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  Mr. 
  A. 
  Fleck 
  on 
  the 
  

  

  column 
  has 
  been 
  formed 
  by 
  the 
  alpha 
  particle 
  there 
  would 
  in 
  

   all 
  probability 
  be 
  an 
  extremely 
  rapid 
  lateral 
  diffusion 
  of 
  the 
  

   ions, 
  so 
  that 
  before 
  the 
  ions 
  have 
  sensibly 
  moved 
  under 
  the 
  

   action 
  of 
  the 
  electric 
  field 
  we 
  may 
  regard 
  the 
  column 
  as 
  

   consisting 
  of 
  a 
  core 
  (which 
  in 
  air 
  at 
  one 
  atmosphere 
  contains 
  

   about 
  26 
  per 
  cent, 
  of 
  the 
  ions) 
  surrounded 
  by 
  a 
  fringe. 
  

   The 
  recombination 
  occurs 
  mainly 
  in 
  the 
  core. 
  

  

  If 
  Langevin's 
  theory 
  is 
  indeed 
  applicable 
  as 
  the 
  above 
  

   considerations 
  would 
  appear 
  to 
  indicate, 
  this 
  would 
  afford 
  a 
  

   further 
  proof 
  that 
  the 
  recombination 
  in 
  the 
  alpha 
  particle 
  

   columns 
  is 
  between 
  ions 
  formed 
  from 
  different 
  atoms 
  and 
  is 
  

   not 
  the 
  initial 
  recombination 
  in 
  the 
  sense 
  originally 
  under- 
  

   stood 
  by 
  Bragg, 
  viz., 
  that 
  between 
  an 
  electron 
  and 
  its 
  parent 
  

   atom. 
  It 
  is 
  probable 
  that 
  such 
  initial 
  recombination 
  does 
  

   actually 
  occur, 
  but 
  it 
  does 
  not 
  appear 
  to 
  be 
  prevented 
  to 
  any 
  

   appreciable 
  extent 
  by 
  the 
  electric 
  fields 
  employed 
  in 
  ordinary 
  

   laboratory 
  practice. 
  

  

  Summary. 
  

  

  (1) 
  A 
  method 
  was 
  devised 
  to 
  compare 
  the 
  ionization 
  due 
  

   to 
  a 
  single 
  alpha 
  particle 
  when 
  measured 
  in 
  a 
  longitudinal 
  

   and 
  transverse 
  field. 
  The 
  results 
  confirm 
  the 
  view 
  of 
  Moulin 
  

   and 
  Langevin 
  that 
  the 
  upward 
  slope 
  characteristic 
  of 
  the 
  

   alpha-ray 
  ionization 
  curve 
  when 
  a 
  longitudinal 
  field 
  is 
  em- 
  

   ployed, 
  is 
  due 
  entirely 
  to 
  recombination 
  of 
  ions 
  in 
  the 
  column. 
  

   The 
  suggestion 
  of 
  Wellischand 
  Bronson 
  that 
  the 
  slope 
  is 
  due 
  

   in 
  part 
  to 
  ionization 
  by 
  collision 
  is 
  shown 
  to 
  be 
  untenable. 
  

  

  (2) 
  It 
  is 
  shown 
  that 
  Langevin^s 
  theory 
  of 
  recombination 
  

   appears 
  to 
  be 
  applicable 
  to 
  the 
  ionization 
  produced 
  by 
  a 
  single 
  

   alpha 
  particle 
  ; 
  also 
  the 
  theory 
  enables 
  an 
  estimate 
  of 
  the 
  

   mean 
  cross-section 
  of 
  the 
  column 
  to 
  be 
  computed. 
  

  

  Sloane 
  Laboratory, 
  Yale 
  University, 
  

   June 
  I, 
  1913. 
  

  

  XL. 
  The 
  Disintegration 
  of 
  Uranium 
  X. 
  By 
  Alexander 
  

   Fleck, 
  B.Sc, 
  Assistant 
  in 
  the 
  Departme7it 
  of 
  Physical 
  

   Chemistry, 
  Glasgow 
  University 
  *. 
  

  

  THE 
  only 
  direct 
  disintegration 
  product 
  of 
  uranium 
  that 
  is 
  

   generally 
  accepted 
  is 
  uranium 
  X. 
  Two 
  other 
  products 
  

   were 
  described 
  by 
  Danne 
  f 
  and 
  Antonoff 
  J, 
  but 
  the 
  existence 
  

  

  * 
  Communicated 
  by 
  Frederick 
  Soddy, 
  M.A., 
  F.R.S. 
  

   f 
  Danne, 
  Compi. 
  Rend, 
  cxlviii. 
  p. 
  337 
  (1909) 
  ; 
  Le 
  Radium, 
  vi. 
  p. 
  42. 
  

   (1909). 
  

  

  J 
  Antonoff, 
  Phil. 
  Mag. 
  [6] 
  xxii. 
  p. 
  419 
  (1911). 
  

  

  