﻿THE 
  ESTABLISHMENT 
  OF 
  MERIDIAN 
  LINES 
  

  

  PRELIMINARY 
  REMARKS 
  

  

  The 
  Compass 
  Needi,e 
  

  

  Variations 
  and 
  imperfections. 
  — 
  The 
  propriety 
  of 
  using 
  a 
  mag- 
  

   netic 
  needle 
  for 
  determining 
  direction 
  in 
  ordinary 
  land 
  surveying 
  

   is 
  indeed 
  questionable. 
  When 
  we 
  know 
  that 
  so 
  called 
  ' 
  ' 
  variation 
  

   of 
  the 
  compass 
  needle 
  ' 
  ' 
  is 
  changing 
  from 
  year 
  to 
  year 
  (secular 
  

   variation); 
  when 
  we 
  remember 
  that 
  there 
  is 
  an 
  annual 
  variation, 
  

   or 
  change 
  from 
  season 
  to 
  season, 
  and 
  a 
  diurnal 
  or 
  daily 
  change 
  ; 
  

   when 
  we 
  observe 
  the 
  sensitiveness 
  of 
  the 
  needle 
  to 
  extreme 
  changes 
  

   in 
  temperature, 
  its 
  deflection 
  by 
  local 
  attraction 
  and 
  magnetic 
  

   storms, 
  or 
  its 
  sluggishness 
  from 
  a 
  worn 
  center 
  or 
  loss 
  of 
  magnetism 
  ; 
  

   when 
  finally 
  we 
  know 
  that 
  no 
  non-reversing 
  needle 
  ever 
  does 
  

   indicate 
  the 
  exact 
  magnetic 
  meridian 
  because 
  its 
  physical 
  axis 
  is 
  

   never 
  exactly 
  the 
  same 
  as 
  its 
  magnetic 
  axis 
  ; 
  then 
  we 
  must 
  admit 
  

   that 
  even 
  though 
  the 
  instrument 
  is 
  in 
  perfect 
  adjustment, 
  the 
  

   chances 
  of 
  laying 
  off 
  two 
  coincident 
  lines 
  from 
  any 
  given 
  starting 
  

   point, 
  at 
  different 
  intervals 
  of 
  time 
  with 
  one 
  and 
  the 
  same 
  com- 
  

   pass 
  are 
  indeed 
  slight. 
  Different 
  men 
  with 
  different 
  instruments 
  

   at 
  different 
  times, 
  have 
  naturally, 
  as 
  we 
  all 
  know, 
  come 
  to 
  very 
  

   different 
  conclusions 
  regarding 
  the 
  location 
  of 
  many 
  corners 
  and 
  

   boundary 
  lines. 
  

  

  Without 
  going 
  into 
  details 
  regarding 
  the 
  troubles 
  thus 
  brought 
  

   about, 
  it 
  is 
  more 
  to 
  the 
  point 
  to 
  make 
  inquiries 
  as 
  to 
  how 
  the 
  

   present 
  methods 
  of 
  determining 
  direction 
  can 
  be 
  improved 
  upon. 
  

  

  The 
  Transit, 
  With 
  or 
  Without 
  Solar 
  Attachment 
  

  

  Its 
  use. 
  — 
  No 
  one 
  who 
  has 
  ever 
  become 
  familiar 
  with 
  an 
  engi- 
  

   neer's 
  or 
  surveyor's 
  transit 
  can 
  go 
  back 
  to 
  compass 
  surveying 
  with 
  

   any 
  degree 
  of 
  satisfaction 
  except 
  in 
  mere 
  preliminary 
  or 
  recon- 
  

   naissance 
  work. 
  Again, 
  the 
  ordinary 
  transit 
  is 
  equipped 
  with 
  a 
  

   needle, 
  so 
  that 
  whatever 
  merit 
  may 
  be 
  in 
  such 
  a 
  mechanism, 
  is 
  

  

  