﻿HEAT 
  PRODUCED 
  BY 
  THE 
  COMPRESSION 
  OF 
  A 
  GAS. 
  293 
  

  

  in 
  the 
  expression 
  for 
  it 
  being 
  obtained 
  by 
  dividing 
  the 
  numbers 
  tabulated 
  at 
  the 
  end 
  

   of 
  Regnault's 
  eighth 
  Memoire 
  by 
  760. 
  The 
  considerableness 
  of 
  the 
  deviations 
  

   from 
  the 
  gaseous 
  laws 
  which 
  equation 
  (II.) 
  indicates, 
  is 
  seen 
  at 
  once 
  by 
  comparing 
  

   the 
  numbers 
  in 
  Col. 
  2 
  with 
  those 
  in 
  Col. 
  3 
  of 
  the 
  preceding 
  Table, 
  and 
  observing 
  

   that 
  the 
  coefficient 
  of 
  [<r] 
  in 
  (II.) 
  is, 
  for 
  each 
  temperature 
  shown 
  in 
  that 
  Table, 
  

   obtained 
  by 
  dividing 
  the 
  corresponding 
  number 
  in 
  Col. 
  2 
  by 
  that 
  in 
  Col. 
  3. 
  Col. 
  4 
  

   shows 
  what 
  the 
  values 
  of 
  /x 
  would 
  be 
  if 
  the 
  density 
  of 
  saturated 
  steam 
  at 
  100° 
  were 
  

   yfjfr 
  6 
  instead 
  of 
  j^r-p 
  and, 
  for 
  other 
  temperatures, 
  varied 
  according 
  to 
  the 
  gaseous 
  

  

  laws. 
  

  

  8. 
  This 
  subject 
  has 
  been 
  very 
  carefully 
  examined 
  by 
  Clausius, 
  who 
  has 
  indi- 
  

   cated 
  the 
  great 
  deviations 
  from 
  the 
  gaseous 
  laws 
  of 
  density 
  that 
  Mayer's 
  hypothesis 
  

   requires 
  in 
  saturated 
  steam, 
  and 
  has 
  given 
  an 
  empirical 
  formula 
  for 
  the 
  density 
  

   of 
  saturated 
  steam 
  founded 
  on 
  that 
  hypothesis, 
  and 
  on 
  Regnault's 
  observations 
  

   on 
  the 
  pressure 
  and 
  latent 
  heat. 
  In 
  this 
  direction 
  theory 
  can 
  go 
  no 
  farther, 
  for 
  

   want 
  of 
  experimental 
  data, 
  although, 
  from 
  what 
  we 
  know 
  of 
  gases 
  and 
  saturated 
  

   vapours, 
  it 
  may 
  be 
  doubted 
  whether 
  such 
  excessive 
  deviations, 
  in 
  the 
  case 
  of 
  

   steam, 
  from 
  the 
  laws 
  of 
  a 
  " 
  perfect 
  gas" 
  are 
  rendered 
  probable 
  by 
  a 
  hypothesis 
  

   resting 
  on 
  no 
  experimental 
  evidence 
  whatever.* 
  

  

  9. 
  To 
  Joule 
  we 
  are 
  indebted 
  for 
  a 
  most 
  important 
  series 
  of 
  experimental 
  

   researches 
  on 
  the 
  relation 
  between 
  the 
  thermal 
  effects, 
  the 
  external 
  mechanical 
  

   effects, 
  and 
  the 
  internal 
  mechanical 
  effects 
  {vis 
  viva 
  destroyed 
  by 
  fluid 
  friction) 
  

   due 
  to 
  compressions 
  and 
  expansions 
  of 
  air 
  in 
  various 
  circumstances.f 
  These 
  re- 
  

   searches 
  afford 
  actual 
  tests 
  which, 
  so 
  far 
  as 
  they 
  go, 
  are 
  verifications 
  of 
  the 
  

   truth 
  of 
  Mayer's 
  hypothesis 
  for 
  temperatures 
  between 
  50° 
  and 
  60° 
  Fahr., 
  founded 
  

   on 
  two 
  distinct 
  methods, 
  either 
  of 
  which 
  is 
  perfect 
  in 
  principle, 
  and 
  might 
  be 
  

   made 
  the 
  foundation 
  of 
  experiments 
  at 
  any 
  temperature 
  whatever. 
  

  

  10. 
  The 
  first 
  of 
  these 
  methods 
  consists 
  simply 
  in 
  determining, 
  by 
  direct 
  experi- 
  

   ment, 
  the 
  heat 
  evolved 
  by 
  the 
  expenditure 
  of 
  a 
  given 
  amount 
  of 
  work 
  in 
  com- 
  

   pressing 
  air, 
  and 
  comparing 
  it 
  with 
  the 
  quantity 
  of 
  heat 
  created 
  by 
  the 
  same 
  

   amount 
  of 
  work 
  in 
  Joule's 
  original 
  experiments 
  on 
  the 
  heat 
  developed 
  by 
  mag- 
  

   neto-electricity, 
  and 
  by 
  the 
  friction 
  of 
  fluids 
  in 
  motion. 
  

  

  11. 
  The 
  second 
  method 
  is 
  especially 
  remarkable, 
  as 
  affording, 
  in 
  each 
  experi- 
  

   ment, 
  an 
  independent 
  test 
  of 
  the 
  truth 
  of 
  Mayer's 
  hypothesis 
  for 
  air 
  at 
  the 
  tem- 
  

   perature 
  used, 
  without 
  requiring 
  any 
  knowledge 
  of 
  the 
  absolute 
  value 
  of 
  the 
  me- 
  

   chanical 
  equivalent 
  of 
  heat. 
  In 
  Joule's 
  actual 
  experiments, 
  the 
  test 
  is 
  simply 
  

  

  * 
  Joule's 
  experimental 
  verification 
  of 
  Mayer's 
  law 
  for 
  temperatures 
  of 
  from 
  50° 
  to 
  60° 
  Fahr., 
  

   shews, 
  if 
  rigorously 
  exact, 
  that 
  the 
  density 
  of 
  saturated 
  steam 
  at 
  about 
  1 
  0° 
  centigrade 
  must 
  be 
  V^? 
  6 
  

   of 
  what 
  was 
  assumed 
  for 
  it 
  in 
  the 
  calculations 
  of 
  my 
  former 
  paper, 
  but 
  does 
  not 
  go 
  towards 
  indi- 
  

   cating 
  any 
  deviation 
  from 
  the 
  gaseous 
  laws 
  of 
  variation 
  in 
  the 
  density 
  of 
  saturated 
  steam 
  at 
  different 
  

   temperatures. 
  

  

  f 
  Philosophical 
  Magazine, 
  May 
  1845. 
  

  

  VOL. 
  XX. 
  PART 
  II. 
  4 
  K 
  

  

  