﻿Telescopic 
  Vision. 
  gQj 
  

  

  telescope. 
  Let 
  us 
  suppose 
  that 
  he 
  begins 
  by 
  makine 
  the 
  

   adjustments 
  which 
  correspond 
  to 
  a 
  12°-i„ch 
  iCop| 
  em 
  

   ployed 
  upon 
  Neptune 
  ; 
  and 
  that 
  he 
  illuminates 
  the 
  pro-planet 
  

  

  ouate 
  1 
  m 
  ^ 
  lmU1 
  V 
  ntensi 
  ^-V 
  1 
  ™ 
  ih 
  this 
  intensity 
  easily 
  

   legmatecl 
  the 
  author 
  reflected 
  a 
  sunbeam 
  horizontillv 
  

  

  SfcS 
  K^ 
  ?° 
  heli 
  ° 
  Sta 
  ? 
  H 
  ' 
  ha 
  ™« 
  removed 
  oTofS 
  

  

  H*tbe„^"t 
  0n 
  rT-'- 
  lenS 
  °, 
  and 
  the 
  a 
  PP 
  ara 
  ^ 
  a 
  F 
  

   ff 
  th 
  « 
  n 
  , 
  lntr 
  oduced 
  into 
  its 
  path 
  a 
  plano-convex 
  lens 
  of 
  

   tolerably 
  long 
  tocus 
  (about 
  70 
  cm.) 
  which 
  happened 
  to 
  be 
  at 
  

   hand 
  and 
  by 
  it 
  formed 
  an 
  image 
  of 
  the 
  sun 
  at 
  a 
  distance 
  of 
  

   some 
  five 
  or 
  six 
  centimetres 
  to 
  "the 
  right 
  of 
  z<. 
  This 
  "m 
  a 
  °e 
  

   of 
  the 
  snn 
  was 
  th 
  source 
  of 
  the 
  d; 
  f 
  • 
  ^ 
  S 
  

  

  illuminate 
  object 
  z. 
  For 
  some 
  observations 
  fhi 
  £ht 
  is 
  too 
  

   bright, 
  and 
  to 
  moderate 
  it, 
  pieces 
  of 
  the 
  kind 
  of 
  Luteal 
  dark 
  

   Klass 
  which 
  is 
  made 
  in 
  large 
  panes 
  for 
  export 
  to 
  India 
  were 
  

   mtroduced-one, 
  two 
  or 
  three 
  of 
  them 
  as 
  requSd-at 
  

   E, 
  between 
  screen 
  Z' 
  and 
  lens 
  L'. 
  These 
  provided 
  four 
  

   ex&nt, 
  lnteDSlty 
  ' 
  Whi 
  ° 
  h 
  ^ 
  f0Und 
  ^eient 
  for 
  Z 
  

  

  ,J?f' 
  V*^.*^? 
  ° 
  f 
  these 
  dark 
  shad 
  ^ 
  the 
  observer 
  sees 
  

   satisfactorily* 
  the 
  .mage 
  of 
  the 
  pro-planet 
  z> 
  i„ 
  the 
  pro 
  

   telescope 
  and 
  can 
  measure 
  the 
  apparent 
  diameter 
  of 
  P 
  the" 
  

   pro-planet 
  by 
  employing 
  on 
  the 
  pro-telescope 
  the^ep 
  ece 
  pro! 
  

   Tided 
  with 
  an 
  eyepiece 
  micrometer 
  scale-see 
  § 
  "H 
  335 
  

   of 
  the 
  > 
  August 
  number 
  of 
  this 
  magazine. 
  If 
  now 
  he 
  

   opens 
  the 
  ins 
  diaphragm 
  at 
  C, 
  he 
  wilf 
  see 
  how 
  the 
  Janet 
  

   would 
  appear 
  in 
  a 
  telescope 
  of 
  laro- 
  er 
  aperture 
  inrl 
  t„ 
  „ 
  i 
  

  

  uient 
  goes 
  on 
  increasing 
  until 
  the 
  aperture 
  has 
  been 
  B 
  

  

  Ssl?£5? 
  corresponds 
  t0 
  tL 
  aperture 
  of 
  ™^ 
  

  

  ape 
  4 
  n,ir5i"i 
  n 
  be 
  tt0 
  Th 
  earnW 
  , 
  hattl 
  l 
  e 
  effeCt 
  ° 
  f 
  Usin 
  « 
  *™^ 
  

  

  dilates 
  and 
  ceases 
  to 
  be 
  uniformly 
  bright 
  beeom\ 
  ? 
  n£ 
  1? 
  

   bright 
  towards 
  its 
  edge 
  : 
  it 
  now 
  Ih.A^Tly^ 
  

  

  a 
  a 
  ni 
  sir 
  i^ 
  hin 
  the 
  ^ 
  due 
  to 
  *• 
  ^rs»r 
  = 
  

  

  I 
  Phil 
  Mag. 
  S. 
  6. 
  Vol. 
  16. 
  No. 
  95. 
  Nov. 
  1908. 
  3 
  G 
  

  

  