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  191 
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  VIII. 
  — 
  Note 
  as 
  to 
  the 
  Dynamical 
  Equivalent 
  of 
  Temperature 
  in 
  Liquid 
  Water, 
  and 
  

   the 
  Specif 
  c 
  Heat 
  of 
  Atmospheric 
  Air 
  and 
  Steam, 
  being 
  a 
  Supplement 
  to 
  a 
  Paper 
  

   On 
  the 
  Mechanical 
  Action 
  of 
  Heat. 
  By 
  William 
  John 
  Macquorn 
  Rankine, 
  

   Civil 
  Engineer, 
  F.R.S.E., 
  F.R.S.S.A., 
  &c. 
  

  

  (Read 
  2d 
  December 
  1850.) 
  

  

  (33*.) 
  In 
  my 
  paper 
  on 
  the 
  Mechanical 
  Action 
  of 
  Heat, 
  published 
  in 
  the 
  1st 
  

   Part 
  of 
  the 
  20th 
  Volume 
  of 
  the 
  Transactions 
  of 
  the 
  Royal 
  Society 
  of 
  Edinburgh, 
  

   some 
  of 
  the 
  numerical 
  results 
  depend 
  upon 
  the 
  dynamical 
  equivalent 
  of 
  a 
  degree 
  

   of 
  temperature 
  in 
  liquid 
  water. 
  The 
  value 
  of 
  that 
  quantity 
  which 
  I 
  then 
  used, 
  was 
  

   calculated 
  from 
  the 
  experiments 
  of 
  De 
  la 
  Roche 
  and 
  Berard 
  on 
  the 
  apparent 
  

   specific 
  heat 
  of 
  atmospheric 
  air 
  under 
  constant 
  pressure, 
  as 
  compared 
  with 
  liquid 
  

   water. 
  

  

  The 
  experiments 
  of 
  Mr 
  Joule 
  on 
  the 
  production 
  of 
  heat 
  by 
  friction, 
  give, 
  for 
  

   the 
  specific 
  heat 
  of 
  liquid 
  water, 
  an 
  equivalent 
  about 
  one-ninth 
  part 
  greater 
  than 
  

   that 
  which 
  is 
  determined 
  from 
  those 
  of 
  De 
  la 
  Roche 
  and 
  Berard. 
  I 
  was 
  for- 
  

   merly 
  disposed 
  to 
  ascribe 
  this 
  discrepancy 
  in 
  a 
  great 
  measure 
  to 
  the 
  smallness 
  of 
  

   the 
  differences 
  of 
  temperature 
  measured 
  by 
  Mr 
  Joule, 
  and 
  to 
  unknown 
  causes 
  

   of 
  loss 
  of 
  power 
  in 
  his 
  apparatus, 
  such 
  as 
  the 
  production 
  of 
  sound 
  and 
  of 
  electri- 
  

   city 
  ; 
  but, 
  subsequently 
  to 
  the 
  publication 
  of 
  my 
  paper, 
  I 
  have 
  seen 
  the 
  detailed 
  

   account 
  of 
  Mr 
  Joule's 
  last 
  experiments 
  in 
  the 
  Philosophical 
  Transactions 
  for 
  

   1850, 
  which 
  has 
  convinced 
  me, 
  that 
  the 
  uncertainty 
  arising 
  from 
  the 
  smallness 
  

   of 
  the 
  elevations 
  of 
  temperature, 
  is 
  removed 
  by 
  the 
  multitude 
  of 
  experiments 
  

   (being 
  forty 
  on 
  water, 
  fifty 
  on 
  mercury, 
  and 
  twenty 
  on 
  cast 
  iron) 
  ; 
  that 
  the 
  agree- 
  

   ment 
  amongst 
  the 
  results 
  from 
  substances 
  so 
  different, 
  shews 
  that 
  the 
  error 
  by 
  

   unknown 
  losses 
  of 
  power 
  is 
  insensible, 
  or 
  nearly 
  so 
  ; 
  and 
  that 
  the 
  necessary 
  con- 
  

   clusion 
  is, 
  that 
  the 
  dynamical 
  value 
  assigned 
  by 
  Mr 
  Joule 
  to 
  the 
  specific 
  heat 
  of 
  

   liquid 
  water, 
  viz. 
  : 
  — 
  772 
  feet 
  per 
  degree 
  of 
  Fahrenheit, 
  does 
  not 
  err 
  by 
  more 
  than 
  

   two, 
  or, 
  at 
  the 
  utmost, 
  three 
  feet 
  ; 
  and 
  therefore, 
  that 
  the 
  discrepancy 
  originates 
  

   chiefly 
  in 
  the 
  experiments 
  of 
  De 
  la 
  Roche 
  and 
  Berard. 
  

  

  I 
  therefore 
  take 
  the 
  earliest 
  opportunity 
  of 
  correcting 
  such 
  of 
  my 
  calculations 
  

   as 
  require 
  it, 
  so 
  as 
  to 
  correspond 
  with 
  Mr 
  Joule's 
  equivalent. 
  They 
  relate 
  to 
  the 
  

   specific 
  heat 
  of 
  atmospheric 
  air 
  as 
  compared 
  with 
  liquid 
  water, 
  and 
  to 
  that 
  of 
  

   steam, 
  and 
  are 
  contained 
  in 
  the 
  second 
  and 
  third 
  Sections 
  of 
  my 
  paper, 
  Articles 
  14 
  

   and 
  20 
  ; 
  Equations 
  28, 
  34, 
  and 
  36. 
  

  

  VOL. 
  XX. 
  PART 
  II. 
  3 
  E 
  

  

  