﻿Wellisch 
  and 
  Woodrow 
  — 
  Columnar 
  Ionization. 
  215 
  

  

  ionization 
  is 
  due 
  in 
  part 
  to 
  the 
  extra 
  ionization 
  thus 
  obtained. 
  

   We 
  should 
  expect, 
  therefore, 
  that 
  when 
  the 
  electric 
  force 
  is 
  

   sufficiently 
  great 
  the 
  electric 
  current 
  would 
  be 
  slightly 
  greater 
  

   when 
  the 
  field 
  is 
  longitudinal 
  or 
  parallel 
  to 
  the 
  alpha-particle 
  

   column 
  than 
  when 
  it 
  is 
  transverse 
  or 
  perpendicular 
  to 
  it. 
  The 
  

   present 
  paper 
  describes 
  a 
  series 
  of 
  experiments 
  which 
  were 
  

   devised 
  to 
  compare 
  the 
  ionization 
  resulting 
  from 
  a 
  longitudinal 
  

   and 
  transverse 
  field 
  for 
  the 
  case 
  of 
  a 
  single 
  alpha-particle 
  

   column. 
  The 
  results 
  of 
  the 
  experiments 
  confirm 
  the 
  accepted 
  

   view 
  of 
  the 
  phenomenon 
  as 
  advanced 
  by 
  Langevin 
  and 
  Moulin,* 
  

   namely 
  that 
  the 
  ' 
  lack 
  of 
  saturation 
  ' 
  of 
  the 
  ionization 
  current 
  

   is 
  due 
  to 
  the 
  columnar 
  recombination, 
  and 
  no 
  evidence 
  was 
  

   obtained 
  which 
  would 
  indicate 
  the 
  existence 
  of 
  unstable 
  atoms 
  

   in 
  the 
  alpha-ray 
  columns. 
  

  

  In 
  Section 
  5, 
  some 
  theoretical 
  considerations 
  based 
  on 
  Lan- 
  

   gevin's 
  theory 
  of 
  recombination 
  are 
  given 
  in 
  which 
  the 
  subject 
  

   is 
  treated 
  from 
  a 
  slightly 
  different 
  standpoint 
  from 
  that 
  

   adopted 
  by 
  Moulin. 
  

  

  Description 
  of 
  the 
  Experimental 
  Method. 
  

  

  2. 
  It 
  was 
  first 
  shown 
  by 
  Moulin 
  that 
  lack 
  of 
  saturation 
  does 
  

   not 
  come 
  into 
  evidence 
  when 
  the 
  field 
  is 
  transverse 
  to 
  the 
  

   alpha-ray 
  column 
  nor, 
  at 
  low 
  pressures, 
  when 
  the 
  field 
  is 
  lon- 
  

   gitudinal. 
  This 
  experimental 
  fact 
  formed 
  the 
  basis 
  of 
  the 
  

   method 
  employed 
  for 
  the 
  comparison 
  of 
  the 
  ionization 
  result- 
  

   ing 
  from 
  the 
  application 
  of 
  a 
  longitudinal 
  and 
  a 
  transverse- 
  

   field 
  to 
  a 
  single 
  alpha-particle 
  column. 
  

  

  Consider 
  a 
  single 
  alpha-particle 
  column 
  formed 
  in 
  air 
  (1) 
  at 
  a 
  

   pressure 
  of 
  one 
  atmosphere, 
  (2) 
  at 
  a 
  pressure^? 
  which 
  is 
  a 
  small 
  

   fraction 
  of 
  an 
  atmosphere, 
  say 
  about 
  one-third. 
  Let 
  i 
  x 
  and 
  i 
  2 
  

   denote 
  the 
  number 
  of 
  ions 
  due 
  to 
  a 
  small 
  portion 
  of 
  the 
  path 
  (in 
  

   the 
  present 
  case 
  this 
  was 
  4 
  mm 
  in 
  length) 
  for 
  the 
  two 
  pressures 
  

   respectively. 
  This 
  ionization 
  may 
  be 
  measured 
  with 
  either 
  a 
  

   longitudinal 
  or 
  a 
  transverse 
  field. 
  Let 
  

  

  i 
  i 
  * 
  K 
  

  

  -± 
  = 
  r, 
  and 
  -r 
  = 
  r 
  t 
  

  

  h 
  \ 
  

  

  when 
  the 
  ionization 
  is 
  measured 
  in 
  a 
  longitudinal 
  and 
  trans- 
  

   verse 
  field 
  respectively. 
  

  

  In 
  general, 
  r, 
  will 
  be 
  different 
  from 
  r 
  t 
  : 
  this 
  arises 
  from 
  the 
  

   fact 
  that 
  the 
  current 
  at 
  one 
  atmosphere 
  when 
  measured 
  in 
  the 
  

   longitudinal 
  field 
  depends 
  upon 
  the 
  electric 
  field 
  over 
  a 
  wide 
  

   range, 
  while 
  in 
  the 
  other 
  the 
  currents 
  readily 
  assume 
  values 
  

   which 
  are 
  independent 
  of 
  the 
  field. 
  

  

  * 
  Moulin, 
  Comp. 
  Rend., 
  cxlviii, 
  p. 
  1757, 
  1909. 
  

  

  