﻿512 
  Prof. 
  Wellisch 
  and 
  Dr. 
  Woodrow: 
  Experiments 
  

  

  active 
  deposit 
  settled 
  on 
  the 
  cathode 
  ; 
  or 
  more 
  generally 
  

   that 
  the 
  cathode 
  activity 
  was 
  a 
  measure 
  of 
  the 
  degree 
  of 
  

   saturation 
  o£ 
  the 
  electric 
  current. 
  

  

  On 
  investigating 
  experimentally 
  the 
  activity 
  distribution 
  

   when 
  the 
  radium 
  emanation 
  was 
  present 
  in 
  air 
  at 
  a 
  pressure 
  

   of 
  260 
  mm., 
  it 
  was 
  found 
  that 
  for 
  potentials 
  above 
  80 
  volts 
  

   the 
  cathode 
  activity 
  did 
  not 
  perceptibly 
  increase 
  ; 
  but 
  the 
  

   curves 
  connecting 
  the 
  percentage 
  of 
  cathode 
  activity 
  and 
  

   the 
  ionization 
  with 
  the 
  potential-difference 
  had 
  the 
  character- 
  

   istic 
  horizontal 
  portion 
  which 
  suggests 
  that 
  saturation 
  has 
  

   been 
  attained. 
  On 
  the 
  other 
  hand, 
  the 
  measurements 
  showed 
  

   that 
  there 
  was 
  still 
  about 
  17 
  per 
  cent, 
  of 
  the 
  active 
  deposit 
  

   which 
  failed 
  to 
  reach 
  the 
  cathode. 
  

  

  These 
  experimental 
  results 
  appeared 
  to 
  indicate 
  that 
  the 
  

   saturation 
  obtained 
  for 
  alpha 
  particle 
  ionization 
  at 
  pressures 
  

   below 
  about 
  one-half 
  of 
  an 
  atmosphere 
  was 
  only 
  apparent 
  : 
  

   the 
  results 
  were 
  most 
  suitably 
  explained 
  on 
  the 
  supposition 
  

   that 
  part 
  of 
  the 
  electric 
  current 
  observed 
  at 
  one 
  atmosphere 
  

   was 
  due 
  to 
  the 
  ionization 
  by 
  collision 
  with 
  molecules 
  which, 
  

   though 
  electrically 
  neutral, 
  had 
  been 
  brought 
  into 
  an 
  un- 
  

   stable 
  condition 
  by 
  the 
  action 
  of 
  the 
  alpha 
  particle. 
  These 
  

   " 
  neutrons" 
  would 
  be 
  in 
  the 
  most 
  favourable 
  position 
  for 
  

   ionization 
  when 
  the 
  electric 
  field 
  was 
  parallel 
  to 
  the 
  alpha-ray 
  

   column 
  and 
  also 
  when 
  the 
  pressure 
  was 
  not 
  too 
  low. 
  

  

  On 
  this 
  view, 
  the 
  characteristic 
  upward 
  slope 
  of 
  the 
  curve 
  

   connecting 
  the 
  electric 
  current 
  with 
  the 
  field 
  for 
  alpha 
  

   particle 
  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 
  

   Langevin's 
  theory 
  of 
  recombination 
  are 
  given 
  in 
  which 
  the 
  

   subject 
  is 
  treated 
  from 
  a 
  slightly 
  different 
  standpoint 
  from 
  

   that 
  adopted 
  by 
  Moulin. 
  

  

  * 
  Moulin, 
  Compt. 
  Rend, 
  cxlviii. 
  p. 
  1757 
  (1909). 
  

  

  