298 ( booker — Influence of a Serif* Spark 



appear rises to a maximum rapidly and falls off to zero 

 for a large spark distance. The streamers are brightest 

 at the maximum current value and are always connected 

 with a large current. The corresponding negative 

 curves show no such a maximum. With increasing volt- 

 age the positive current increases very rapidly. When a 

 current of air was sweeping through the tube the maxi- 

 mum in the positive current was much decreased as 

 shown by fig. 11. . 



The ordinary characteristic current-voltage curves as 

 obtained in the process of experiments without a series 

 spark give the negative characteristic as lying above the 

 positive. This relative position is maintained in all 

 cases, with one or two minor exceptions. 



When a short spark is placed in series with the corona 

 these positions are reversed and the positive curve lies 

 above the negative, except at the starting point where the 

 curves cross giving a lower starting potential for the 

 negative wire (see fig. 12). However, the starting- 

 potential with the spark in series is higher than for the 

 other case. It might be pointed out also that the char- 

 acteristics taken with a series spark are more widely 

 separated than those taken without, showing a wider 

 variation in the current from the positive and negative 

 wires for a given voltage. 



It was found when the spark gap was closed while 

 current was flowing that the current would drop in a 

 short time to a position on the ordinary characteristic 

 curve. For instance, if the wire is positive at 11,000 

 volts and a 0-12 mm. spark is in series, a current of 

 6-2. 10 -4 amperes will flow. Short-circuiting the spark 

 gap will cause the current to drop to the value 4-6. 10" 4 

 amperes which is a point on the ordinary positive charac- 

 teristic curve. Similarly by short-circuiting the spark 

 gap when the wire is negative the current will increase 

 to a value which lies on the ordinary negative character- 

 istic. These observations again show that the positive 

 streamers carry a large current. 



Without a spark gap in series with the tube the 

 ordinary uniform positive glow is formed by ionization 

 in the gas near the wire where the field strength is greater 

 than thirty kilovolts per centimeter, the current being- 

 carried by both positive and negative ions. The usual 

 negative corona discharge begins critically as a uniform 



