﻿140 
  

  

  Transactions, 
  — 
  Miscellaneuus, 
  

  

  Example 
  as 
  before. 
  

  

  ^ 
  Sum. 
  

   Diff. 
  

  

  1° 
  18' 
  33"-8 
  = 
  

  

  8' 
  19"-9 
  = 
  499-9 
  

  

  499'9 
  reversed 
  

  

  •0005675 
  

  

  4713-8 
  

   9994 
  

  

  18855 
  

  

  4242 
  

  

  424 
  

  

  42 
  

  

  2356300 
  

  

  5765000 
  = 
  0005675 
  reversed 
  

  

  11782 
  

  

  1414 
  

  

  165 
  

  

  12 
  

  

  Diff. 
  of 
  altitude 
  = 
  1337-3 
  feet 
  

   Even 
  when 
  a 
  book 
  of 
  logarithms 
  is 
  available, 
  the 
  calculation 
  by 
  logs 
  

   will 
  be 
  more 
  expeditiously 
  performed 
  by 
  using 
  the 
  logs 
  of 
  the 
  above 
  

   quantities 
  than 
  by 
  using 
  the 
  log 
  tangent. 
  

  

  

  Example. 
  

  

  

  

  1° 
  18' 
  33" 
  -8 
  = 
  

  

  4713-8 
  

  

  log 
  

  

  3-673371 
  

  

  8' 
  19" 
  -9 
  = 
  

  

  499-9 
  

  

  log 
  

  

  2-698883 
  

  

  Constant 
  log 
  -0005675 
  

  

  = 
  

  

  

  6-753966 
  

  

  1337-3 
  feet 
  = 
  3-126220 
  

  

  With 
  regard 
  to 
  the 
  actual 
  results 
  obtained 
  by 
  this 
  method, 
  I 
  may 
  

   mention 
  that 
  in 
  the 
  cu'cuit 
  of 
  50 
  miles 
  previously 
  referred 
  to, 
  the 
  altitudes 
  

   closed 
  to 
  18 
  feet, 
  and 
  in 
  the 
  circuit 
  of 
  60 
  miles, 
  the 
  error 
  in 
  closing 
  -was 
  

   only 
  2 
  feet. 
  

  

  It 
  is 
  thus 
  evident 
  that 
  this 
  method 
  is 
  quite 
  capable 
  of 
  giving 
  reliable 
  

   results 
  in 
  hilly 
  country, 
  and 
  is 
  well 
  adapted 
  for 
  the 
  topographical 
  survey 
  of 
  

   a 
  new 
  country. 
  A 
  line 
  of 
  stations 
  might 
  be 
  selected 
  in 
  the 
  most 
  accessible 
  

   positions, 
  and 
  each 
  line 
  used 
  as 
  a 
  base 
  from 
  which 
  to 
  extend 
  triangles 
  on 
  

   either 
  side, 
  and 
  as 
  every 
  line 
  is 
  determined 
  independently, 
  there 
  would 
  bene 
  

   accumulation 
  of 
  error. 
  

  

  On 
  the 
  contrary, 
  by 
  observing 
  to 
  distant 
  hills 
  on 
  either 
  side, 
  the 
  distances 
  

   found 
  would 
  check 
  each 
  other, 
  and 
  any 
  erroneous 
  result 
  could 
  be 
  rejected. 
  

  

  In 
  very 
  level 
  country, 
  where 
  the 
  refraction 
  is 
  too 
  uncertain 
  to 
  give 
  

   reliable 
  results 
  by 
  this 
  method, 
  other 
  methods 
  may 
  be 
  employed, 
  such 
  as 
  

   chained 
  lines, 
  or 
  triangulation 
  from 
  a 
  measured 
  base, 
  etc. 
  

  

  