﻿Scattering 
  of 
  a 
  Particles 
  by 
  Gases, 
  

  

  711 
  

  

  It 
  should 
  be 
  noted 
  that 
  Geiger 
  and 
  Marsden 
  found 
  that 
  

   the 
  " 
  single 
  " 
  scattering 
  per 
  atom 
  was 
  proportional 
  to 
  the 
  

   square 
  of 
  the 
  atomic 
  weight. 
  This 
  undoubtedly 
  holds 
  in 
  

   the 
  case 
  of 
  heavy 
  elements 
  for 
  large 
  angles 
  of 
  scattering, 
  

   where 
  the 
  a 
  particle 
  passes 
  close 
  to 
  the 
  nucleus. 
  It 
  is 
  a 
  

   different 
  matter, 
  however, 
  when 
  the 
  scattering 
  angle 
  is 
  only 
  

   about 
  1/10 
  of 
  a 
  degree, 
  as 
  in 
  the 
  present 
  experiment. 
  It 
  

   is 
  to 
  be 
  anticipated 
  that 
  under 
  such 
  conditions 
  this 
  simple 
  

   law 
  would 
  be 
  widely 
  departed 
  from, 
  especially 
  in 
  the 
  case 
  of 
  

   heavy 
  atoms 
  for 
  which 
  the 
  number 
  of 
  electrons 
  is 
  large. 
  

  

  The 
  following 
  table 
  gives 
  the 
  observed 
  and 
  calculated 
  

   scattering 
  coefficient 
  for 
  an 
  atom 
  of 
  each 
  of 
  the 
  elements 
  

   examined. 
  The 
  value 
  of 
  ?i, 
  the 
  number 
  of 
  electronic 
  charges 
  

   assumed 
  for 
  the 
  nucleus, 
  is 
  given 
  in 
  the 
  second 
  column. 
  For 
  

   a 
  comparison 
  of 
  the 
  calculated 
  with 
  the 
  experimental 
  values, 
  

   carbon 
  is 
  assumed 
  in 
  both 
  to 
  have 
  a 
  scattering 
  coefficient 
  of 
  

   *40 
  on 
  the 
  arbitrary 
  scale. 
  The 
  scattering 
  coefficient 
  for 
  

   nitrogen 
  is 
  deduced 
  on 
  the 
  assumption 
  that 
  air 
  is 
  composed 
  

   of 
  80 
  per 
  cent, 
  of 
  N 
  with 
  20 
  per 
  cent 
  of 
  0. 
  

  

  

  

  Relative 
  scattering 
  per 
  atom. 
  

  

  

  Gas. 
  

  

  Assumed 
  

   value 
  of 
  n. 
  

  

  

  

  Calculated 
  values. 
  

  

  Experimental 
  

  

  values. 
  

  

  H 
  atom 
  ... 
  

  

  1 
  

  

  •0190 
  

  

  •0176 
  

  

  

  He 
  „ 
  ... 
  

  

  2 
  

  

  •057 
  

  

  •061 
  

  

  

  C 
  „ 
  ... 
  

  

  6 
  

  

  •40_ 
  

  

  ;40 
  

  

  

  N 
  „ 
  ... 
  

  

  7 
  

  

  •53 
  

  

  •48 
  

  

  

  O 
  „ 
  ... 
  

  

  8 
  

  

  •69 
  

  

  •53 
  

  

  

  s 
  „ 
  ... 
  

  

  16 
  

  

  2-58 
  

  

  161 
  

  

  

  Considering 
  the 
  difficulty 
  of 
  determining 
  with 
  accuracy 
  

   the 
  scattering 
  by 
  the 
  light 
  gases, 
  the 
  agreement 
  between 
  the 
  

   simple 
  theory 
  and 
  experiment 
  is 
  as 
  close 
  as 
  could 
  be 
  expected 
  

   for 
  hydrogen, 
  helium, 
  and 
  carbon. 
  The 
  probable 
  explanation 
  

   of 
  the 
  divergence 
  between 
  theory 
  and 
  experiment 
  for 
  the 
  

   heavier 
  atoms, 
  like 
  sulphur, 
  has 
  already 
  been 
  outlined. 
  From 
  

   the 
  experiments 
  of 
  Greiger 
  and 
  Marsden 
  (loc. 
  cit.) 
  on 
  the 
  

   large 
  angle 
  scattering 
  of 
  a, 
  particles 
  by 
  carbon, 
  it 
  is 
  clear 
  

   that 
  the 
  carbon 
  atom 
  behaves 
  as 
  if 
  the 
  nucleus 
  carries 
  a 
  

   charge 
  of 
  about 
  six 
  units. 
  Assuming 
  this 
  value 
  of 
  n 
  for 
  

   carbon, 
  the 
  results 
  indicate 
  that 
  the 
  hydrogen 
  nucleus 
  has 
  a 
  

   charge 
  of 
  one 
  fundamental 
  unit 
  and 
  the 
  helium 
  nucleus 
  of 
  

  

  two 
  units. 
  

  

  This 
  value 
  for 
  helium 
  is 
  to 
  be 
  anticipated 
  from 
  

   3B2 
  

  

  