﻿High-Frequency 
  Discharges 
  in 
  Geissler 
  Tabes. 
  979 
  

  

  instantaneous 
  current 
  or 
  some 
  other 
  factor, 
  such 
  as 
  the 
  oscil- 
  

   latory 
  nature 
  of 
  the 
  discharge, 
  is 
  the 
  primary 
  cause 
  or 
  not 
  

   does 
  not 
  appear 
  clearly 
  shown. 
  It 
  is 
  usually 
  considered 
  that 
  

   the 
  red 
  spectrum 
  is 
  that 
  of 
  low 
  current 
  density, 
  whilst 
  the 
  

   blue 
  spectrum 
  requires 
  higher 
  current 
  densities 
  for 
  its 
  pro- 
  

   duction. 
  On 
  the 
  other 
  hand, 
  temperature 
  may 
  be 
  an 
  

   important 
  influence, 
  as 
  reviewed 
  by 
  Sheard*, 
  who 
  gives 
  a 
  

   bibliography 
  of 
  work 
  on 
  the 
  spectrum 
  of 
  argon. 
  From 
  his 
  

   ow 
  T 
  n 
  experiments 
  this 
  author 
  shows 
  that 
  a 
  fairly 
  complete 
  

   transformation 
  from 
  red 
  to 
  blue 
  spectrum 
  can 
  be 
  obtained 
  

   by 
  use 
  of 
  increasing 
  capacities 
  in 
  the 
  secondary 
  discharge 
  

   circuit. 
  It 
  does 
  not 
  appear 
  that 
  the 
  conclusion 
  arrived 
  at, 
  

   viz. 
  that 
  current 
  density 
  is 
  the 
  determining 
  factor, 
  straightway 
  

   follows. 
  For 
  with 
  variation 
  of 
  the 
  capacity 
  w 
  r 
  e 
  vary 
  also 
  

   the 
  frequency 
  of 
  discharge, 
  and 
  with 
  larger 
  condensers 
  the 
  

   increased 
  interval 
  between 
  successive 
  discharges, 
  as 
  well 
  as 
  

   the 
  damping 
  factor 
  of 
  the 
  circuit, 
  may 
  not 
  be 
  without 
  in- 
  

   fluence. 
  The 
  question 
  was 
  returned 
  to 
  recently 
  by 
  Stead 
  f. 
  

   Using 
  a 
  battery 
  of 
  small 
  storage 
  cells, 
  he 
  endeavoured 
  by 
  

   simply 
  altering 
  the 
  conditions 
  to 
  produce 
  the 
  red 
  and 
  blue 
  

   spectra 
  at 
  will 
  with 
  direct 
  current. 
  All 
  attempts 
  in 
  this 
  

   direction, 
  however, 
  failed. 
  

  

  Now, 
  using 
  the 
  Poulsen 
  high-frequency 
  generator, 
  the 
  

   current 
  can 
  be 
  varied 
  over 
  wide 
  limits 
  simply 
  by 
  adjusting 
  

   the 
  closeness 
  of 
  coupling 
  between 
  the 
  discharge 
  and 
  gene- 
  

   rating 
  circuits. 
  The 
  same 
  frequency 
  is 
  maintained 
  throughout 
  

   any 
  series 
  of 
  experiments, 
  and 
  the 
  effect 
  of 
  increased 
  energy 
  

   in 
  the 
  discharge 
  circuit 
  can 
  be 
  noted. 
  In 
  these 
  experiments 
  

   it 
  can 
  be 
  assumed 
  with 
  moderate 
  certainty 
  that 
  the 
  current 
  

   and 
  voltage 
  rise 
  together, 
  the 
  resistance 
  of 
  the 
  tube 
  not 
  

   varying 
  greatly. 
  This 
  was 
  actually 
  found 
  to 
  be 
  broadly 
  

   true 
  in 
  several 
  cases 
  which 
  were 
  examined. 
  The 
  conditions 
  

   are 
  therefore 
  different 
  from 
  those 
  of 
  Stead, 
  who 
  used 
  a 
  

   Wehnelt 
  cathode. 
  Owing 
  to 
  the 
  copious 
  supply 
  of 
  electrons 
  

   from 
  his 
  heated 
  cathode 
  at 
  higher 
  voltages, 
  the 
  effective 
  re- 
  

   sistance 
  of 
  the 
  discharge 
  tube 
  would 
  be 
  greatly 
  diminished, 
  

   the 
  current 
  rising 
  more 
  rapidly 
  than 
  the 
  voltage. 
  

  

  At 
  frequencies 
  of 
  0*2 
  x 
  10 
  6 
  and 
  1*1 
  x 
  10 
  6 
  precisely 
  similar 
  

   results 
  were 
  noted 
  due 
  to 
  current 
  variation. 
  The 
  spectrum, 
  

   originally 
  red, 
  gradually 
  became 
  mixed, 
  and, 
  finally, 
  at 
  the 
  

   highest 
  currents 
  used, 
  it 
  was 
  almost 
  the 
  pure 
  blue 
  spectrum. 
  

   There 
  was 
  much 
  heating 
  in 
  the 
  capillary 
  in 
  these 
  experiments, 
  

   and 
  it 
  seemed 
  possible 
  that 
  this 
  was 
  the 
  cause 
  of 
  the 
  change 
  

  

  * 
  Sheard, 
  Phys. 
  Key. 
  xxvii. 
  pp. 
  258-266 
  (1908). 
  

   t 
  Stead, 
  Proc. 
  Camb. 
  Phil. 
  Soc. 
  xvi. 
  pp. 
  607-609. 
  

  

  