﻿414 
  Dr. 
  H. 
  E. 
  Ives 
  on 
  the 
  Resolution 
  of 
  Mixed 
  

  

  go 
  more 
  fully 
  into 
  the 
  question 
  of 
  visual 
  diffusivity 
  with 
  

   mixed 
  colours. 
  The 
  outcome 
  of 
  this 
  further 
  study 
  has 
  been 
  

   to 
  establish 
  the 
  experimental 
  conditions 
  pre-requisite 
  to 
  the 
  

   detection 
  of 
  the 
  resolution 
  of 
  mixed 
  colours 
  by 
  the 
  different 
  

   visual 
  diffusivity 
  of 
  the 
  components. 
  With 
  the 
  proper 
  con- 
  

   ditions, 
  not 
  only 
  has 
  it 
  been 
  possible 
  to 
  resolve 
  purple 
  into 
  

   red 
  and 
  blue, 
  but 
  observations 
  have 
  been 
  made 
  on 
  both 
  

   monochromatic 
  and 
  compound 
  yellows, 
  with 
  results 
  of 
  

   interest 
  in 
  colour-vision 
  theory. 
  

  

  2. 
  Experimental 
  procedure. 
  

  

  In 
  making 
  the 
  experiments 
  recorded 
  in 
  the 
  paper 
  on 
  

   " 
  Visual 
  Diffusivity," 
  full 
  use 
  was 
  made 
  of 
  the 
  fact 
  that 
  the 
  

   eye 
  is 
  very 
  sensitive 
  to 
  a 
  break 
  in 
  the 
  continuity 
  of 
  a 
  straight 
  

   line. 
  The 
  two 
  coloured 
  strips 
  under 
  observation 
  were 
  set 
  

   slightly 
  out 
  of 
  line, 
  and 
  then 
  passed 
  before 
  the 
  eye 
  at 
  a 
  speed 
  

   such 
  that 
  they 
  appeared 
  to 
  form 
  a 
  continuous 
  instead 
  of 
  a 
  

   broken 
  line. 
  In 
  attempting 
  to 
  resolve 
  a 
  purple 
  into 
  red 
  and 
  

   blue 
  this 
  peculiarity 
  of 
  the 
  eye 
  was 
  not 
  taken 
  advantage 
  of.. 
  

   A 
  purple 
  strip 
  was 
  moved 
  across 
  the 
  visual 
  field 
  and 
  evidences 
  

   of 
  widening 
  or 
  duplication 
  were 
  looked 
  for. 
  To 
  this 
  the 
  eve 
  

   is 
  much 
  less 
  sensitive. 
  

  

  On 
  reconsidering 
  the 
  problem 
  recently 
  it 
  was 
  realized 
  that 
  

   the 
  criterion 
  of 
  linear 
  continuity 
  should, 
  if 
  possible, 
  be 
  used 
  

   to 
  judge 
  of 
  a 
  resolution 
  of 
  the 
  kind 
  expected. 
  The 
  arrange- 
  

   ment 
  of 
  coloured 
  areas 
  finally 
  decided 
  upon 
  was 
  that 
  of 
  a 
  

   continuous 
  slit 
  — 
  red 
  at 
  one 
  end, 
  blue 
  at 
  the 
  other, 
  with 
  purple 
  

   in 
  the 
  middle, 
  the 
  purple 
  being 
  the 
  mixture 
  of 
  the 
  two 
  end 
  

   colours. 
  This 
  arrangement 
  is 
  shown 
  in 
  fig. 
  1 
  a. 
  When 
  this 
  

   strip 
  was 
  moved 
  across 
  the 
  field 
  it 
  was 
  hoped 
  that 
  not 
  only 
  

   would 
  the 
  red 
  and 
  blue 
  be 
  displaced, 
  in 
  agreement 
  with 
  the 
  

   previous 
  experiments, 
  but 
  that 
  it 
  would 
  be 
  evident 
  that 
  the 
  

   displacements 
  overlapped, 
  in 
  the 
  manner 
  shown 
  in 
  fig. 
  1 
  b.. 
  

   That 
  is, 
  instead 
  of 
  looking 
  for 
  the 
  duplicity 
  of 
  the 
  portion 
  p, 
  

   which 
  could 
  not 
  be 
  detected 
  previously, 
  attention 
  would 
  be 
  

   directed 
  to 
  a 
  possible 
  widening 
  which 
  would 
  continue 
  the 
  

   straight 
  line 
  of 
  both 
  parts, 
  r 
  and 
  b. 
  

  

  The 
  production 
  of 
  such 
  an 
  overlapping 
  red 
  and 
  blue 
  

   strip,, 
  which 
  could 
  be 
  placed 
  in 
  the 
  disk 
  apparatus 
  formerly 
  

   used, 
  was 
  first 
  attempted 
  by 
  photographs 
  on 
  an 
  autochrome 
  

   plate, 
  but 
  the 
  purity 
  of 
  the 
  resultant 
  colours 
  was 
  not 
  satis- 
  

   factory. 
  The 
  final 
  apparatus 
  used 
  was 
  a 
  simple 
  colour- 
  

   projection 
  scheme, 
  the 
  requisite 
  motion 
  of 
  the 
  colour 
  patches 
  

   being 
  provided 
  for 
  by 
  the 
  movement 
  of 
  a 
  mirror 
  before 
  the 
  

   eye. 
  A 
  plan 
  of 
  it 
  is 
  shown 
  in 
  fig. 
  2, 
  where 
  a 
  is 
  a 
  box 
  con- 
  

   taining 
  two 
  point-source 
  tungsten 
  lamps, 
  controlled 
  by 
  separate- 
  

  

  