﻿Homogeneous 
  Secondary 
  Rontgen 
  Radiations. 
  553 
  

  

  The 
  secondary 
  radiation 
  from 
  these 
  substances 
  is 
  approxi- 
  

   mately 
  twice 
  as 
  intense 
  in 
  the 
  direction 
  opposite 
  to 
  that 
  o£ 
  

   propagation 
  of 
  the 
  primary 
  rays 
  as 
  the 
  average 
  in 
  directions 
  

   at 
  right 
  angles, 
  when 
  the 
  primary 
  beam 
  consists 
  of 
  rays 
  

   of 
  the 
  easily 
  absorbed 
  type 
  (g). 
  (Polarization 
  produces 
  

   variation 
  in 
  different 
  directions 
  at 
  right 
  angles 
  to 
  the 
  

   primary 
  beam.) 
  

  

  This 
  ratio 
  varies 
  somewhat 
  with 
  a 
  variation 
  in 
  the 
  cha- 
  

   racter 
  of 
  the 
  primary 
  rays, 
  but 
  has 
  not 
  been 
  found 
  to 
  exceed 
  

   2:1. 
  

  

  The 
  results 
  of 
  all 
  the 
  experiments 
  when 
  an 
  easily 
  absorbed 
  

   primary 
  was 
  used 
  as 
  the 
  exciting 
  beam, 
  may 
  be 
  explained 
  on 
  

   the 
  theory 
  as 
  given 
  by 
  Professor 
  J. 
  J. 
  Thomson 
  * 
  shortly 
  

   after 
  the 
  earliest 
  systematic 
  experiments 
  on 
  light 
  gases. 
  

   The 
  electric 
  displacement 
  in 
  the 
  primary 
  Pontgen 
  pulses 
  

   when 
  passing 
  over 
  the 
  electrons 
  produces 
  accelerations 
  in 
  

   these 
  in 
  the 
  direction 
  of 
  that 
  displacement, 
  and 
  thus 
  causes 
  

   the 
  emission 
  of 
  secondary 
  pulses 
  of 
  equal 
  thickness. 
  The 
  

   natural 
  deductions 
  from 
  this 
  theory 
  have 
  all 
  been 
  strikingly 
  

   verified 
  by 
  experiments 
  on 
  substances 
  of 
  low 
  atomic 
  weight 
  

   when 
  subject 
  to 
  an 
  easily 
  absorbed 
  primary 
  beam. 
  

  

  Before 
  the 
  phenomena 
  of 
  secondary 
  X-rays 
  from 
  these 
  

   light 
  atoms 
  may 
  be 
  said 
  to 
  be 
  fully 
  understood, 
  we 
  must 
  

   explain 
  the 
  effects 
  produced 
  when 
  the 
  primary 
  rays 
  change 
  

   to 
  those 
  of 
  more 
  penetrating 
  type. 
  In 
  experiments 
  that 
  

   have 
  been 
  described 
  the 
  secondary 
  rays 
  began 
  to 
  differ 
  

   in 
  penetrating 
  power 
  from 
  the 
  primary, 
  — 
  they 
  were 
  more 
  

   easily 
  absorbed 
  ; 
  they 
  gave 
  less 
  evidence 
  of 
  polarization 
  of 
  

   the 
  primary 
  beam, 
  the 
  variation 
  falling 
  from 
  about 
  20 
  per 
  

   cent, 
  to 
  6 
  or 
  7 
  per 
  cent, 
  in 
  experiments 
  made 
  while 
  the 
  

   primary 
  became 
  more 
  penetrating 
  ; 
  the 
  ratio 
  of 
  intensity 
  of 
  

   secondary 
  radiation 
  in 
  the 
  direction 
  opposite 
  to 
  that 
  of 
  

   propagation 
  of 
  the 
  primary 
  beam 
  to 
  that 
  in 
  one 
  at 
  right 
  

   angles 
  dropped 
  considerably 
  ; 
  the 
  ratio 
  of 
  ionization 
  in 
  

   the 
  secondary 
  electroscope 
  to 
  that 
  in 
  one 
  testing 
  the 
  primary 
  

   beam 
  increased 
  slightly. 
  

  

  These 
  results 
  might 
  be 
  explained 
  qualitatively 
  either 
  by 
  

   the 
  introduction 
  of 
  a 
  secondary 
  radiation 
  of 
  different 
  type 
  

   superposed 
  on 
  the 
  almost 
  perfectly 
  scattered, 
  or 
  by 
  the 
  

   scattering 
  becoming 
  more 
  imperfect 
  by 
  the 
  introduction 
  

   of 
  forces 
  of 
  considerable 
  magnitude 
  other 
  than 
  those 
  pro- 
  

   duced 
  directly 
  by 
  the 
  primary 
  pulses 
  during 
  the 
  passage 
  

   of 
  those 
  primary 
  pulses 
  over 
  the 
  electrons, 
  or 
  by 
  the 
  intro- 
  

  

  * 
  ' 
  Conduction 
  of 
  Electricity 
  through 
  Gases 
  ' 
  (2nd 
  edition) 
  p. 
  321. 
  

  

  