﻿5G6 
  

  

  Dr. 
  C. 
  G. 
  Barkla 
  and 
  Mr. 
  C. 
  A. 
  Sadler 
  on 
  

  

  plates 
  of 
  thickness 
  shown 
  in 
  column 
  I 
  of 
  Table 
  VI. 
  were 
  

   placed 
  in 
  the 
  primary 
  beam, 
  and 
  the 
  deflexions 
  of 
  the 
  primary 
  

   and 
  secondary 
  electroscopes 
  were 
  diminished 
  by 
  the 
  amount 
  

   given 
  in 
  columns 
  III 
  and 
  IV. 
  

  

  Table 
  VI. 
  

  

  Eadiation 
  from 
  Copper 
  (thin 
  sheet 
  absorbing 
  14*5 
  per 
  cent, 
  

   of 
  primary 
  rays.) 
  

  

  I. 
  

  

  Thickness 
  

  

  of 
  Al 
  

   in 
  Primary 
  

  

  beam 
  in 
  

   centimetres. 
  

  

  II. 
  

  

  Absorption 
  

   of 
  Primary 
  

  

  byCu 
  

   (•00293 
  cm.) 
  

   after 
  passing 
  

   through 
  Al 
  

   in 
  column 
  1. 
  

  

  III. 
  

  

  Percentage 
  

  

  of 
  Primary 
  

  

  absorbed 
  by 
  Al 
  

  

  in 
  column 
  I. 
  

  

  IV. 
  

  

  Percentage 
  

  

  diminution 
  of 
  

  

  Secondary 
  

  

  byAl 
  

  

  in 
  column 
  I. 
  

  

  absorbing 
  

  

  Primary. 
  

  

  V. 
  

  

  Eatio 
  of 
  

   Ionizations 
  

   in 
  Secondary 
  

   and 
  Primary 
  

   electroscopes 
  

   (relative). 
  

  

  

  

  84 
  

  

  

  

  

  

  1 
  

  

  •0032 
  

  

  82-8 
  

  

  12-2 
  

  

  136 
  

  

  ■98 
  

  

  •0064 
  

  

  81-4 
  

  

  249 
  

  

  25-5 
  

  

  •99 
  

  

  •0104 
  

  

  803 
  

  

  34-2 
  

  

  331 
  

  

  1-01 
  

  

  •0168 
  

  

  77 
  "5 
  

  

  46-7 
  

  

  46-6 
  

  

  1-00 
  

  

  •0208 
  

  

  75-9 
  

  

  51-1 
  

  

  51-4 
  

  

  •99 
  

  

  •0312 
  

  

  723 
  

  

  62-9 
  

  

  029 
  

  

  1-00 
  

  

  •0416 
  

  

  09-6 
  

  

  70-2 
  

  

  70-5 
  

  

  •99 
  

  

  •0520 
  

  

  652 
  

  

  746 
  

  

  75-0 
  

  

  •98 
  

  

  •0728 
  

  

  604 
  

  

  82-4 
  

  

  82-3 
  

  

  1-00 
  

  

  •0936 
  

  

  57 
  

  

  85-8 
  

  

  858 
  

  

  1-00 
  

  

  •124 
  

  

  51-2 
  

  

  88-6 
  

  

  88-9 
  

  

  •97 
  

  

  •248 
  

  

  41-7 
  

  

  95-4 
  

  

  95 
  3 
  

  

  1-02 
  

  

  In 
  fig. 
  2 
  the 
  ionization 
  produced 
  by 
  the 
  primary 
  beam 
  in 
  

   air 
  is 
  indicated 
  by 
  abscissae 
  and 
  that 
  produced 
  by 
  the 
  corre- 
  

   sponding 
  secondary 
  beam 
  from 
  a 
  thin 
  sheet 
  of 
  copper 
  as 
  

   ordinates, 
  when 
  different 
  portions 
  of 
  the 
  primary 
  beam 
  have 
  

   been 
  absorbed. 
  

  

  As 
  the 
  secondary 
  beam 
  is 
  practically 
  homogeneous 
  we 
  have 
  

   exhibited 
  the 
  relation 
  between 
  the 
  ionization 
  produced 
  by 
  a 
  

   primary 
  beam 
  in 
  the 
  air, 
  and 
  its 
  power 
  of 
  producing 
  secondary 
  

   rays 
  in 
  copper. 
  We 
  are 
  thus 
  led 
  to 
  the 
  conclusion 
  that 
  the 
  

   intensity 
  of 
  this 
  homogeneous 
  secondary 
  radiation 
  set 
  up 
  in 
  

   a 
  thin 
  sheet 
  of 
  copper 
  is 
  proportional 
  to 
  the 
  number 
  of 
  ions 
  

   the 
  primary 
  beam 
  would 
  produce 
  in 
  a 
  thin 
  layer 
  of 
  air. 
  

   Thus 
  if 
  two 
  beams 
  of 
  Rontgen 
  rays, 
  which 
  in 
  passing 
  through 
  

  

  