﻿418 
  Dr. 
  H. 
  E. 
  Ives 
  on 
  the 
  Resolution 
  of 
  Mixed 
  

  

  For 
  the 
  yellow 
  light 
  tests 
  the 
  apparatus 
  as 
  above 
  described 
  

   was 
  provided 
  with 
  red 
  and 
  green 
  glasses 
  of 
  narrow 
  spectral 
  

   transmissions 
  for 
  the 
  mixed 
  yellow, 
  and 
  a 
  monochromatic 
  

   illuminator 
  k 
  was 
  added, 
  illuminating 
  an 
  opal 
  glass 
  I, 
  which 
  

   could 
  be 
  viewed 
  through 
  an 
  opening 
  in 
  the 
  screen 
  e. 
  By 
  this 
  

   means 
  either 
  red 
  light 
  or 
  green 
  light 
  or 
  their 
  mixture, 
  or 
  a 
  

   monochromatic 
  yellow 
  matching 
  the 
  mixed 
  yellow 
  may 
  be 
  

   obtained, 
  disposed 
  in 
  any 
  desired 
  way 
  along 
  the 
  slit/. 
  

  

  The 
  slit 
  was 
  first 
  arranged 
  to 
  show 
  half 
  red 
  and 
  half 
  green, 
  

   and 
  the 
  intensities 
  adjusted 
  until 
  on 
  movement 
  or" 
  the 
  mirror 
  

   the 
  lag 
  of 
  green 
  behind 
  red 
  was 
  well 
  shown. 
  This 
  occurs 
  at 
  

   a 
  rather 
  low 
  intensity, 
  and 
  care 
  must 
  be 
  taken 
  to 
  have 
  ab- 
  

   solutely 
  no 
  stray 
  light 
  in 
  the 
  room. 
  (In 
  these 
  experiments 
  

   the 
  slit 
  /was 
  placed 
  over 
  a 
  hole 
  in 
  a 
  door 
  between 
  two 
  rooms, 
  

   so 
  that 
  an 
  assistant 
  could 
  make 
  the 
  necessary 
  manipulations, 
  

   without 
  any 
  stray 
  light 
  reaching 
  the 
  observer.) 
  When 
  this 
  

   condition 
  was 
  found 
  the 
  screens/ 
  were 
  placed 
  so 
  that 
  the 
  

   middle 
  of 
  the 
  slit 
  showed 
  the 
  compound 
  yellow. 
  This 
  com- 
  

   pound 
  yellow 
  was 
  clearly 
  resolved 
  by 
  lateral 
  motion 
  across 
  the 
  

   field 
  of 
  view. 
  In 
  fact, 
  the 
  resolution 
  was 
  even 
  more 
  satis- 
  

   factory 
  than 
  it 
  had 
  been 
  with 
  purple, 
  because 
  the 
  two 
  edges 
  

   of 
  the 
  centre 
  patch 
  were 
  seen 
  on 
  several 
  occasions 
  to 
  be 
  red 
  

   and 
  green. 
  This 
  greater 
  success 
  is 
  probably 
  due 
  to 
  the 
  very 
  

   distinct 
  difference 
  in 
  appearance 
  between 
  yellow 
  and 
  its 
  

   constituents. 
  

  

  The 
  next 
  point 
  taken 
  up 
  was 
  the 
  behaviour 
  of 
  the 
  pure 
  

   yellow, 
  adjusted 
  to 
  be 
  a 
  subjective 
  match 
  with 
  the 
  compound 
  

   yellow, 
  and 
  arranged 
  to 
  exactly 
  take 
  its 
  place 
  between 
  the 
  

   red 
  and 
  green. 
  It 
  was 
  at 
  once 
  apparent 
  that 
  pure 
  yellow 
  

   does 
  not 
  separate 
  into 
  red 
  and 
  green. 
  This 
  fact 
  is 
  strikingly 
  

   shown 
  by 
  arranging 
  the 
  slit 
  so 
  as 
  to 
  be 
  all 
  compound 
  yellow, 
  

   except 
  a 
  small 
  portion 
  of 
  pure 
  yellow. 
  When 
  stationary 
  the 
  slit 
  

   appears 
  alike 
  thoughout 
  its 
  whole 
  length 
  in 
  brightness, 
  hue, 
  and 
  

   definition. 
  But 
  upon 
  moving 
  the 
  image 
  sideways, 
  or 
  oscil- 
  

   lating 
  it, 
  the 
  compound 
  yellow 
  immediately 
  broadens 
  out 
  and 
  

   becomes 
  ill-defined, 
  the 
  pure 
  yellow 
  remaining 
  narrow 
  and 
  

   sharp. 
  The 
  appearance 
  is 
  identical 
  with 
  that 
  produced 
  by 
  a 
  

   weak 
  prism, 
  and 
  again 
  demonstrates 
  that 
  this 
  phenomenon 
  

   provides 
  a 
  new, 
  if 
  rough, 
  method 
  of 
  spectrum 
  analysis. 
  

  

  5. 
  Discussion. 
  

  

  The 
  results 
  obtained 
  with 
  purple 
  light 
  are 
  of 
  chief 
  interest 
  

   as 
  justifying 
  the 
  assumption 
  made 
  in 
  the 
  flicker-photometer 
  

   theory, 
  that 
  each 
  colour 
  is 
  transmitted 
  with 
  its 
  own 
  cha- 
  

   racteristic 
  speed, 
  irrespective 
  of 
  whether 
  it 
  occurs 
  alone 
  or 
  

  

  