﻿Colours 
  by 
  Differential 
  Visual 
  Diffusivity. 
  417 
  

  

  It 
  appears 
  from 
  this 
  that 
  we 
  have 
  here 
  a 
  new 
  method 
  of 
  

   colour 
  analysis, 
  dependent 
  on 
  the 
  properties 
  of 
  the 
  eye 
  and 
  

   not 
  on 
  those 
  o£ 
  an 
  inanimate 
  physical 
  instrument. 
  It 
  is 
  of 
  

   interest 
  to 
  apply 
  this 
  new 
  method 
  to 
  other 
  mixed 
  colours 
  — 
  in 
  

   particular 
  to 
  yellow. 
  

  

  4. 
  Results 
  with 
  monochromatic 
  and 
  compound 
  yelloiv. 
  

  

  Yellow 
  is 
  of 
  peculiar 
  interest 
  in 
  the 
  study 
  of 
  colour 
  vision 
  

   because 
  the 
  same 
  sensation 
  may 
  be 
  produced 
  in 
  two 
  different 
  

   ways. 
  One 
  is 
  by 
  the 
  pure 
  yellow 
  of 
  the 
  spectrum, 
  the 
  other 
  

   is 
  by 
  the 
  mixture 
  of 
  red 
  and 
  green 
  light. 
  Unlike 
  the 
  blue- 
  

   green 
  of 
  the 
  spectrum, 
  which 
  may 
  be 
  matched 
  similarly 
  by 
  a 
  

   mixture 
  of 
  the 
  colours 
  to 
  either 
  side, 
  yellow 
  gives 
  a 
  sensation 
  

   totally 
  distinct 
  in 
  character 
  from 
  its 
  components. 
  So 
  defi- 
  

   nitely 
  is 
  this 
  so 
  that 
  the 
  psychological 
  elementary 
  colours, 
  

   not 
  recognizable 
  as 
  mixtures, 
  are 
  red, 
  yellow 
  , 
  green, 
  and 
  blue. 
  

   MacDougall, 
  Schenck, 
  and 
  others 
  consider 
  it 
  probable 
  that 
  

   the 
  red 
  and 
  green 
  sensations 
  have 
  been 
  developed 
  from 
  a 
  

   more 
  primitive 
  yellow 
  sensation, 
  the 
  latter 
  one 
  of 
  the 
  two 
  

   sensations 
  (warm 
  and 
  cold), 
  into 
  which 
  primitive 
  mono- 
  

   chromatic 
  vision 
  first 
  separated. 
  

  

  Trial 
  by 
  this 
  new 
  method 
  (provided 
  it 
  proved 
  sensitive 
  

   enough 
  to 
  give 
  definite 
  results) 
  offered 
  the 
  possibility 
  of 
  

   answering 
  the 
  following 
  questions, 
  suggested 
  by 
  the 
  nature 
  

   of 
  yellow 
  light, 
  as 
  just 
  discussed 
  : 
  — 
  

  

  (1) 
  Does 
  a 
  mixed 
  yellow 
  become 
  resolved 
  into 
  its 
  con- 
  

   stituent 
  red 
  and 
  green 
  ? 
  

  

  (2) 
  Does 
  a 
  pure 
  yellow 
  become 
  resolved 
  into 
  a 
  red 
  and 
  a 
  

   green 
  ? 
  

  

  If 
  the 
  answer 
  to 
  both 
  these 
  questions 
  is 
  affirmative, 
  it 
  

   might 
  be 
  interpreted 
  as 
  meaning 
  that 
  the 
  action 
  of 
  both 
  

   kinds 
  of 
  yellow 
  light 
  is 
  to 
  break 
  down 
  two 
  substances, 
  red 
  

   and 
  green, 
  at 
  the 
  surface 
  of 
  incidence, 
  which 
  then 
  travel 
  back 
  

   at 
  different 
  speeds 
  to 
  a 
  point 
  where 
  the 
  double 
  product 
  either 
  

   combines 
  into 
  a 
  yellow 
  substance 
  or 
  is 
  interpreted 
  as 
  yellow. 
  

  

  If 
  the 
  answer 
  to 
  both 
  these 
  questions 
  is 
  negative, 
  it 
  might 
  

   be 
  interpreted 
  as 
  meaning 
  that 
  either 
  kind 
  of 
  yellow 
  light 
  

   breaks 
  down 
  a 
  yellow 
  substance, 
  which 
  travels 
  back 
  with 
  its 
  

   own 
  individual 
  velocity, 
  i. 
  e., 
  that 
  colour 
  fusion 
  takes 
  place 
  

   at 
  the 
  surface 
  of 
  incidence. 
  A 
  third 
  possible 
  answer 
  — 
  namely, 
  

   that 
  the 
  mixed 
  colour 
  is 
  resolved 
  and 
  the 
  pure 
  is 
  not 
  — 
  might 
  

   be 
  interpreted 
  to 
  mean 
  that 
  distinct 
  red, 
  yellow, 
  and 
  green 
  

   substances 
  are 
  broken 
  down 
  by 
  the 
  light, 
  travel 
  back 
  with 
  

   their 
  appropriate 
  velocities, 
  and 
  that 
  red 
  and 
  green 
  fusion 
  

   occurs 
  after 
  this 
  transmission. 
  The 
  answer 
  to 
  these 
  questions 
  

   can 
  be 
  obtained 
  only 
  by 
  experiment. 
  

  

  