﻿16 
  

  

  ON 
  THE 
  DIURNAL, 
  VARIATION 
  

  

  The 
  observations 
  of 
  Capt. 
  Parry 
  and 
  Lieut. 
  Foster 
  at 
  Port 
  Bowen, 
  

   are 
  of 
  the 
  more 
  interest, 
  that, 
  from 
  the 
  peculiarity 
  of 
  their 
  situation, 
  

   there 
  was 
  but 
  one 
  point 
  of 
  maximum 
  and 
  one 
  of 
  minimum 
  variation 
  

   during 
  twenty-four 
  hours. 
  These 
  observations 
  were 
  made 
  nearly 
  

   every 
  hour 
  of 
  the 
  day 
  and 
  night. 
  The 
  latitude 
  of 
  Port 
  Bowen 
  is 
  

   73° 
  14' 
  N., 
  and 
  the 
  variation 
  of 
  the 
  needle 
  124° 
  W. 
  

  

  As 
  far 
  as 
  the 
  observations 
  of 
  Lieut. 
  Hood, 
  at 
  Fort 
  Enterprize, 
  war- 
  

   rant 
  any 
  conclusion, 
  it 
  is 
  coincident 
  with 
  that 
  just 
  noticed 
  ; 
  the 
  point 
  

   of 
  maximum 
  easterly 
  variation 
  and 
  that 
  of 
  minimum 
  easterly 
  varia- 
  

   tion 
  are 
  clearly 
  shown 
  in 
  his 
  observations. 
  Fort 
  Enterprize 
  is 
  in 
  lati- 
  

   tude 
  64° 
  28' 
  N., 
  and 
  the 
  mean 
  variation 
  is 
  about 
  36° 
  24' 
  E. 
  

  

  The 
  second 
  conclusion 
  which 
  the 
  foregoing 
  observations 
  seem 
  to 
  me 
  

   to 
  warrant 
  is, 
  that, 
  through 
  the 
  irregularities 
  which 
  they 
  present, 
  there 
  

   is 
  shown 
  a 
  general 
  horary 
  variation 
  as 
  the 
  primary 
  phenomenon 
  and 
  

   the 
  effects 
  of 
  meteorological 
  changes 
  as 
  modifying 
  causes; 
  often 
  over- 
  

   coming 
  the 
  diurnal 
  variation, 
  and 
  impressing 
  their 
  own 
  alterations 
  

   upon 
  the 
  variation 
  of 
  the 
  needle. 
  

  

  To 
  examine 
  the 
  first 
  part 
  of 
  this 
  deduction, 
  I 
  will 
  follow, 
  in 
  their 
  

   general 
  features, 
  the 
  several 
  curves 
  traced 
  to 
  represent 
  the 
  observations, 
  

   omitting 
  No. 
  3 
  on 
  account 
  of 
  its 
  peculiarities. 
  

  

  1. 
  The 
  variation 
  is 
  at 
  its 
  maximum 
  during 
  the 
  day, 
  at 
  or 
  near 
  the 
  

   hour 
  of 
  highest 
  temperature. 
  The 
  greatest 
  difference 
  between 
  these 
  

   times 
  is 
  two 
  hours 
  and 
  a 
  half. 
  But 
  the 
  day 
  maximum 
  seems 
  subject 
  

   to 
  great 
  changes 
  of 
  position 
  ; 
  in 
  one 
  case 
  occurring 
  at 
  noon, 
  in 
  another 
  

   not 
  until 
  5 
  P.M. 
  These 
  deductions 
  are 
  shown 
  in 
  the 
  tabular 
  view 
  

   which 
  follows. 
  

  

  Number 
  of 
  

   Curve. 
  

  

  Hour 
  of 
  Maxi- 
  

   mum 
  Variation. 
  

  

  Hour 
  of 
  Maxi- 
  

   mum 
  Temp. 
  

  

  General 
  character 
  of 
  the 
  weather. 
  

  

  No. 
  1. 
  

  

  12 
  M. 
  

  

  2$ 
  P.M. 
  

  

  C 
  Nimbus 
  before 
  noon, 
  and 
  clear 
  just 
  before 
  

   I 
  noon. 
  

  

  No. 
  2. 
  

  

  3 
  P.M. 
  

  

  4* 
  P.M. 
  

  

  Clear, 
  with 
  floating 
  clouds. 
  

  

  No. 
  4. 
  

  

  3 
  to 
  5 
  P.M. 
  

  

  2\ 
  P.M. 
  

  

  Generally 
  clear, 
  follows 
  unsettled 
  weather. 
  

  

  No. 
  5. 
  

  

  2 
  Ho 
  4 
  P.M. 
  

  

  2 
  P.M. 
  

  

  f 
  Clear. 
  Needle 
  stationary 
  from 
  2k 
  to 
  4 
  

   \ 
  P.M. 
  No 
  proper 
  maximum. 
  

  

  No. 
  6. 
  

  

  2 
  to 
  3i 
  P.M. 
  

  

  2 
  J 
  to 
  4 
  P.M. 
  

  

  Raining 
  in 
  (he 
  morning. 
  Weather 
  variable. 
  

  

  No. 
  7. 
  

  

  4§ 
  P.M. 
  

  

  4 
  P.M. 
  

  

  Cloudy. 
  Weather 
  variable. 
  

  

  No. 
  8. 
  

  

  4 
  P.M. 
  

  

  3| 
  P.M. 
  

  

  Clear. 
  

  

  No. 
  9. 
  

  

  1 
  to 
  4 
  P.M. 
  

  

  4 
  P.M. 
  

  

  C 
  Cloudy. 
  The 
  observation 
  of 
  the 
  needle 
  

   \ 
  at 
  4 
  P.M. 
  was 
  uncertain. 
  

  

  