﻿1875.] 
  

  

  Specific 
  Gravity 
  of 
  Sea-water. 
  

  

  305 
  

  

  his 
  theory 
  of 
  oceanic 
  circulation, 
  owing 
  to 
  difference 
  of 
  density 
  of 
  the 
  

   water 
  in 
  its 
  different 
  parts, 
  he 
  found 
  the 
  want 
  of 
  information 
  on 
  this 
  

   important 
  subject. 
  At 
  his 
  request, 
  the 
  late 
  Professor 
  Hubbard, 
  of 
  

   the 
  National 
  Observatory, 
  U.S., 
  instituted 
  a 
  series 
  of 
  experiments, 
  from 
  

   which 
  he 
  was 
  enabled 
  to 
  lay 
  down 
  a 
  curve 
  of 
  the 
  volumes 
  of 
  sea-water 
  at 
  

   all 
  temperatures, 
  from 
  considerably 
  below 
  the 
  freezing-point 
  to 
  much 
  

   above 
  what 
  obtains 
  even 
  in 
  tropical 
  atmospheres. 
  The 
  results 
  are 
  pub- 
  

   lished 
  in 
  Maury's 
  ' 
  Sailing 
  Directions,' 
  1858, 
  vol. 
  i. 
  p. 
  237, 
  and 
  have 
  evi- 
  

   dently 
  been 
  carried 
  out 
  with 
  great 
  care. 
  The 
  composition 
  of 
  different 
  

   oceanic 
  waters 
  varies, 
  even 
  in 
  extreme 
  cases, 
  within 
  such 
  close 
  limits, 
  that 
  

   the 
  law 
  of 
  thermal 
  expansion 
  is 
  sensibly 
  the 
  same 
  for 
  all 
  of 
  them 
  ; 
  of 
  this 
  

   Hubbard's 
  experiments 
  afford 
  satisfactory 
  proof. 
  In 
  the 
  Table 
  which 
  gives 
  

   the 
  results 
  of 
  all 
  his 
  experiments 
  he 
  takes 
  the 
  volume 
  of 
  water 
  at 
  60° 
  F. 
  

   as 
  his 
  unit. 
  In 
  order 
  to 
  avoid 
  much 
  useless 
  calculation, 
  I 
  have 
  been 
  in 
  

   the 
  habit 
  of 
  reducing 
  my 
  results 
  to 
  the 
  same 
  temperature 
  (15 
  0, 
  56 
  C), 
  

   while, 
  for 
  a 
  like 
  reason, 
  I 
  have 
  retained 
  the 
  specific 
  gravity 
  of 
  distilled 
  

   water 
  at 
  4° 
  C. 
  as 
  the 
  unit. 
  The 
  choice 
  of 
  a 
  common 
  temperature 
  to 
  

   which 
  the 
  results 
  should 
  be 
  reduced, 
  and 
  of 
  a 
  unit 
  of 
  specific 
  gravities, 
  is 
  

   a 
  purely 
  conventional 
  matter 
  ; 
  and 
  in 
  choosing 
  the 
  above-mentioned 
  ones, 
  

   in 
  the 
  first 
  instance 
  I 
  was 
  moved 
  solely 
  by 
  a 
  desire 
  to 
  save 
  calculation. 
  

   For 
  every 
  water, 
  however, 
  there 
  is 
  one 
  temperature 
  to 
  which 
  it 
  would 
  be 
  

   natural 
  to 
  reduce 
  its 
  specific 
  gravity 
  — 
  namely, 
  the 
  temperature 
  which 
  the 
  

   water 
  had 
  when 
  in 
  its 
  place 
  in 
  the 
  ocean 
  ; 
  and 
  in 
  this 
  sense 
  all 
  my 
  results 
  

   during 
  the 
  cruise 
  have 
  been 
  reduced. 
  Hubbard's 
  Table 
  of 
  the 
  change 
  of 
  

   volume 
  of 
  a 
  mass 
  of 
  sea-water 
  with 
  change 
  of 
  temperature 
  enables 
  us 
  

   very 
  easily 
  to 
  reduce 
  any 
  observed 
  specific 
  gravity 
  from 
  the 
  temperature 
  

   of 
  observation 
  to 
  any 
  other 
  temperature, 
  say 
  15°-56 
  C. 
  In 
  the 
  paper 
  

   it 
  is 
  transcribed 
  from 
  the 
  ' 
  Sailing 
  Directions.' 
  In 
  the 
  following 
  

   Table 
  the 
  volumes 
  for 
  every 
  Centigrade 
  degree 
  from 
  — 
  1° 
  C. 
  to 
  + 
  30° 
  C. 
  

   are 
  given 
  : 
  — 
  

  

  Table 
  I. 
  

  

  Temp. 
  

   °C. 
  

  

  Volume. 
  

  

  Temp. 
  

   °C. 
  

  

  Volume. 
  

  

  Temp. 
  

   °C. 
  

  

  Volume. 
  

  

  Temp. 
  

   °C. 
  

  

  Volume. 
  

  

  -1 
  

  

  0-99792 
  

  

  +7 
  

  

  0-99853 
  

  

  + 
  15 
  

  

  0-99987 
  

  

  +23 
  

  

  1-00194 
  

  

  

  

  795 
  

  

  8 
  

  

  866 
  

  

  16 
  

  

  1-00010 
  

  

  24 
  

  

  224 
  

  

  +1 
  

  

  799 
  

  

  9 
  

  

  878 
  

  

  17 
  

  

  034 
  

  

  25 
  

  

  256 
  

  

  2 
  

  

  804 
  

  

  10 
  

  

  893 
  

  

  18 
  

  

  059 
  

  

  26 
  

  

  288 
  

  

  3 
  

  

  812 
  

  

  11 
  

  

  910 
  

  

  19 
  

  

  086 
  

  

  27 
  

  

  320 
  

  

  4 
  

  

  820 
  

  

  12 
  

  

  927 
  

  

  20 
  

  

  111 
  

  

  28 
  

  

  352 
  

  

  5 
  

  

  830 
  

  

  13 
  

  

  947 
  

  

  21 
  

  

  137 
  

  

  29 
  

  

  385 
  

  

  6 
  

  

  840 
  

  

  14 
  

  

  967 
  

  

  22 
  

  

  164 
  

  

  30 
  

  

  420 
  

  

  