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  Primary 
  and 
  Secondary 
  Gamma 
  Rays. 
  

  

  Addendum. 
  

  

  Since 
  completing 
  this 
  work 
  I 
  have 
  obtained 
  a 
  copy 
  of 
  

   F. 
  E. 
  Hackett's 
  paper 
  in 
  the 
  Transactions 
  of 
  the 
  Royal 
  

   Dublin 
  Society 
  (Jan. 
  1909) 
  entitled 
  " 
  The 
  Secondary 
  Eadia- 
  

   tions 
  excited 
  by 
  7 
  Eays/'' 
  

  

  His 
  method 
  differed 
  from 
  mine, 
  for 
  his 
  apparatus 
  was 
  so 
  

   arranged 
  that 
  the 
  emergent 
  secondary 
  rays 
  passed 
  obliquely 
  

   to 
  a 
  testing 
  vessel 
  which 
  was 
  not 
  itself 
  traversed 
  by 
  the 
  

   exciting 
  7 
  rays. 
  

  

  His 
  results 
  are 
  shown 
  graphically 
  by 
  me 
  in 
  fig. 
  6. 
  As 
  the 
  

   primary 
  7 
  rays 
  were 
  screened 
  by 
  only 
  2 
  mm. 
  of 
  lead, 
  it 
  is 
  

   evident 
  that 
  these 
  rays 
  will 
  partly 
  consist 
  of 
  a 
  soft 
  type 
  ; 
  and 
  

   indeed 
  the 
  shape 
  of 
  the 
  curve 
  (fig. 
  6) 
  is 
  such 
  that 
  it 
  lies 
  

  

  Fiff. 
  6. 
  

  

  ATOM/C 
  y/£/G^r 
  

  

  between 
  curves 
  I. 
  and 
  II. 
  fig. 
  5, 
  that 
  is, 
  between 
  the 
  curves 
  

   for 
  uranium 
  and 
  secondary 
  7. 
  It 
  will 
  be 
  remembered 
  that 
  the 
  

   uranium 
  7 
  rays 
  in 
  my 
  experiment 
  were 
  hardened 
  by 
  passage 
  

  

  