﻿Wellisch 
  and 
  Woodrow 
  — 
  Columnar 
  Ionization. 
  229 
  

  

  The 
  value 
  of 
  Q 
  of 
  the 
  saturation 
  current 
  per 
  sq. 
  cm. 
  for 
  a 
  

   single 
  column 
  can 
  be 
  readily 
  deduced 
  after 
  the 
  curve 
  C 
  has 
  

   been 
  plotted. 
  Langevin 
  found 
  that 
  for 
  C0 
  2 
  at 
  a 
  pressure 
  of 
  

   one 
  atmosphere 
  e 
  = 
  0*51 
  ; 
  the 
  values 
  of 
  y 
  and 
  x 
  were 
  obtained 
  

   corresponding 
  to 
  a 
  field 
  of 
  200 
  volts 
  per 
  cm. 
  and 
  Q 
  was 
  then 
  

  

  deduced 
  by 
  means 
  of 
  the 
  relation 
  x 
  = 
  — 
  °. 
  The 
  value 
  ob- 
  

  

  tained 
  was 
  *551 
  E. 
  S. 
  unit. 
  The 
  ionization 
  current 
  in 
  C0 
  2 
  was 
  

   measured 
  at 
  the 
  same 
  relative 
  part 
  of 
  the 
  range 
  of 
  the 
  alpha 
  

   particle 
  as 
  that 
  in 
  air 
  ; 
  and 
  assuming 
  that 
  the 
  total 
  ionization 
  

   in 
  C0 
  2 
  is 
  103 
  times 
  that 
  in 
  air, 
  it 
  was 
  easy 
  to 
  calculate 
  the 
  

   number 
  of 
  ions 
  produced 
  by 
  each 
  alpha 
  particle 
  within 
  the 
  

   ionization 
  vessel. 
  The 
  calculation 
  gave 
  the 
  area 
  of 
  cross-sec- 
  

   tion 
  S 
  = 
  1*42 
  X 
  10" 
  5cm2 
  and 
  the 
  radius 
  of 
  the 
  column 
  E 
  = 
  

   0-0021 
  m 
  . 
  

  

  The 
  large 
  values 
  obtained 
  for 
  the 
  mean 
  cross-section 
  of 
  the 
  

   columns 
  may 
  at 
  first 
  appear 
  surprising. 
  Professor 
  Bumstead* 
  

   has 
  already 
  suggested 
  that 
  a 
  considerable 
  part 
  of 
  the 
  ioniza- 
  

   tion 
  in 
  the 
  columns 
  may 
  be 
  indirect 
  and 
  be 
  clue 
  to 
  the 
  

   action 
  of 
  electrons 
  liberated 
  from 
  the 
  atoms 
  by 
  the 
  action 
  

   of 
  the 
  alpha 
  particle. 
  These 
  electrons 
  would 
  have 
  a 
  range 
  of 
  

   the 
  order 
  of 
  0'J 
  mm 
  in 
  air 
  at 
  a 
  pressure 
  of 
  one 
  atmosphere. 
  

   Apart 
  from 
  this 
  suggestion, 
  however, 
  it 
  should 
  be 
  remembered 
  

   that 
  the 
  cross-section 
  is 
  that 
  of 
  the 
  column 
  after 
  the 
  ions 
  have 
  

   in 
  considerable 
  measure 
  been 
  separated 
  by 
  the 
  processes 
  of 
  

   diffusion 
  and 
  molecular 
  agitation. 
  After 
  the 
  column 
  has 
  been 
  

   formed 
  by 
  the 
  alpha 
  particle 
  there 
  would 
  in 
  all 
  probability 
  be 
  

   an 
  extremely 
  rapid 
  lateral 
  diffusion 
  of 
  the 
  ions, 
  so 
  that 
  before 
  

   the 
  ions 
  have 
  sensibly 
  moved 
  under 
  the 
  action 
  of 
  the 
  electric 
  

   field 
  we 
  may 
  regard 
  the 
  column 
  as 
  consisting 
  of 
  a 
  core 
  (which 
  

   in 
  air 
  at 
  one 
  atmosphere 
  contains 
  about 
  26 
  per 
  cent 
  of 
  the 
  

   ions) 
  surrounded 
  by 
  a 
  fringe. 
  The 
  recombination 
  occurs 
  

   mainly 
  in 
  the 
  core. 
  

  

  If 
  Langevin's 
  theory 
  is 
  indeed 
  applicable 
  as 
  the 
  above 
  con- 
  

   siderations 
  would 
  appear 
  to 
  indicate, 
  this 
  would 
  afford 
  a 
  further 
  

   proof 
  that 
  the 
  recombination 
  in 
  the 
  alpha-particle 
  columns 
  is 
  

   between 
  ions 
  formed 
  from 
  different 
  atoms 
  and 
  is 
  not 
  the 
  

   initial 
  recombination 
  in 
  the 
  sense 
  originally 
  understood 
  by 
  

   Bragg, 
  viz., 
  that 
  between 
  an 
  electron 
  and 
  its 
  parent 
  atom. 
  It 
  

   is 
  probable 
  that 
  such 
  initial 
  recombination 
  does 
  actually 
  occur, 
  

   but 
  it 
  does 
  not 
  appear 
  to 
  be 
  prevented 
  to 
  any 
  appreciable 
  

   extent 
  by 
  the 
  electric 
  fields 
  employed 
  in 
  ordinary 
  laboratory 
  

   practice. 
  

  

  * 
  Bumstead 
  and 
  McGougan, 
  Phil. 
  Mag. 
  (6), 
  xxiv, 
  p. 
  482, 
  1912. 
  

  

  