﻿CORRECTION 
  TO 
  BAROMETER 
  FOR 
  FORCE 
  OF 
  WIND. 
  

  

  383 
  

  

  ocity 
  in 
  Miles 
  

  

  Pressure 
  in 
  

  

  Pounds 
  

  

  Depression 
  

  

  per 
  Hour. 
  

  

  per 
  Square 
  

  

  s 
  Foot. 
  

  

  in 
  Inches. 
  

  

  14-2 
  

  

  1 
  

  

  

  •010 
  

  

  20-0 
  

  

  2 
  

  

  

  •015 
  \ 
  

  

  

  24-5 
  

  

  3 
  

  

  

  •020 
  

  

  

  28-3 
  

  

  4 
  

  

  

  •025 
  

  

  

  31-6 
  

  

  5 
  

  

  

  •030 
  

  

  > 
  Observed 
  

  

  34-6 
  

  

  6 
  

  

  

  •035 
  

  

  

  37-4 
  

  

  7 
  

  

  

  •040 
  

  

  

  40-0 
  

  

  8 
  

  

  

  •045 
  1 
  

  

  

  42-4 
  

  

  9 
  

  

  

  •050 
  

  

  44-7 
  

  

  10 
  

  

  

  •055 
  

  

  .61-6 
  

  

  19 
  

  

  

  •100 
  

  

  

  In 
  this 
  table, 
  I 
  have 
  distinguished 
  the 
  observed 
  depressions 
  corresponding 
  to 
  

   the 
  observed 
  pressures, 
  and 
  have 
  extended 
  the 
  table, 
  shewing 
  that 
  the 
  depression 
  

   would 
  be 
  one-tenth 
  of 
  an 
  inch 
  for 
  a 
  pressure 
  of 
  19 
  lb. 
  per 
  square 
  foot, 
  supposing 
  

   the 
  depressions 
  follow 
  the 
  same 
  law 
  ; 
  but 
  I 
  do 
  not 
  assert 
  that 
  they 
  do, 
  and 
  rather 
  

   think 
  it 
  probable 
  that 
  they 
  do 
  not, 
  with 
  the 
  higher 
  velocities 
  ; 
  but 
  this 
  is 
  a 
  mat- 
  

   ter 
  for 
  further 
  investigation. 
  

  

  It 
  is 
  not, 
  therefore, 
  correct 
  to 
  speak 
  of 
  these 
  depressions 
  as 
  oscillations 
  in 
  the 
  

   level 
  of 
  the 
  mercury, 
  above 
  and 
  below 
  a 
  sort 
  of 
  mean 
  tidal 
  line 
  ; 
  they 
  are 
  simply 
  

   caused 
  by 
  diminished 
  pressure, 
  and 
  the 
  barometer 
  resumes 
  its 
  original 
  position 
  

   without 
  passing 
  it, 
  when 
  the 
  gale 
  or 
  gust 
  of 
  wind 
  passes 
  away. 
  With 
  a 
  pressure 
  

   of 
  2 
  lb. 
  per 
  square 
  foot 
  during 
  the 
  lulls 
  in 
  a 
  gale, 
  and, 
  with 
  gusts, 
  giving 
  a 
  pressure 
  

   of 
  from 
  6 
  to 
  7 
  lb., 
  we 
  find 
  the 
  barometer 
  is 
  *015 
  always 
  below 
  what 
  it 
  should 
  be, 
  

   and 
  the 
  effect 
  of 
  the 
  gust 
  is 
  indicated 
  by 
  a 
  further 
  depression 
  of 
  035 
  and 
  -040 
  ; 
  so 
  

   that 
  by 
  the 
  indications 
  of 
  barometer 
  alone, 
  we 
  are 
  able 
  approximately 
  to 
  estimate 
  

   the 
  additional 
  force 
  of 
  the 
  gust 
  without 
  reference 
  to 
  the 
  anemometer, 
  and 
  by 
  com- 
  

   paring 
  the 
  readings 
  of 
  the 
  barometer 
  in 
  an 
  exposed 
  and 
  in 
  a 
  sheltered 
  position, 
  

   we 
  may 
  estimate 
  the 
  force 
  of 
  the 
  wind 
  at 
  the 
  time 
  of 
  observation. 
  In 
  applying 
  

   the 
  correction 
  for 
  the 
  force 
  of 
  the 
  wind, 
  the 
  depression 
  due 
  to 
  the 
  force 
  during 
  the 
  

   lulls, 
  should 
  be 
  added 
  to 
  the 
  reading 
  of 
  the 
  barometer 
  when 
  at 
  its 
  highest 
  point. 
  

  

  Now 
  the 
  corrections 
  hitherto 
  considered 
  absolutely 
  necessary 
  to 
  the 
  readings 
  

   of 
  the 
  barometer, 
  with 
  the 
  view 
  of 
  having 
  the 
  results 
  in 
  a 
  form 
  strictly 
  com- 
  

   parable 
  from 
  different 
  places 
  of 
  observation, 
  are, 
  for 
  barometers 
  with 
  cisterns, 
  

   without 
  zero-points, 
  

  

  1st, 
  For 
  the 
  capillary 
  action 
  of 
  the 
  tube. 
  

  

  2d, 
  For 
  temperature 
  to 
  reduce 
  the 
  readings 
  to 
  what 
  they 
  would 
  be 
  at 
  32'. 
  

  

  3d, 
  For 
  capacity, 
  depending 
  on 
  the 
  relation 
  of 
  the 
  area 
  of 
  the 
  surface 
  of 
  the 
  

   mercury 
  in 
  the 
  cistern 
  to 
  the 
  area 
  of 
  that 
  in 
  the 
  tube. 
  

  

  And, 
  4th, 
  For 
  altitude 
  above 
  the 
  level 
  of 
  the 
  sea. 
  

  

  Now, 
  if 
  we 
  assume 
  the 
  observed 
  height 
  of 
  the 
  barometer 
  to 
  be 
  29 
  500 
  inches 
  

   at 
  the 
  temperature 
  of 
  40", 
  the 
  size 
  of 
  the 
  tube 
  to 
  be 
  -35 
  inches, 
  and 
  its 
  capacity 
  

   ^th 
  of 
  the 
  cistern, 
  and 
  the 
  neutral 
  point 
  of 
  the 
  instrument 
  at 
  29750, 
  the 
  height 
  

  

  