﻿Fluorescent 
  Absorption 
  directly 
  if 
  it 
  exists. 
  943 
  

  

  •absorbing 
  tank 
  by 
  one-hall:, 
  without 
  altering 
  the 
  intensity 
  o£ 
  

   the 
  source 
  behind 
  it, 
  the 
  source 
  of 
  course 
  being 
  considered 
  

   as 
  the 
  light 
  after 
  transmission 
  through 
  the 
  first 
  nicol. 
  

  

  The 
  weakening 
  by 
  the 
  first 
  nicol 
  is 
  an 
  advantage, 
  for 
  the 
  

   percentage 
  absorption 
  is 
  greater 
  when 
  the 
  intensity 
  of 
  the 
  

   source 
  is 
  small, 
  according 
  to 
  Nichols 
  and 
  Merritt, 
  who 
  found 
  

   that 
  the 
  fluorescent 
  solution 
  apparently 
  absorbed 
  a 
  certain 
  

   definite 
  quantity 
  of 
  light 
  regardless 
  of 
  the 
  amount 
  of 
  light 
  

   sent 
  through 
  it, 
  a 
  circumstance 
  at 
  variance 
  with 
  all 
  the 
  

   known 
  laws 
  of 
  absorption. 
  By 
  the 
  addition 
  of 
  the 
  nicols 
  

   the 
  percentage 
  change 
  should 
  be 
  doubled, 
  yet 
  even 
  in 
  this 
  

   •case 
  no 
  effect 
  could 
  be 
  seen, 
  though 
  calculation 
  showed 
  that 
  

   with 
  the 
  intensities 
  used 
  a 
  change 
  of 
  at 
  least 
  20 
  per 
  cent. 
  

   was 
  to 
  be 
  expected. 
  

  

  It 
  was 
  next 
  determined 
  to 
  use 
  a 
  monochromatic 
  illuminator 
  

   •as 
  the 
  source 
  of 
  light, 
  and 
  work 
  with 
  the 
  wave-length 
  most 
  

   favourable 
  for 
  the 
  exhibition 
  of 
  the 
  phenomenon, 
  as 
  deter- 
  

   mined 
  by 
  Nichols 
  and 
  Merritt. 
  The 
  light 
  from 
  the 
  slit 
  of 
  

   the 
  instrument 
  after 
  passing 
  through 
  the 
  rotating 
  disk 
  was 
  

   focussed 
  on 
  the 
  eye 
  by 
  means 
  of 
  a 
  small 
  lens, 
  which 
  thus 
  

   appeared 
  filled 
  with 
  a 
  uniform 
  illumination. 
  Between 
  the 
  

   lens 
  and 
  the 
  eye 
  was 
  placed 
  the 
  fluorescent 
  tank, 
  illuminated 
  

   with 
  a 
  beam 
  from 
  the 
  arc, 
  coming 
  through 
  an 
  adjacent 
  

   aperture 
  in 
  the 
  disk. 
  The 
  monochromatic 
  illuminator 
  was 
  

   illuminated 
  with 
  a 
  Nernst 
  lamp, 
  and 
  the 
  arc 
  was 
  focussed 
  

   on 
  the 
  disk 
  by 
  means 
  of 
  the 
  movable 
  lens. 
  No 
  effect 
  was 
  

   observed 
  in 
  this 
  case. 
  

  

  It 
  is 
  necessary 
  of 
  course 
  in 
  using 
  this 
  method 
  to 
  make 
  

   sure 
  that 
  the 
  motion 
  of 
  the 
  lens 
  and 
  the 
  accompanying 
  shift 
  

   in 
  the 
  direction 
  of 
  the 
  transmitted 
  beam 
  causes 
  no 
  change 
  

   in 
  the 
  intensity 
  of 
  the 
  fluorescent 
  solution. 
  It 
  is 
  not 
  difficult 
  

   to 
  fulfil 
  this 
  condition 
  if 
  the 
  width 
  of 
  the 
  transmitted 
  beam 
  

   and 
  the 
  distance 
  of 
  the 
  tank 
  are 
  properly 
  attended 
  to. 
  

  

  As 
  a 
  last 
  resort, 
  the 
  method 
  was 
  still 
  further 
  improved 
  by 
  

   weakening 
  the 
  intensity 
  of 
  the 
  fluorescent 
  tank 
  by 
  prismatic 
  

   dispersion, 
  and 
  the 
  spectrophotometer 
  was 
  added 
  to 
  the 
  

   apparatus. 
  By 
  this 
  means 
  the 
  transmitted 
  light 
  which 
  we 
  

   observe 
  can 
  be 
  made 
  practically 
  monochromatic, 
  and 
  we 
  see 
  

   superposed 
  on 
  it 
  only 
  that 
  portion 
  of 
  the 
  fluorescent 
  light 
  in 
  

   the 
  same 
  part 
  of 
  the 
  spectrum. 
  This 
  method 
  is 
  therefore 
  

   superior 
  to 
  the 
  use 
  of 
  the 
  polarizing 
  prisms, 
  and 
  we 
  have 
  in 
  

   addition 
  a 
  comparison 
  field 
  of 
  exactly 
  the 
  same 
  colour, 
  with 
  

   a 
  vanishing 
  line 
  between 
  the 
  two 
  fields. 
  This 
  latter 
  modifi- 
  

   cation 
  is 
  by 
  far 
  the 
  best 
  of 
  all, 
  for 
  if 
  the 
  fields 
  are 
  matched 
  

   when 
  the 
  flashes 
  are 
  in 
  step, 
  the 
  line 
  of 
  demarcation 
  should 
  

   -appear 
  when 
  the 
  flashes 
  are 
  thrown 
  out 
  of 
  step. 
  The 
  

  

  