﻿Pope, 
  — 
  A 
  Methad 
  of 
  measuring 
  Position 
  of 
  Double 
  Stars. 
  141 
  

  

  Abt. 
  X. 
  — 
  A 
  Description 
  of 
  inexpensive 
  Apiparatus 
  for 
  measuring 
  the 
  Angles 
  of 
  

   Position 
  and 
  Distances 
  of 
  Double 
  Stars, 
  and 
  the 
  Method 
  of 
  using 
  it. 
  

   By 
  James 
  H. 
  Pope. 
  

   Plate 
  I. 
  

   [Read 
  before 
  the 
  Otago 
  Institute, 
  13th 
  August, 
  1878.] 
  

   Undoubtedly 
  anyoue 
  who 
  wishes 
  to 
  make 
  observations 
  of 
  double 
  stars 
  

   should 
  provide 
  himself 
  with 
  a 
  first-class 
  telescope 
  equatorially 
  mounted, 
  

   having 
  an 
  aperture 
  of 
  fi-om 
  eight 
  to 
  ten 
  inches 
  ; 
  he 
  should 
  place 
  this 
  

   telescope 
  in 
  a 
  commodious 
  and 
  well 
  built 
  observatory 
  and 
  should 
  procure 
  a 
  

   first-class 
  filar 
  micrometer 
  and 
  a 
  galvanic 
  chronograph. 
  He 
  should 
  have 
  

   perfect 
  illuminating 
  apparatus, 
  so 
  that 
  the 
  micrometer 
  wires 
  may 
  appear 
  as 
  

   bright 
  lines 
  on 
  a 
  dark 
  field 
  or 
  as 
  dark 
  hues 
  on 
  a 
  bright 
  field, 
  and 
  he 
  should 
  

   be 
  able 
  at 
  will 
  to 
  employ 
  whatever 
  tint 
  he 
  wishes 
  to 
  give 
  to 
  his 
  field 
  or 
  his 
  

   wires. 
  Besides 
  all 
  this, 
  his 
  telescope 
  should 
  be 
  accurately 
  driven 
  by 
  clock- 
  

   work, 
  so 
  that 
  he 
  may 
  keex3 
  a 
  star 
  in 
  one 
  part 
  of 
  the 
  field 
  of 
  view 
  as 
  long 
  as 
  

   he 
  wishes 
  to 
  do 
  so, 
  and 
  may 
  have 
  both 
  hands 
  at 
  perfect 
  hberty 
  to 
  take 
  

   angles 
  of 
  position 
  and 
  to 
  measure 
  the 
  distances 
  between 
  the 
  components 
  of 
  

   double 
  stars. 
  Biit, 
  unfortunately, 
  this 
  apparatus 
  is 
  extremely 
  expensive. 
  

   Cooke 
  of 
  York 
  will 
  provide 
  every 
  requisite 
  for 
  some 
  ^61200 
  ; 
  it 
  is 
  not 
  every 
  

   one 
  that 
  can 
  quite 
  see 
  liis 
  way 
  to 
  spend 
  such 
  a 
  sum. 
  There 
  are 
  many 
  

   enthusiastic 
  studeuts 
  of 
  astronomy 
  who 
  are 
  anxious 
  to 
  engage 
  in 
  this 
  kind 
  

   of 
  work, 
  but 
  think 
  it 
  quite 
  out 
  of 
  their 
  power 
  to 
  do 
  so 
  on 
  account 
  of 
  these 
  

   same 
  pecuniary 
  dif&culties. 
  The 
  following 
  pa^Der 
  attempts 
  to 
  show 
  how 
  

   good 
  work 
  in 
  this 
  department 
  of 
  astronomy 
  may 
  be 
  done 
  at 
  a 
  very 
  trifling 
  

   expense, 
  and 
  to 
  make 
  it 
  evident 
  that 
  the 
  possessor 
  of 
  a 
  good 
  telescope 
  may, 
  

   with 
  a 
  small 
  expenditure 
  of 
  trouble 
  and 
  a 
  still 
  smaller 
  expenditure 
  of 
  money, 
  

   hope 
  to 
  be 
  in 
  a 
  position 
  to 
  take 
  measures 
  of 
  double 
  stars, 
  that 
  will 
  be 
  worth 
  

   preserving 
  in 
  the 
  scientific 
  records 
  of 
  the 
  day. 
  Here 
  I 
  would 
  say, 
  once 
  for 
  

   all, 
  that 
  the 
  methods 
  described 
  in 
  this 
  paper 
  are, 
  many 
  of 
  them, 
  not 
  new. 
  

   Some 
  of 
  them 
  were 
  invented 
  by 
  Sir 
  John 
  Herscliell, 
  some 
  by 
  other 
  

   astronomers. 
  For 
  many 
  of 
  the 
  details 
  the 
  writer 
  alone 
  is 
  responsible. 
  For 
  

   working 
  out 
  the 
  mechanical 
  construction, 
  and 
  for 
  many 
  most 
  valuable 
  

   improvements 
  in 
  the 
  water-clock 
  used 
  in 
  the 
  method, 
  the 
  writer 
  has 
  to 
  thank 
  

   Mr. 
  Forsyth, 
  station-master, 
  Caversham. 
  All 
  that 
  the 
  writer 
  claims 
  to 
  

   have 
  done 
  is 
  to 
  have 
  worked 
  out 
  a 
  complete 
  system 
  (the 
  materials 
  for 
  which 
  

   have 
  been 
  derived 
  from 
  various 
  sources), 
  by 
  means 
  of 
  which 
  double 
  star 
  

   observation 
  is 
  placed 
  within 
  the 
  reach 
  of 
  a 
  large 
  class 
  of 
  students 
  of 
  the 
  

   starry 
  heavens, 
  who 
  are 
  debarred 
  from 
  pursuing 
  this 
  fascinating 
  branch 
  of 
  

   astronomy 
  by 
  the 
  great 
  expense 
  involved 
  in 
  procuring 
  the 
  instruments 
  

   ordinarily 
  used 
  in 
  it. 
  

  

  