﻿Transformations 
  of 
  X- 
  Rays, 
  131 
  

  

  nickel 
  may 
  be 
  due 
  to 
  oxidation 
  o£ 
  the 
  cobalt 
  or 
  the 
  nickel. 
  

   The 
  author 
  has 
  found, 
  however, 
  that 
  if 
  iron 
  be 
  used 
  as 
  a 
  

   tertiary 
  radiator, 
  and 
  the 
  secondary 
  radiations 
  from 
  the 
  group 
  

   of 
  metals 
  Cr-Ag 
  successively 
  fall 
  upon 
  the 
  iron 
  in 
  the 
  manner 
  

   described 
  earlier 
  in 
  the 
  paper, 
  the 
  results 
  obtained 
  are 
  exactly 
  

   similar 
  whether 
  the 
  radiator 
  is 
  coated 
  with 
  a 
  layer 
  of 
  rust 
  or 
  

   brightly 
  polished, 
  the 
  relative 
  values 
  of 
  k 
  being 
  the 
  same 
  in 
  

   the 
  two 
  cases. 
  

  

  The 
  result 
  (I)) 
  would 
  not 
  have 
  been 
  obtained 
  if 
  the 
  nickel 
  

   experimented 
  with 
  had 
  contained 
  an 
  impurity 
  which 
  emitted 
  

   a 
  characteristic 
  type 
  of 
  radiation 
  ^' 
  harder 
  " 
  or 
  '' 
  softer 
  " 
  than 
  

   that 
  characteristic 
  of 
  nickel. 
  For 
  the 
  harder 
  couiponent 
  of 
  

   the 
  secondary 
  beam 
  (whether 
  due 
  to 
  the 
  nickel 
  or 
  the 
  im- 
  

   purity) 
  would 
  have 
  excited 
  the 
  softer 
  component 
  radiation 
  

   in 
  the 
  tertiary 
  radiator, 
  and 
  this 
  would 
  have 
  been 
  detected 
  

   if 
  the 
  impurity 
  had 
  been 
  present 
  to 
  any 
  appreciable 
  extent. 
  

  

  Summary 
  of 
  Results. 
  

  

  (1) 
  The 
  characteristic 
  Rontgen 
  radiation 
  from 
  a 
  substance 
  

   is 
  found 
  to 
  be 
  identical 
  in 
  character 
  whether 
  it 
  is 
  emitted 
  as 
  

   a 
  secondary 
  or 
  a 
  tertiary 
  radiation. 
  In 
  each 
  case 
  (a) 
  the 
  

   radiation 
  is 
  homogeneous, 
  (h) 
  the 
  absorption 
  coefficients 
  of 
  

   the 
  radiation 
  by 
  other 
  substances 
  are 
  the 
  same, 
  and 
  indepen- 
  

   dent 
  of 
  the 
  penetrating 
  power 
  of 
  the 
  exciting 
  radiation 
  by 
  

   which 
  these 
  homogeneous 
  beams 
  are 
  produced. 
  

  

  (2) 
  Using 
  the 
  homogeneous 
  secondary 
  beams 
  emitted 
  by 
  

   the 
  members 
  of 
  the 
  group 
  of 
  metals 
  Cr-Ag, 
  excited 
  by 
  

   suitable 
  primary 
  beams, 
  the 
  emission 
  of 
  tertiary 
  radiation 
  

   by 
  the 
  earlier 
  members 
  of 
  the 
  group 
  Cr-Ag 
  when 
  excited 
  

   by 
  these 
  secondary 
  beams 
  was 
  found 
  to 
  be 
  governed 
  by 
  the 
  

   following 
  laws 
  : 
  — 
  (a) 
  With 
  a 
  given 
  substance 
  as 
  radiator, 
  

   its 
  characteristic 
  radiation 
  is 
  only 
  excited 
  by 
  those 
  secondary 
  

   beams 
  which 
  are 
  more 
  penetrating 
  than 
  the 
  tertiary 
  radiation 
  

   characteristic 
  of 
  the 
  substance. 
  (6) 
  When 
  the 
  secondary 
  

   beam 
  is 
  only 
  just 
  more 
  penetrating 
  than 
  the 
  tertiary 
  the 
  

   intensity 
  of 
  the 
  latter 
  is 
  small, 
  but 
  as 
  the 
  secondary 
  beam 
  

   becomes 
  more 
  penetrating 
  a 
  very 
  rapid 
  increase 
  in 
  the 
  in- 
  

   tensity 
  of 
  the 
  tertiary 
  radiation 
  to 
  a 
  maximum 
  takes 
  place, 
  

   (c) 
  As 
  the 
  secondary 
  beam 
  becomes 
  more 
  penetrating 
  still, 
  

   the 
  intensity 
  of 
  the 
  tertiary 
  radiation 
  decays 
  as 
  a 
  linear 
  

   function 
  of 
  the 
  ionization 
  produced 
  in 
  a 
  given 
  volume 
  of 
  air 
  

   by 
  the 
  secondary 
  beam. 
  

  

  (3) 
  It 
  has 
  been 
  found 
  that 
  when 
  the 
  secondary 
  homo- 
  

   geneous 
  beams 
  from 
  the 
  group 
  of 
  metals 
  Cr-Ag 
  are 
  absorbed 
  

   by 
  thin 
  sheets 
  of 
  metals 
  from 
  the 
  same 
  group, 
  a 
  big 
  increase 
  

   in 
  the 
  absorption 
  takes 
  place 
  when 
  the 
  secondary 
  beams 
  

  

  K2 
  

  

  