﻿562 
  

  

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

  

  on 
  

  

  through 
  aluminium 
  "0416 
  cm. 
  in 
  thickness, 
  while 
  only 
  '7 
  per 
  

   cent. 
  o£ 
  the 
  copper 
  radiation 
  got 
  through. 
  The 
  ratio 
  of 
  the 
  

   ionization 
  due 
  to 
  the 
  copper 
  radiation 
  to 
  that 
  due 
  to 
  the 
  rays 
  

   scattered 
  from 
  paper, 
  after 
  transmission 
  through 
  -0416 
  cm. 
  

   Al 
  had 
  dropped 
  to 
  *401 
  : 
  1. 
  After 
  transmission 
  through 
  

   •0782 
  cm. 
  of 
  Al 
  the 
  two 
  radiations 
  appeared 
  approximately 
  

   equal 
  in 
  penetrating 
  power, 
  the 
  last 
  '26 
  per 
  cent, 
  of 
  the 
  

   copper 
  radiation 
  being 
  much 
  more 
  penetrating 
  than 
  the 
  

   homogeneous 
  radiation 
  which 
  had 
  been 
  practically 
  all 
  

   absorbed. 
  When 
  the 
  two 
  transmitted 
  radiations 
  were 
  ap- 
  

   proximately 
  of 
  the 
  same 
  character, 
  the 
  ratio 
  of 
  their 
  ionizing 
  

   effects 
  was 
  about 
  *18 
  : 
  1 
  ; 
  or 
  from 
  equal 
  masses 
  of 
  copper 
  

   and 
  paper 
  — 
  disregarding 
  all 
  internal 
  absorptions 
  the 
  inten- 
  

   sities 
  of 
  the 
  penetrating 
  rays 
  were 
  in 
  the 
  ratio 
  1*8 
  : 
  1. 
  

  

  Table 
  V. 
  

  

  I. 
  

  

  Thickne-s 
  of 
  Al 
  

  

  in 
  path 
  of 
  

  

  Secondary 
  beams. 
  

  

  II. 
  

  

  Percentage 
  

  

  of 
  Cu 
  radiation 
  

  

  absorbed. 
  

  

  III. 
  

  

  Percentage 
  

  

  of 
  Paper 
  radiation 
  

  

  absorbed. 
  

  

  . 
  IV 
  \ 
  

  

  Ratio 
  of 
  ionizations 
  

   due 
  to 
  

  

  Secondary 
  beams 
  

   from 
  equal 
  masses 
  

  

  of 
  Cu 
  and 
  Paper. 
  

  

  Q 
  

  

  

  

  

  

  195-5 
  :1 
  

  

  •0208 
  

  

  94-5 
  

  

  51-8 
  

  

  22-1 
  : 
  1 
  

  

  •0416 
  

  

  99-3 
  

  

  60 
  

  

  4-01 
  : 
  1 
  

  

  •0574 
  

  

  99-G 
  

  

  71 
  

  

  1-94 
  : 
  1 
  

  

  •0782 
  

  

  99-74 
  

  

  78 
  

  

  1-88:1 
  

  

  •0990 
  

  

  99-S 
  

  

  83 
  

  

  1-83 
  : 
  1 
  

  

  Allowing 
  for 
  the 
  small 
  extra 
  absorption 
  of 
  the 
  penetrating- 
  

   portion 
  of 
  the 
  copper 
  radiation 
  in 
  the 
  copper 
  plate 
  itself 
  

   above 
  that 
  of 
  the 
  corresponding 
  rays 
  in 
  the 
  paper 
  — 
  quantities 
  

   which 
  were 
  determined 
  by 
  separate 
  experiments 
  — 
  the 
  radia- 
  

   tion 
  from 
  copper 
  must 
  have 
  contained 
  approximately 
  twice 
  

   as 
  much 
  of 
  the 
  penetrating 
  radiation 
  as 
  the 
  radiation 
  from 
  

   paper. 
  

  

  By 
  using 
  a 
  thicker 
  copper 
  plate 
  as 
  radiator 
  the 
  intensity 
  

   of 
  secondary 
  radiation 
  was 
  increased, 
  but 
  the 
  correction 
  for 
  

   absorption 
  in 
  the 
  metal 
  itself 
  was 
  also 
  increased 
  so 
  that 
  the 
  

   result 
  could 
  not 
  be 
  regarded 
  as 
  more 
  accurate, 
  this 
  correction 
  

   not 
  being 
  obtainable 
  with 
  great 
  accuracy. 
  The 
  conclusion 
  

   was 
  however 
  practically 
  identical 
  with 
  the 
  above. 
  We 
  thus 
  

   see 
  that 
  mixed 
  with 
  the 
  homogeneous 
  radiation 
  from 
  copper 
  

  

  