254 



WHITEHEAD— HIGH VOLTAGE CORONA IN AIR. 



members being 29.5 cms. and 49.3 cms., respectively, and the length 

 of the central section of the outside member 76.2 cm. The capacity 

 of the condenser as measured was 8.28 X lO"^^ microfarads. 



In making observations the voltage of the generator O was 

 slowly raised and at the instant corona appeared, as indicated by the 

 galvanometer Go and telephone T, the galvanometer G^ reading the 



Fig. 6. Air Condenser. 



condenser charging current was read, and at the same time the 

 temperature and pressure at / and P. The frequency was also 

 accurately measured by comparison with a standard tuning fork. 

 The reading of the calibrated galvanometer G^ gives the charging 

 current of the air condenser M which, with the frequency, leads to 

 the maximum value of the alternating electromotive force corre- 

 sponding to corona formation. It only remains therefore to connect 

 this critical value of voltage with the conditions as to temperature 

 and pressure to arrive at the law of corona formation. 



The form of the relation between voltage, temperature and 

 pressure and the diameter of the corona forming wire, as agreed 



