THE RELIGHTING OF THE CARBON ARC. VATE 
conditions of the change from the non-luminous to the 
luminous discharge are, therefore, in some instances, more 
complicated than those in the case previously considered, 
and the explanation of the development of the arc suggested 
in the paper just mentioned is not sufficient to account for 
all the features observed in this investigation. further 
data are required before a complete description can be 
given. 
The conditions associated with a change from the non- 
luminous to the luminous discharge, in the case of the 
ordinary carbon arc, are seen inthe wave forms of current 
and potential difference in connection with alternating 
current arc lamps. 
Figure 1, showing curves of the volts at the brushes of 
the machine, of current in the circuit, and of the potential 
difierence between the carbons of the lamp, is copied from 
figure 14 of a paper by Mr. Duddell and Prof. Marchant 
on “Experiments on Alternate Current Arcs by aid of 
Oscillographs,’” in which many other illustrations will be 
found. 
ig ele 
aes PINT AGe a 
ys — Current. a ie 
! 1 POT are: Ve 
Waves of current and potential difference in connection with 
an alternating current arc lamp.—Duddell and Marchant. 
3 Journ. Inst. Elect. Eng,, xxviii, p. 1, 1899. 
