﻿706 
  

  

  Prof. 
  Rutherford 
  and 
  Mr. 
  Nuttall 
  on 
  

  

  Variation 
  of 
  scattering 
  with 
  the 
  distance 
  between 
  the 
  plates. 
  

  

  A 
  few 
  experiments 
  were 
  made 
  to 
  determine 
  approximately 
  

   the 
  variation 
  of 
  scattering 
  with 
  the 
  distance 
  between 
  the 
  

   plates. 
  The 
  latter 
  distance 
  was 
  varied 
  from 
  *173 
  mm. 
  to 
  

   *89 
  mm. 
  ; 
  the 
  corresponding 
  least 
  angles 
  of 
  scattering 
  to 
  

   deflect 
  the 
  ex. 
  particles 
  against 
  the 
  faces 
  of 
  the 
  plates 
  varying 
  

   from 
  0°'069 
  to 
  0°'356. 
  

  

  The 
  collected 
  results 
  are 
  shown 
  in 
  Table 
  II. 
  The 
  relative 
  

   scattering 
  coefficients 
  are 
  compared 
  by 
  observing 
  from 
  the 
  

   curves 
  the 
  pressure 
  of 
  gas 
  required 
  to 
  scatter 
  50 
  per 
  cent, 
  

   of 
  the 
  initial 
  number 
  of 
  a 
  particles. 
  

  

  Table 
  II. 
  

  

  Distance 
  d 
  apart 
  

   of 
  plates. 
  

  

  Relative 
  scattering 
  

   coefficient 
  \. 
  

  

  X 
  . 
  d5/4. 
  

  

  •172 
  mm. 
  

   •325 
  

  

  •586 
  

   •890 
  

  

  •562 
  

   •256 
  

   •126 
  

   •0712 
  

  

  •618 
  

   •627 
  

   •643 
  

   •615 
  

  

  Within 
  the 
  limits 
  employed, 
  the 
  scattering 
  appears 
  to 
  vary 
  

   rather 
  more 
  rapidly 
  than 
  the 
  inverse 
  of 
  the 
  linear 
  distance 
  d 
  

   between 
  the 
  plates 
  and 
  to 
  be 
  nearly 
  proportional 
  to 
  d~ 
  5 
  ^. 
  

  

  It 
  will 
  be 
  shown 
  later 
  that 
  the 
  scattering 
  coefficient 
  

   increases 
  rapidly 
  with 
  decrease 
  of 
  velocity 
  of 
  the 
  a 
  particle. 
  

   A 
  correction 
  has 
  consequently 
  to 
  be 
  applied 
  to 
  reduce 
  the 
  

   amount 
  of 
  scattering 
  to 
  a 
  standard 
  velocity. 
  This 
  correction 
  

   has 
  been 
  made 
  in 
  the 
  results 
  of 
  Table 
  II. 
  

  

  Variation 
  of 
  scattering 
  with 
  atomic 
  weight. 
  

  

  The 
  gases 
  whose 
  scattering 
  coefficients 
  were 
  compared 
  

   were 
  as 
  follows: 
  — 
  air, 
  hydrogen, 
  helium, 
  methane, 
  carbon 
  

   dioxide, 
  and 
  sulphuretted 
  hydrogen. 
  A 
  few 
  experiments 
  

   were 
  made 
  on 
  the 
  scattering 
  produced 
  by 
  the 
  heavy 
  vapours, 
  

   methyl 
  iodide 
  and 
  ethyl 
  bromide, 
  but 
  they 
  are 
  not 
  included 
  

   in 
  this 
  paper. 
  In 
  all 
  cases 
  two 
  sets 
  of 
  experiments 
  were 
  

   performed: 
  (1) 
  experiments 
  on 
  the 
  scattering 
  and 
  absorption 
  

   combined, 
  and 
  (2) 
  experiments 
  on 
  the 
  absorption 
  alone. 
  The 
  

   latter 
  were 
  in 
  agreement 
  with 
  the 
  stopping 
  powers 
  of 
  the 
  

   gases 
  as 
  calculated 
  by 
  Bragg's* 
  square-root 
  law. 
  

  

  The 
  distance 
  between 
  the 
  plates 
  was 
  kept 
  constant 
  during 
  

  

  * 
  W. 
  H. 
  Bragg, 
  Phil. 
  Mag. 
  x. 
  p. 
  318 
  (1905). 
  

  

  