﻿on 
  Columnar 
  Ionization, 
  513 
  

  

  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 
  longitudinal. 
  This 
  experimental 
  fact 
  formed 
  the 
  basis 
  

   of 
  the 
  method 
  employed 
  for 
  the 
  comparison 
  of 
  the 
  ionization 
  

   resulting 
  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 
  p 
  

   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 
  

  

  ~ 
  =n 
  and 
  — 
  = 
  r 
  t 
  

  

  when 
  the 
  ionization 
  is 
  measured 
  in 
  a 
  longitudinal 
  and 
  

   transverse 
  field 
  respectively. 
  

  

  In 
  general, 
  ri 
  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. 
  

  

  On 
  the 
  hypothesis 
  of 
  Wellisch 
  and 
  Bronson 
  it 
  was 
  to 
  be 
  

   expected 
  that 
  n 
  would 
  be 
  greater 
  than 
  r 
  t 
  for 
  large 
  values 
  of 
  

   the 
  field 
  ; 
  whereas 
  on 
  the 
  Langevin-Moulin 
  theory 
  n 
  should 
  

   be 
  less 
  than 
  r 
  t 
  , 
  except 
  when 
  saturation 
  was 
  attained, 
  in 
  which 
  

   case 
  we 
  should 
  have 
  ri 
  = 
  r 
  t 
  . 
  

  

  In 
  order 
  to 
  determine 
  the 
  value 
  of 
  ri 
  corresponding 
  to 
  any 
  

   value 
  of 
  the 
  field, 
  the 
  ionization 
  currents 
  due 
  to 
  the 
  alpha 
  

   rays 
  from 
  a 
  polonium 
  source 
  were 
  measured 
  in 
  a 
  longitudinal 
  

   field 
  for 
  air 
  at 
  one 
  atmosphere 
  and 
  for 
  air 
  at 
  a 
  lower 
  

   pressure 
  p. 
  The 
  ratio 
  of 
  these 
  currents 
  gives 
  the 
  value 
  of 
  

   Ti 
  and 
  is 
  independent 
  of 
  the 
  actual 
  number 
  of 
  alpha 
  particles 
  

   entering 
  the 
  measuring 
  apparatus 
  and 
  also 
  of 
  the 
  electrical 
  

   capacity 
  of 
  the 
  system 
  ; 
  in 
  fact 
  it 
  is 
  the 
  ratio 
  which 
  would 
  

   be 
  obtained 
  for 
  the 
  ionization 
  due 
  to 
  a 
  single 
  alpha 
  particle. 
  

  

  The 
  ratio 
  r% 
  was 
  determined 
  in 
  a 
  similar 
  manner 
  by 
  obtaining 
  

   the 
  corresponding 
  currents 
  in 
  the 
  transverse 
  field. 
  

  

  Description 
  of 
  Apparatus 
  and 
  Experimental 
  Procedure. 
  

  

  3. 
  By 
  the 
  kind 
  permission 
  of 
  Prof. 
  Bumstead 
  we 
  were 
  

   enabled 
  to 
  avail 
  ourselves 
  of 
  the 
  ionization 
  vessel 
  which 
  had 
  

  

  