﻿108 
  Mr. 
  C. 
  A. 
  Sadler 
  on 
  the 
  

  

  It 
  has 
  been 
  shown 
  * 
  that 
  i£ 
  the 
  radiating 
  substance 
  be 
  an 
  

   element 
  o£ 
  lew 
  atomic 
  weight 
  — 
  as 
  hydrogen, 
  oxygen, 
  or 
  

   carbon 
  — 
  it 
  emits 
  a 
  radiation 
  similar 
  in 
  penetrating 
  power 
  

   to 
  the 
  primary 
  producing 
  it 
  ; 
  its 
  penetrating 
  power 
  varying 
  

   with 
  that 
  of 
  the 
  producing 
  primary. 
  This 
  type 
  of 
  radiation, 
  

   which 
  will 
  be 
  referred 
  to 
  as 
  a 
  " 
  scattered 
  '^ 
  radiation, 
  may 
  be 
  

   considered 
  as 
  produced 
  by 
  an 
  acceleration 
  of 
  one 
  or 
  more 
  

   electrons 
  in 
  the 
  atom 
  of 
  the 
  radiating 
  substance, 
  due 
  to 
  the 
  

   action 
  of 
  forces 
  in 
  the 
  primary 
  pulse. 
  

  

  From 
  an 
  element 
  of 
  greater 
  atomic 
  weight 
  than 
  that 
  of 
  

   calcium 
  (40) 
  — 
  and 
  possibly 
  from 
  other 
  elements 
  of 
  lower 
  

   atomic 
  weight 
  under 
  very 
  penetrating 
  primary 
  beams 
  — 
  ^the 
  

   emitted 
  radiation 
  has 
  been 
  shown 
  to 
  consist 
  of 
  scattered 
  

   radiation, 
  and 
  superposed 
  upon 
  this, 
  a 
  type 
  of 
  radiation 
  

   which 
  is 
  characteristic 
  of 
  the 
  radiating 
  element. 
  The 
  pene- 
  

   trating 
  power 
  of 
  this 
  radiation 
  is 
  a 
  constant 
  quantity 
  peculiar 
  

   to 
  the 
  substance 
  and 
  is 
  independent 
  of 
  the 
  penetrating 
  po^^er 
  

   of 
  the 
  primary 
  producing 
  it. 
  Moreover, 
  this 
  radiation 
  appears 
  

   to 
  be 
  entirely 
  homogeneous 
  in 
  character, 
  and 
  experiments 
  

   point 
  to 
  the 
  conclusion 
  that 
  the 
  radiating 
  electrons 
  producing 
  

   this 
  type 
  of 
  radiation 
  are 
  no 
  longer 
  appreciably 
  under 
  the 
  

   influence 
  of 
  the 
  forces 
  in 
  the 
  primary 
  pulse. 
  

  

  This 
  homogeneous 
  radiation 
  is 
  only 
  produced 
  when 
  the 
  

   penetrating 
  power 
  of 
  the 
  primary 
  is 
  greater 
  than 
  that 
  

   of 
  the 
  homogeneous 
  radiation 
  characteristic 
  of 
  the 
  radiator. 
  

  

  From 
  the 
  group 
  of 
  elements 
  Cr-Ag 
  the 
  ionization 
  pro- 
  

   duced 
  by 
  the 
  homogeneous 
  portion 
  of 
  the 
  secondary 
  radiation, 
  

   emitted 
  when 
  any 
  of 
  its 
  members 
  is 
  subjected 
  to 
  a 
  sufficiently 
  

   penetrating 
  primary, 
  is 
  many 
  times 
  greater 
  than 
  that 
  produced 
  

   by 
  the 
  scattered 
  portion 
  — 
  in 
  the 
  case 
  of 
  copper 
  as 
  radiator 
  

   this 
  ratio 
  is 
  as 
  high 
  as 
  150 
  : 
  1. 
  

  

  The 
  homogeneous 
  radiation 
  from 
  chromium 
  is 
  very 
  "soft" 
  

   much 
  softer 
  indeed 
  than 
  any 
  ordinary 
  primary 
  beam, 
  and 
  

   from 
  chromium 
  down 
  to 
  silver 
  and 
  probably 
  beyond, 
  the 
  

   penetrating 
  power 
  of 
  the 
  characteristic 
  radiation 
  increases 
  

   with 
  increase 
  of 
  atomic 
  weight 
  ; 
  the 
  radiation 
  from 
  silver 
  

   being 
  many 
  times 
  more 
  penetrating 
  than 
  that 
  from 
  

   chromium. 
  

  

  One 
  of 
  the 
  chief 
  difficulties 
  experienced 
  in 
  the 
  investigation 
  

   of 
  X-ray 
  phenomena 
  has 
  been 
  the 
  heterogeneity 
  of 
  the 
  

   primary 
  beams 
  hitherto 
  available. 
  Even 
  where 
  devices 
  are 
  

   adopted 
  to 
  ensure 
  that 
  the 
  current 
  through 
  the 
  X-ray 
  bulb 
  

   used 
  as 
  a 
  source 
  of 
  primary 
  rays 
  is 
  uni-directional 
  and 
  of 
  

   nearly 
  constant 
  strength, 
  the 
  primary 
  so 
  obtained 
  consists 
  of 
  

   a 
  mixture 
  of 
  constituents 
  of 
  difEerent 
  penetrating 
  power 
  ; 
  so 
  

   * 
  Barkla 
  & 
  Sadler, 
  Phil. 
  Mag. 
  Oct. 
  1908 
  pp. 
  550-584. 
  

  

  