﻿Homogeneous 
  Secondary 
  Rontgen 
  Radiations. 
  571 
  

  

  and 
  to 
  a 
  less 
  extent 
  to 
  elements 
  of 
  neighbouring 
  atomic 
  

   weight. 
  

  

  That 
  this 
  special 
  penetrating 
  power 
  is 
  not 
  due 
  to 
  the 
  con- 
  

   stituent 
  easily 
  absorbed 
  by 
  the 
  radiating 
  substance 
  having 
  

   been 
  sifted 
  out 
  before 
  emergence 
  through 
  the 
  surface 
  layer 
  

   might 
  be 
  inferred 
  from 
  the 
  fact 
  of 
  its 
  homogeneous 
  character, 
  

   unless 
  of 
  all 
  the 
  constituents 
  in 
  the 
  radiation 
  as 
  emitted 
  from 
  

   the 
  atom 
  itself 
  this 
  was 
  the 
  only 
  one 
  transmitted 
  through 
  

   even 
  fairly 
  thin 
  layers 
  of 
  the 
  substance. 
  But 
  we 
  find 
  other 
  

   secondary 
  rays 
  transmitted 
  with 
  almost 
  the 
  same 
  facility. 
  

   We 
  may 
  conclude, 
  therefore, 
  that 
  it 
  is 
  not 
  merely 
  from 
  the 
  

   surface 
  of 
  relatively 
  thick 
  sheets 
  that 
  the 
  radiation 
  emerges 
  

   in 
  a 
  homogeneous 
  state, 
  but 
  that 
  it 
  is 
  so 
  emitted 
  by 
  the 
  

   atoms 
  themselves. 
  The 
  special 
  power 
  of 
  penetration 
  is 
  thus 
  

   a 
  specific 
  property 
  of 
  the 
  secondary 
  rays 
  and 
  does 
  not 
  appear 
  

   to 
  be 
  due 
  to 
  previous 
  selective 
  absorption. 
  

  

  Tertiary 
  Rays. 
  — 
  Some 
  of 
  the 
  most 
  interesting 
  phenomena 
  

   in 
  connexion 
  with 
  these 
  homogeneous 
  rays 
  were 
  those 
  shown 
  

   by 
  experiments 
  made 
  in 
  order 
  to 
  investigate 
  the 
  special 
  

   penetrating 
  power 
  of 
  these 
  rays. 
  

  

  When 
  the 
  characteristic 
  homogeneous 
  radiation 
  from 
  iron 
  

   was 
  passed 
  through 
  a 
  thin 
  sheet 
  of 
  copper 
  — 
  a 
  substance 
  

   whose 
  characteristic 
  radiation 
  is 
  of 
  more 
  penetrating 
  type 
  — 
  

   it 
  was 
  partially 
  absorbed, 
  and 
  the 
  transmitted 
  radiation 
  

   appeared 
  unchanged 
  in 
  character. 
  

  

  When, 
  however, 
  the 
  radiation 
  from 
  copper 
  was 
  passed 
  

   through 
  iron 
  there 
  was 
  superposed 
  on 
  the 
  copper 
  radiation 
  a 
  

   considerable 
  quantity 
  of 
  iron 
  radiation 
  ; 
  when 
  the 
  thickness 
  

   of 
  the 
  absorbing 
  plate 
  of 
  iron 
  was 
  sufficient 
  to 
  produce 
  almost 
  

   complete 
  absorption, 
  the 
  bulk 
  of 
  the 
  transmitted 
  radiation 
  

   was 
  iron 
  radiation. 
  

  

  Similar 
  experiments 
  were 
  made 
  on 
  copper 
  and 
  zinc. 
  The 
  

   radiation 
  from 
  the 
  former, 
  which 
  is 
  more 
  absorbable 
  than 
  

   that 
  from 
  the 
  latter, 
  when 
  passed 
  through 
  zinc 
  was 
  trans- 
  

   mitted 
  without 
  admixture 
  of 
  other 
  radiations, 
  but 
  when 
  the 
  

   radiation 
  from 
  zinc 
  was 
  transmitted 
  through 
  copper 
  it 
  became 
  

   more 
  like 
  the 
  copper 
  radiation. 
  The 
  effect 
  was 
  not 
  so 
  well 
  

   marked 
  as 
  in 
  the 
  case 
  of 
  the 
  transmission 
  of 
  copper 
  radiation 
  

   through 
  iron. 
  

  

  Thus 
  a 
  characteristic 
  homogeneous 
  radiation 
  was 
  emitted 
  

   by 
  a 
  metal 
  when 
  the 
  primary 
  beam 
  to 
  which 
  the 
  metal 
  was 
  

   exposed 
  was 
  of 
  more 
  penetrating 
  type 
  than 
  the 
  characteristic 
  

   radiation. 
  When 
  the 
  primary 
  was 
  of 
  a 
  more 
  absorbable 
  type, 
  

   this 
  characteristic 
  secondary 
  radiation 
  was 
  not 
  emitted*. 
  

  

  * 
  Details 
  of 
  these 
  experiments 
  will 
  be 
  given 
  later. 
  

  

  