﻿OF 
  THE 
  HORIZONTAL 
  NEEDLE. 
  21 
  

  

  The 
  ill 
  sustained 
  nightly 
  maximum 
  of 
  No. 
  2 
  was 
  accompanied 
  by 
  

   a 
  fog 
  ; 
  so 
  was 
  the 
  variable 
  nightly 
  part 
  of 
  curve 
  No. 
  7, 
  where 
  a 
  fog 
  

   began 
  to 
  collect 
  at 
  eight 
  in 
  the 
  evening. 
  The 
  nightly 
  rise 
  of 
  curves 
  

   No. 
  5 
  and 
  No. 
  9. 
  ceased 
  with 
  the 
  coming 
  up 
  of 
  clouds 
  and 
  of 
  haze. 
  

   The 
  well 
  sustained 
  height 
  of 
  No. 
  2 
  was 
  during 
  a 
  clear 
  night, 
  as 
  was 
  

   the 
  case 
  with 
  No. 
  4. 
  

  

  The 
  steady 
  rain 
  of 
  Sept. 
  3d 
  and 
  4th, 
  does 
  not 
  seem 
  materially 
  to 
  

   have 
  affected 
  the 
  regularity 
  of 
  the 
  curve. 
  

  

  In 
  conclusion, 
  I 
  would 
  make 
  two 
  brief 
  remarks. 
  The 
  first 
  relates 
  

   to 
  the 
  observation 
  of 
  two 
  tides 
  of 
  variation 
  while 
  there 
  is 
  but 
  one 
  of 
  

   temperature. 
  This 
  would 
  seem 
  to 
  be 
  adverse 
  to 
  the 
  supposed 
  influ- 
  

   ence 
  of 
  heat 
  were 
  it 
  not 
  that 
  we 
  find 
  the 
  same 
  agent 
  producing 
  two 
  

   fluctuations 
  of 
  the 
  barometer 
  ; 
  when 
  we 
  shall 
  be 
  as 
  well 
  acquainted 
  

   with 
  the 
  effects 
  of 
  local 
  and 
  of 
  general 
  variation 
  of 
  temperature 
  upon 
  

   the 
  magnet, 
  as 
  we 
  are 
  of 
  its 
  effects 
  upon 
  atmospheric 
  air, 
  the 
  question 
  

   will 
  be 
  near 
  to 
  its 
  solution. 
  

  

  The 
  second 
  remark 
  relates 
  to 
  the 
  effect 
  of 
  the 
  electrical 
  changes 
  in 
  

   the 
  atmosphere, 
  or 
  of 
  changes 
  of 
  temperature 
  upon 
  the 
  needle 
  ; 
  the 
  

   meteorological 
  phenomena 
  noticed 
  to 
  affect 
  the 
  variation, 
  probably 
  act 
  

   through, 
  if 
  they 
  are 
  not 
  produced 
  by 
  one 
  or 
  both 
  of 
  these 
  changes. 
  

   The 
  experiments 
  of 
  Cavallo 
  have 
  shown, 
  at 
  least 
  with 
  regard 
  to 
  the 
  

   parts 
  of 
  the 
  atmosphere 
  not 
  very 
  far 
  from 
  the 
  earth's 
  surface, 
  that 
  

   there 
  is 
  perpetual 
  electrical 
  excitement, 
  and 
  frequent 
  change. 
  If 
  his 
  

   experiments 
  had 
  led 
  to 
  any 
  conclusions 
  other 
  than 
  the 
  most 
  general, 
  

   they 
  might 
  perhaps 
  have 
  thrown 
  light 
  upon 
  our 
  subject. 
  Where 
  

   so 
  much 
  yet 
  remains 
  to 
  be 
  known, 
  even 
  the 
  imperfect 
  labour 
  here 
  pre- 
  

   sented 
  may 
  not 
  be 
  without 
  its 
  fruits. 
  

  

  vol. 
  v.- 
  

  

  