1420 
thread as in the last experiments, and to make certain that the 
disturbances which had occurred would be impossible. The mereury 
thread C, see fig. 4, at the ends of which the potential was to be 
measured was for this purpose lengthened at both ends by an auxiliary 
mercury thread of larger section. We will call these auxiliary 
threads A and 5, 
L 
han hh AM 
hee, 
Miek Fig. 5. 
By measuring the potential difference at the extremities of both 
auxiliary threads it could be ascertained that any heating above the 
vanishing point could not be the consequence of the introduction 
of heat which had entered the extremities of the resistance C which 
was to be examined through conduction. For this heat could only 
enter through the sentinel wires, and these could only become 
dangerous to the experiment after betraying a heating above the 
vanishing point by showing a potential fall. 
On the ground of the experience in the last experiments, the 
connecting wires carrying the current in to the resistance (compare 
the diagrammatical fig. 4 and the perspective fig. 5) were again of 
mercury, in order to prevent Joure heat being transported to the 
resistance, while sealed in platinum wires to which copper wires 
were soldered served as potential wires. The sentinel thread A had 
