on the Direct Current Corona. 



285 



The corona tube acts like a condenser charging up and 

 discharging at intervals depending on the length of the 

 spark gap. It can be arranged so that, for long sparks, 

 only one spark passes per second, or for short sparks, 

 several thousand pass per second, and as each spark 

 passes it will register a sharp click in the telephone 

 receiver. On decreasing the spark length from the 



Fig. 3. 



14 



12 



10 



8 



x) 



c 

 o 

 o 



0) 

 CO 



I* 



CD 



w 4 



u 

 a 



Pi 

 CO 2 





1 













\ 









\ 



\ 

























V-— 



















, 



+ 



1 2 



Spark Length 



nun, 



Fig. 3. Spark -length frequency curves. 



longest sparking distance the sparks will jump faster and 

 faster until for very short spark lengths the sound in the 

 telephone passes practically out of the audible range. 



For a given spark length more sparks pass per second 

 if the axial wire is charged negatively than when it is 

 charged positively. This is to be expected since the 

 current passes through the tube easier when the wire is 

 negative. For a given constant line voltage and air at 

 atmospheric pressure, plotting the spark length against 

 the frequency of the passing sparks for both positive 

 and negative wires, curves as shown in fig. 3 are obtained. 



