300 Grooher — Influence of a Series Spark. 



up on the condenser until the potential difference of the 

 spark gap is sufficient to break down the air between the 

 electrodes. An instantaneous unidirectional en rrent will 

 How across the spark gap and at the same time the poten- 

 tial across the tube will increase to a point where Hie 

 corona is formed. The current now through the tube will 

 immediately reduce the potential of the spark gap below 

 its critical point and the circuit will be broken. The pro- 

 cess is then repeated. 



The more nearly uniform appearance of the negative 

 corona can now be explained as a superimposed building 

 up and decay of the negative glow discharge through its 

 different stages as the potential on the tube fluctuates. 

 The positive streamers have at times been observed at 

 critical voltages on rough wires when no spark was in 

 series. These streamers are similar to the positive brush 

 discharges observed from pointed electrodes maintained 

 at high positive potentials. Their characteristic pres- 

 ence in the corona tube when a spark is in series is due 

 probably to the sudden impression of a strong field and 

 may be accompanied by a discharge of positive metallic 

 ions, since it has been observed that the surface of the 

 wire becomes disintegrated at points where these stream- 

 ers are maintained. 



Summary. 



1. A spark gap in series with the discharge tube 

 affects the positive and negative corona in very charac- 

 teristic and striking ways. 



2. The changes are due to intermittent currents. 



3. A hot-lime-cathode Braun tube has been developed 

 and used in observing the weak pulsating currents which 

 pass through the spark and the corona tube. 



4. Evidence has been given to show the relation of 

 the corona to the arc discharge. 



5. An attempt at an explanation of the pulsating cur- 

 rent has been made. 



In conclusion I wish to thank Dr. Jakob Kunz for sug- 

 gesting this work and for his kind interest and help dur- 

 ing its progress. I am also indebted to Professor A. P. 

 Carman who has provided the necessary facilities for 

 the investigation. 



Laboratory of Physics, University of Illinois, December, 1917. 



