252 



WHITEHEAD— HIGH VOLTAGE CORONA IN AIR. 



is ionized and therefore becomes conducting, resulting in a sharp 

 deflection of the galvanometer Gg. Fig. 5 is a series of curves show- 

 ing how sharply the galvanometer deflection occurs as related to 

 corona voltage. 



The corona has an audible sound even in the open. When the 

 corona wire is enclosed, as in the corona voltmeter, this sound is 

 gathered and intensified.' At atmospheric pressure the ear placed 

 at a small opening in the case C will detect the very first appear- 

 ance of corona, which will be very sharply marked. In order that 

 the sound may be utilized, when the pressure is of value other than 

 that of the atmosphere, a telephone transmitter is included inside 



to 



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Tertiary Coil Volts 

 ii^.5 Galvanoweter as Detector of Corona 



the casing connected with the receiver outside, as shown at T, Fig. 

 4. The telephone gives a clear note on the first appearance of 

 corona and the indications of telephone and galvanometer are 

 exactly contemporaneous, as indicated in Fig. 5. 



In order to calibrate the instrument and thus determine ac- 



