﻿198 
  0. 
  N, 
  Rood— 
  Flicker 
  Photometer. 
  

  

  relative 
  intensity 
  of 
  the 
  two 
  lamps, 
  since 
  such 
  variation 
  would 
  

   at 
  least 
  not 
  have 
  tended 
  to 
  increase 
  the 
  accuracy 
  of 
  the 
  results. 
  

   In 
  order 
  to 
  exhibit 
  the 
  working 
  of 
  the 
  instrument 
  in 
  the 
  

   hands 
  of 
  other 
  persons, 
  I 
  give 
  below 
  results 
  obtained 
  by 
  six 
  

   good 
  observers, 
  with 
  each 
  of 
  whom 
  I 
  compared 
  my 
  own 
  color- 
  

   vision 
  ; 
  they 
  contain 
  an 
  element 
  which 
  furnishes 
  a 
  rather 
  

   severe 
  test 
  of 
  the 
  correctness 
  of 
  the 
  whole 
  procedure 
  that 
  is 
  

   entirely 
  wanting 
  in 
  the 
  tables 
  above 
  given. 
  Each 
  of 
  the 
  six 
  

   persons 
  was 
  successively, 
  for 
  the 
  time 
  being, 
  assumed 
  to 
  have 
  

   standard 
  color 
  vision, 
  viz 
  : 
  their 
  perception 
  of 
  red, 
  green 
  and 
  

   blue 
  was 
  taken 
  as 
  100 
  in 
  each 
  case, 
  and 
  I 
  determined 
  my 
  varia- 
  

   tions 
  from 
  it, 
  both 
  of 
  us 
  using 
  the 
  pairs, 
  red-blue, 
  red-green, 
  

   and 
  blue-green. 
  In 
  this 
  mode 
  of 
  procedure 
  it 
  was 
  possible 
  to 
  

   obtain 
  two 
  values 
  for 
  my 
  perception 
  of 
  green 
  as 
  compared 
  with 
  

   theirs, 
  a 
  direct 
  one 
  founded 
  on 
  our 
  joint 
  experiment 
  on 
  the 
  

   pair 
  red-green, 
  and 
  an 
  indirect 
  one 
  derived 
  from 
  our 
  joint 
  

   observations 
  on 
  the 
  pair 
  green-blue, 
  my 
  value 
  for 
  blue 
  having 
  

   first 
  been 
  obtained 
  by 
  a 
  third 
  joint 
  experiment 
  on 
  the 
  pair 
  red- 
  

   blue. 
  If 
  all 
  the 
  readings 
  obtained 
  by 
  the 
  person 
  used 
  as 
  a 
  

   standard 
  and 
  by 
  the 
  one 
  undergoing 
  examination 
  are 
  correct, 
  then 
  

   the 
  direct 
  and 
  the 
  indirect 
  value 
  for 
  the 
  green 
  should 
  coincide. 
  

   Attention 
  is 
  again 
  called 
  to 
  the 
  fact 
  that 
  tlie 
  indirect 
  value 
  is 
  

   obtained 
  by 
  the 
  use 
  of 
  an 
  intermediate 
  color. 
  Below 
  is 
  a 
  table 
  

   showing 
  the 
  variations 
  in 
  percentages 
  between 
  these 
  direct 
  and 
  

   indirect 
  values 
  of 
  the 
  green. 
  

  

  Dr. 
  Dennett 
  

  

  -0-32 
  

  

  Mr. 
  Parker 
  

  

  -fl-77 
  

  

  Miss 
  Furness 
  

  

  -1-04 
  

  

  Dr. 
  Tufts 
  

  

  + 
  3-l'7 
  

  

  Dr. 
  Hallock 
  

  

  -t-0-41 
  

  

  Mr. 
  Wade 
  

  

  — 
  0-69 
  

  

  The 
  general 
  conclusion 
  to 
  be 
  drawn 
  from 
  the 
  numerical 
  

   results 
  given 
  in 
  this 
  paper 
  would 
  seem 
  to 
  be, 
  that 
  the 
  accuracy 
  

   attainable 
  with 
  the 
  flicker 
  photometer, 
  as 
  at 
  present 
  constructed 
  

   and 
  using 
  light 
  of 
  difi:erent 
  colors 
  almost 
  spectral 
  in 
  hue, 
  is 
  

   about 
  the 
  same 
  as 
  with 
  ordinary 
  photometers 
  using 
  plain 
  white 
  

   light, 
  or 
  light 
  of 
  exactly 
  the 
  same 
  color. 
  

   New 
  York, 
  May 
  8th, 
  1899. 
  

  

  