﻿420 
  Dr. 
  H. 
  E. 
  Ives 
  on 
  the 
  Resolution 
  of 
  Mixed 
  

  

  presented 
  to 
  it 
  or 
  any 
  " 
  wave-length 
  " 
  theory 
  by 
  the 
  facts 
  o£ 
  

   colour 
  mixture 
  and 
  colour 
  blindness 
  are 
  very 
  great. 
  In 
  

   particular, 
  the 
  production 
  of 
  white 
  by 
  various 
  pairs 
  of 
  com- 
  

   plementaries 
  of 
  different 
  centres 
  of 
  gravity, 
  and 
  the 
  neutral 
  

   points 
  in 
  the 
  spectra 
  of 
  the 
  two 
  types 
  of 
  red-green 
  blind, 
  

   present 
  serious 
  difficulty 
  of 
  interpretation. 
  

  

  A 
  great 
  deal 
  of 
  evidence 
  points 
  to 
  the 
  pro 
  liability 
  of 
  

   vision 
  being 
  a 
  process 
  of 
  photochemical 
  decomposition, 
  in 
  

   which 
  either 
  the 
  decomposition 
  products 
  or 
  electric 
  currents 
  

   set 
  up 
  by 
  the 
  process 
  pass 
  along 
  the 
  nerve 
  tracks 
  at 
  the 
  

   speeds 
  characteristic 
  of 
  nerve 
  impulses. 
  Apart 
  from 
  the 
  

   facts 
  of 
  colour 
  mixture 
  and 
  colour 
  blindness 
  there 
  is 
  no 
  

   reason 
  why 
  the 
  number 
  of 
  separate 
  decomposable 
  retinal 
  

   substances 
  should 
  not 
  be 
  very 
  large. 
  There 
  is 
  nothing 
  in 
  

   the 
  present 
  experimental 
  work 
  to 
  indicate 
  that 
  the 
  number 
  

   is 
  restricted 
  to 
  the 
  red, 
  yellow, 
  green, 
  and 
  blue 
  experimented 
  

   with, 
  although 
  the 
  method 
  is 
  so 
  crude 
  as 
  a 
  means 
  of 
  spectrum 
  

   analysis 
  that 
  it 
  would 
  be 
  difficult 
  to 
  show 
  conclusively 
  that 
  

   a 
  much 
  greater 
  number 
  of 
  speeds 
  of 
  transmission 
  than 
  four 
  

   are 
  exhibited 
  in 
  the 
  length 
  of 
  the 
  visible 
  spectrum. 
  As 
  the 
  

   method 
  stands, 
  it 
  is 
  inferior 
  as 
  a 
  means 
  of 
  colour 
  analysis 
  to 
  

   the 
  single 
  prism 
  and 
  wide 
  slit 
  first 
  employed 
  to 
  exhibit 
  the 
  

   spectrum. 
  For 
  an 
  answer 
  to 
  the 
  question 
  of 
  how 
  man}' 
  

   reacting 
  substances 
  of 
  different 
  velocities 
  of 
  transmission 
  

   exist, 
  the 
  resolving 
  power 
  should 
  be 
  more 
  nearly 
  that 
  re- 
  

   quired 
  to 
  show 
  the 
  Fi 
  aunhofer 
  lines. 
  What 
  is 
  required 
  to 
  

   effect 
  an 
  improvement 
  comparable 
  with 
  the 
  instrumental 
  

   advance 
  quoted 
  is 
  some 
  drug 
  which 
  will 
  slow 
  down 
  the 
  rate 
  

   of 
  transmission 
  of 
  the 
  visual 
  impressions, 
  or 
  the 
  " 
  time 
  

   machine" 
  of 
  Mr. 
  H. 
  G. 
  Wells. 
  

  

  Actually 
  the 
  mixture 
  phenomena 
  point 
  to 
  the 
  existence 
  of 
  

   three, 
  and 
  only 
  three, 
  such 
  reacting 
  substances 
  — 
  a 
  red, 
  a 
  

   green, 
  and 
  a 
  blue. 
  The 
  question 
  of 
  paramount. 
  interest 
  then 
  

   is, 
  how 
  can 
  the 
  different 
  behaviour 
  of 
  the 
  spectrally 
  pure 
  

   yellow 
  and 
  its 
  subjectively 
  equivalent 
  mixed 
  yellow 
  be 
  

   harmonized 
  with 
  three-colour 
  theory 
  ? 
  It 
  is 
  evident 
  that 
  

   the 
  " 
  three 
  different 
  types 
  of 
  nerve 
  fibre 
  " 
  postulated 
  by 
  

   Young, 
  or 
  the 
  " 
  three 
  different, 
  independent, 
  and 
  mutually 
  

   unopposed 
  elementary 
  activities 
  u 
  in 
  the 
  statement 
  of 
  the 
  

   theory 
  by 
  Helmholtz, 
  must 
  be 
  located 
  (if 
  existent) 
  at 
  some 
  

   distance 
  along 
  the 
  conducting 
  path 
  between 
  receiving 
  surface 
  

   and 
  brain. 
  By 
  this 
  new 
  method 
  of 
  analysis 
  we 
  can 
  actually 
  

   see 
  red 
  and 
  green 
  being 
  transmitted 
  a 
  certain 
  distance 
  at 
  

   different 
  speeds* 
  before 
  combining 
  to 
  make 
  yellow, 
  and 
  we 
  

  

  * 
  Or 
  possibly 
  with 
  the 
  same 
  speed 
  for 
  different 
  distances. 
  In 
  this 
  

   connexion 
  see 
  Koenig-, 
  "Ueber 
  die 
  lichtempfindliehe 
  Schicht 
  in 
  der 
  

   Netzhaut 
  des 
  menschlichen 
  Anges," 
  Ges. 
  Abh. 
  p. 
  333. 
  

  

  