﻿High-Frequency 
  Discharges 
  in 
  Geissler 
  Tubes. 
  971 
  

  

  wire, 
  which 
  could 
  be 
  variably 
  coupled 
  with 
  the 
  inductance 
  

   of 
  the 
  generator. 
  The 
  Geissler 
  tube 
  T 
  was 
  inserted 
  across 
  

   the 
  condenser 
  terminals, 
  and 
  the 
  current 
  was 
  measured 
  as 
  

   hitherto 
  described. 
  This 
  arrangement 
  was 
  found 
  to 
  be 
  par- 
  

   ticularly 
  suitable 
  in 
  the 
  case 
  of 
  discharges 
  with 
  internal 
  

   electrodes, 
  owing 
  to 
  the 
  ease 
  with 
  which 
  the 
  current 
  in 
  

   the 
  discharge 
  circuit 
  could 
  be 
  adjusted, 
  simply 
  by 
  altering 
  

   the 
  degree 
  of 
  coupling 
  with 
  the 
  generator. 
  

  

  Character 
  of 
  Discharge. 
  

  

  Whilst 
  it 
  was 
  readily 
  possible 
  to 
  obtain 
  feeble 
  discharges 
  

   similar 
  to 
  those 
  obtainable 
  using 
  an 
  induction 
  coil, 
  the 
  

   majority 
  of 
  the 
  discharges 
  from 
  the 
  Poulsen-arc 
  generator 
  

   were 
  of 
  extraordinary 
  brightness, 
  far 
  surpassing 
  that 
  obtained 
  

   by 
  the 
  other 
  methods 
  available. 
  The 
  advantage 
  of 
  this 
  lay 
  

   in 
  the 
  fact 
  that 
  very 
  short 
  exposures 
  were 
  necessary 
  using 
  

   this 
  type 
  of 
  discharge, 
  and 
  greater 
  average 
  constancy 
  of 
  the 
  

   conditions 
  of 
  discharge 
  was 
  maintained 
  for 
  these 
  short 
  in- 
  

   tervals. 
  It 
  should 
  be 
  mentioned 
  that 
  in 
  the 
  first 
  method 
  of 
  

   producing 
  the 
  discharge 
  the 
  current 
  through 
  the 
  discharge 
  

   tube 
  could 
  be 
  varied 
  ad 
  lib. 
  by 
  altering 
  the 
  position 
  of 
  

   the 
  direct 
  coupling 
  lead 
  on 
  the 
  oscillatory 
  circuit 
  coil 
  D, 
  

   fig. 
  2. 
  

  

  Of 
  the 
  gases 
  used 
  in 
  this 
  work, 
  the 
  Irvdrogen, 
  oxygen, 
  and 
  

   nitrogen 
  were 
  prepared 
  and 
  purified 
  by 
  the 
  writer. 
  In 
  the 
  

   case 
  of 
  air, 
  this 
  was 
  carefully 
  freed 
  from 
  water 
  vapour 
  and 
  

   carbon 
  dioxide. 
  The 
  gases 
  neon, 
  helium, 
  argon, 
  and 
  carbon 
  

   dioxide 
  were 
  of 
  guaranteed 
  purity, 
  as 
  supplied 
  by 
  Hilger 
  in 
  

   tubes 
  with 
  aluminium 
  electrodes. 
  

  

  The 
  form 
  of 
  the 
  bulb 
  discharge 
  was 
  found 
  to 
  vary 
  greatly 
  

   according 
  to 
  the 
  pressure 
  and 
  current 
  in 
  use, 
  and 
  as 
  similar 
  

   effects 
  appeared 
  with 
  all 
  the 
  gases 
  used 
  in 
  the 
  external 
  

   electrode 
  tubes, 
  these 
  will 
  now 
  be 
  described. 
  The 
  diagrams 
  

   in 
  fig. 
  4 
  are 
  representative 
  of 
  the 
  bulb, 
  a 
  and 
  c 
  correspond- 
  

   ing 
  to 
  low 
  current-density 
  bulbs 
  at 
  the 
  pressures 
  indicated. 
  

   It 
  will 
  be 
  noticed 
  that 
  the 
  shaded 
  portion 
  of 
  the 
  bulb 
  discharge, 
  

   Avhich 
  shows 
  the 
  weak 
  spectrum 
  of 
  the 
  capillary 
  positive 
  

   column, 
  contracts 
  towards 
  the 
  capillary 
  when 
  the 
  pressure 
  is 
  

   reduced. 
  At 
  the 
  same 
  time 
  the 
  negative 
  glow, 
  corresponding 
  

   to 
  the 
  cathode 
  glow 
  with 
  internal 
  electrodes, 
  makes 
  its 
  

   appearance 
  just 
  below 
  the 
  mercury 
  cups. 
  When 
  the 
  current 
  

   density 
  through 
  the 
  tube 
  is 
  greatly 
  increased, 
  at 
  the 
  higher 
  

   pressures 
  the 
  bulb 
  discharge 
  contracts 
  laterally, 
  as 
  shown 
  in 
  

  

  3 
  U2 
  

  

  