﻿The 
  Flicker 
  Photometer 
  and 
  the 
  Iris. 
  

  

  181 
  

  

  must 
  be 
  atropinized 
  in 
  order 
  to 
  secure 
  a 
  condition 
  which 
  

   satisfies 
  the 
  logical 
  requirements 
  of 
  the 
  test. 
  

  

  The 
  arrangements 
  for 
  producing 
  flicker 
  are 
  shown 
  in 
  

   figure 
  1. 
  The 
  sources 
  of 
  light 
  were 
  two 
  10 
  candle-power 
  

  

  Fig.1. 
  

  

  Od 
  

  

  The 
  Apparatus 
  for 
  producing 
  Flicker. 
  

  

  a 
  and 
  d 
  are 
  1G 
  c.-p. 
  lamps 
  on 
  a 
  110 
  D. 
  C. 
  circuit. 
  

  

  b 
  is 
  dark 
  blue 
  coloured 
  surface. 
  

  

  c 
  is 
  au 
  orange 
  coloured 
  surface. 
  

  

  e 
  is 
  the 
  card-board 
  disk 
  shown 
  in 
  g. 
  

  

  /is 
  the 
  tube 
  through 
  which 
  the 
  observations 
  were 
  made. 
  

  

  lamps, 
  which 
  are 
  shown 
  at 
  a 
  and 
  d 
  in 
  the 
  figure. 
  The 
  

   constancy 
  of 
  illumination 
  of 
  the 
  lamps 
  was 
  controlled 
  by 
  a 
  

   voltmeter 
  in 
  circuit 
  with 
  the 
  lamps. 
  The 
  light 
  from 
  

   the 
  lamps 
  was 
  reflected 
  from 
  the 
  two 
  oblique 
  surfaces 
  

   h 
  and 
  c. 
  Surface 
  h 
  was 
  coloured 
  blue 
  and 
  surface 
  c 
  

   an 
  orange. 
  The 
  sectored 
  disk 
  g 
  was 
  placed 
  at 
  e, 
  where 
  

   by 
  its 
  rotation 
  it 
  intercepted 
  the 
  light 
  of 
  the 
  lamps 
  

   which 
  was 
  reflected 
  from 
  surfaces 
  b 
  and 
  c. 
  The 
  eye 
  of 
  the 
  

   observer 
  was 
  placed 
  at 
  the 
  end 
  of 
  the 
  tube/, 
  through 
  which 
  

   two 
  flickering 
  coloured 
  surfaces, 
  which 
  divided 
  the 
  field 
  of 
  

   vision 
  equally, 
  appeared. 
  Although 
  the 
  arrangement 
  chosen 
  

   for 
  this 
  experiment 
  differed 
  somewhat 
  from 
  those 
  used 
  in 
  

   colour-photometry 
  in 
  that 
  two 
  flickering 
  surfaces 
  are 
  shown 
  

   in 
  the 
  field 
  of 
  vision, 
  the 
  arrangement 
  was 
  found 
  very 
  

   suitable 
  for 
  our 
  experiment. 
  By 
  varying 
  the 
  speed 
  of 
  the 
  

   motor, 
  a 
  series 
  of 
  flickers 
  were 
  produced 
  which 
  were 
  arranged 
  

   subjectively 
  in 
  a 
  series 
  from 
  very 
  coarse 
  to 
  fine, 
  with 
  the 
  

   following 
  designations 
  : 
  very 
  coarse 
  ; 
  coarse 
  ; 
  medium 
  : 
  fine; 
  

   and 
  just 
  visible. 
  These 
  designations 
  proved 
  to 
  be 
  very 
  

   useful, 
  since 
  it 
  was 
  possible 
  by 
  means 
  of 
  them 
  to 
  compare 
  

   the 
  -peed 
  of 
  rotation 
  which 
  caused 
  a 
  just 
  noticeable 
  flicker 
  

  

  