﻿718 
  Prof. 
  E. 
  Rutherford 
  and 
  Mr. 
  H. 
  Robinson 
  on 
  the 
  

  

  products 
  radium 
  B 
  and 
  radium 
  C 
  in 
  equilibrium 
  with 
  it. 
  

   He 
  showed 
  that 
  the 
  ft 
  rays 
  from 
  radium 
  B 
  + 
  C 
  were 
  ex- 
  

   ceedingly 
  complex, 
  and 
  was 
  able 
  to 
  show 
  the 
  presence 
  of 
  

   nearly 
  30 
  homogeneous 
  groups 
  of 
  ft 
  rays 
  from 
  these 
  two 
  

   products 
  together. 
  In 
  a 
  later 
  paper 
  * 
  he 
  has 
  used 
  a 
  some- 
  

   what 
  different 
  and 
  more 
  certain 
  method 
  for 
  determining 
  the 
  

   velocity 
  of 
  each 
  of 
  the 
  groups, 
  and 
  has 
  given 
  a 
  corrected 
  

   list 
  of 
  25 
  lines. 
  

  

  There 
  is 
  a 
  very 
  marked 
  distinction 
  between 
  the 
  emission 
  

   of 
  a 
  and 
  ft 
  particles 
  from 
  a 
  radioactive 
  atom. 
  As 
  is 
  well 
  

   known, 
  the 
  atom 
  of 
  each 
  a-ray 
  product 
  emits 
  during 
  its 
  

   tranformation 
  only 
  one 
  a 
  particle, 
  which 
  is 
  expelled 
  with 
  

   a 
  definite 
  velocity 
  characteristic 
  of 
  the 
  substance. 
  Since 
  it 
  

   is 
  also 
  known 
  from 
  the 
  experiments 
  of 
  Makower, 
  Moseley, 
  

   Duane 
  and 
  Danysz 
  that 
  each 
  atom 
  of 
  radium 
  B 
  and 
  C 
  in 
  

   disintegrating 
  does 
  not 
  emit 
  more 
  than 
  one 
  or 
  two 
  ft 
  particles, 
  

   it 
  is 
  clear 
  that 
  each 
  atom 
  cannot 
  contribute 
  one 
  ft 
  particle 
  to 
  

   each 
  group. 
  This 
  is 
  also 
  borne 
  out 
  by 
  the 
  fact 
  that 
  the 
  

   photographic 
  intensities 
  of 
  neighbouring 
  groups 
  of 
  ft 
  rays 
  

   differ 
  markedly 
  from 
  one 
  another. 
  In 
  order 
  to 
  explain 
  

   these 
  anomalies, 
  Rutherford 
  f 
  suggested 
  that 
  a 
  single 
  

   ft 
  particle 
  of 
  definite 
  velocity 
  was 
  set 
  free 
  by 
  the 
  trans- 
  

   formation 
  of 
  each 
  atom. 
  This 
  ft 
  particle 
  in 
  escaping 
  from 
  

   the 
  atom 
  set 
  the 
  electronic 
  distribution 
  in 
  vibration, 
  and 
  in 
  

   consequence 
  lost 
  energy 
  in 
  multiples 
  of 
  certain 
  units 
  de- 
  

   pending 
  on 
  the 
  system 
  set 
  in 
  vibration. 
  The 
  decrease 
  of 
  

   energy 
  of 
  the 
  issuing 
  ft 
  particle 
  due 
  to 
  these 
  causes 
  was 
  

   variable 
  in 
  different 
  atoms, 
  depending 
  upon 
  the 
  chance 
  of 
  

   passing 
  through 
  or 
  close 
  to 
  the 
  systems 
  to 
  be 
  set 
  in 
  vibration. 
  

   On 
  this 
  view, 
  the 
  large 
  number 
  of 
  homogeneous 
  groups 
  of 
  

   ft 
  particles 
  emitted 
  from 
  a 
  single 
  radioactive 
  substance 
  was 
  

   to 
  be 
  ascribed 
  not 
  to 
  a 
  single 
  atom 
  but 
  to 
  a 
  statistical 
  effect 
  

   of 
  a 
  large 
  number 
  of 
  atoms. 
  The 
  energy 
  lost 
  by 
  the 
  

   escaping 
  ft 
  particle 
  was 
  converted 
  into 
  energy 
  of 
  the 
  7-ray 
  

   form, 
  and 
  different 
  types 
  of 
  7 
  rays 
  would 
  be 
  emitted 
  de- 
  

   pending 
  on 
  the 
  systems 
  set 
  in 
  vibration. 
  Taking 
  this 
  view, 
  

   the 
  appearance 
  of 
  homogeneous 
  groups 
  of 
  ft 
  rays 
  was 
  

   intimately 
  connected 
  with 
  the 
  excitation 
  of 
  different 
  types 
  

   of 
  7 
  rays 
  in 
  the 
  atom. 
  This 
  hypothesis 
  is 
  strongly 
  supported 
  

   by 
  the 
  observation 
  that 
  all 
  those 
  radioactive 
  substances 
  which 
  

   emit 
  well-defined 
  groups 
  of 
  ft 
  rays 
  also 
  give 
  rise 
  to 
  marked 
  

   7 
  radiation. 
  In 
  order 
  to 
  throw 
  light 
  on 
  this 
  question, 
  

   Rutherford 
  and 
  Richardson 
  % 
  have 
  analysed 
  the 
  7 
  radiation 
  

  

  * 
  Danysz, 
  Le 
  Radium, 
  x. 
  p. 
  4 
  (1913). 
  

  

  t 
  Rutherford, 
  Phil. 
  Mag. 
  Oct. 
  and 
  Dec. 
  1912. 
  

  

  t 
  Rutherford 
  and 
  Richardson, 
  Phil. 
  Mag. 
  May 
  and 
  August 
  1913. 
  

  

  