﻿238 
  COLLECTION 
  OF 
  OBSERVATIONS 
  ON 
  THE 
  

  

  effect 
  of 
  the 
  clouds 
  in 
  preventing 
  the 
  rise 
  of 
  the 
  thermometer 
  being 
  

   taken 
  at 
  f 
  of 
  a 
  degree, 
  gives, 
  in 
  addition 
  to 
  a 
  rise 
  of 
  2° 
  prevented, 
  a 
  

   depression 
  of 
  5|° 
  produced, 
  making 
  7^° 
  for 
  the 
  effect 
  on 
  the 
  air. 
  In 
  

   the 
  eclipse 
  of 
  1831 
  the 
  observed 
  effect 
  on 
  the 
  temperature 
  of 
  the 
  air, 
  

   not 
  taking 
  into 
  account 
  the 
  rise 
  which 
  would 
  in 
  other 
  circumstances 
  

   have 
  been 
  produced, 
  was 
  4f° 
  Fahrenheit, 
  which 
  was, 
  however, 
  much 
  

   more 
  felt 
  than 
  the 
  present, 
  the 
  fall 
  being 
  from 
  35^° 
  Fahrenheit 
  to 
  30f°. 
  

  

  A 
  thermometer 
  with 
  the 
  bulb 
  blackened 
  by 
  writing 
  ink, 
  and 
  con- 
  

   fined 
  in 
  a 
  plate 
  glass 
  case, 
  fell 
  from 
  101°, 
  at 
  which 
  it 
  stood 
  at 
  1 
  P.M., 
  

   to 
  46° 
  at 
  2 
  h. 
  30 
  m., 
  which 
  was 
  the 
  lowest 
  point 
  that 
  it 
  attained, 
  the 
  

   depression 
  amounting 
  to 
  55° 
  in 
  one 
  hour 
  and 
  a 
  half, 
  from 
  the 
  effect 
  of 
  

   the 
  clouds 
  and 
  of 
  the 
  eclipse. 
  In 
  the 
  eclipse 
  of 
  1831 
  the 
  depression 
  of 
  

   a 
  similar 
  instrument 
  not 
  protected 
  from 
  the 
  air 
  was 
  36°. 
  The 
  variable 
  

   effect 
  of 
  the 
  temperature 
  of 
  the 
  air 
  renders 
  such 
  comparisons 
  very 
  

   vague. 
  

  

  The 
  time 
  of 
  greatest 
  obscuration 
  from 
  clouds 
  coincided 
  nearly 
  with 
  

   that 
  from 
  the 
  eclipse, 
  and 
  the 
  varying 
  density 
  of 
  the 
  clouds 
  rendered 
  

   the 
  photometer 
  of 
  no 
  service, 
  and 
  disappointed 
  me 
  in 
  observations 
  

   which 
  had 
  been 
  arranged 
  for 
  that 
  instrument. 
  The 
  photometer, 
  which 
  

   in 
  1831 
  exhibited 
  at 
  the 
  time 
  of 
  greatest 
  obscuration 
  a 
  quantity 
  of 
  

   light 
  from 
  the 
  direct 
  action 
  of 
  the 
  sun 
  amounting 
  to 
  4° 
  in 
  56.5, 
  or 
  ^, 
  

   gave 
  but 
  2 
  for 
  the 
  same 
  quantity 
  on 
  the 
  present 
  occasion. 
  This 
  remark 
  

   applies 
  only 
  to 
  the 
  direct 
  light, 
  for 
  that 
  which 
  was 
  reflected 
  was 
  greater 
  

   than 
  in 
  1831. 
  The 
  dew 
  point, 
  which 
  at 
  7 
  A.M. 
  was 
  at 
  28°, 
  fell, 
  on 
  

   the 
  formation 
  of 
  clouds, 
  and 
  was 
  at 
  1 
  h. 
  40 
  m. 
  24°, 
  and 
  at 
  2 
  h. 
  40 
  m. 
  

   23*°. 
  

  

  A 
  series 
  of 
  magnetic 
  observations 
  on 
  the 
  dip, 
  intensity 
  and 
  variation 
  

   were 
  made, 
  and 
  the 
  results 
  will 
  at 
  a 
  future 
  date 
  be 
  communicated. 
  

   They 
  may 
  have 
  an 
  important 
  bearing 
  on 
  the 
  theory 
  of 
  the 
  diurnal 
  

   variation. 
  

  

  