﻿of 
  Radium 
  in 
  an 
  Electric 
  Field. 
  327 
  

  

  66 
  per 
  cent 
  of 
  the 
  positive 
  ions 
  on 
  the 
  average 
  escaped 
  from 
  

   the 
  a-particle 
  column, 
  the 
  corresponding 
  figure 
  for 
  the 
  posi- 
  

   tively 
  charged 
  recoil 
  atoms 
  was 
  only 
  38 
  per 
  cent. 
  This 
  slow- 
  

   ness 
  with 
  which 
  the 
  recoil 
  atoms 
  diffuse 
  is 
  readily 
  ascribable 
  to 
  

   their 
  relatively 
  large 
  size 
  and 
  mass. 
  Of 
  those 
  ions 
  and 
  recoil 
  

   atoms 
  which 
  do 
  not 
  escape 
  by 
  diffusion 
  from 
  the 
  column 
  

   approximately 
  the 
  same 
  fraction 
  is 
  brought 
  over 
  by 
  any 
  given 
  

   potential 
  ; 
  it 
  seems 
  that 
  there 
  is 
  here 
  some 
  compensating 
  influ- 
  

   ence 
  at 
  work 
  ; 
  probably 
  the 
  greater 
  tendency 
  of 
  the 
  recoil 
  atoms 
  

   to 
  recombine 
  with 
  negative 
  ions 
  is- 
  partly 
  balanced 
  by 
  the 
  

   smaller 
  number 
  of 
  encounters 
  with 
  these 
  ions. 
  

  

  The 
  existence 
  of 
  a 
  definite 
  limiting 
  value 
  to 
  the 
  percentage 
  

   cathode 
  activity 
  has 
  been 
  ascribed 
  above 
  to 
  a 
  continual 
  process 
  

   of 
  gain 
  and 
  loss 
  of 
  charge 
  which 
  occurs 
  during 
  the 
  recoil 
  

   motion 
  of 
  the 
  active 
  deposit 
  particle. 
  It 
  is 
  to 
  be 
  expected 
  

   that 
  this 
  limiting 
  value 
  will 
  depend 
  upon 
  the 
  nature 
  of 
  the 
  gas 
  

   into 
  which 
  the 
  particle 
  recoils 
  ; 
  the 
  experimental 
  determination 
  

   showed 
  that 
  this 
  was 
  in 
  general 
  the 
  case 
  although 
  the 
  limiting 
  

   value 
  for 
  hydrogen 
  was 
  within 
  the 
  limits 
  of 
  error 
  the 
  same 
  as 
  

   that 
  for 
  air. 
  The 
  fact 
  that 
  the 
  value 
  for 
  ether 
  is 
  as 
  small 
  as 
  

   10 
  per 
  cent 
  is 
  surprising 
  and 
  is 
  in 
  all 
  probability 
  to 
  be 
  ascribed 
  

   to 
  the 
  ease 
  with 
  which 
  the 
  molecules 
  of 
  ether 
  are 
  ionized. 
  

  

  