﻿$22 
  Prof. 
  Bragg 
  and 
  Mr. 
  Madsen 
  : 
  An 
  Experimental 
  

  

  various 
  substances. 
  This 
  was 
  done 
  by 
  the 
  measurement 
  of 
  

   the 
  current 
  under 
  three 
  different 
  arrangements 
  : 
  — 
  

  

  (a) 
  When 
  those 
  parts 
  of 
  the 
  top 
  and 
  bottom 
  walls 
  of 
  the 
  

  

  chamber 
  through 
  which 
  the 
  y 
  rays 
  passed 
  were 
  

  

  made 
  of 
  the 
  thinnest 
  Al 
  foil 
  (/>/>, 
  gg, 
  in 
  the 
  figure). 
  

   (IS) 
  When 
  a 
  plate 
  of 
  the 
  substance, 
  of 
  proper 
  thickness, 
  

  

  was 
  so 
  placed 
  at 
  pp 
  that 
  the 
  rays 
  passed 
  through 
  it 
  

  

  into 
  the 
  chamber. 
  

   (c) 
  When 
  a 
  plate 
  of 
  the 
  same 
  substance 
  1 
  was 
  made 
  to 
  form 
  

  

  part 
  of 
  the 
  top 
  wall. 
  ;it 
  <i<j, 
  m) 
  that 
  the 
  y 
  rays 
  struck 
  

  

  it 
  after 
  crossing 
  the 
  chamber. 
  

  

  We 
  took 
  !> 
  — 
  </ 
  as 
  a 
  measurement 
  of 
  the 
  emergence 
  radiation, 
  

   c 
  — 
  a 
  as 
  a 
  measurement 
  of 
  the 
  incident. 
  Some 
  results 
  which 
  

   wo 
  obtained 
  in 
  this 
  way 
  arc 
  contained 
  in 
  the 
  following 
  table, 
  

   in 
  which 
  the 
  numbers 
  refer 
  to 
  the 
  movement 
  of 
  the 
  scale 
  in 
  

   30 
  seconds, 
  10=1 
  nun. 
  : 
  — 
  

  

  Comparison 
  of 
  Emergence 
  and 
  Incidence 
  Radiations. 
  

  

  

  Soft 
  j 
  

  

  Incidence. 
  

  

  rays. 
  

  

  1-] 
  mergence. 
  

  

  Hard 
  

  

  Incidence. 
  

  

  y 
  rays. 
  

   Emergence. 
  

  

  c 
  

  

  17o 
  

   280 
  

   340 
  

   4-7 
  

   558 
  

   618 
  

   1051 
  

  

  1723 
  

  

  2280 
  

   1810 
  

   1575 
  

  

  1350 
  

  

  1*160 
  

   1170 
  

   2001 
  

  

  58 
  

   120 
  

   I.-.4 
  

   103 
  

   202 
  

   224 
  

   333 
  

   497 
  

  

  1150 
  

   795 
  

   685 
  

   560 
  

   523 
  

   485 
  

   303 
  

   470 
  

  

  Al 
  

  

  s 
  

  

  Fe 
  .. 
  

  

  Cu 
  

  

  Zn 
  

  

  Sn 
  

  

  Pb 
  

  

  The 
  figures 
  here 
  given 
  show 
  the 
  very 
  large 
  want 
  of 
  symmetry 
  

   between 
  the 
  radiations 
  on 
  the 
  two 
  sides 
  of 
  a 
  plate. 
  Our 
  

   previous 
  experiments 
  proved 
  the 
  existence 
  of 
  this 
  want 
  of 
  

   symmetry 
  ; 
  but 
  it 
  is 
  now 
  shown 
  more 
  clearly 
  and 
  

   satisfactorily. 
  

  

  The 
  results 
  still 
  require 
  correction 
  before 
  they 
  can 
  be 
  

   considered 
  accurate. 
  It 
  will 
  be 
  clear 
  that 
  b 
  — 
  a, 
  the 
  emergence 
  

   radiation, 
  is 
  too 
  small 
  in 
  all 
  cases, 
  because 
  the 
  screen, 
  when 
  

   placed 
  on 
  the 
  bottom 
  of 
  the 
  chamber, 
  stops 
  a 
  certain 
  amount 
  

   of 
  /3 
  radiation, 
  which 
  is 
  made 
  in 
  the 
  air 
  just 
  underneath 
  the 
  

   plate, 
  and 
  is 
  out 
  of 
  reach 
  of 
  the 
  magnet, 
  as 
  well 
  as 
  some 
  fast 
  

   ]3 
  radiation 
  which 
  comes 
  from 
  lower 
  down, 
  and 
  is 
  strong 
  

   enough 
  to 
  escape 
  from 
  the 
  magnetic 
  field. 
  This 
  is 
  reckoned 
  

   in 
  a, 
  but 
  not 
  in 
  b 
  ; 
  so 
  that 
  on 
  this 
  account 
  all 
  the 
  emergence 
  

   radiations 
  are 
  too 
  small 
  by 
  a 
  certain 
  constant 
  amount. 
  We 
  

   have 
  not 
  yet 
  succeeded 
  in 
  determining 
  this 
  constant 
  with 
  any 
  

  

  