﻿OF 
  THE 
  HORIZONTAL 
  NEEDLE. 
  

  

  15 
  

  

  box 
  became 
  thoroughly 
  dry, 
  and 
  at 
  night 
  the 
  needle 
  was 
  covered 
  over 
  

   to 
  prevent 
  a 
  reduction 
  of 
  temperature 
  which 
  would 
  have 
  produced 
  a 
  

   deposit 
  of 
  dew 
  upon 
  it. 
  The 
  effects 
  shown 
  in 
  the 
  following 
  table 
  are 
  

   therefore 
  due 
  to 
  comparatively 
  sudden 
  variations 
  of 
  temperature.* 
  

  

  The 
  broken 
  lines 
  representing 
  the 
  observations 
  will 
  be 
  found 
  on 
  

   No. 
  10, 
  Plate 
  III* 
  

  

  TABLE 
  X. 
  

  

  Hour. 
  

  

  N. 
  Pole 
  W. 
  

  

  Temp. 
  

  

  Remarks. 
  

  

  

  Deg. 
  Min. 
  

  

  Deg. 
  

  

  

  7§ 
  A.M. 
  

  

  3 
  17.5 
  

  

  

  C 
  Sept. 
  8. 
  

  

  \ 
  Clear. 
  Needle 
  covered. 
  

  

  S§ 
  A.M. 
  

  

  3 
  '06.0 
  

  

  

  Needle 
  uncovered. 
  

  

  n 
  A.M. 
  

  

  3 
  13.5 
  

  

  

  Hazy. 
  Cumulus. 
  

  

  10 
  A.M. 
  

  

  3 
  22.2 
  

  

  94 
  

  

  C 
  Vibrating 
  between 
  3° 
  20'.6 
  and 
  3° 
  23'. 
  8. 
  

   1 
  Therm, 
  in 
  needle 
  box. 
  

  

  

  

  

  11 
  A.M. 
  

  

  3 
  39.6 
  

  

  104 
  

  

  Scattered 
  cumulus. 
  

   C 
  Vibrating 
  between 
  3° 
  38'.3 
  and 
  3° 
  26'. 
  2. 
  

  

  12 
  M. 
  

  

  3 
  32.2 
  

  

  

  3 
  Scattered 
  cumulus. 
  Sun 
  occasionally 
  

   £ 
  clouded. 
  

  

  1 
  P.M. 
  

  

  3 
  38.3 
  

  

  97 
  

  

  Ditto. 
  

  

  2 
  P.M. 
  

  

  2 
  59.2 
  

  

  94 
  

  

  

  3 
  P.M. 
  

  

  2 
  59.2 
  

  

  86 
  

  

  Sun 
  under 
  a 
  cloud. 
  

  

  4 
  P.M. 
  

  

  2 
  59.2 
  

  

  82 
  

  

  Cloudy. 
  

  

  61 
  P.M. 
  

  

  2 
  26.0 
  

  

  67 
  

  

  Sun 
  has 
  set 
  clear. 
  

  

  8 
  P.M. 
  

  

  2 
  44.9 
  

  

  60 
  

  

  Cumulus. 
  Cumulo-stratus. 
  

  

  10 
  P.M. 
  

  

  2 
  52.0 
  

  

  54 
  

  

  

  The 
  first 
  conclusion 
  which 
  I 
  would 
  draw 
  from 
  a 
  review 
  of 
  the 
  

   entire 
  series 
  of 
  observations 
  is, 
  that 
  there 
  were, 
  for 
  the 
  time 
  embraced 
  by 
  

   them, 
  two 
  maxima 
  and 
  two 
  minima 
  of 
  westerly 
  variation, 
  within 
  every 
  

   twenty-four 
  hours. 
  This 
  fact 
  is 
  distinctly 
  shown 
  in 
  each 
  of 
  the 
  curves, 
  

   and 
  will 
  be 
  pointed 
  out 
  particularly 
  by 
  endeavouring 
  to 
  determine 
  the 
  

   hours 
  of 
  maximum 
  and 
  minimum 
  variation. 
  

  

  This 
  result 
  agrees 
  with 
  that 
  obtained 
  by 
  Mr 
  Canton, 
  from 
  his 
  ex- 
  

   tended 
  series 
  of 
  observations, 
  and 
  subsequently 
  by 
  Mr 
  Gilpin. 
  Col. 
  

   Beaufoy, 
  still 
  later 
  (1S13 
  to 
  1822), 
  had 
  evidence 
  of 
  the 
  occurrence 
  of 
  

   the 
  same 
  maxima 
  and 
  minima, 
  though 
  he 
  seems 
  not 
  to 
  have 
  been 
  able 
  

   to 
  fix 
  the 
  time 
  of 
  the 
  evening 
  minimum. 
  

  

  * 
  Very 
  little 
  consideration 
  will 
  serve 
  to 
  show 
  that 
  these 
  effects 
  cannot 
  be 
  ranked 
  with 
  those 
  

   recorded 
  by 
  Mr 
  Fox 
  in 
  the 
  Philosophical 
  Magazine 
  for 
  October 
  1833. 
  

  

  