﻿and 
  Secondary 
  Gamma 
  Rays. 
  279 
  

  

  There 
  is 
  some 
  evidence 
  of 
  a 
  slight 
  change 
  due 
  to 
  the 
  

   hardening 
  o£ 
  the 
  rays 
  by 
  screening. 
  The 
  results 
  given, 
  the 
  

  

  Flo-. 
  2. 
  

  

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  \ 
  

  

  N^ 
  

  

  ^'^'^^^^^ 
  

  

  

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  ^ 
  

  

  

  

  

  

  C 
  At 
  

  

  J^eCcfZn. 
  

  

  IJNCIDEJS/T 
  

   IT 
  EMERGEN:r 
  

  

  A9 
  

  

  P^ 
  

  

  ATOM/C 
  WE/ 
  GMT 
  

  

  mean 
  of 
  many 
  experiments, 
  might 
  have 
  been 
  expected 
  and 
  

   predicted 
  from 
  the 
  known 
  character 
  of 
  the 
  incident 
  secondary 
  

   radiation 
  due 
  to 
  7 
  rays, 
  which, 
  like 
  that 
  due 
  to 
  /5 
  rays, 
  follows 
  

   the 
  order 
  of 
  atomic 
  weights. 
  

  

  Effect 
  of 
  Reversing 
  Plates 
  A 
  and 
  B. 
  

  

  If 
  a 
  plate 
  of 
  any 
  given 
  substance 
  is 
  kept 
  constantly 
  at 
  C, 
  

   and 
  if 
  readings 
  of 
  the 
  electroscope 
  are 
  taken 
  when 
  two 
  dif- 
  

   ferent 
  metal 
  plates 
  are 
  at 
  A 
  and 
  B, 
  and 
  also 
  for 
  those 
  same 
  

   plates 
  in 
  reverse 
  order, 
  then 
  the 
  two 
  readings 
  are 
  not 
  the 
  

   same. 
  The 
  change 
  observed 
  is 
  not 
  due 
  to 
  an 
  alteration 
  of 
  

   the 
  intensity 
  of 
  the 
  7 
  rays 
  traversing 
  the 
  electroscope, 
  but 
  to 
  

   the 
  negative 
  electrons, 
  or 
  corpuscles, 
  which 
  constitute 
  the 
  

   emergent 
  secondary 
  radiation 
  from 
  plate 
  B. 
  Hence 
  the 
  

   advantage 
  of 
  the 
  reversal 
  method, 
  using 
  two 
  plates 
  ; 
  for 
  with 
  

   single 
  plates 
  there 
  is 
  an 
  uncertain 
  decrease 
  in 
  the 
  y 
  rays 
  

   depending 
  on 
  thickness 
  and 
  density. 
  Nor 
  is 
  it 
  necessary 
  to 
  

   use 
  a 
  magnetic 
  field 
  to 
  remove 
  negative 
  rays 
  approaching 
  

   the 
  face 
  of 
  A 
  from 
  the 
  screens, 
  for 
  these 
  are 
  absorbed 
  by 
  the 
  

   plates. 
  

  

  It 
  has 
  been 
  shown 
  by 
  many 
  observers 
  that 
  when 
  very 
  thin 
  

   plates 
  are 
  placed 
  in 
  the 
  path 
  of 
  the 
  7 
  rays 
  near 
  an 
  electroscope, 
  

   the 
  effects 
  due 
  to 
  such 
  thin 
  plates 
  are 
  small, 
  but 
  on 
  increasing 
  

  

  U2 
  

  

  