DISCHARGE OF ELECTRICITY FROM GLOWING OARBON. 205 
For the flow of positive electricity from the hot carbon 
it is sufficient to say that any increase, above the value 
for zero current, in the potential of the hot carbon, gives 
a much smaller current than a decrease of the same amount. 
This smaller current, however, under the circumstances of 
our experiments, is not the definite measure of the stream 
of positive ions from the hot carbon; it is the resultant of 
such a stream and one of negative ions from the cooler 
electrode. 
LS) 
Milliampéres. 
C) 
CH Ca 
3 OMG oie 400 6. 
30 60 90 
Volis -befrween Carbaons. 
The current of negative electricity from the hot carbon 
depends on the temperature of the carbon, on the potential 
difference between the electrodes and on the distance 
separating them. At low voltages the current is of the 
order of a milliampere and is not accompanied by any 
luminosity. As the potential difference increases, a 
critical value, depending on the temperature and on the 
distance between the carbons, is reached at which an arc 
forms, and the current jumps instantly from milliamperes 
