294 Croaker — Influence of a Series Spark 



inside diameter. The current recorded is that passing 

 in the corona discharge just before arcing takes place. 

 It is seen that it is nearly constant for all pressures. 



Curve B, fig. 9, shows the relation between pressure 

 and arc-over voltage for this constant current. The 

 conclusions which have been drawn from the available 

 data are as follows : 



1. For a given configuration of electrodes the arc- 

 over takes place as soon as the current has reached a 

 certain value which is nearly constant for all pressures. 



2. Arc-over occurs at lower voltages for smaller 

 wires. 



3. For a constant current the arc-over voltage for the 

 positive wire is nearly a linear function of the pressure, 

 and may be written 



V= (flP + b) cR 



where, V = arc-over voltage, P = pressure, R = Radius 

 of wire, and a, b, c, are constants. 



4. At low pressures arc-over for the negative wire 

 occurs at a less voltage than for the positive wire. 



5. At high pressures (near atmospheric) arc-over for 

 the positive wire takes place at a less voltage than for 

 the negative wire. 



The water resistance connected between the generators 

 and the main bus bar was replaced by a 0-5 ampere fuse 

 in order to see if it had any effect on the corona discharge 

 with and without a spark. The visual forms were 

 studied with the coaxial cylinders (the inner one No. 20 

 copper wire) as well as with parallel (No. 20 copper) 

 wires as electrodes. 



With the cylindrical electrodes the general results 

 obtained showed that the usual characteristic visual 

 forms of the corona discharge were not materially altered 

 either for positive wire or negative wire, with and with- 

 out a series spark. The only noticeable change was an 

 increased brightness in the positive uniform glow, 

 streamers and negative beads. With the water resist- 

 ance cut out the available energy was increased about 100 

 times or in other words to 10 kilowatts. The negative 

 beads and the positive streamers while much brighter 

 were also in a more agitated state moving rapidly back 

 and forth on the wire and would go over into the arcing 

 stage much easier than they would with water resist- 



