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  PROCEEDINGS 
  OF 
  THE 
  FOURTH 
  ENTOMOLOGICAL 
  MEETliSTG 
  

  

  A 
  noticeable 
  point 
  is 
  the 
  individual 
  difference 
  between 
  the 
  two 
  flies 
  ; 
  

   it 
  is 
  possible 
  that 
  they 
  were 
  of 
  different 
  sexes, 
  but 
  the 
  sex 
  was 
  unfor- 
  

   tunately 
  not 
  noted 
  in 
  either 
  case. 
  The 
  general 
  range 
  of 
  vision 
  of 
  Fly 
  

   A 
  seems 
  to 
  be 
  not 
  more 
  than 
  about 
  frds 
  of 
  that 
  of 
  Fly 
  B. 
  

  

  The 
  fact 
  that 
  the 
  brownish-fawn 
  (" 
  puttoo 
  ") 
  hat 
  had 
  to 
  be 
  moved 
  

   6-10 
  inches, 
  while 
  a 
  piece 
  of 
  white 
  paper 
  j^th 
  its 
  area 
  had 
  to 
  be 
  moved 
  

   only 
  4-6 
  inches 
  indicates 
  that 
  contrast 
  as 
  well 
  as 
  size 
  is 
  probably 
  a 
  

   factor. 
  The 
  hat 
  was 
  not 
  conspicuous 
  against 
  the 
  background 
  of 
  trees, 
  

   tree-trunks 
  and 
  grass 
  ; 
  the 
  white 
  paper 
  and 
  the 
  fan 
  showed 
  up 
  in 
  fairly 
  

   strong 
  relief, 
  the 
  paper 
  being 
  the 
  brighter. 
  The 
  comparison 
  of 
  the 
  

   three 
  was 
  carefully 
  repeated 
  several 
  times, 
  and 
  on 
  each 
  occasion 
  the 
  

   hat 
  was 
  the 
  least 
  disturbing, 
  although 
  larger 
  than 
  either 
  of 
  the 
  others. 
  

   It 
  is 
  conceivable 
  that 
  a 
  considerable 
  amount 
  of 
  information 
  as 
  to 
  the 
  

   colour-sense 
  of 
  the 
  insects 
  might 
  be 
  obtained 
  by 
  more 
  elaborate 
  experi- 
  

   ments 
  with 
  pure 
  colours 
  and 
  controlled 
  contrasts. 
  

  

  In 
  the 
  case 
  of 
  our 
  own 
  perception 
  of 
  motion 
  the 
  main 
  consideration 
  

   seems 
  to 
  be 
  the 
  plane 
  angle 
  subtended 
  at 
  two 
  points 
  representing 
  the 
  

   eye 
  by 
  the 
  initial 
  and 
  final 
  positions 
  of 
  the 
  moving 
  body, 
  the 
  size 
  of 
  

   the 
  body 
  itself 
  having 
  comparatively 
  little 
  influence. 
  In 
  other 
  words, 
  

   an 
  elephant 
  moving 
  its 
  body 
  a 
  foot 
  forward 
  would 
  produce 
  no 
  greater 
  

   impression 
  of 
  movement 
  {i.e., 
  would 
  not 
  arrest 
  our 
  attention 
  to 
  a 
  greater 
  

   degree) 
  than 
  a 
  dog 
  moving 
  the 
  same 
  distance 
  at 
  the 
  same 
  pace. 
  The 
  

   amount 
  of 
  lateral 
  shift 
  of 
  an 
  easily-seen 
  object 
  which 
  would 
  be 
  necessary 
  

   to 
  attract 
  our 
  attention 
  to 
  any 
  given 
  degree 
  would 
  then 
  be 
  directly 
  

   proportional 
  to 
  its 
  distance 
  from 
  the 
  eye, 
  and 
  within 
  limits 
  would 
  be 
  

   practically 
  independent 
  of 
  the 
  size 
  of 
  the 
  moving 
  object. 
  My 
  knowledge 
  

   of 
  human 
  psychology 
  and 
  physiology 
  is 
  insufficient 
  to 
  enable 
  me 
  to 
  say 
  

   that 
  this 
  is 
  a 
  correct 
  statement 
  of 
  the 
  facts 
  in 
  the 
  case 
  of 
  the 
  human 
  

   being, 
  but 
  if 
  it 
  be 
  so, 
  then 
  we 
  have 
  in 
  the 
  case 
  of 
  the 
  fly 
  a 
  very 
  different 
  

   state 
  of 
  affairs, 
  as 
  will 
  be 
  evident 
  from 
  an 
  inspection 
  of 
  the 
  curves 
  in 
  

   the 
  diagram. 
  

  

  As 
  my 
  body 
  was 
  used 
  as 
  the 
  moving 
  object 
  in 
  all 
  the 
  trials 
  with 
  

   Fly 
  B, 
  the 
  numbers 
  shown 
  in 
  curve 
  B 
  are 
  more 
  directly 
  comparable 
  

   than 
  those 
  obtained 
  with 
  Fly 
  A. 
  Taking 
  curve 
  B, 
  it 
  will 
  be 
  seen 
  that 
  

   the 
  degree 
  of 
  lateral 
  movement 
  necessary 
  increases 
  rapidly 
  with 
  increas- 
  

   ing 
  distance, 
  and 
  is 
  by 
  no 
  means 
  directly 
  proportional 
  to 
  it 
  as 
  is 
  (pre- 
  

   sumed 
  to 
  be) 
  the 
  case 
  in 
  human 
  beings. 
  

  

  On 
  the 
  other 
  hand, 
  it 
  appears 
  that 
  the 
  results 
  harmonize 
  fairly 
  

   well 
  with 
  the 
  assumption 
  that 
  the 
  amount 
  of 
  lateral 
  motion 
  of 
  the 
  

   moving 
  body, 
  which 
  is 
  necessary 
  to 
  induce 
  movement 
  in 
  the 
  fly, 
  is 
  pro- 
  

   portional 
  to 
  the 
  square 
  of 
  the 
  distance. 
  That 
  is 
  to 
  say, 
  the 
  disturbing 
  

   or 
  attention-arresting 
  perception 
  of 
  motion 
  is 
  proportional 
  to 
  the 
  area 
  

  

  