﻿of 
  Radium 
  in 
  an 
  Electric 
  Field. 
  325 
  

  

  decreased 
  as 
  a 
  result 
  of 
  columnar 
  recombination 
  of 
  the 
  posi- 
  

   tively 
  charged 
  particles 
  with 
  negative 
  ions 
  ; 
  and 
  with 
  very 
  small 
  

   potentials 
  the 
  charged 
  particles 
  recombine 
  with 
  negative 
  

   ions 
  in 
  the 
  volume 
  of 
  the 
  gas. 
  Small 
  traces 
  of 
  water 
  vapor 
  

   have 
  a 
  considerable 
  effect 
  in 
  diminishing 
  the 
  number 
  of 
  posi- 
  

   tively 
  charged 
  particles 
  ; 
  the 
  water 
  vapor 
  appears 
  to 
  be 
  effec- 
  

   tive 
  in 
  bringing 
  about 
  increased 
  recombination, 
  both 
  volume 
  

   and 
  columnar, 
  between 
  the 
  charged 
  particles 
  and 
  the 
  negative 
  

   ions. 
  

  

  It 
  has 
  been 
  shown 
  in 
  Section 
  5 
  that 
  even 
  in 
  air 
  which 
  has 
  

   been 
  thoroughly 
  dried 
  the 
  recombination 
  between 
  the 
  charged 
  

   deposit 
  particles 
  and 
  the 
  negative 
  ions 
  is 
  greater 
  than 
  the 
  

   recombination 
  between 
  the 
  positive 
  and 
  negative 
  ions. 
  This 
  

   result, 
  which 
  is 
  in 
  all 
  probability 
  to 
  be 
  ascribed 
  to 
  the 
  larger 
  

   size 
  and 
  mass 
  of 
  the 
  deposit 
  particles, 
  is 
  not 
  in 
  accord 
  with 
  the 
  

   experimental 
  result 
  of 
  H. 
  W. 
  Schmidt,* 
  who 
  came 
  to 
  the 
  con- 
  

   clusion 
  that 
  as 
  far 
  as 
  recombination 
  and 
  mobility 
  are 
  concerned 
  

   the 
  active 
  particles 
  behave 
  as 
  positive 
  ions. 
  

  

  The 
  process 
  which 
  accompanies 
  the 
  deposit 
  of 
  the 
  active 
  

   particles 
  on 
  the 
  cathode 
  appears 
  to 
  be 
  most 
  suitably 
  explained 
  

   in 
  the 
  following 
  manner. 
  At 
  the 
  moment 
  of 
  expulsion 
  of 
  the 
  

   a-particle 
  from 
  the 
  atom 
  of 
  emanation 
  the 
  residual 
  part 
  recoils 
  

   into 
  the 
  gas 
  ; 
  in 
  air 
  at 
  a 
  pressure 
  of 
  1 
  atmosphere 
  the 
  range 
  of 
  

   this 
  recoil 
  atom 
  has 
  been 
  shown 
  to 
  be 
  about 
  T 
  V 
  mm 
  - 
  -^ 
  s 
  ^ 
  

   moves 
  through 
  the 
  gas 
  the 
  recoil 
  atom 
  produces 
  a 
  large 
  num- 
  

   ber 
  of 
  ions 
  and 
  in 
  the 
  act 
  of 
  ionization 
  it 
  is 
  possible 
  that 
  the 
  

   recoil 
  atom 
  may 
  lose 
  its 
  positive 
  charge. 
  On 
  the 
  other 
  hand 
  

   recoil 
  atoms 
  which 
  at 
  any 
  time 
  are 
  uncharged 
  may 
  regain 
  a 
  

   positive 
  charge, 
  so 
  that 
  if 
  we 
  consider 
  a 
  large 
  number 
  of 
  recoil 
  

   atoms 
  there 
  will 
  at 
  any 
  given 
  moment 
  be 
  a 
  certain 
  fraction 
  

   which 
  carry 
  a 
  positive 
  charge, 
  the 
  remainder 
  being 
  practically 
  

   all 
  neutral. 
  The 
  process 
  is 
  in 
  many 
  respects 
  similar 
  to 
  that 
  

   which 
  is 
  known 
  to 
  occur 
  in 
  the 
  case 
  of 
  canal 
  rays. 
  During 
  the 
  

   motion 
  of 
  recoil 
  the 
  atom 
  is 
  practically 
  unaffected 
  by 
  any 
  

   applied 
  electric 
  field, 
  so 
  that 
  initially 
  the 
  relative 
  number 
  of 
  

   uncharged 
  and 
  charged 
  recoil 
  atoms 
  is 
  independent 
  of 
  the 
  

   applied 
  potential. 
  However, 
  when 
  the 
  recoil 
  atom 
  has 
  reached 
  

   the 
  end 
  of 
  its 
  path, 
  if 
  it 
  be 
  positively 
  charged 
  it 
  may 
  lose 
  its 
  

   charge 
  by 
  recombination 
  with 
  a 
  negative 
  ion 
  formed 
  in 
  the 
  

   column 
  ; 
  this 
  recombination 
  can 
  be 
  prevented 
  by 
  increasing 
  

   sufficiently 
  the 
  applied 
  potential. 
  Moreover 
  for 
  small 
  applied 
  

   potentials 
  a 
  positively 
  charged 
  recoil 
  atom 
  may 
  recombine 
  

   with 
  a 
  negative 
  ion 
  in 
  the 
  volume 
  of 
  the 
  gas. 
  

  

  When 
  both 
  columnar 
  and 
  volume 
  recombination 
  are 
  avoided 
  

   by 
  the 
  application 
  of 
  a 
  sufficiently 
  high 
  potential 
  the 
  distribu- 
  

   tion 
  of 
  the 
  active 
  deposit 
  on 
  the 
  electrodes 
  is 
  determined 
  

  

  *H. 
  W. 
  Schmidt, 
  Phys. 
  Zeitschr., 
  ix, 
  p. 
  184, 
  1908. 
  

  

  