﻿130 
  Mr. 
  C. 
  A. 
  Sadler 
  on 
  the 
  

  

  decrease 
  in 
  the 
  value 
  of 
  — 
  , 
  can 
  merely 
  be 
  a 
  matter 
  for 
  

  

  A 
  

  

  conjecture, 
  but 
  it 
  is 
  hoped 
  that 
  the 
  data 
  obtained 
  in 
  

   subsequent 
  experiments 
  will 
  throw 
  more 
  light 
  upon 
  the 
  

   phenomena*. 
  

  

  It 
  will 
  be 
  observed 
  that 
  in 
  determining 
  these 
  relationships 
  

   the 
  atomic 
  weight 
  of 
  nickel 
  is 
  nowhere 
  assumed, 
  but 
  the 
  

   results 
  obtained 
  all 
  point 
  to 
  the 
  conclusion 
  that 
  the 
  beha\dour 
  

   of 
  nickel, 
  whether 
  as 
  radiator 
  or 
  absorber 
  of 
  X-rays, 
  is 
  such 
  

   that 
  we 
  should 
  expect 
  its 
  atomic 
  weight 
  to 
  lie 
  between 
  those 
  

   of 
  cobalt 
  and 
  copper. 
  

  

  The 
  evidence 
  for 
  this, 
  obtained 
  during 
  the 
  course 
  of 
  these 
  

   experiments, 
  may 
  be 
  briefly 
  summarized 
  as 
  follows 
  : 
  — 
  

  

  (a) 
  The 
  secondary 
  homogeneous 
  radiation 
  from 
  cobalt 
  

   excites 
  7io 
  homogeneous 
  tertiary 
  radiation 
  in 
  nickel. 
  

  

  (b) 
  The 
  secondary 
  homogeneous 
  radiation 
  from 
  nickel 
  

   excites 
  no 
  homogeneous 
  tertiary 
  radiation 
  in 
  nickel. 
  

  

  (c) 
  The 
  secondary 
  homogeneous 
  radiation 
  from 
  nickel 
  does 
  

   excite 
  homogeneous 
  tertiary 
  radiation 
  in 
  cobalt, 
  and 
  to 
  an 
  

   extent 
  to 
  be 
  expected 
  for 
  the 
  radiation 
  from 
  a 
  substance 
  of 
  

   atomic 
  weight 
  about 
  midway 
  between 
  those 
  of 
  cobalt 
  and 
  

   copper. 
  

  

  But 
  it 
  has 
  been 
  shown 
  for 
  the 
  group 
  of 
  metals 
  Cr-Ag 
  

   that 
  

  

  (1) 
  The 
  penetrating 
  power 
  of 
  the 
  radiation 
  characteristic 
  

  

  of 
  any 
  member 
  of 
  the 
  group 
  increases 
  with 
  its 
  atomic 
  

   weight 
  t- 
  

  

  (2) 
  The 
  radiation 
  characteristic 
  of 
  a 
  substance 
  is 
  only 
  

  

  excited 
  by 
  a 
  more 
  penetrating 
  radiation 
  J. 
  

  

  If 
  the 
  atomic 
  weight 
  of 
  nickel 
  were 
  greater 
  than 
  that 
  of 
  

   cobalt, 
  then 
  by 
  (1) 
  we 
  should 
  expect 
  to 
  find 
  its 
  characteristic 
  

   radiation 
  to 
  be 
  more 
  penetrating 
  than 
  that 
  of 
  cobalt, 
  and 
  

   consequently 
  by 
  (2) 
  that 
  the 
  radiation 
  from 
  nickel 
  should 
  

   excite 
  in 
  cobalt 
  its 
  characteristic 
  radiation, 
  while 
  the 
  radiation 
  

   from 
  cobalt 
  should 
  not 
  excite 
  the 
  radiation 
  characteristic 
  of 
  

   nickel. 
  If, 
  on 
  the 
  other 
  hand, 
  the 
  atomic 
  weight 
  of 
  nickel 
  

   were 
  less 
  than 
  that 
  of 
  cobalt, 
  then 
  the 
  results 
  would 
  be 
  the 
  

   reverse 
  of 
  the 
  former. 
  

  

  It 
  has 
  been 
  suggested 
  that 
  the 
  anomalous 
  behaviour 
  of 
  

  

  * 
  Note. 
  Experiments 
  now 
  in 
  progress 
  indicate 
  that 
  when 
  the 
  exciting 
  

   beam 
  is 
  more 
  penetrating 
  than 
  the 
  radiation 
  characteristic 
  of 
  the 
  tertiary 
  

   radiator, 
  part 
  of 
  the 
  energy 
  absorbed 
  reappears 
  as 
  an 
  easily 
  absorbed 
  cor- 
  

   puscular 
  radiation, 
  and 
  this 
  effect 
  becomes 
  more 
  pronounced 
  as 
  the 
  

   exciting 
  beam 
  becomes 
  more 
  penetrating. 
  

  

  t 
  Barkla 
  & 
  Sadler, 
  Phil. 
  Mag. 
  Sept. 
  1907, 
  pp. 
  812-828 
  ; 
  also 
  Phil. 
  

   Mag. 
  May 
  1909. 
  

  

  t 
  Barkla 
  & 
  Sadler, 
  Phil. 
  Mag. 
  Oct. 
  1908 
  ; 
  also 
  present 
  paper. 
  

  

  