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  LXXXV. 
  The 
  Spectra 
  of 
  High-Frequency 
  Discharges 
  in 
  

   Geissler 
  Tabes. 
  By 
  Robert 
  W. 
  Lawson, 
  M.Sc^Pemberton 
  

   Fellow 
  of 
  the 
  University 
  of 
  Durham 
  *. 
  

  

  [Plates 
  XXI. 
  & 
  XXII.] 
  

  

  IT 
  is 
  a 
  well-known 
  fact 
  that 
  a 
  variety 
  of 
  spectra 
  can 
  be 
  

   obtained 
  with 
  many 
  elements 
  according 
  to 
  their 
  mode 
  

   of 
  electrical 
  excitation, 
  and 
  hence 
  it 
  is 
  highly 
  desirable 
  to 
  

   examine 
  their 
  spectra 
  as 
  obtained 
  by 
  different 
  methods. 
  

   Snch 
  a 
  procedure 
  may 
  greatly 
  assist 
  in 
  the 
  determination 
  of 
  

   the 
  underlying 
  causes 
  for 
  the 
  production 
  of 
  one 
  or 
  other 
  

   of 
  the 
  spectra 
  of 
  the 
  element 
  concerned. 
  In 
  the 
  case 
  of 
  

   vacuum 
  tubes 
  the 
  pressure 
  of 
  the 
  gas, 
  its 
  temperature 
  and 
  

   purity, 
  the 
  current 
  density 
  and 
  voltage 
  employed, 
  are 
  all 
  

   known 
  to 
  influence 
  the 
  character 
  of 
  the 
  discharge, 
  but 
  in 
  a 
  

   way 
  not 
  clearly 
  understood. 
  When 
  a 
  condensed 
  discharge 
  

   is 
  used, 
  the 
  investigator 
  is 
  led 
  to 
  ask 
  himself 
  whether 
  it 
  is 
  

   the 
  maximum 
  value 
  of 
  the 
  current 
  during 
  each 
  train 
  of 
  

   oscillations, 
  or 
  some 
  mean 
  value 
  which 
  determines 
  the 
  pro- 
  

   duction 
  of 
  a 
  different 
  spectrum 
  from 
  that 
  of 
  the 
  uncondensed 
  

   discharge. 
  On 
  the 
  other 
  hand, 
  is 
  the 
  production 
  of 
  the 
  new 
  

   spectrum 
  at 
  all 
  influenced 
  by 
  the 
  fact 
  that 
  the 
  discharge 
  is 
  

   oscillatory 
  in 
  character? 
  If 
  this 
  last 
  be 
  the 
  determining 
  

   influence, 
  then 
  the 
  condenser 
  spectrum 
  should 
  be 
  obtained 
  

   when 
  any 
  type 
  of 
  oscillatory 
  discharge 
  is 
  used. 
  

  

  In 
  the 
  present 
  work 
  the 
  source 
  of 
  current 
  was 
  the 
  Poulsen- 
  

   arc 
  high-frequency 
  generator. 
  This 
  consists 
  essentially 
  of 
  a 
  

   magnetically 
  deflected 
  arc, 
  burning 
  in 
  a 
  coal-gas 
  atmosphere, 
  

   between 
  a 
  water-cooled 
  anode 
  of 
  copper 
  and 
  a 
  cathode 
  of 
  

   carbon. 
  Across 
  the 
  arc 
  terminals 
  are 
  placed 
  a 
  condenser 
  

   and 
  an 
  inductance 
  in 
  series, 
  and 
  the 
  resulting 
  oscillations 
  

   in 
  this 
  oscillatory 
  circuit 
  can 
  be 
  maintained 
  constant 
  over 
  

   comparatively 
  long 
  periods. 
  Moreover, 
  in 
  such 
  a 
  case, 
  the 
  

   oscillations 
  are 
  undamped, 
  and 
  hence 
  give 
  rise 
  to 
  a 
  more 
  

   uniform 
  current 
  than 
  that 
  obtained 
  in 
  the 
  ordinary 
  condenser 
  

   spark-gap 
  discharge, 
  where 
  the 
  oscillations 
  are 
  strongly 
  

   damped. 
  

  

  The 
  occurrence 
  of 
  many 
  terrestrially 
  unknown 
  lines 
  in 
  the 
  

   spectra 
  of 
  certain 
  celestial 
  bodies 
  made 
  it 
  still 
  more 
  desirable 
  

   to 
  examine 
  gaseous 
  spectra 
  by 
  the 
  present 
  method. 
  In 
  this 
  

   respect, 
  the 
  green 
  lines 
  of 
  nebulium 
  (A, 
  5007) 
  and 
  of 
  coronium 
  

   (X 
  5303) 
  deserve 
  special 
  mention, 
  as 
  undoubtedly 
  the 
  type 
  of 
  

   excitation 
  existing 
  in 
  the 
  nebula 
  and 
  coronal 
  halos 
  differs 
  

   from 
  that 
  hitherto 
  used 
  in 
  the 
  laboratory. 
  

  

  * 
  Communicated 
  by 
  the 
  Author. 
  

  

  