with connecting pieces in which were 
platinum wires for measuring the resistance, was carefully filled 
with mercury at the air pump. The measuring wires were immersed 
in the mercury, without touching the current wires. According to 
the ordinary laws of current distribution the resistance of this 
composite conductor should disappear below 4°.19 K. Whether the 
mercury is in a glass or a metal capillary makes no difference to 
the conduction. Thus for instance, if one was to coil up such a 
steel capillary filled with mereury, and press the coils against each 
other without insulating them, the coil could still serve as a magnetic 
coil below 4°.19 K.; the coiled up mercury thread would be 
resistance-free, and the steel would take the part of the insulator, 
which otherwise separates the different windings of the current 
path in a magnetic coil. On the other hand if the above reasoning 
is correct, a mercury thread, that is provided with a close fitting 
steel covering should retain its resistance below 4°.19 K. though the 
current is lowered below the threshold value. 
In several experiments with the above mentioned steel capillary, 
in accordance with the last conclusion, the resistance of the mercury 
thread did not disappear. Yet we must not conclude from this that 
the remaining resistance is given to the mercury by the contact 
with the steel. There only needs to be one little gap in the mereury 
which extends over the whole section, to cause the appearance of 
ordinary resistance of the amount according to the potential diffe- 
rence. If the resistance had disappeared in the experiments, there 
would on the other hand have been room for the question whether 
there had been contact between the steel and the mercury. With 
mercury in a steel capillary the result of the experiment remains 
always doubtful. We may therefore mention here, that afterwards 
9 
Proceedings Royal Acad. Amsterdam. Vol. XV. 
