208 J. A. POLLOCK AND A. B. B. RANCLAUD. 
The relation, as given by our observations, between the 
temperature of the hot carbon and the critical value of the 
potential difference between the electrodes necessary to 
start arcing, is shown in figure 7 for distances of 1,2 and3 
millimetres between the carbons. 
ios 77 
Critical Voltage for Arcing. 
Temperature Centigrade. 
The relation between the temperature of the hot carbon and the 
critical value of the potential difference between the electrodes 
necessary to start arcing, for distances of 1, 2 and 3 millimetres 
between the carbons. 
All the observations given in this paper, with the excep- 
tion of those in the following table, refer to the case where 
the hot and cool carbons are in the same horizontal plane. 
