﻿520 
  Prof. 
  Wellisch 
  and 
  Dr. 
  Woodrow 
  : 
  Experiments 
  

  

  with 
  the 
  view 
  generally 
  accepted, 
  the 
  current 
  resulting 
  from 
  

   alpha-ray 
  ionization 
  has 
  the 
  same 
  saturation 
  value 
  whether 
  

   the 
  electric 
  field 
  is 
  longitudinal 
  or 
  transverse, 
  the 
  continued 
  

   slope 
  of 
  the 
  ionization 
  curve 
  for 
  the 
  longitudinal 
  field 
  being 
  

   due 
  entirely 
  to 
  " 
  lack 
  of 
  saturation 
  " 
  occasioned 
  by 
  the 
  

   recombination 
  of 
  ions. 
  

  

  It 
  is 
  worthy 
  of 
  mention 
  here 
  that 
  experiments 
  were 
  per- 
  

   formed 
  to 
  determine 
  the 
  shape 
  of 
  the 
  ionization 
  curve 
  in 
  the 
  

   longitudinal 
  field 
  at 
  pressures 
  of 
  about 
  10 
  mm. 
  of 
  mercury 
  

   when 
  the 
  electric 
  field 
  was 
  sufficiently 
  increased 
  to 
  produce 
  

   ionization 
  by 
  collision. 
  The 
  curve 
  obtained 
  was 
  that 
  to 
  be 
  

   expected 
  from 
  Townsend's 
  theory 
  and 
  no 
  evidence 
  of 
  any 
  

   anomalous 
  behaviour 
  was 
  observed. 
  

  

  Having 
  proved 
  to 
  our 
  satisfaction 
  that 
  the 
  characteristic 
  

   shape 
  of 
  the 
  ionization 
  curve 
  for 
  the 
  longitudinal 
  field 
  was 
  

   to 
  be 
  ascribed 
  entirely 
  to 
  the 
  effect 
  of 
  recombination 
  of 
  ions, 
  

   it 
  became 
  a 
  point 
  of 
  interest 
  to 
  ascertain 
  if 
  possible 
  the 
  rela- 
  

   tive 
  effects 
  of 
  columnar 
  and 
  volume 
  recombination. 
  Moulin 
  * 
  

   has 
  already 
  given 
  a 
  method 
  for 
  determining 
  the 
  shape 
  of 
  the 
  

   current-field 
  curve, 
  when 
  volume 
  recombination 
  is 
  absent,, 
  

   that 
  is, 
  when 
  no 
  recombination 
  takes 
  place 
  between 
  ions 
  

   formed 
  in 
  different 
  columns. 
  Moulin' 
  s 
  method 
  consisted 
  in 
  

   determining 
  the 
  effect 
  of 
  volume 
  recombination 
  by 
  com- 
  

   paring 
  the 
  curve 
  obtained 
  for 
  a 
  transverse 
  field 
  with 
  that 
  

   obtained 
  by 
  using 
  X-rays 
  as 
  the 
  ionizing 
  source. 
  The 
  

   ideal 
  curve 
  corresponding 
  to 
  absence 
  of 
  volume 
  recom- 
  

   bination 
  in 
  a 
  longitudinal 
  field 
  was 
  obtained 
  by 
  means 
  of 
  a 
  

   series 
  of 
  calculations 
  referred 
  to 
  the 
  ideal 
  curve 
  of 
  the 
  

   transverse 
  field. 
  

  

  In 
  the 
  present 
  experiments 
  a 
  more 
  direct 
  method 
  was 
  

   employed 
  to 
  obtain 
  these 
  ideal 
  curves 
  for 
  a 
  longitudinal 
  

   field. 
  This 
  method 
  consisted 
  in 
  determining 
  how 
  the 
  frac- 
  

   tion 
  (i/T) 
  of 
  the 
  saturation 
  current 
  (I) 
  which 
  corresponds 
  

   to 
  any 
  given 
  value 
  of 
  the 
  electric 
  field 
  depends 
  upon 
  the 
  

   value 
  of 
  this 
  saturation 
  current. 
  Three 
  sources 
  of 
  polonium 
  

   were 
  employed 
  and 
  a 
  fourth 
  determination 
  was 
  possible 
  as 
  a 
  

   result 
  of 
  an 
  appreciable 
  decay 
  of 
  the 
  weakest 
  of 
  these 
  sources. 
  

   In 
  fig. 
  4 
  are 
  given 
  curves 
  which 
  show 
  how 
  i/I 
  varies 
  with 
  I 
  

   for 
  different 
  values 
  of 
  X 
  in 
  the 
  longitudinal 
  field. 
  The 
  

   curves 
  are 
  plotted 
  from 
  the 
  values 
  given 
  in 
  Table 
  VII. 
  

   These 
  curves 
  are 
  produced 
  so 
  as 
  to 
  intersect 
  the 
  axis 
  of 
  

   ordinates 
  : 
  the 
  ordinates 
  thus 
  cut 
  off 
  represent 
  the 
  fraction 
  

   of 
  the 
  saturation 
  current 
  which 
  would 
  be 
  obtained 
  by 
  the 
  

  

  * 
  Moulin, 
  Ann. 
  Chim. 
  Phys. 
  [8] 
  xxii. 
  p. 
  26 
  (1911). 
  

  

  