﻿Fluorescent 
  Absorption 
  directly 
  if 
  it 
  exists. 
  941 
  

  

  The 
  importance 
  o£ 
  the 
  phenomenon, 
  if 
  it 
  exists, 
  makes 
  a 
  

   method 
  of 
  showing 
  it 
  directly 
  much 
  to 
  be 
  desired. 
  The 
  

   strangeness 
  of 
  the 
  apparent 
  laws 
  o£ 
  this 
  new 
  type 
  o£ 
  absorp- 
  

   tion 
  makes 
  one 
  suspicious 
  that 
  some 
  unforeseen 
  error 
  has 
  

   crept 
  in, 
  which 
  may 
  account 
  for 
  the 
  whole 
  thing. 
  The 
  in- 
  

   tensities 
  are 
  measured 
  by 
  varying 
  the 
  width 
  of 
  the 
  slit 
  of 
  the 
  

   spectrophotometer 
  which 
  delivers 
  light 
  to 
  the 
  comparison 
  

   field, 
  and 
  no 
  mention 
  is 
  made 
  whether 
  the 
  slit 
  was 
  calibrated 
  

   or 
  not. 
  It 
  is 
  possible 
  that 
  a 
  wide 
  slit 
  was 
  used 
  in 
  all 
  cases, 
  

   and 
  that 
  calibration 
  was 
  unnecessary. 
  I 
  have 
  recently 
  de- 
  

   vised 
  two 
  methods, 
  one 
  for 
  showing 
  the 
  phenomenon 
  directly 
  

   if 
  it 
  exists, 
  and 
  the 
  other 
  for 
  detecting 
  the 
  error 
  in 
  the 
  

   spectrophotometric 
  method, 
  should 
  it 
  be 
  present. 
  

  

  The 
  latter 
  is 
  very 
  simple, 
  and 
  though 
  I 
  have 
  not 
  tried 
  it, 
  I 
  

   recommend 
  it 
  in 
  any 
  subsequent 
  work 
  which 
  may 
  be 
  done 
  

   with 
  the 
  spectrophotometer 
  upon 
  the 
  subject. 
  

  

  Substitute 
  for 
  the 
  fluorescent 
  tank 
  a 
  piece 
  of 
  thin 
  plate 
  

   glass 
  at 
  an 
  angle 
  of 
  45° 
  to 
  the 
  axis 
  of 
  the 
  collimator, 
  which 
  

   reflects 
  light 
  from 
  an 
  illuminated 
  screen 
  into 
  the 
  instrument. 
  

   Measure 
  the 
  intensities 
  as 
  in 
  the 
  case 
  of 
  the 
  fluorescent 
  

   solution, 
  first 
  the 
  light 
  from 
  the 
  transparent 
  reflector, 
  then 
  

   the 
  light 
  from 
  the 
  source 
  behind 
  the 
  reflector, 
  the 
  latter 
  un- 
  

   illuminated, 
  and 
  then 
  both 
  together 
  ; 
  first 
  adjusting 
  the 
  

   relative 
  intensities 
  so 
  that 
  they 
  are 
  about 
  the 
  same 
  as 
  in 
  the 
  

   actual 
  experiment. 
  If 
  the 
  method 
  is 
  at 
  fault 
  the 
  sum 
  of 
  the 
  

   intensities 
  will 
  differ 
  from 
  the 
  total. 
  It 
  is 
  possible 
  that 
  some 
  

   physiological 
  effect 
  comes 
  in, 
  and 
  I 
  have 
  not 
  had 
  enough 
  

   experience 
  with 
  photometric 
  work 
  to 
  know 
  whether, 
  in 
  all 
  

   cases, 
  the 
  sum 
  of 
  the 
  intensities 
  of 
  two 
  sources 
  of 
  lights 
  

   measured 
  separately, 
  is 
  numerically 
  equal 
  to 
  the 
  total 
  intensity 
  

   of 
  the 
  two 
  measured 
  simultaneously. 
  The 
  method 
  which 
  I 
  

   have 
  outlined 
  above 
  should 
  answer 
  the 
  question 
  however. 
  

  

  The 
  method 
  for 
  showing 
  the 
  phenomenon 
  directly, 
  inde- 
  

   pendent 
  of 
  any 
  measurements, 
  I 
  have 
  given 
  a 
  thorough 
  trial, 
  

   and 
  can 
  see 
  no 
  objections 
  to 
  it. 
  In 
  brief, 
  I 
  make 
  the 
  illumi- 
  

   nations 
  rapidly 
  intermittent 
  with 
  a 
  rotating 
  perforated 
  disk, 
  

   and 
  bring 
  them 
  into 
  step 
  and 
  out 
  of 
  step 
  in 
  alternation. 
  

   When 
  they 
  are 
  in 
  step 
  the 
  tank 
  is 
  fluorescing 
  while 
  it 
  

   transmits 
  the 
  light 
  from 
  the 
  source 
  behind 
  it. 
  When 
  out 
  

   of 
  step 
  the 
  tank 
  is 
  in 
  darkness 
  while 
  passing 
  the 
  light 
  from 
  

   behind. 
  If 
  fluorescent 
  absorption 
  is 
  present 
  the 
  total 
  illu- 
  

   mination 
  should 
  be 
  greater 
  when 
  the 
  flashes 
  come 
  out 
  of 
  step, 
  

   for 
  in 
  this 
  case 
  there 
  is 
  no 
  fluorescence 
  during 
  transmission. 
  

  

  I 
  have 
  tried 
  the 
  method 
  under 
  various 
  conditions, 
  and 
  

   in 
  no 
  case 
  have 
  I 
  found 
  any 
  evidence 
  of 
  the 
  effect. 
  It 
  is 
  

  

  