﻿616 
  Dr. 
  J. 
  A. 
  Gray 
  on 
  the 
  Scattering 
  and 
  

  

  independent 
  of 
  the 
  nature 
  of 
  the 
  radiator. 
  There 
  seem 
  to 
  be 
  

   two 
  possible 
  explanations. 
  

  

  (1) 
  7 
  rays 
  become 
  softer 
  the 
  more 
  matter 
  they 
  penetrate, 
  

   not 
  taking 
  into 
  account 
  any 
  possible 
  effect 
  due 
  to 
  scattering. 
  

   We 
  should 
  then 
  have 
  a 
  continuous 
  production 
  of 
  soft 
  

   7 
  rays, 
  and 
  the 
  former 
  explanation 
  of 
  scattering 
  might 
  hold 
  

   good, 
  

  

  (2) 
  When 
  homogeneous 
  y 
  rays 
  are 
  scattered 
  there 
  is 
  a 
  

   change 
  of 
  quality, 
  the 
  scattered 
  rays 
  being 
  softer 
  the 
  greater 
  

   the 
  angle 
  of 
  scattering. 
  

  

  With 
  respect 
  to 
  the 
  first 
  possibility 
  there 
  is 
  no 
  evidence 
  

   of 
  such 
  a 
  transformation. 
  Experiments 
  on 
  characteristic 
  

   X 
  radiations 
  indicate 
  that 
  the 
  rays 
  are 
  homogeneous 
  and 
  

   suffer 
  no 
  change 
  in 
  direct 
  transmission 
  through 
  matter 
  

   except 
  by 
  being 
  diminished 
  in 
  intensity. 
  Even 
  admitting 
  

   this 
  possibility 
  there 
  are 
  other 
  difficulties. 
  In 
  the 
  experi- 
  

   ments 
  of 
  Madsen 
  and 
  Florance 
  the 
  scattered 
  rays 
  had 
  to 
  

   pass 
  through 
  a 
  certain 
  amount 
  of 
  lead 
  before 
  entering 
  the 
  

   electroscope. 
  As 
  lead 
  absorbs 
  the 
  incident 
  rays 
  so 
  much 
  

   more 
  quickly 
  than 
  the 
  harder 
  emergent 
  rays 
  their 
  results 
  

   may 
  not 
  give 
  a 
  fair 
  comparison. 
  To 
  test 
  this 
  the 
  following 
  

   experiment 
  was 
  made. 
  

  

  Readings 
  were 
  taken 
  of 
  the 
  relative 
  intensities 
  of 
  the 
  

   radiations 
  scattered 
  from 
  a 
  carbon 
  radiator 
  in 
  directions 
  

   making 
  angles 
  35°, 
  90°, 
  130° 
  with 
  that 
  of 
  the 
  primary 
  rays. 
  

   The 
  carbon 
  radiator 
  was 
  the 
  one 
  used 
  previously 
  in 
  scattering- 
  

   experiments 
  (Table 
  I.). 
  The 
  same 
  electroscope 
  E 
  was 
  used, 
  

   the 
  scattered 
  rays 
  entering 
  and 
  leaving 
  the 
  electroscope 
  

   through 
  carbon 
  plates. 
  

  

  A 
  l5 
  A 
  2 
  , 
  A 
  3 
  (fig. 
  2) 
  represent 
  three 
  positions 
  of 
  the 
  active 
  

   material 
  equidistant 
  (31'5 
  cm.) 
  from 
  the 
  radiator 
  R. 
  The 
  

   electroscope 
  was 
  screened 
  as 
  before. 
  The 
  absorption 
  of 
  

   primary 
  rays 
  in 
  the 
  radiator 
  was 
  about 
  the 
  same 
  in 
  each 
  

   case. 
  The 
  readings 
  obtained 
  were 
  : 
  

  

  A 
  1? 
  angle 
  of 
  scattering 
  35°, 
  scattered 
  radiation 
  1*40. 
  

   A 
  2 
  , 
  „ 
  „ 
  90 
  , 
  j, 
  ,, 
  0'6l. 
  

  

  A 
  3 
  , 
  „ 
  „ 
  130°, 
  „ 
  „ 
  0-63. 
  

  

  We 
  should 
  correct 
  for 
  absorption 
  of 
  the 
  scattered 
  radiation 
  

   in 
  the 
  radiator 
  and 
  in 
  the 
  carbon 
  plate 
  in 
  front 
  of 
  the 
  

   electroscope. 
  Correcting 
  for 
  absorption 
  in 
  the 
  latter 
  plate 
  

   the 
  numbers 
  become 
  

  

  1-77, 
  0-82, 
  0-99. 
  

  

  It 
  thus 
  appears 
  as 
  if 
  less 
  radiation 
  is 
  scattered 
  through 
  90° 
  

  

  