﻿576 
  Dr. 
  0. 
  G. 
  Barkla 
  and 
  Mr. 
  C. 
  A. 
  Sadler 
  on 
  

  

  W-Bi 
  Group. 
  

  

  The 
  radiations 
  from 
  the 
  elements 
  with 
  atomic 
  weights 
  from 
  

   that 
  of 
  tungsten 
  to 
  that 
  of 
  bismuth 
  have 
  not 
  been 
  examined 
  

   minutely. 
  They, 
  however, 
  appear 
  to 
  be 
  very 
  similar 
  to 
  the 
  

   rays 
  from 
  Cu, 
  Zn, 
  &c. 
  The 
  ionization 
  produced 
  by 
  these 
  

   rays 
  is 
  of 
  the 
  order 
  of 
  magnitude 
  of 
  that 
  produced 
  by 
  the 
  

   rays 
  from 
  elements 
  of 
  the 
  Cr-Zn 
  group 
  ; 
  but 
  there 
  appears 
  

   slightly 
  more 
  variation 
  in 
  the 
  character 
  due 
  to 
  changes 
  in 
  

   the 
  primary 
  rays. 
  

  

  Though 
  accurate 
  observations 
  have 
  not 
  been 
  made, 
  it 
  appears 
  

   probable 
  that 
  the 
  radiation 
  is 
  a 
  mixture 
  of 
  the 
  scattered 
  with 
  

   the 
  homogeneous 
  rays, 
  the 
  proportional 
  effect 
  of 
  the 
  scattered 
  

   being 
  greater 
  than 
  in 
  the 
  radiation 
  from 
  Cu, 
  Zn, 
  &c. 
  

  

  Conclusions. 
  

  

  Secondary 
  Rontgen 
  rays 
  of 
  two 
  distinct 
  types 
  are 
  emitted 
  

   hj 
  substances 
  subject 
  to 
  a 
  beam 
  of 
  X-rays. 
  One, 
  a 
  scattered 
  

   radiation 
  produced 
  by 
  the 
  motion 
  of 
  electrons 
  controlled 
  by 
  

   the 
  electric 
  force 
  in 
  the 
  primary 
  Rontgen 
  pulses, 
  has 
  been 
  

   dealt 
  with 
  in 
  previous 
  papers 
  by 
  one 
  of 
  us, 
  and 
  has 
  been 
  

   further 
  discussed 
  in 
  this 
  paper 
  with 
  the 
  H-S 
  group 
  of 
  

   elements. 
  The 
  other, 
  a 
  homogeneous 
  radiation 
  characteristic 
  

   of 
  the 
  element 
  emitting 
  it, 
  and 
  produced 
  by 
  the 
  motion 
  of 
  

   electrons 
  uncontrolled 
  by 
  the 
  electric 
  force 
  in 
  the 
  primary 
  

   pulses, 
  has 
  been 
  but 
  briefly 
  mentioned. 
  

  

  All 
  the 
  phenomena 
  of 
  secondary 
  X-rays 
  so 
  far 
  observed 
  by 
  

   us 
  may 
  be 
  explained 
  by 
  means 
  of 
  these 
  two. 
  

  

  The 
  experimental 
  results 
  of 
  these 
  investigations, 
  both 
  on 
  

   the 
  scattered 
  radiation 
  and 
  the 
  homogeneous 
  radiation, 
  are 
  

   summarized 
  below. 
  In 
  order 
  to 
  make 
  the 
  summary 
  more 
  

   complete, 
  we 
  have 
  introduced 
  several 
  results 
  which 
  have 
  

   been 
  previously 
  published. 
  The 
  references 
  for 
  these 
  

   are 
  given. 
  

  

  Experimental 
  Results. 
  — 
  Scattered 
  X-rays 
  — 
  those 
  produced 
  

   by 
  the 
  motion 
  of 
  electrons 
  controlled 
  by 
  the 
  primary 
  pulses 
  — 
  

   constitute 
  the 
  bulk 
  of 
  the 
  secondary 
  radiation 
  from 
  elements 
  

   of 
  the 
  H-S 
  group 
  when 
  these 
  are 
  subject 
  to 
  a 
  primary 
  beam 
  

   of 
  low 
  to 
  moderate 
  penetrating 
  power. 
  

  

  Scattered 
  X-rays 
  are 
  also 
  emitted 
  by 
  many 
  elements 
  of 
  

   higher 
  atomic 
  weight 
  — 
  probably 
  by 
  all 
  — 
  when 
  subject 
  to 
  

   such 
  a 
  primary 
  beam 
  ; 
  but 
  unless 
  the 
  primary 
  is 
  very 
  soft 
  

   they 
  are 
  accompanied 
  by 
  homogeneous 
  secondary 
  X-rays 
  

   (characteristic 
  of 
  the 
  radiating 
  element) 
  which 
  produce 
  

   much 
  greater 
  ionizations. 
  

  

  