﻿()J4 
  Method 
  of 
  Showing 
  Fluorescent 
  Absorption 
  direct!//. 
  

  

  arrangement 
  of 
  the 
  apparatus 
  is 
  shown 
  in 
  the 
  figure, 
  which 
  

   is 
  a 
  view 
  from 
  above. 
  

  

  C 
  

  

  Light 
  from 
  the 
  arc 
  passes 
  through 
  the 
  two 
  lenses 
  A 
  and 
  

   B, 
  the 
  former 
  of 
  which 
  moves 
  on 
  a 
  hinged 
  arm, 
  as 
  shown 
  in 
  

   the 
  lower 
  figure, 
  and 
  is 
  brought 
  to 
  a 
  focus 
  on 
  the 
  perforated 
  

   disk. 
  The 
  pencil 
  diverging 
  Erom 
  the 
  Hocus 
  formed 
  by 
  A 
  

   falls 
  upou 
  a 
  diffusing 
  Bcreen 
  of 
  thin 
  porcelain 
  D, 
  and 
  illumi- 
  

   oates 
  flu- 
  whirr 
  screen 
  E. 
  Light 
  Erom 
  the 
  other 
  lens 
  

   illuminates 
  the 
  fluorescent 
  tank 
  F. 
  One 
  collimator 
  of 
  the 
  

   spectrophotometer 
  receives 
  the 
  light 
  from 
  E 
  and 
  F 
  either 
  

   simultaneously 
  or 
  in 
  succession, 
  according 
  to 
  the 
  position 
  o£ 
  

   the 
  lens 
  A. 
  illuminating 
  tin- 
  silver 
  strip 
  which 
  crosses 
  the 
  

   centre 
  of 
  the 
  field 
  of 
  the 
  instrument 
  in 
  a 
  horizontal 
  direction. 
  

   The 
  other 
  collimator 
  receives 
  light 
  from 
  the 
  white 
  screen 
  

   ( 
  ;. 
  ami 
  illuminates 
  the 
  remainder 
  of 
  the 
  field. 
  The 
  telescope 
  

   is 
  set 
  so 
  that 
  the 
  field 
  is 
  illuminated 
  with 
  monochromatic 
  

   light 
  of 
  wave-length 
  5180, 
  for 
  which 
  Nichols 
  and 
  Merritt 
  

   found 
  the 
  largest 
  value 
  of 
  the 
  fluorescent 
  absorption, 
  and 
  

   the 
  two 
  halves 
  of 
  the 
  field 
  adjusted 
  to 
  equality, 
  the 
  line 
  of 
  

   demarcation 
  disappearing. 
  The 
  lens 
  A 
  is 
  then 
  shifted, 
  

   throwing 
  the 
  flashes 
  out 
  of 
  step. 
  If 
  fluorescent 
  absorption 
  

   was 
  present 
  before, 
  it 
  should 
  be 
  absent 
  now, 
  since 
  F 
  is 
  dark 
  

   when 
  the 
  light 
  from 
  E 
  passes 
  through 
  it, 
  and 
  the 
  silver 
  strip 
  

   should 
  consequently 
  brighten 
  and 
  become 
  visible. 
  Abso- 
  

   lutely 
  no 
  change 
  could 
  be 
  seen, 
  however, 
  which 
  makes 
  it 
  

   <eem 
  certain 
  that 
  the 
  absorption 
  is 
  the 
  same 
  in 
  the 
  two- 
  

  

  cases. 
  

  

  