﻿564 
  Dr. 
  C, 
  G. 
  Barkla 
  and 
  Mr. 
  C. 
  A. 
  Sadler 
  on 
  

  

  radiation 
  is 
  about 
  45 
  times 
  that 
  o£ 
  the 
  scattered 
  radiation 
  

   from 
  an 
  equal 
  mass 
  o£ 
  paper, 
  and 
  about 
  J 
  the 
  total 
  energy 
  

   absorbed 
  in 
  the 
  copper 
  *. 
  

  

  Though 
  it 
  is 
  impossible 
  by 
  such 
  experiments 
  to 
  determine 
  

   the 
  energy 
  with 
  accuracy, 
  we 
  may 
  safely 
  conclude 
  that 
  the 
  

   energy 
  of 
  the 
  homogeneous 
  radiation 
  is 
  many 
  times 
  greater 
  

   than 
  the 
  energy 
  of 
  secondary 
  radiation 
  scattered 
  from 
  an 
  

   equal 
  mass 
  of 
  one 
  of 
  the 
  light 
  elements. 
  

  

  Comparisons 
  of 
  the 
  ionizations 
  produced 
  by 
  the 
  rays 
  from 
  

   other 
  elements 
  of 
  this 
  group 
  have 
  been 
  made. 
  They 
  are 
  all 
  

   of 
  the 
  same 
  order 
  of 
  magnitude. 
  

  

  Distribution. 
  — 
  It 
  has 
  been 
  shown 
  by 
  one 
  of 
  us 
  that 
  the 
  

   secondary 
  radiation 
  from 
  thick 
  copper, 
  when 
  this 
  is 
  subject 
  

   to 
  a 
  primary 
  beam 
  of 
  ordinary 
  penetrating 
  power, 
  is 
  approxi- 
  

   mately 
  equally 
  intense 
  in 
  a 
  direction 
  almost 
  opposite 
  to 
  that 
  

   of 
  propagation 
  of 
  the 
  primary 
  and 
  in 
  a 
  direction 
  at 
  right 
  

   angles. 
  As 
  probably 
  98 
  per 
  cent, 
  of 
  the 
  ionization 
  produced 
  

   by 
  the 
  secondary 
  radiation 
  from 
  thick 
  copper 
  is 
  due 
  to 
  the 
  

   homogeneous 
  rays, 
  this 
  may 
  be 
  said 
  to 
  be 
  the 
  result 
  for 
  the 
  

   homogeneous 
  rays 
  alone. 
  

  

  From 
  thick 
  iron, 
  however, 
  the 
  radiation 
  varied 
  in 
  intensify 
  

   by 
  an 
  amount 
  represented 
  by 
  the 
  ratio 
  1*1 
  : 
  1 
  in 
  these 
  two 
  

   directions. 
  But 
  as 
  we 
  have 
  shown, 
  the 
  heterogeneity 
  of 
  

   the 
  radiation 
  from 
  thick 
  sheets 
  of 
  iron 
  is 
  more 
  marked, 
  and 
  

   this 
  can 
  be 
  accounted 
  for 
  by 
  the 
  fact 
  that 
  from 
  iron 
  the 
  

   homogeneous 
  rays 
  are 
  very 
  easily 
  absorbed, 
  consequently 
  

   scattered 
  rays 
  emerge 
  from 
  a 
  much 
  thicker 
  layer 
  and 
  appear 
  

   in 
  more 
  than 
  their 
  normal 
  proportion. 
  The 
  ratio 
  l'l 
  : 
  1 
  

   verifies 
  this 
  by 
  showing 
  the 
  presence 
  of 
  a 
  radiation 
  which 
  is 
  

   controlled 
  by 
  the 
  electric 
  field 
  in 
  the 
  primary 
  pulses. 
  

  

  The 
  result 
  is 
  of 
  the 
  order 
  of 
  magnitude 
  that 
  would 
  be 
  

   given 
  by 
  a 
  mixture 
  of 
  scattered 
  rays 
  of 
  about 
  the 
  same 
  

   intensity 
  as 
  found 
  in 
  the 
  radiation 
  from 
  copper 
  with 
  the 
  

   characteristic 
  radiation 
  uniformly 
  distributed. 
  

  

  Polarization 
  Experiments. 
  — 
  Though 
  very 
  careful 
  experi- 
  

   ments 
  have 
  been 
  made 
  with 
  iron, 
  copper, 
  and 
  zinc 
  as 
  

   secondary 
  radiators 
  placed 
  in 
  a 
  partially 
  polarized 
  primary 
  

   beam 
  of 
  Rontgen 
  radiation, 
  the 
  secondary 
  rays 
  from 
  these 
  

   have 
  not 
  been 
  found 
  to 
  give 
  evidence 
  of 
  any 
  polarity. 
  Thus 
  

   the 
  intensity 
  of 
  secondary 
  radiation 
  in 
  a 
  given 
  direction 
  is 
  

   independent 
  of 
  the 
  position 
  of 
  the 
  plane 
  of 
  polarization 
  of 
  

   the 
  primary 
  beam 
  producing 
  the 
  radiation 
  ; 
  in 
  other 
  words, 
  

  

  * 
  The 
  homogeneous 
  radiation 
  has 
  been 
  assumed 
  to 
  be 
  distributed 
  

   uniformly 
  in 
  all 
  directions 
  and 
  the 
  scattered 
  radiation 
  to 
  be 
  proportional 
  

   to 
  sin 
  2 
  0, 
  where 
  is 
  the 
  angle 
  between 
  the 
  direction 
  of 
  radiation 
  con- 
  

   sidered 
  and 
  that 
  of 
  acceleration 
  of 
  the 
  radiating 
  electron. 
  

  

  