﻿I" 
  413 
  

  

  XL 
  VIII. 
  The 
  Resolution 
  of 
  Mixed 
  Colours 
  by 
  Differential 
  

   Visual 
  iJirj'usivitf/. 
  By 
  Herbert 
  E. 
  Iyes^ 
  Ph.D., 
  Captain, 
  

   Sig.R.C, 
  U.S.A.* 
  

  

  1. 
  Introduction. 
  

  

  2. 
  Experimental 
  procedure. 
  

  

  3. 
  Results 
  with 
  purple 
  light. 
  

  

  4. 
  Results 
  with 
  monochromatic 
  and 
  compound 
  yello 
  v. 
  

  

  5. 
  Discussion. 
  

  

  1. 
  Introduction. 
  

  

  UNDER 
  the 
  title 
  4i 
  Visual 
  Diffusivity/' 
  the 
  writer 
  de- 
  

   scribed 
  some 
  time 
  ago 
  f 
  experiments 
  on 
  the 
  lagging 
  

   of 
  different 
  colour 
  impressions 
  relatively 
  to 
  each 
  other. 
  These 
  

   were 
  predicted 
  on 
  the 
  basis 
  of 
  a 
  theory 
  developed 
  to 
  explain 
  

   the 
  behaviour 
  of 
  the 
  flicker 
  photometer 
  t. 
  An 
  essential 
  part 
  

   of 
  this 
  theory 
  was 
  the 
  ascription 
  to 
  each 
  colour 
  impression 
  

   of 
  a 
  characteristic 
  rate 
  of 
  transmission 
  along 
  the 
  visual 
  

   ehannel. 
  In 
  developing 
  the 
  theory 
  it 
  was 
  assumed 
  that 
  each 
  

   colour 
  acted 
  quite 
  independently. 
  

  

  In 
  two 
  instances 
  it 
  appeared 
  necessary 
  to 
  modify 
  this 
  last 
  

   assumption. 
  One 
  was 
  the 
  case 
  of 
  alternated 
  colours 
  exposed 
  

   for 
  unequal 
  lengths 
  of 
  time. 
  Here 
  the 
  flicker-photometer 
  

   theory 
  apparently 
  called 
  for 
  much 
  greater 
  effects 
  of 
  dis- 
  

   symmetry 
  than 
  experiment 
  showed. 
  The 
  other 
  was 
  the 
  

   failure 
  of 
  an 
  attempt 
  to 
  resolve 
  a 
  purple 
  into 
  its 
  constituents 
  

   by 
  moving 
  it 
  across 
  the 
  field 
  of 
  view. 
  It 
  was 
  concluded 
  in 
  

   the 
  light 
  of 
  these 
  experiments 
  that 
  some 
  mutual 
  action 
  of 
  

   colours 
  in 
  the 
  act 
  of 
  transmission 
  must 
  take 
  place. 
  

  

  Later 
  work 
  on 
  the 
  flicker-photometer 
  theory 
  showed 
  that 
  

   when 
  the 
  complete 
  equations 
  were 
  employed, 
  dispensing 
  with 
  

   the 
  earlier 
  assumption 
  that 
  the 
  effect 
  of 
  varying 
  speed 
  could 
  

   be 
  neglected, 
  the 
  case 
  of 
  unequal 
  exposures 
  did 
  not 
  require 
  

   the 
  assumption 
  that 
  the 
  individual 
  colours 
  affect 
  each 
  other 
  

   in 
  transmission. 
  There 
  remained 
  then 
  to 
  be 
  explained 
  the 
  

   failure 
  to 
  resolve 
  purple 
  in 
  the 
  manner 
  described. 
  In 
  view 
  

   of 
  the 
  very 
  satisfactory 
  quantitative 
  success 
  of 
  the 
  flicker- 
  

   photometer 
  theory 
  as 
  demonstrated 
  by 
  the 
  more 
  recent 
  work 
  

   with 
  the 
  polarization 
  design, 
  it 
  appeared 
  highly 
  desirable 
  to 
  

  

  * 
  Communicated 
  by 
  the 
  Author. 
  

  

  t 
  " 
  Visual 
  Diffusivity," 
  Ives, 
  Phil. 
  Mag. 
  Jan. 
  1917, 
  p. 
  18. 
  

  

  X 
  ''Theory 
  of 
  the 
  Flicker 
  Photometer," 
  Ives 
  and 
  Kingsburv, 
  Phil. 
  

   Mag. 
  Nov. 
  1914, 
  p. 
  708, 
  and 
  April 
  1916, 
  p. 
  290. 
  "A 
  Polarization 
  Flicker 
  

   Photometer 
  and 
  some 
  Data 
  of 
  Theoretical 
  Bearing 
  obtained 
  with 
  it," 
  

   Ives, 
  Phil. 
  Mag. 
  April 
  1 
  917, 
  p. 
  360. 
  " 
  Hue 
  Difference 
  and 
  Flicker 
  Photo- 
  

   meter 
  Speed," 
  Ives, 
  Phil. 
  Mag. 
  August 
  1917, 
  p. 
  99. 
  

  

  