﻿570 
  Dr. 
  C. 
  G. 
  Barkla 
  and 
  Mr. 
  C. 
  A. 
  Sadler 
  on 
  

  

  rapidity 
  of 
  the 
  fall 
  of 
  transparency 
  diminishing 
  with 
  an 
  

   increase 
  of 
  atomic 
  weight. 
  In 
  the 
  case 
  of 
  very 
  soft 
  rays 
  

   this 
  decline 
  becomes 
  a 
  slight 
  incline. 
  

  

  Fio-. 
  3. 
  

  

  60 
  80 
  100 
  IPO 
  10-0 
  

  

  Atomic 
  We/cxr 
  of 
  flaso/ree/i. 
  

  

  200 
  

  

  By 
  using 
  thin 
  plates 
  of 
  absorbing 
  elements 
  and 
  testing 
  by 
  

   the 
  ionization 
  method 
  the 
  percentage 
  diminution 
  of 
  intensity 
  

   of 
  the 
  secondary 
  beams 
  by 
  transmission 
  through 
  these 
  plates, 
  

   it 
  was 
  easy 
  to 
  calculate 
  the 
  thickness 
  and 
  hence 
  the 
  mass 
  

   per 
  unit 
  cross-section 
  necessary 
  to 
  absorb 
  a 
  given 
  proportion 
  

   — 
  in 
  this 
  case 
  75 
  per 
  cent. 
  Some 
  of 
  these 
  results 
  we 
  have 
  

   given 
  in 
  a 
  previous 
  paper 
  (f) 
  *. 
  They 
  show 
  that 
  in 
  place 
  of 
  

   the 
  usual 
  relation 
  between 
  transparency 
  and 
  atomic 
  weight 
  

   there 
  is 
  a 
  strongly 
  marked 
  deviation 
  in 
  each 
  case 
  in 
  the 
  

   neighbourhood 
  of 
  the 
  atomic 
  weight 
  of 
  the 
  radiator, 
  the 
  rays 
  

   from 
  an 
  element 
  being 
  especially 
  penetrating 
  to 
  that 
  element 
  

  

  * 
  In 
  the 
  paper 
  referred 
  to 
  the 
  numbers 
  given 
  in 
  Table 
  II. 
  represent 
  

   mass 
  in 
  grammes, 
  not 
  thickness 
  in 
  centimetres 
  as 
  stated. 
  

  

  