Energy in the Electrodeless Discharge. 



203 



mrn wide and 7 cm long. The outside 



the top. This space was 



diameter of the vessel was 6 # 5 cm . The electrodes were rings of 

 aluminium, extending around at the top and bottom of the 

 annular space. They are shown in section at EE and E, E,. 



The surface of each electrode was 7'38 sq cm and the distance 

 between them 6 cm . A constant difference of potential of 220 

 volts was maintained at these electrodes by the source B. At this 

 potential no current passed between the electrodes except when 

 the discharge was passing. This arrangement of the electrodes 

 made the field of the E.M.F. of the electrodes perpendicular to 

 that produced by the oscillations in the coil C. The compo- 

 nent of ionic velocity under the first E.M.F. was independent 



of that produced by the coil. It was found necessary to enclose 

 the spark gap in an atmosphere of hydrogen in order to obtain 

 a uniform discharging potential. The period of the alterna- 

 ting current driving the induction coil was 40 cycles per second, 

 thus giving 80 sparks per second at the spark gap. This rapid 

 succession of discharges gave uniform average readings on the 

 two galvanomters G and M. 



If the vessel V were removed from the coil C, on the pass- 

 age of the sparks, the galvanometer G indicated a large current, 

 being in these experiments 15'8 amperes. 



The discharge was allowed to continue until the conditions 

 became steady, and the galvanometer showed a steady deflec- 

 tion. When the vessel, properly exhausted, was put in the 

 coil, the white electrodeless discharge appeared, and the current 

 indicated by the galvanometer became very much less. In 

 some cases the reading dropped hack from 15*8 amperes 

 to about 11 amperes. The amount of drop-back was depend- 



