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  XXXIX. 
  — 
  On 
  the 
  Absolute 
  Zero 
  of 
  the 
  Perfect 
  Gas 
  Thermometer 
  ; 
  being 
  a 
  Note 
  to 
  a 
  

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

   C.E., 
  F.R.S.E., 
  F.R.S.S.A., 
  &c. 
  

  

  (Read 
  January 
  4, 
  1853.) 
  

  

  Temperature 
  being 
  measured 
  by 
  the 
  pressure 
  of 
  a 
  perfect 
  gas 
  at 
  constant 
  

   density, 
  the 
  absolute 
  zero 
  of 
  temperature 
  is 
  that 
  point 
  on 
  the 
  thermometric 
  scale 
  

   at 
  which, 
  if 
  it 
  were 
  possible 
  to 
  maintain 
  a 
  perfect 
  gas 
  at 
  so 
  low 
  a 
  temperature, 
  

   the 
  pressure 
  would 
  be 
  null. 
  

  

  The 
  position 
  of 
  this 
  point 
  is 
  of 
  great 
  importance, 
  both 
  theoretically 
  and 
  prac- 
  

   tically 
  ; 
  for 
  by 
  reckoning 
  temperatures 
  from 
  it, 
  the 
  laws 
  of 
  phenomena 
  depending 
  

   on 
  heat 
  are 
  reduced 
  to 
  a 
  more 
  simple 
  form 
  than 
  they 
  are 
  when 
  any 
  other 
  zero 
  is 
  

   adopted. 
  

  

  As 
  we 
  cannot 
  obtain 
  any 
  substance 
  in 
  the 
  perfectly 
  gaseous 
  condition 
  (that 
  is 
  

   to 
  say, 
  entirely 
  devoid 
  of 
  cohesion), 
  we 
  cannot 
  determine 
  the 
  position 
  of 
  the 
  abso- 
  

   lute 
  thermometric 
  zero 
  by 
  direct 
  experiment, 
  which 
  furnishes 
  us 
  with 
  approxi- 
  

   mate 
  positions 
  only. 
  Those 
  approximate 
  positions 
  are 
  always 
  too 
  high 
  ; 
  because 
  

   the 
  effect 
  of 
  cohesion 
  is 
  to 
  make 
  the 
  pressure 
  of 
  a 
  gas 
  diminish 
  more 
  rapidly 
  with 
  

   a 
  diminution 
  of 
  temperature, 
  than 
  if 
  it 
  were 
  devoid 
  of 
  cohesion. 
  

  

  As 
  a 
  gas 
  is 
  rarefied, 
  the 
  cohesion 
  of 
  its 
  particles 
  diminishes, 
  not 
  only 
  in 
  absolute 
  

   amount, 
  but 
  also 
  in 
  the 
  proportion 
  which 
  it 
  bears 
  to 
  the 
  pressure 
  due 
  to 
  heat. 
  

   The 
  gas, 
  therefore, 
  approaches 
  more 
  and 
  more 
  nearly 
  to 
  the 
  stateo 
  f 
  a 
  perfect 
  gas 
  

   as 
  its 
  density 
  diminishes 
  ; 
  and 
  from 
  a 
  series 
  of 
  experiments 
  on 
  the 
  rate 
  of 
  increase 
  

   of 
  its 
  elasticity 
  with 
  temperature, 
  at 
  progressively 
  diminishing 
  densities, 
  may 
  be 
  

   calculated 
  the 
  positions 
  of 
  a 
  series 
  of 
  points 
  on 
  the 
  thermometric 
  scale, 
  approach- 
  

   ing 
  more 
  and 
  more 
  nearly 
  to 
  the 
  true 
  absolute 
  zero. 
  

  

  By 
  observing 
  the 
  law 
  which 
  those 
  successive 
  approximations 
  follow, 
  the 
  true 
  

   position 
  of 
  the 
  absolute 
  zero 
  can 
  be 
  determined. 
  

  

  Having 
  performed 
  this 
  operation 
  by 
  means 
  of 
  a 
  graphic 
  process, 
  soon 
  after 
  the 
  

   publication 
  of 
  the 
  experiments 
  of 
  M. 
  Regnault 
  on 
  the 
  elasticity 
  and 
  expansion 
  

   of 
  gases, 
  I 
  stated 
  the 
  result 
  in 
  a 
  paper 
  on 
  the 
  Elasticity 
  of 
  Vapours 
  {Edinburgh 
  

   Neiv 
  Philosophical 
  Journal, 
  July 
  1849), 
  and 
  also 
  in 
  a 
  paper 
  on 
  the 
  Mechanical 
  

   Action 
  of 
  Heat 
  (Trans. 
  Royal 
  Soc. 
  Edin. 
  vol. 
  xx., 
  Part 
  1), 
  viz., 
  that 
  the 
  absolute 
  

   zero 
  is 
  

  

  274-6 
  centigrade 
  degrees, 
  1 
  , 
  , 
  ,, 
  , 
  ■, 
  . 
  

  

  .^i 
  nn 
  , 
  n 
  t-, 
  > 
  below 
  the 
  temperature 
  of 
  melting 
  ice 
  ; 
  

  

  or 
  494-28 
  degrees 
  of 
  Fahrenheit, 
  J 
  

  

  or 
  46228 
  degrees 
  below 
  the 
  ordinary 
  zero 
  of 
  Fahrenheit's 
  scale. 
  

  

  VOL. 
  XX. 
  PART 
  IV. 
  7 
  N 
  

  

  