﻿and 
  Secondary 
  Gamma 
  Rayi 
  

  

  277 
  

  

  sometimes 
  entirely 
  inside 
  a 
  closed 
  hollow 
  cylinder 
  o£ 
  iron 
  or 
  

   lead 
  o£ 
  the 
  desired 
  thickness, 
  sometimes 
  in 
  a 
  cylinder 
  such 
  as 
  H, 
  

  

  Fiff. 
  1. 
  

  

  WlfWU^Wmj- 
  

  

  with 
  an 
  open 
  end 
  so 
  that 
  a 
  cone 
  of 
  rays 
  was 
  produced 
  passing 
  

   through 
  the 
  electroscope, 
  12 
  cm. 
  long. 
  The 
  results 
  obtained 
  

   by 
  these 
  two 
  methods 
  were 
  not 
  different 
  when 
  suitable 
  metal 
  

   screens 
  were 
  placed 
  at 
  S. 
  Plates 
  o£ 
  various 
  substances 
  were 
  

   placed 
  at 
  A, 
  B, 
  C, 
  D; 
  these 
  will 
  always 
  be 
  referred 
  to 
  as 
  

   plates, 
  and 
  in 
  the 
  order 
  A, 
  B, 
  C, 
  D, 
  and 
  the 
  electroscope 
  will 
  

   always 
  be 
  understood 
  as 
  between 
  B 
  and 
  C. 
  It 
  must 
  further 
  

   be 
  noted 
  that 
  the 
  7 
  rays 
  from 
  the 
  radium 
  C 
  traversed 
  the 
  

   electroscope 
  and 
  produced 
  ionization, 
  and 
  that 
  the 
  secondary 
  

   rays 
  from 
  the 
  top, 
  bottom, 
  and 
  two 
  walls 
  of 
  the 
  electroscope 
  

   further 
  contributed 
  to 
  the 
  total 
  ionization 
  ; 
  and 
  no 
  attempt 
  

   has 
  been 
  made 
  to 
  make 
  deductions 
  for 
  these. 
  It 
  was 
  merely 
  

   desired 
  to 
  ascertain 
  the 
  effects 
  of 
  reversing 
  the 
  plates 
  at 
  A 
  

   and 
  B, 
  and 
  those 
  at 
  C 
  and 
  D. 
  

   An 
  example 
  will 
  make 
  this 
  clear. 
  

  

  Plates 
  at 
  A. 
  B. 
  C. 
  J). 
  Divisions 
  a 
  minute. 
  

   Al 
  Pb 
  Pb 
  Al 
  36-4 
  

  

  Pb 
  Al 
  Pb 
  Al 
  36-0 
  

  

  Al 
  Pb 
  Al 
  Pb 
  30-1 
  

  

  Pb 
  Al 
  Al 
  Pb 
  29-7 
  

  

  The 
  last 
  column 
  gives 
  the 
  four 
  readings 
  obtained 
  for 
  the 
  

   stated 
  four 
  arrangements 
  of 
  the 
  plates. 
  The 
  order 
  given 
  was 
  

   always 
  followed 
  ; 
  and 
  in 
  future 
  the 
  results 
  may 
  be 
  given 
  as 
  

   percentages, 
  thus, 
  

  

  (Al, 
  Pb) 
  100, 
  99, 
  83-5, 
  81. 
  

  

  Substituting 
  carbon 
  for 
  aluminium 
  the 
  readings 
  gave 
  

  

  (C, 
  Pb) 
  100, 
  105, 
  80, 
  84. 
  

  

  Phil. 
  Mag. 
  S. 
  6. 
  Vol. 
  18. 
  No. 
  104. 
  Auc/. 
  1909. 
  U 
  

  

  