XIII]
USE OF BALLAST WITH ARC LAMPS
543
io amperes, V/O = A. Now suppose the arc length were
nged say by bringing the electrodes in contact. In this case
re would be the full line voltage, no volts across the rheostat
ithe current would be 110/6 = 18.3 amperes. Suppose the arc
jth were increased until the potential at the arc was 60 volts.
; potential across the rheostat would then be 110 — 60 = 50
ts. The current would then be 50/6 = 8.2 amperes. In this
mple the conditions are what is known as stable, that is, as the
length is decreased the current is increased, but does not reach
infinite value, and as the arc length is increased the current
rcascs but it does not become zero.
297. Lateral and Face Views of an Inclined Carbon Arc with 20
Amperes of Direct Current.
his picture shows that with the inclined carbons in proper position, the
tive crater on the upper carbon faces toward the condenser. It is evident
that as the carbon bums away the crater will get farther and farther above
principal axis of the projection apparatus.
n additional exposure was made to bring out the carbons as with fig. 292-