﻿122 
  Mr. 
  C. 
  A. 
  Sadler 
  on 
  the 
  

  

  passage 
  of 
  the 
  secondary 
  beam 
  through 
  the 
  substance 
  o£ 
  the 
  

   tertiary 
  radiator. 
  

  

  It 
  has 
  been 
  found* 
  that 
  if 
  the 
  values 
  of 
  X^ 
  for 
  the 
  radiations 
  

   from 
  the 
  group 
  Cr 
  to 
  Ag 
  for 
  any 
  absorber, 
  such 
  as 
  silver, 
  ii^ 
  

   which 
  no 
  homogeneous 
  radiation 
  is 
  excited 
  by 
  the 
  radiations 
  

   from 
  any 
  member 
  of 
  the 
  group, 
  be 
  plotted 
  as 
  ordinates 
  against 
  

   the 
  corresponding 
  values 
  of 
  Xj 
  for 
  aluminium, 
  in 
  which 
  also 
  

   no 
  homogeneous 
  radiation 
  is 
  excited, 
  as 
  abscissse 
  ; 
  the 
  points 
  

   so 
  obtained 
  lie 
  on 
  straight 
  lines, 
  and 
  these 
  straight 
  lines 
  pass 
  

   through 
  a 
  common 
  point. 
  

  

  Similarly, 
  if 
  we 
  plot 
  as 
  ordinates 
  the 
  values 
  of 
  Xi 
  for 
  any 
  

   of 
  the 
  early 
  members 
  of 
  the 
  group 
  Cr-Ag 
  as 
  absorber, 
  in 
  

   which 
  the 
  homogeneous 
  type 
  of 
  radiation 
  u 
  excited 
  by 
  the 
  

   radiation 
  from 
  those 
  members 
  of 
  the 
  group 
  of 
  higher 
  atomic 
  

   weight 
  ; 
  it 
  has 
  been 
  found, 
  that 
  up 
  to 
  the 
  point 
  corresponding 
  

   to 
  the 
  atomic 
  weight 
  of 
  the 
  absorber, 
  the 
  relation 
  is 
  also 
  

   linear, 
  and 
  if 
  the 
  straight 
  line 
  be 
  produced, 
  it 
  passes 
  through 
  

   the 
  common 
  point 
  previously 
  mentioned. 
  The 
  values 
  of 
  Xi 
  

   for 
  the 
  radiation 
  from 
  the 
  radiators 
  of 
  higher 
  atomic 
  weight 
  

   are 
  abnormally 
  increased, 
  the 
  increase 
  being 
  attendant 
  upon 
  

   the 
  excitation 
  of 
  tertiary 
  radiation. 
  

  

  This 
  increase 
  is 
  discussed 
  in 
  the 
  paper 
  on 
  " 
  The 
  Absorption 
  

   of 
  X 
  Rays 
  " 
  previously 
  referred 
  to. 
  

  

  In 
  the 
  actual 
  experiments 
  to 
  determine 
  the 
  values 
  of 
  R 
  

   with 
  the 
  various 
  combinations 
  of 
  secondary 
  and 
  tertiary 
  

   radiators, 
  it 
  was 
  found 
  necessary 
  to 
  alter 
  the 
  position 
  of 
  the 
  

   quadrants 
  of 
  the 
  tertiary 
  electroscope 
  from 
  time 
  to 
  time, 
  

   owing 
  to 
  a 
  slight 
  shift 
  of 
  zero, 
  due 
  to 
  small 
  progressive 
  varia- 
  

   tions 
  in 
  the 
  applied 
  potentials. 
  In 
  this 
  way 
  small 
  changes 
  in 
  

   the 
  sensitiveness 
  of 
  the 
  instrument 
  were 
  introduced. 
  The 
  

   sensitiveness 
  could, 
  however, 
  be 
  maintained 
  constant 
  during 
  

   a 
  period 
  of 
  three 
  or 
  four 
  hours 
  during 
  any 
  given 
  day. 
  

  

  In 
  order 
  to 
  obtain 
  true 
  relative 
  values 
  for 
  the 
  ionizations, 
  

   ihe 
  secondary 
  radiation 
  from 
  arsenic 
  was 
  made 
  to 
  fall 
  upon 
  

   each 
  of 
  the 
  tertiary 
  radiators 
  placed 
  successively 
  in 
  the 
  position 
  

   Eg, 
  the 
  sensitiveness 
  of 
  the 
  electroscope 
  remaining 
  constant 
  

   during 
  this 
  series 
  of 
  observations. 
  Values 
  of 
  R 
  were 
  obtained 
  

   in 
  this 
  way 
  for 
  Zn, 
  Cu, 
  Ni, 
  and 
  Fe 
  as 
  tertiary 
  radiators, 
  the 
  

   surfaces 
  in 
  each 
  case 
  being 
  brightly 
  polished, 
  of 
  the 
  same 
  size, 
  

   and 
  thick 
  enough 
  to 
  totally 
  absorb 
  the 
  incident 
  beam. 
  These 
  

   values 
  of 
  R 
  plotted 
  as 
  ordinates 
  against 
  the 
  atomic 
  weight 
  of 
  

   the 
  radiators 
  as 
  abscissae, 
  were 
  found 
  to 
  lie 
  on 
  a 
  smooth 
  curve 
  

   (see 
  fig. 
  3). 
  

  

  In 
  the 
  case 
  of 
  Cr 
  and 
  Co, 
  being 
  unable 
  to 
  obtain 
  them 
  

   pure 
  in 
  the 
  form 
  of 
  flat 
  plates, 
  radiators 
  were 
  made 
  in 
  the 
  

   * 
  Barkla 
  & 
  Sadler, 
  Phil. 
  Mag. 
  May 
  1909. 
  

  

  