﻿978 
  Mr. 
  R. 
  W. 
  Lawson 
  on 
  the 
  Spectra 
  of 
  

  

  frozen 
  out 
  of 
  the 
  apparatus 
  by 
  immersing 
  a 
  side 
  tube 
  in 
  a 
  

   mixture 
  of 
  solid 
  carbon 
  dioxide 
  and 
  ether. 
  A 
  mercury- 
  

   sealed 
  tap 
  was 
  necessary 
  in 
  the 
  case 
  of 
  oxygen 
  to 
  separate 
  

   the 
  tube 
  from 
  the 
  rest 
  of 
  the 
  apparatus, 
  including 
  the 
  pump. 
  

   This 
  was 
  for 
  the 
  purpose 
  of 
  avoiding 
  contamination 
  of 
  the 
  

   oxygen 
  with 
  tap-grease. 
  

  

  Under 
  all 
  the 
  conditions 
  of 
  voltage, 
  current, 
  and 
  gas- 
  

   pressure 
  available, 
  the 
  compound 
  line-spectrum 
  was 
  alone 
  

   obtainable 
  at 
  ordinary 
  temperatures. 
  Changes 
  in 
  pressure 
  

   between 
  the 
  limits 
  of 
  1 
  mm. 
  and 
  2$ 
  mm. 
  were 
  found 
  to 
  pro- 
  

   duce 
  no 
  changes 
  in 
  relative 
  intensity 
  of 
  the 
  lines 
  of 
  the 
  

   compound 
  oxygen 
  spectrum, 
  the 
  same 
  current 
  being 
  used 
  

   for 
  comparative 
  purposes. 
  The 
  diameter 
  of 
  the 
  capillary 
  of 
  

   the 
  silica 
  tube 
  was 
  1*6 
  mm. 
  and 
  the 
  maximum 
  value 
  of 
  the 
  

   current 
  used 
  was 
  0*114 
  ampere. 
  At 
  the 
  higher 
  currents 
  

   the 
  carbon 
  monoxide 
  spectrum 
  showed 
  strongly, 
  but 
  the 
  

   oxygen 
  spectrum 
  was 
  unaffected. 
  

  

  With 
  low 
  current 
  density 
  discharges 
  at 
  low 
  temperatures 
  

   (C0 
  2 
  -ether 
  mixture) 
  the 
  continuous 
  spectrum 
  of 
  oxygen 
  was 
  

   obtained, 
  but 
  this 
  merged 
  into 
  the 
  compound 
  line-spectrum 
  

   as 
  the 
  current 
  was 
  increased. 
  

  

  When 
  the 
  discharge 
  was 
  examined 
  in 
  Geissler 
  tubes 
  with 
  

   internal 
  electrodes, 
  the 
  spectra 
  observed 
  were 
  not 
  found 
  to 
  

   differ 
  from 
  those 
  obtained 
  under 
  similar 
  circumstances 
  in 
  the 
  

   silica 
  tube. 
  

  

  Argon. 
  

  

  Argon 
  possessing 
  three 
  different 
  spectra, 
  it 
  is 
  a 
  particularly 
  

   suitable 
  gas 
  to 
  test 
  under 
  the 
  conditions 
  used 
  in 
  these 
  ex- 
  

   periments. 
  The 
  red 
  spectrum 
  is 
  that 
  usually 
  produced 
  by 
  

   use 
  of 
  the 
  uncondensed 
  induction-coil 
  discharge 
  ; 
  the 
  blue 
  

   spectrum 
  is 
  that 
  of 
  the 
  condensed 
  discharge 
  ; 
  whilst 
  the 
  

   white 
  spectrum 
  is 
  the 
  result 
  of 
  mixed 
  conditions, 
  and 
  is 
  

   composed 
  of 
  the 
  mixed 
  red 
  and 
  blue 
  spectra 
  with 
  numerous 
  

   modifications. 
  Trowbridge* 
  has 
  shown 
  that 
  the 
  use 
  of 
  a 
  

   condenser 
  is 
  necessary 
  to 
  produce 
  the 
  blue 
  spectrum 
  with 
  an 
  

   induction 
  coil. 
  He 
  attributes 
  the 
  production 
  of 
  the 
  blue 
  

   spectrum 
  by 
  Kayser 
  t 
  without 
  the 
  use 
  of 
  a 
  condenser 
  in 
  the 
  

   secondary, 
  to 
  the 
  fact 
  that 
  the 
  secondary 
  was 
  probably 
  in 
  

   resonance 
  with 
  the 
  primary 
  of 
  the 
  induction 
  coil, 
  in 
  which 
  

   circuit 
  was 
  the 
  usual 
  primary 
  condenser. 
  By 
  removal 
  of 
  the 
  

   primary 
  condensers 
  the 
  red 
  spectrum 
  only 
  was 
  obtained. 
  

   It 
  appears 
  then 
  that 
  a 
  condenser 
  is 
  necessary 
  for 
  the 
  pro- 
  

   duction 
  of 
  the 
  blue 
  spectrum 
  of 
  argon, 
  but 
  whether 
  large 
  

  

  * 
  Trowbridge 
  and 
  Richards, 
  Phil. 
  Mag. 
  xliii. 
  1897. 
  

   + 
  Kayser, 
  Astroph. 
  Journ. 
  iv. 
  1896. 
  

  

  