﻿OF 
  THE 
  HORIZONTAL 
  NEEDLE. 
  

  

  17 
  

  

  2. 
  The 
  westerly 
  variation 
  decreases 
  from 
  this 
  variable 
  maximum 
  to 
  

   a 
  minimum, 
  which 
  is 
  near 
  the 
  hour 
  of 
  sunset. 
  The 
  time 
  of 
  this 
  

   minimum 
  is 
  included 
  within 
  the 
  narrow 
  limits 
  of 
  5| 
  and 
  7 
  o'clock.* 
  

  

  Number 
  of 
  Curve. 
  

  

  Hour 
  of 
  Minimum 
  

   Variation. 
  

  

  Hour 
  of 
  Sunset. 
  

  

  Remarks. 
  

  

  No. 
  1. 
  

   No. 
  2. 
  

   No. 
  4. 
  

   No. 
  5. 
  

   No. 
  6. 
  

   No. 
  7. 
  

  

  No. 
  8. 
  

  

  H. 
  Min. 
  

  

  6 
  45 
  P.M. 
  

  

  7 
  00 
  P.M. 
  

   7 
  00 
  P.M. 
  

   6 
  20 
  P.M. 
  

   6 
  00 
  P.M. 
  

   6 
  00 
  P.M. 
  

  

  6 
  45 
  P.M. 
  

  

  H. 
  Min. 
  -, 
  

   6 
  33 
  P.M. 
  

   6 
  32 
  P.M. 
  

   6 
  29 
  P.M. 
  

   6 
  28 
  P.M. 
  

   6 
  27 
  P.M. 
  

   6 
  26 
  P.M. 
  

  

  Clear 
  in 
  the 
  afternoon 
  and 
  at 
  sunset. 
  

  

  Sun 
  sets 
  clear. 
  

  

  Sun 
  sets 
  clear. 
  

  

  Cirrus. 
  

  

  Cloudy. 
  Weather 
  variable. 
  

  

  Sun 
  sets 
  in 
  clouds. 
  

  

  6 
  24 
  P.M. 
  

  

  C 
  Sun 
  sets 
  clear. 
  Sinks 
  below 
  hill 
  at 
  

   (_ 
  6h. 
  5m. 
  

  

  No. 
  9. 
  

   No. 
  10. 
  

  

  5 
  45 
  P.M. 
  

   7 
  16 
  P.M. 
  

  

  6 
  23 
  P.M.- 
  

   6 
  21 
  P.M. 
  

  

  Sun 
  sets 
  in 
  clouds. 
  

   C 
  Sun 
  sets 
  clear. 
  The 
  hour 
  of 
  minimum 
  

   < 
  is 
  calculated, 
  the 
  observations 
  show 
  

   £ 
  that 
  it 
  was 
  after 
  6|h. 
  

  

  3. 
  The 
  variation 
  increases 
  from 
  the 
  minimum 
  just 
  determined 
  to 
  a 
  

   variable 
  maximum 
  which 
  is 
  reached 
  at 
  or 
  about 
  midnight. 
  On 
  the 
  

   nights 
  when 
  the 
  weather 
  was 
  not 
  variable, 
  this 
  appears, 
  from 
  the 
  fol- 
  

  

  lowing 
  table, 
  to 
  be 
  true. 
  

  

  Number 
  of 
  Curve. 
  

  

  Hour 
  of 
  Maximum 
  

   Variation. 
  

  

  1 
  

   Remarks. 
  

  

  ■ 
  

  

  

  H. 
  Min. 
  

  

  

  No. 
  1. 
  

  

  12 
  40 
  A.M. 
  

  

  Clear. 
  

  

  No. 
  2. 
  

  

  9 
  25 
  P.M. 
  

  

  Succeeded 
  by 
  a 
  fog. 
  

  

  No. 
  4. 
  

  

  11 
  10 
  P.M. 
  

  

  Clear. 
  

  

  No. 
  5. 
  

  

  8 
  15 
  P.M. 
  

  

  Cloudy. 
  Clouds 
  increase 
  in 
  density 
  after 
  this 
  hour. 
  

  

  No. 
  6. 
  

  

  12 
  00 
  m. 
  

  

  Raining 
  before 
  and 
  after 
  this 
  hour. 
  

  

  No. 
  7. 
  

  

  12 
  00 
  m. 
  

  

  Fog. 
  

  

  No. 
  8. 
  

  

  11 
  40 
  P.M. 
  

  

  Clear. 
  

  

  No. 
  9. 
  

  

  

  Stationary 
  from 
  9 
  until 
  12. 
  

  

  4. 
  From 
  this 
  maximum 
  there 
  is 
  a 
  descent, 
  more 
  or 
  less 
  irregular, 
  

   to 
  a 
  morning 
  minimum, 
  between 
  8 
  and 
  9 
  o'clock, 
  

  

  * 
  This 
  places 
  the 
  evening 
  minimum 
  at 
  a 
  much 
  earlier 
  hour 
  than 
  that 
  given 
  by 
  other 
  ob- 
  

   servers, 
  and 
  from 
  results 
  which 
  I 
  have 
  obtained 
  since, 
  in 
  the 
  city 
  of 
  Philadelphia, 
  I 
  am 
  

   inclined 
  to 
  suppose 
  it 
  to 
  have 
  resulted 
  from 
  some 
  peculiarity 
  in 
  the 
  locality 
  or 
  season. 
  

   VOL. 
  V. 
  E 
  

  

  