﻿OF 
  THE 
  HORIZONTAL 
  NEEDLE. 
  

  

  19 
  

  

  were 
  considerable. 
  After 
  making 
  this 
  correction, 
  the 
  daily 
  maximum 
  

   appears 
  to 
  be 
  nearly 
  at 
  the 
  hour 
  on 
  which 
  it 
  occured 
  in 
  clear 
  weather. 
  

  

  Table 
  of 
  Mean 
  Variation 
  

  

  and 
  Temperature 
  from 
  noon 
  of 
  August 
  29th 
  to 
  noon 
  

  

  of 
  Sept 
  

  

  amber 
  7tl 
  

  

  i, 
  1832. 
  

  

  Hour. 
  

  

  N. 
  Pole 
  W. 
  

  

  No. 
  of 
  

   Obs. 
  

  

  Temp. 
  

   Fahr. 
  

  

  No. 
  of 
  

   Obs. 
  

  

  Hour. 
  

  

  N. 
  Pole 
  W. 
  

  

  No. 
  of 
  

   Obs. 
  

  

  Temp. 
  

   Fahr. 
  

  

  No. 
  of 
  

   Obs. 
  

  

  

  Deg. 
  Min. 
  

  

  

  Deg. 
  

  

  

  

  Deg. 
  Min. 
  

  

  

  Deg. 
  

  

  

  12 
  M. 
  

  

  3 
  23.3 
  

  

  9 
  

  

  71.2 
  

  

  9 
  

  

  12 
  m. 
  

  

  3 
  29.3 
  

  

  8 
  

  

  63.0 
  

  

  8 
  

  

  1 
  P.M. 
  

  

  3 
  24.1 
  

  

  9 
  

  

  72.6 
  

  

  9 
  

  

  1 
  A.M. 
  

  

  3 
  28.3 
  

  

  7 
  

  

  61.6 
  

  

  7 
  

  

  2 
  P.M. 
  

  

  3 
  24.5 
  

  

  9 
  

  

  73.5 
  

  

  9 
  

  

  2 
  A.M. 
  

  

  3 
  28.4 
  

  

  4 
  

  

  60.1 
  

  

  3 
  

  

  3 
  P.M. 
  

  

  3 
  24.9 
  

  

  9 
  

  

  73.5 
  

  

  7 
  

  

  3 
  A.M. 
  

  

  3 
  27.5 
  

  

  4 
  

  

  57.S 
  

  

  4 
  

  

  4 
  P.M. 
  

  

  3 
  24.7 
  

  

  9 
  

  

  74.0 
  

  

  6 
  

  

  4 
  A.M. 
  

  

  3 
  26.9 
  

  

  4 
  

  

  57.4 
  

  

  4 
  

  

  5 
  P.M. 
  

  

  3 
  24.4 
  

  

  8 
  

  

  73.5 
  

  

  6 
  

  

  5 
  A.M. 
  

  

  3 
  26.2 
  

  

  4 
  

  

  57.0 
  

  

  4 
  

  

  6 
  P.M. 
  

  

  3 
  20.5 
  

  

  9 
  

  

  70.5 
  

  

  8 
  

  

  6 
  A.M. 
  

  

  3 
  25.1 
  

  

  4 
  

  

  58.3 
  

  

  4 
  

  

  7 
  P.M. 
  

  

  3 
  22.8 
  

  

  9 
  

  

  68.7 
  

  

  9 
  

  

  7 
  A.M. 
  

  

  3 
  20.7 
  

  

  4 
  

  

  63.3 
  

  

  4 
  

  

  8 
  P.M. 
  

  

  3 
  25.4 
  

  

  9 
  

  

  66.3 
  

  

  9 
  

  

  8 
  A.M. 
  

  

  3 
  20.7 
  

  

  9 
  

  

  65.4 
  

  

  8 
  

  

  9 
  P.M. 
  

  

  3 
  27.8 
  

  

  9 
  

  

  64.5 
  

  

  7 
  

  

  9 
  A.M. 
  

  

  3 
  19.2 
  

  

  9 
  

  

  66.2 
  

  

  9 
  

  

  10 
  P.M. 
  

  

  3 
  27.8 
  

  

  9 
  

  

  63.7 
  

  

  9 
  

  

  10 
  A.M. 
  

  

  3 
  20.2 
  

  

  8 
  

  

  67.9 
  

  

  7 
  | 
  

  

  11 
  P.M. 
  

  

  3 
  28.3 
  

  

  9 
  

  

  63.2 
  

  

  9 
  

  

  11 
  A.M. 
  

  

  3 
  21.4 
  

  

  7 
  

  

  67.7 
  

  

  8 
  | 
  

  

  The 
  two 
  tides 
  of 
  variation 
  appear 
  distinctly 
  from 
  the 
  mean 
  results, 
  

   and 
  with 
  but 
  slight 
  irregularities 
  in 
  their 
  increase 
  or 
  decrease. 
  The 
  day 
  

   maximum 
  is 
  at 
  3 
  P.M. 
  The 
  evening 
  minimum 
  at 
  7, 
  or 
  with 
  pro- 
  

   bably 
  more 
  truth, 
  as 
  shown 
  by 
  the 
  dotted 
  lines 
  in 
  No. 
  11, 
  Plate 
  III.*, 
  

   at 
  6 
  h. 
  26 
  m. 
  The 
  night 
  maximum 
  is 
  at 
  midnight. 
  The 
  morning 
  

   minimum 
  at 
  9 
  o'clock. 
  

  

  The 
  mean 
  variation, 
  according 
  to 
  this 
  table, 
  for 
  the 
  place 
  of 
  obser- 
  

   vation, 
  is 
  3° 
  24'.7. 
  

  

  The 
  greatest 
  observed 
  variation 
  3° 
  3 
  4'. 
  9, 
  and 
  the 
  least 
  3° 
  10'. 
  6 
  in- 
  

   cluding 
  all 
  the 
  curves 
  traced. 
  The 
  first 
  of 
  these 
  is 
  the 
  midnight 
  

   maximum 
  of 
  No. 
  8, 
  and 
  the 
  second 
  the 
  morning 
  minimum 
  of 
  No. 
  4. 
  

   The 
  latitude 
  of 
  the 
  place, 
  which 
  was 
  about 
  one 
  mile 
  from 
  the 
  village 
  of 
  

   West 
  Chester, 
  is 
  about 
  39° 
  58', 
  and 
  its 
  longitude 
  about 
  21 
  miles 
  west 
  

   from 
  Philadelphia. 
  

  

  The 
  effect 
  of 
  ordinary 
  meteorological 
  phenomena 
  upon 
  the 
  variation 
  

   was 
  first 
  noticed, 
  I 
  believe, 
  by 
  Mr 
  Christie, 
  who 
  gives 
  a 
  table 
  illustra- 
  

   tive 
  of 
  the 
  effect 
  produced 
  by 
  the 
  occurrence 
  of 
  a 
  rain 
  ; 
  he 
  has 
  not, 
  that 
  

   I 
  am 
  aware, 
  followed 
  up 
  the 
  observation 
  to 
  which 
  I 
  allude. 
  Lieut. 
  

   Foster 
  infers 
  that 
  ordinary 
  meteorological 
  phenomena 
  do 
  not 
  affect 
  the 
  

   variation 
  of 
  the 
  needle 
  ; 
  a 
  result 
  which 
  the 
  different 
  nature 
  of 
  the 
  

  

  