﻿Telescopic 
  Vision. 
  

  

  977 
  

  

  the 
  appearance 
  became 
  that 
  represented 
  in 
  fig. 
  6*, 
  and 
  

   was 
  then 
  utterly 
  unlike 
  the 
  real 
  object. 
  The 
  semicircle 
  has 
  

  

  Fig:. 
  6. 
  

  

  disappeared 
  and 
  instead 
  o£ 
  it 
  and 
  the 
  one 
  straight 
  canal 
  

   across 
  the 
  triangle 
  we 
  have 
  what 
  appear 
  to 
  be 
  three 
  canals 
  of 
  

   nearly 
  equal 
  thickness 
  aud 
  abutting 
  nearly 
  perpendicularly 
  

   upon 
  the 
  three 
  sides 
  of 
  the 
  entire 
  triangular 
  space. 
  And 
  at 
  

   the 
  same 
  time 
  ' 
  carets 
  i 
  have 
  developed 
  themselves 
  at 
  the 
  

   outer 
  ends 
  of 
  these 
  three 
  optically 
  produced 
  canals. 
  These 
  

   misleading 
  appearances, 
  which 
  sometimes 
  metamorphose 
  an 
  

   object 
  into 
  something 
  utterly 
  unlike 
  itself, 
  are 
  of 
  the 
  

   same 
  kind 
  as 
  those 
  by 
  which 
  the 
  Astronomer 
  who 
  

   occupies 
  himself 
  upon 
  minute 
  details, 
  is 
  but 
  too 
  liable 
  to 
  be 
  

   misled, 
  unless 
  he 
  diligently 
  avails 
  himself 
  of 
  some 
  such 
  aids 
  

   as 
  those 
  which 
  the 
  author 
  has 
  ventured 
  in 
  this 
  memoir 
  to 
  

   recommend. 
  

  

  NOTES. 
  

  

  Note 
  1. 
  On 
  control 
  observations 
  upon 
  the 
  Moon. 
  — 
  When 
  

   in 
  last 
  month's 
  Phil. 
  Mag. 
  (see 
  p. 
  807), 
  recommending 
  the 
  

   Astronomer 
  diligently 
  to 
  make 
  control 
  observations 
  upon 
  the 
  

   Moon 
  when 
  nearly 
  full, 
  the 
  author 
  omitted 
  to 
  point 
  out 
  that 
  

   valuable 
  observations 
  of 
  this 
  kind 
  can 
  be 
  made 
  without 
  

   having 
  to 
  provide 
  the 
  auxiliary 
  telescope 
  there 
  suggested. 
  

   With 
  that 
  telescope 
  the 
  exact 
  optical 
  conditions 
  of 
  the 
  obser- 
  

   vations 
  upon 
  Mars 
  can 
  be 
  reproduced, 
  including 
  the 
  vision 
  of 
  

   Mars 
  in 
  the 
  astronomical 
  telescope, 
  and 
  of 
  the 
  Moon 
  in 
  the 
  

   control 
  apparatus, 
  under 
  equal 
  magnification. 
  

  

  To 
  make 
  observations 
  with 
  the 
  naked 
  eye 
  we 
  have 
  only 
  to 
  

  

  * 
  In 
  looking 
  at 
  fig. 
  6 
  the 
  reader 
  is 
  requested 
  to 
  exercise 
  his 
  imagi- 
  

   nation, 
  for 
  none 
  of 
  the 
  features 
  as 
  seen 
  in 
  the 
  microscope 
  had 
  the 
  hard 
  

   outlines 
  of 
  our 
  diagram 
  of 
  them. 
  The 
  three 
  ' 
  canals 
  ' 
  were 
  dusky 
  streaks 
  

   with 
  straight 
  but 
  nebulous 
  edges, 
  and 
  the 
  boundary 
  of 
  the 
  triangular 
  

   bright 
  space 
  was 
  also 
  nebulous. 
  The 
  ' 
  carets 
  ' 
  were 
  the 
  darkest 
  parts 
  of 
  

   the 
  image. 
  

  

  Phil 
  Mag. 
  S. 
  6. 
  Vol. 
  16. 
  No. 
  96. 
  Dec. 
  1908. 
  

  

  3S 
  

  

  