WHITEHEAD— HIGH VOLTAGE CORONA IN AIR. 



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the opposite terminal, an outer air-tight containing case in which 

 the air pressure may be varied, and convenient means for determin- 

 ing accurately the first appearance of corona. All of these features 

 are indicated in diagrammatical form in Fig. 4. 



In Fig. 4 ^ is the central wire, or rod. B is the concentric 



Fig. 4- 



cylinder forming the opposite terminal which is connected to 

 ground ; C is the outer air-tight containing case with air pressure 

 control at the pump P ; and £ is a high voltage insulating bushing 

 for connecting the source of high potential A'' to the corona rod A ; 

 H is a porcelain insulator maintaining the lower end of A in fixed 

 position. 



Two simple methods have been developed for detecting the 

 initial appearance of corona as the voltage on A is slowly raised. 

 The first of these makes use of the fact that the presence of corona 

 sets up a copious state of ionization. The cylinder B is therefore 

 perforated, and just outside cylinder B a continuous surrounding 

 cylinder F is placed, carefully insulated from B. Connection is 

 made to this outer cylinder through the galvanometer Go either 

 directly to ground or with a continuous electromotive force in series. 

 At the first beginnings of corona the air between cylinders B and F 



