﻿Investigation 
  of 
  the 
  Nature 
  of 
  y 
  Rays. 
  923 
  

  

  accuracy. 
  We 
  believe 
  it 
  to 
  be 
  mainly 
  due 
  to 
  the 
  fast 
  ft 
  rays, 
  

   which 
  emerge 
  with 
  hard 
  y 
  rays 
  from 
  the 
  upper 
  surfaces 
  of 
  

   the 
  magnet 
  poles, 
  of 
  the 
  lead 
  block, 
  and 
  of 
  the 
  plug. 
  It 
  

   •cannot 
  be 
  much 
  less 
  when 
  the 
  plug 
  is 
  removed, 
  and 
  must 
  

   therefore 
  be 
  of 
  more 
  relative 
  importance 
  to 
  the 
  results 
  for 
  

   hard 
  rays 
  than 
  for 
  soft, 
  since 
  the 
  total 
  observed 
  effects 
  are 
  

   smaller 
  in 
  the 
  former 
  case. 
  Its 
  magnitude 
  is, 
  perhaps, 
  

   indicated 
  with 
  some 
  accuracy 
  by 
  the 
  fact 
  that 
  when 
  a 
  lead 
  

   plug 
  of 
  3 
  cm. 
  thickness 
  was 
  used 
  the 
  emergence 
  radiation 
  of 
  

   tellurium 
  seemed 
  to 
  be 
  nearly 
  zero 
  : 
  the 
  substance 
  had 
  

   -stopped 
  almost 
  as 
  much 
  as 
  it 
  generated. 
  It 
  can 
  easily 
  be 
  

   •seen 
  from 
  what 
  follows 
  that 
  tellurium 
  should 
  probably 
  have 
  

   less 
  emergence 
  radiation 
  than 
  any 
  other 
  substance, 
  yet 
  it 
  

   'ought 
  to 
  approach 
  half 
  the 
  value 
  for 
  carbon 
  ; 
  and 
  this 
  would 
  

   imply 
  that 
  the 
  value 
  of 
  the 
  constant 
  was 
  about 
  300 
  for 
  the 
  

   hard 
  rays, 
  and 
  perhaps 
  rather 
  more 
  for 
  the 
  soft. 
  On 
  the 
  

   other 
  hand, 
  c 
  — 
  a, 
  the 
  incidence 
  radiation, 
  is 
  too 
  large, 
  because 
  

   the 
  plate 
  that 
  is 
  placed 
  on 
  the 
  top 
  of 
  the 
  chamber 
  at 
  qq 
  not 
  

   only 
  gives 
  rise 
  to 
  the 
  incidence 
  radiation 
  to 
  be 
  measured, 
  but 
  

   •also 
  turns 
  back 
  to 
  a 
  greater 
  or 
  less 
  extent 
  the 
  /3 
  rays 
  striking 
  

   it 
  from 
  below. 
  This 
  effect 
  increases 
  with 
  the 
  atomic 
  weight, 
  

   and 
  must 
  be 
  of 
  some 
  importance 
  in 
  the 
  case 
  of 
  Sn 
  and 
  Pb. 
  

   As 
  it 
  is 
  clear 
  that 
  these 
  corrections 
  will 
  increase 
  the 
  want 
  of 
  

   symmetry, 
  already 
  obvious 
  enough, 
  and 
  as 
  we 
  are 
  hardly 
  in 
  a 
  

   position 
  as 
  yet 
  to 
  make 
  the 
  corrections 
  with 
  accuracy, 
  and 
  as 
  

   we 
  hope 
  to 
  diminish 
  our 
  experimental 
  errors 
  in 
  the 
  future, 
  

   we 
  have 
  for 
  the 
  present 
  left 
  these 
  figures 
  uncorrected. 
  

  

  In 
  the 
  first 
  of 
  these 
  papers 
  we 
  showed 
  that 
  the 
  incidence 
  

   radiation 
  should 
  be 
  somewhat 
  less 
  than 
  p 
  times 
  the 
  emergence 
  

   radiation, 
  where 
  p 
  is 
  the 
  reflexion 
  constant 
  of 
  the 
  substance 
  

   in 
  question 
  for 
  /3 
  rays. 
  The 
  above 
  table 
  does 
  indeed 
  show 
  

   that 
  the 
  ratio 
  of 
  the 
  two 
  radiations 
  increases 
  w 
  ith 
  the 
  atomic 
  

   weight, 
  and 
  therefore 
  with 
  p; 
  but 
  the 
  quantitative 
  com- 
  

   parison 
  appears 
  poor. 
  But 
  it 
  is 
  to 
  be 
  remembered 
  that 
  

   {1) 
  corrections 
  yet 
  to 
  be 
  made 
  will 
  alter 
  the 
  figures 
  somewhat, 
  

   making, 
  for 
  example, 
  the 
  emergence 
  radiation 
  of 
  Pb 
  greater, 
  

   •and 
  the 
  incidence 
  radiation 
  smaller 
  ; 
  (2) 
  the 
  quantity 
  p 
  is 
  

   somewhat 
  indefinite. 
  It 
  is 
  true 
  that 
  McClelland 
  has 
  made 
  

   •careful 
  measurements 
  of 
  p 
  for 
  various 
  substances 
  ; 
  so 
  also 
  has 
  

   H. 
  W. 
  Schmidt 
  ; 
  and 
  the 
  two 
  sets 
  of 
  results 
  do 
  not 
  agree 
  

   very 
  well. 
  This 
  is 
  not 
  to 
  be 
  wondered 
  at, 
  for 
  the 
  quality 
  of 
  

   the 
  secondary 
  radiation 
  due 
  to 
  (3 
  rays 
  is 
  different 
  to 
  that 
  of 
  

   the 
  incident, 
  and 
  depends 
  on 
  the 
  nature 
  of 
  the 
  reflector. 
  For 
  

   instance, 
  there 
  is 
  some 
  very 
  soft 
  radiation, 
  of 
  which 
  half 
  is 
  

   absorbed 
  in 
  25 
  cm. 
  of 
  air. 
  The 
  experimental 
  value 
  of 
  p 
  will 
  

   therefore 
  depend 
  on 
  how 
  close 
  the 
  ionization-chamber 
  which 
  

   receives 
  the 
  secondary 
  radiation 
  is 
  placed 
  to 
  the 
  reflecting- 
  

  

  