﻿16 
  Trowbridge 
  and 
  Richards 
  — 
  The 
  Spectra 
  of 
  Argon. 
  

  

  fortable 
  shock, 
  and 
  it 
  is 
  probable 
  that 
  the 
  discharge 
  of 
  the 
  

   whole 
  battery 
  would 
  be 
  instantly 
  fatal. 
  The 
  great 
  heat 
  of 
  this 
  

   full 
  discharge 
  immediately 
  shatters 
  a 
  Geissler 
  tube, 
  the 
  glass 
  

   being 
  splintered 
  throughout 
  the 
  whole 
  length 
  of 
  the 
  capillary. 
  

   Hence 
  a 
  resistance 
  of 
  several 
  million 
  ohms 
  was 
  "usually 
  inter- 
  

   posed 
  between 
  the 
  battery 
  and 
  the 
  rest 
  of 
  the 
  apparatus. 
  This 
  

   resistance 
  was 
  also 
  of 
  service 
  in 
  protecting 
  the 
  experimenters 
  

   from 
  serious 
  accidental 
  shocks. 
  Ordinary 
  distilled 
  water 
  con- 
  

   tained 
  in 
  long 
  tubes 
  with 
  movable 
  electrodes 
  was 
  the 
  most 
  

   convenient 
  resistance 
  for 
  our 
  purpose 
  ; 
  dilute 
  solutions 
  of 
  

   cadmic 
  iodide 
  in 
  amyl 
  alcohol 
  and 
  of 
  cadmic 
  sulphate 
  in 
  water 
  

   between 
  cadmium 
  electrodes, 
  were 
  also 
  sometimes 
  used. 
  Unless 
  

   these 
  liquids 
  are 
  contained 
  in 
  tubes 
  of 
  rather 
  large 
  diameter, 
  

   they 
  are 
  likely 
  to 
  cause 
  irregularities 
  by 
  boiling 
  under 
  the 
  

   influence 
  of 
  the 
  heat 
  of 
  the 
  current. 
  Graphite 
  resistances 
  are 
  

   too 
  combustible 
  for 
  the 
  purpose. 
  

  

  The 
  argon 
  used 
  in 
  our 
  experiments 
  was 
  very 
  kindly 
  given 
  to 
  

   one 
  of 
  us 
  by 
  Lord 
  Rayleigh. 
  It 
  was 
  a 
  portion 
  of 
  the 
  purest 
  

   preparation 
  which 
  had 
  been 
  s 
  used 
  in 
  his 
  final 
  determinations 
  

   of 
  the 
  density 
  of 
  the 
  gas 
  ; 
  and 
  our 
  tubes 
  were 
  carefully 
  

   filled 
  with 
  it 
  by 
  the 
  kindness 
  of 
  F. 
  O. 
  R. 
  Gotze, 
  of 
  Leipzig. 
  

   The 
  preliminary 
  work 
  described 
  in 
  this 
  paper 
  was 
  chiefly 
  done 
  

   with 
  a 
  single 
  tube 
  containing 
  gas 
  at 
  a 
  pressure 
  of 
  about 
  l 
  mm 
  . 
  

   The 
  tube 
  had 
  a 
  wide 
  capillary 
  and 
  was 
  about 
  15 
  cm 
  in 
  total 
  

   length. 
  In 
  such 
  a 
  tube, 
  the 
  red 
  glow 
  of 
  argon 
  is 
  readily 
  

   obtained 
  with 
  a 
  voltage 
  of 
  about 
  two 
  thousand, 
  but 
  not 
  with 
  

   much 
  less. 
  A 
  higher 
  tension 
  of 
  gas 
  demands 
  a 
  higher 
  tension 
  

   of 
  electricity 
  in 
  order 
  to 
  start 
  the 
  discharge, 
  no 
  matter 
  how 
  

   much 
  or 
  how 
  little 
  other 
  resistance 
  is 
  interposed 
  ; 
  but 
  when 
  

   the 
  glow 
  has 
  once 
  started 
  it 
  is 
  continued 
  by 
  means 
  of 
  a 
  much 
  

   smaller 
  electromotive 
  force. 
  This 
  is 
  shown 
  by 
  the 
  fact 
  that 
  a 
  

   Thomson 
  electrostatic 
  voltmeter, 
  connected 
  with 
  the 
  terminals 
  

   of 
  the 
  Geissler 
  tube, 
  indicated 
  differences 
  of 
  potential 
  between 
  

   the 
  ends 
  of 
  the 
  tube 
  ranging 
  from 
  six 
  hundred 
  and 
  thirty 
  volts 
  

   upward. 
  De 
  la 
  Rue 
  and 
  Miller, 
  who 
  found 
  no 
  potential 
  dif- 
  

   ference 
  between 
  the 
  ends 
  of 
  Geissler 
  tubes, 
  must 
  have 
  been 
  

   working 
  with 
  discontinuous 
  discharges. 
  Crookes's 
  estimate 
  

   that 
  27,600 
  volts 
  are 
  necessary 
  to 
  produce 
  the 
  red 
  spectrum 
  is 
  

   evidently 
  excessive. 
  

  

  The 
  introduction 
  of 
  a 
  capacity 
  between 
  the 
  terminals 
  of 
  the 
  

   Geissler 
  tube, 
  for 
  example, 
  two 
  plates 
  of 
  metal 
  sixteen 
  hun- 
  

   dred 
  square 
  centimeters 
  in 
  area 
  separated 
  by 
  plate 
  glass 
  one 
  

   centimeter 
  thick, 
  made 
  no 
  difference 
  in 
  the 
  red 
  glow, 
  so 
  long 
  

   as 
  the 
  connections 
  were 
  good 
  and 
  the 
  condenser 
  quiet.* 
  As 
  

   soon 
  as 
  a 
  spark 
  gap 
  was 
  introduced, 
  or 
  the 
  condenser 
  began 
  to 
  

  

  * 
  Sir 
  W. 
  Thomson 
  (Lord 
  Kelvin) 
  : 
  Papers 
  on 
  Electrostatics 
  and 
  Magnetism. 
  

   MacMillan, 
  1872, 
  p. 
  236. 
  

  

  