﻿and 
  Secondary 
  Gamma 
  Rays, 
  289 
  

  

  Hence 
  we 
  may 
  conclude 
  that 
  the 
  7 
  rays 
  themselves 
  which 
  

   pass 
  through 
  the 
  electroscope 
  are 
  unaffected 
  by 
  the 
  reversal 
  

   oi 
  plates 
  A 
  and 
  B 
  ; 
  also 
  that 
  each 
  face 
  contributes 
  its 
  own 
  

   corpuscular 
  secondary 
  radiation 
  to 
  an 
  extent 
  depending 
  only 
  

   on 
  the 
  atomic 
  weight 
  of 
  the 
  substance 
  of 
  which 
  the 
  interior 
  

   surface 
  layer 
  of 
  that 
  face 
  is 
  composed. 
  This 
  secondary 
  

   radiation 
  is 
  almost 
  independent 
  of 
  the 
  thickness, 
  provided 
  

   the 
  latter 
  exceeds 
  a 
  millimetre 
  or 
  two. 
  Moreover, 
  the 
  

   secondary 
  radiations 
  are 
  so 
  absorbed 
  that 
  there 
  is 
  little 
  or 
  

   no 
  evidence 
  of 
  any 
  continuous 
  rebound 
  from 
  face 
  to 
  face. 
  

   Each 
  surface 
  produces 
  its 
  own 
  secondary 
  radiation 
  to 
  an 
  

   extent 
  which 
  is 
  mainly 
  independent 
  of 
  the 
  character 
  of 
  the 
  

   other 
  faces. 
  

  

  Summary, 
  

  

  1. 
  Change 
  of 
  hardness 
  of 
  the 
  7 
  rays 
  makes 
  little 
  difference 
  

   in 
  the 
  relative 
  intensities 
  of 
  the 
  incident 
  corpuscular 
  secondary 
  

   radiation 
  from 
  various 
  elements, 
  and 
  the 
  intensities 
  follow 
  

   the 
  order 
  of 
  atomic 
  weights 
  of 
  the 
  radiators. 
  (Table 
  I. 
  and 
  

   •curve 
  I. 
  fig. 
  2.) 
  

  

  2. 
  Change 
  in 
  hardness 
  of 
  the 
  7 
  rays 
  makes 
  a 
  marked 
  

   difference 
  in 
  the 
  relative 
  intensities 
  of 
  the 
  emergent 
  corpus- 
  

   cular 
  secondary 
  radiation 
  from 
  various 
  elements. 
  Such 
  radia- 
  

   tions 
  do 
  not 
  follow 
  the 
  order 
  of 
  atomic 
  weight. 
  (Table 
  III., 
  

  

  fig. 
  3.) 
  

  

  3. 
  Hardening 
  of 
  the 
  7 
  rays 
  is 
  readily 
  produced 
  by 
  lead 
  

   screens, 
  but 
  not 
  by 
  iron 
  screens 
  of 
  great 
  thickness. 
  

  

  4. 
  On 
  hardening 
  the 
  7 
  rays 
  the 
  emergent 
  radiation 
  from 
  

   carbon 
  and 
  aluminium 
  is 
  increased 
  relatively 
  to 
  heavier 
  

   substances 
  ; 
  on 
  softening, 
  decreased. 
  (Figs. 
  3, 
  5.) 
  

  

  5. 
  With 
  various 
  radiators, 
  and 
  with 
  the 
  secondary 
  rays 
  

   due 
  to 
  the 
  primary 
  7 
  rays 
  from 
  radium 
  C, 
  the 
  values 
  of 
  \ 
  

   and 
  Xjdy 
  and 
  the 
  emergent 
  corpuscular 
  secondary 
  radiations 
  

   were 
  observed 
  (fig. 
  5). 
  These 
  all 
  indicate 
  the 
  soft 
  character 
  

   of 
  the 
  secondary 
  7 
  rays. 
  

  

  G. 
  The 
  7 
  rays 
  from 
  uranium 
  X 
  caused 
  emergent 
  radiation 
  

   of 
  a 
  character 
  showing 
  that 
  these 
  rays 
  are 
  softer 
  than 
  those 
  

   from 
  radium 
  C, 
  and 
  harder 
  than 
  the 
  secondary 
  7. 
  

  

  7. 
  The 
  gradual 
  changes 
  in 
  the 
  character 
  of 
  the 
  emergent 
  

   corpuscular 
  secondary 
  radiation 
  were 
  observed 
  when 
  the 
  

   exciting 
  rays 
  were 
  varied 
  from 
  a 
  very 
  hard 
  to 
  a 
  very 
  soft 
  

   type. 
  (Figs. 
  3, 
  5.) 
  

  

  8. 
  When 
  reversals 
  of 
  plates 
  are 
  made, 
  as 
  described, 
  the 
  

   four 
  readings 
  obtained 
  are 
  nearly 
  in 
  proportion 
  (Table 
  IV.) 
  

  

  Montreal, 
  April 
  lo, 
  1909. 
  

  

  