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  PROFESSOR 
  WILLIAM 
  THOMSON 
  ON 
  THE 
  

  

  remark, 
  that 
  the 
  measurement 
  actually 
  made 
  is 
  of 
  the 
  quantity 
  of 
  heat 
  emitted 
  by 
  

   a 
  certain 
  weight 
  of 
  water 
  in 
  passing 
  through 
  a 
  calorimetrical 
  apparatus, 
  which 
  it 
  

   enters 
  as 
  saturated 
  steam, 
  and 
  leaves 
  in 
  the 
  liquid 
  state, 
  the 
  result 
  being 
  reduced 
  

   to 
  what 
  would 
  have 
  been 
  found, 
  if 
  the 
  final 
  temperature 
  of 
  the 
  water 
  had 
  been 
  

   exactly 
  0°. 
  For 
  there 
  being 
  no 
  external 
  mechanical 
  effect 
  produced 
  (other 
  than 
  

   that 
  of 
  sound, 
  which 
  it 
  is 
  to 
  be 
  presumed 
  is 
  quite 
  inappreciable), 
  the 
  only 
  external 
  

   effect 
  is 
  the 
  emission 
  of 
  heat. 
  This 
  must, 
  therefore, 
  according 
  to 
  the 
  fundamen- 
  

   tal 
  proposition 
  of 
  the 
  dynamical 
  theory, 
  be 
  independent 
  of 
  the 
  intermediate 
  

   agencies. 
  It 
  follows 
  that, 
  however 
  the 
  steam 
  may 
  rush 
  through 
  the 
  calorimeter, 
  

   and 
  at 
  whatever 
  reduced 
  pressure 
  it 
  may 
  actually 
  be 
  condensed,* 
  the 
  heat 
  

   emitted 
  externally 
  must 
  be 
  exactly 
  the 
  same 
  as 
  if 
  the 
  condensation 
  took 
  place 
  

   under 
  the 
  full 
  pressure 
  of 
  the 
  entering 
  saturated 
  steam, 
  and 
  we 
  conclude 
  that 
  

   the 
  total 
  heat 
  as 
  actually 
  determined 
  from 
  his 
  experiments 
  by 
  Regnault, 
  is 
  the 
  

   quantity 
  of 
  heat 
  that 
  would 
  be 
  required, 
  first 
  to 
  raise 
  the 
  liquid 
  to 
  the 
  specified 
  

   temperature, 
  and 
  then 
  to 
  evaporate 
  it 
  at 
  that 
  temperature 
  ; 
  and 
  that 
  the 
  prin- 
  

   ciple 
  on 
  which 
  he 
  determines 
  the 
  latent 
  heat 
  is 
  correct. 
  Hence, 
  through 
  the 
  

   range 
  of 
  his 
  experiments, 
  that 
  is 
  from 
  0° 
  to 
  230°, 
  we 
  may 
  consider 
  the 
  second 
  of 
  

   the 
  data 
  required 
  for 
  the 
  calculation 
  of 
  /j. 
  as 
  being 
  supplied 
  in 
  a 
  complete 
  and 
  

   satisfactory 
  manner. 
  

  

  34. 
  There 
  remains 
  only 
  the 
  third 
  of 
  the 
  data, 
  or 
  the 
  volume 
  of 
  a 
  given 
  weight 
  

   of 
  saturated 
  steam, 
  for 
  which 
  accurate 
  experiments 
  through 
  an 
  extensive 
  range 
  

   are 
  wanting; 
  and 
  no 
  experimental 
  researches 
  bearing 
  on 
  the 
  subject 
  having 
  been 
  

   made 
  since 
  the 
  time 
  when 
  my 
  former 
  paper 
  was 
  written, 
  I 
  see 
  no 
  reason 
  for 
  

   supposing 
  that 
  the 
  values 
  of 
  \x 
  which 
  I 
  then 
  gave 
  are 
  not 
  the 
  most 
  probable 
  

   that 
  can 
  be 
  obtained 
  in 
  the 
  present 
  state 
  of 
  science 
  ; 
  and, 
  on 
  the 
  understanding 
  

   stated 
  in 
  § 
  33 
  of 
  that 
  paper, 
  that 
  accurate 
  experimental 
  determinations 
  of 
  the 
  den- 
  

   sities 
  of 
  saturated 
  steam 
  at 
  different 
  temperatures 
  may 
  indicate 
  considerable 
  errors 
  

   in 
  the 
  densities 
  which 
  have 
  been 
  assumed 
  according 
  to 
  the 
  " 
  gaseous 
  laws," 
  and 
  may 
  

  

  * 
  If 
  the 
  steam 
  have 
  to 
  rush 
  through 
  a 
  long 
  fine 
  tuhe, 
  or 
  through 
  a 
  small 
  aperture 
  within 
  the 
  

   calorimetrical 
  apparatus, 
  its 
  pressure 
  will 
  be 
  diminished 
  before 
  it 
  is 
  condensed, 
  and 
  there 
  will, 
  there- 
  

   fore, 
  in 
  two 
  parts 
  of 
  the 
  calorimeter 
  be 
  saturated 
  steam 
  at 
  different 
  temperatures 
  (as, 
  for 
  instance, 
  

   would 
  be 
  the 
  case 
  if 
  steam 
  from 
  a 
  high 
  pressure 
  boiler 
  were 
  distilled 
  into 
  the 
  open 
  air) 
  ; 
  yet, 
  on 
  

   account 
  of 
  the 
  heat 
  developed 
  by 
  the 
  fluid 
  friction, 
  which 
  would 
  be 
  precisely 
  the 
  equivalent 
  of 
  the 
  

   mechanical 
  effect 
  of 
  the 
  expansion 
  wasted 
  in 
  the 
  rushing, 
  the 
  heat 
  measured 
  by 
  the 
  calorimeter 
  would 
  

   be 
  precisely 
  the 
  same 
  as 
  if 
  the 
  condensation 
  took 
  place 
  at 
  a 
  pressure 
  not 
  appreciably 
  lower 
  than 
  that 
  

   of 
  the 
  entering 
  steam. 
  The 
  circumstances 
  of 
  such 
  a 
  case 
  have 
  been 
  overlooked 
  by 
  Clatjsius 
  

   (Pogoendorff's 
  Annalen, 
  1850, 
  No. 
  4, 
  p. 
  510), 
  when 
  he 
  expresses 
  with 
  some 
  doubt 
  the 
  opinion 
  that 
  

   the 
  latent 
  heat 
  of 
  saturated 
  steam 
  will 
  be 
  truly 
  found 
  from 
  Regnault's 
  " 
  total 
  heat,'' 
  by 
  deducting 
  

   the 
  sensible 
  heat 
  ; 
  and 
  gives 
  as 
  a 
  reason 
  that, 
  in 
  the 
  actual 
  experiments, 
  the 
  condensation 
  must 
  have 
  

   taken 
  place 
  " 
  under 
  the 
  same 
  pressure, 
  or 
  nearly 
  under 
  the 
  same 
  pressure," 
  as 
  the 
  evaporation. 
  The 
  

   question 
  is 
  not, 
  Did 
  the 
  condensation 
  take 
  place 
  at 
  a 
  lower 
  pressure 
  than 
  that 
  of 
  the 
  entering 
  steam 
  ? 
  

   but, 
  Did 
  Regnault 
  make 
  the 
  steam 
  work 
  an 
  engine 
  in 
  passing 
  through 
  the 
  calorimeter, 
  or 
  was 
  there 
  

   so 
  much 
  noise 
  of 
  steam 
  rushing 
  through 
  it 
  as 
  to 
  convert 
  an 
  appreciable 
  portion 
  of 
  the 
  total 
  heat 
  into 
  

   external 
  mechanical 
  effect 
  ? 
  And 
  a 
  negative 
  answer 
  to 
  this 
  is 
  a 
  sufficient 
  reason 
  for 
  adopting 
  with 
  

   certainty 
  the 
  opinion 
  that 
  the 
  principle 
  of 
  his 
  determination 
  of 
  the 
  latent 
  heat 
  is 
  correct. 
  

  

  