on the Direct Current Corona. 



291 



4. Ca< ) mixed with a small quantity of BaN() 3 insures 

 a longer life to the lime and may be easily applied as 

 a paste. 



5. The anode should be near the cathode, say 1 cm. 

 distant. 



6. The potential may be as low as 300 volts and 

 preferably from a constant source as storage cells. 



7. The pressure must be very low and may even be 

 assisted with charcoal and liquid air. Gases are given 

 off from the lime cathode quite freely necessitating con- 



i 



i 



1 



'VllllAAjvArW\A/i,,AA A ./-v-J 1 



u 



N 2 









\ 





I 





I 





I 



\ 



\ 





\ 



f i 



I 



I ' 



P 







Fig. 8. Currents in the spark and corona tube. 



stant pumping if the tube is to be us^d for any length 

 of time. 



With this hot-lime-cathode apparatus it was easy to 

 observe in the rotating mirror the forms of the current 

 curves when a spark passed and the current flowed 

 through the corona tube. The field coil was connected in 

 series with the circuit, (1) between the spark gap and the 

 corona tube, and (2) between the corona" tube and ground 

 or negative terminal of the generators (see fig. 1). The 

 current forms are sketched in fig. 8 as they were 

 observed in both of these positions and for the condi- 



Am. Jour. Sci.— Fourth Series, Vol. XLV, No. 268.- 

 21 



-April, 1918. 



