﻿Striations 
  in 
  the 
  Electric 
  Discharge. 
  451 
  

  

  any 
  unit 
  are 
  for 
  the 
  most 
  part 
  manufactured 
  in 
  the 
  units 
  

   themselves, 
  so 
  that 
  these 
  units 
  ^vill 
  behave, 
  as 
  Goldstein 
  and 
  

   Spottiswoode 
  and 
  Moulton 
  have 
  observed 
  the 
  striations 
  to 
  

   behave, 
  as 
  if 
  they 
  were 
  to 
  a 
  considerable 
  extent 
  independent 
  

   of 
  each 
  other. 
  The 
  effect 
  of 
  pressure 
  on 
  the 
  distance 
  between 
  

   the 
  striations 
  can 
  easily 
  be 
  understood 
  from 
  this 
  point 
  of 
  

   view, 
  for 
  the 
  lower 
  the 
  pressure 
  the 
  greater 
  will 
  be 
  the 
  dis- 
  

   tance 
  which 
  particles 
  projected 
  with 
  high 
  velocity 
  will 
  travel 
  

   before 
  their 
  velocity 
  is 
  destroyed. 
  Again, 
  the 
  variations 
  in 
  the 
  

   electric 
  field 
  are 
  due 
  to 
  the 
  accumulation 
  of 
  electrical 
  charges 
  

   in 
  the 
  tube. 
  These 
  accumulations 
  may 
  be 
  regarded 
  as 
  elec- 
  

   trified 
  disks 
  whose 
  cross-section 
  is 
  that 
  of 
  the 
  tube 
  ; 
  the 
  distance 
  

   from 
  the 
  disk 
  at 
  which 
  these 
  forces 
  fall 
  to 
  a 
  certain 
  fraction 
  

   of 
  their 
  maximum 
  value 
  will 
  depend 
  upon 
  the 
  diameter 
  of 
  

   the 
  disk; 
  the 
  larger 
  the 
  diameter 
  the 
  greater 
  this 
  distance, 
  

   so 
  that 
  when 
  the 
  diameter 
  of 
  the 
  tube 
  is 
  small 
  the 
  fluctuations 
  

   in 
  the 
  intensity 
  of 
  the 
  electric 
  force 
  will 
  be 
  much 
  more 
  rapid 
  

   than 
  when 
  it 
  is 
  large, 
  and 
  thus 
  we 
  should 
  expect 
  the 
  striations 
  

   to 
  be 
  much 
  nearer 
  together 
  in 
  a 
  narrow 
  tube 
  than 
  in 
  a 
  wide 
  one. 
  

  

  To 
  explain 
  the 
  variations 
  in 
  the 
  luminosity 
  which 
  accom- 
  

   pany 
  these 
  fluctuations 
  in 
  the 
  electric 
  field 
  we 
  must 
  consider 
  

   the 
  variation 
  in 
  the 
  kinetic 
  energy 
  possessed 
  by 
  the 
  positive 
  

   ions 
  when 
  they 
  recombine. 
  The 
  recombination 
  of 
  ions 
  does 
  

   not 
  in 
  general 
  seem 
  to 
  be 
  accompanied 
  by 
  luminosity, 
  unless 
  

   the 
  ions 
  possess 
  a 
  definite 
  amount 
  of 
  kinetic 
  energy. 
  We 
  

   certainly 
  can 
  have 
  a 
  gas 
  with 
  great 
  electrical 
  conductivity, 
  

   and 
  in 
  which 
  a 
  large 
  number 
  of 
  ions 
  are 
  recombining 
  without 
  

   any 
  visible 
  luminosity; 
  it 
  seems 
  as 
  if 
  the 
  ions 
  must 
  have 
  a 
  

   definite 
  amount 
  of 
  kinetic 
  energy 
  for 
  visible 
  light 
  to 
  be 
  de- 
  

   veloped 
  on 
  their 
  recombination. 
  Now 
  in 
  the 
  space 
  between 
  

   two 
  striations 
  the 
  electric 
  field 
  in 
  the 
  part 
  near 
  the 
  cathode 
  

   side 
  of 
  the 
  bright 
  head 
  of 
  a 
  striation 
  — 
  the 
  dark 
  part 
  — 
  is 
  weak; 
  

   here 
  the 
  ions 
  have 
  not 
  got 
  the 
  minimum 
  amount 
  of 
  energy 
  

   requisite 
  for 
  them 
  to 
  be 
  luminous 
  when 
  they 
  recombine; 
  in 
  the 
  

   bright 
  part 
  of 
  the 
  striation 
  the 
  electric 
  field 
  is 
  strong, 
  and 
  

   here 
  the 
  ions 
  get 
  sufficient 
  kinetic 
  energy 
  to 
  enable 
  them 
  to 
  

   give 
  out 
  light 
  when 
  they 
  combine. 
  If 
  the 
  energy 
  required 
  

   for 
  an 
  ion 
  to 
  give 
  out 
  visible 
  light 
  is 
  greater 
  for 
  light 
  at 
  the 
  

   blue 
  end 
  of 
  the 
  spectrum 
  than 
  at 
  the 
  red, 
  we 
  might 
  get 
  blue 
  

   light 
  at 
  one 
  part 
  of 
  the 
  striation, 
  red 
  at 
  another, 
  an 
  eff'ect 
  

   often 
  observed 
  when 
  we 
  have 
  a 
  mixture 
  of 
  mercury 
  vapour 
  

   and 
  hydrogen 
  in 
  the 
  tube 
  ; 
  a 
  similar 
  separation 
  of 
  the 
  spectra 
  

   of 
  the 
  two 
  gases 
  in 
  a 
  striation 
  might 
  also 
  be 
  produced 
  if 
  one 
  

   of 
  the 
  gases 
  were 
  more 
  easily 
  ionized 
  than 
  the 
  other. 
  

  

  I 
  wish 
  to 
  thank 
  my 
  assistant, 
  Mr. 
  Everett, 
  for 
  the 
  assistance 
  

   he 
  has 
  given 
  me 
  in 
  these 
  investigations. 
  

  

  