﻿568 
  

  

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

  

  copper 
  or 
  iron 
  before 
  falling 
  on 
  the 
  copper 
  radiator, 
  the 
  

   ratio 
  of 
  intensity 
  of 
  secondary 
  radiation 
  to 
  ionization 
  pro- 
  

   duced 
  by 
  the 
  primary 
  beam 
  dropped 
  slightly, 
  showing 
  that 
  

   the 
  radiation 
  transmitted 
  through 
  these 
  substances 
  was 
  less 
  

   efficient 
  as 
  a 
  secondary-ray 
  producer 
  in 
  comparison 
  with 
  its 
  

   power 
  of 
  producing 
  ionization 
  in 
  air. 
  This 
  may 
  have 
  been 
  

   due 
  to 
  the 
  fact 
  that 
  in 
  transmission 
  through 
  these 
  plates, 
  a 
  

   gradually 
  increasing 
  quantity 
  of 
  secondary 
  radiation 
  from 
  

   the 
  plates 
  was 
  superposed 
  on 
  the 
  primary. 
  This 
  being 
  in 
  

   one 
  case 
  of 
  the 
  same 
  penetrating 
  power 
  as 
  the 
  secondary 
  

   emitted 
  by 
  the 
  radiator, 
  and 
  in 
  the 
  other 
  more 
  easily 
  absorbed 
  

   than 
  it, 
  would 
  not 
  afterwards 
  produce 
  secondary 
  rays 
  in 
  the 
  

   copper 
  (see 
  later). 
  When 
  the 
  radiation 
  was 
  absorbed 
  by 
  

   zinc, 
  the 
  ratio 
  remained 
  fairly 
  constant. 
  This 
  result 
  would, 
  

   on 
  the 
  corresponding 
  theory, 
  be 
  due 
  to 
  the 
  fact 
  that 
  the 
  

   radiation 
  from 
  zinc 
  is 
  slightly 
  more 
  penetrating 
  than 
  that 
  

   from 
  copper, 
  consequently 
  the 
  zinc 
  radiation 
  acquired 
  in 
  the 
  

   primary 
  beam 
  would 
  be 
  capable 
  of 
  stimulating 
  a 
  feeble 
  

   secondary 
  in 
  copper. 
  (See 
  Table 
  VII.) 
  

  

  Table 
  VII. 
  

  

  Ivadiation 
  from 
  Copper 
  (thin 
  sheet 
  absorbing 
  

   14*5 
  per 
  cent, 
  of 
  primary 
  rays). 
  

  

  I. 
  

  

  II. 
  

  

  III. 
  

  

  Percentage 
  

  

  IV. 
  

  

  Thickness 
  of 
  

  

  Percentage 
  of 
  

  

  diminution 
  of 
  

  

  Eatio 
  of 
  

  

  plate 
  in 
  

  

  Primary 
  

  

  Secondary 
  by 
  

  

  Ionizations 
  in 
  

  

  Primary 
  

  

  absorbed 
  by 
  Zn 
  

  

  Zn 
  in 
  column 
  1 
  

  

  Secondary 
  and 
  

  

  beam. 
  

  

  in 
  column 
  1. 
  

  

  absorbing 
  

  

  Primary 
  

  

  

  

  Primary. 
  

  

  electroscopes. 
  

  

  Zn 
  -00131 
  cm. 
  

  

  594 
  

  

  59-6 
  

  

  •99 
  

  

  •00262 
  „ 
  

  

  77-5 
  

  

  77-6 
  

  

  •99 
  

  

  •00393 
  „ 
  

  

  848 
  

  

  84-8 
  

  

  1-00 
  

  

  •00524 
  „ 
  

  

  89-1 
  

  

  90-1 
  

  

  •91 
  

  

  •00786 
  „ 
  

  

  935 
  

  

  93-6 
  

  

  •98 
  

  

  •01179 
  „ 
  

  

  97-2 
  

  

  963 
  

  

  1-32 
  

  

  Cu 
  -00067 
  cm. 
  

  

  435 
  

  

  45-1 
  

  

  •97 
  

  

  •00134 
  „ 
  

  

  65 
  

  

  66-5 
  

  

  •95 
  

  

  •00296 
  „ 
  

  

  82 
  

  

  84-8 
  

  

  •84 
  

  

  •00592 
  ., 
  

  

  90 
  

  

  91-6 
  

  

  •84 
  

  

  •01184 
  „ 
  

  

  97 
  

  

  98 
  

  

  •66 
  

  

  Fe 
  -00315 
  cm. 
  

  

  77-2 
  

  

  80-8 
  

  

  •84 
  

  

  •00630 
  „ 
  

  

  89-0 
  

  

  91-4 
  

  

  •78 
  

  

  •00945 
  ,, 
  

  

  93-0 
  

  

  95 
  

  

  1 
  

  

  •71 
  

  

  