﻿32 
  P. 
  de 
  Saussure 
  — 
  Graphical 
  Thermodynamics. 
  

  

  MM' 
  determines 
  the 
  value 
  of 
  the 
  quotient 
  — 
  . 
  The 
  heat 
  

  

  as 
  

  

  absorbed 
  in 
  this 
  elementary 
  transformation 
  is 
  given 
  by 
  : 
  

  

  EdH 
  = 
  sdcp 
  + 
  2 
  cpds 
  

   and 
  the 
  corresponding 
  variation 
  of 
  temperature, 
  by 
  : 
  

  

  KEdT 
  = 
  sdcp 
  + 
  cpds 
  

  

  JTT 
  

  

  Dividing 
  member 
  to 
  member, 
  and 
  putting 
  — 
  - 
  = 
  y 
  for 
  abrevia- 
  

  

  a 
  l 
  

  

  tion, 
  we 
  have 
  : 
  

  

  y 
  = 
  sdcp 
  + 
  2 
  cpds 
  

  

  K 
  sdcp 
  -f- 
  cpds 
  ^ 
  

  

  The 
  quotient 
  y 
  — 
  — 
  may 
  be 
  called 
  the 
  specific 
  heat 
  of 
  the 
  

   a 
  l 
  

  

  substance 
  at 
  the 
  state 
  JIT 
  and 
  for 
  the 
  direction 
  MM' 
  (since 
  y 
  

  

  varies 
  with 
  the 
  value 
  of 
  -7-, 
  i. 
  e., 
  the 
  direction 
  of 
  MM'). 
  

  

  dq> 
  ds 
  

  

  When 
  -— 
  has 
  such 
  a 
  value 
  that 
  the 
  direction 
  MM' 
  coincides 
  

   as 
  

  

  with 
  that 
  of 
  the 
  tangent 
  to 
  the 
  curve 
  of 
  constant 
  volume, 
  the 
  

   corresponding 
  value 
  of 
  y 
  is 
  evidently 
  the 
  " 
  specific 
  heat 
  at 
  con- 
  

   stant 
  volume 
  " 
  at 
  the 
  state 
  M 
  7 
  which 
  specific 
  heat 
  we 
  shall 
  

   denote 
  by 
  the 
  letter 
  c. 
  

  

  In 
  the 
  same 
  way, 
  when 
  — 
  has 
  such 
  a 
  value 
  that 
  MM' 
  coin- 
  

   as 
  

  

  cides 
  with 
  the 
  tangent 
  to 
  the 
  curve 
  of 
  constant 
  pressure, 
  the 
  

   corresponding 
  value 
  of 
  y 
  is 
  by 
  definition 
  the 
  " 
  specific 
  heat 
  at 
  

   constant 
  pressure 
  " 
  of 
  the 
  substance 
  at 
  the 
  state 
  M 
  / 
  this 
  spe- 
  

   cific 
  heat 
  will 
  be 
  denoted 
  by 
  the 
  letter 
  C. 
  

  

  The 
  value 
  of 
  y 
  corresponding 
  to 
  a 
  direction 
  parallel 
  to 
  the 
  

   axis 
  of 
  cp 
  may 
  be 
  called 
  for 
  the 
  same 
  reason 
  : 
  the 
  " 
  specific 
  heat 
  

   at 
  constant 
  symbolical 
  volume 
  /" 
  and 
  that 
  corresponding 
  to 
  a 
  

   direction 
  parallel 
  to 
  the 
  axis 
  of 
  s 
  : 
  the 
  " 
  specific 
  heat 
  at 
  con- 
  

   stant 
  symbolical 
  pressure" 
  

  

  Now, 
  equation 
  (10) 
  can 
  be 
  written 
  : 
  

  

  s-^- 
  + 
  2cp 
  

   y 
  as 
  

  

  K 
  — 
  den 
  

  

  Let 
  us 
  produce 
  MM' 
  until 
  it 
  intersects 
  the 
  axis 
  of 
  <p 
  at 
  

   point 
  A, 
  and 
  measure 
  on 
  this 
  axis 
  three 
  equal 
  lengths 
  : 
  om, 
  

   mP 
  and 
  PQ. 
  each 
  one 
  of 
  them 
  equal 
  to 
  the 
  ordinate 
  tp 
  of 
  

   point 
  M 
  ; 
  then, 
  we 
  shall 
  have: 
  

  

  mA=s~- 
  mQ 
  = 
  %cp 
  and 
  mP 
  = 
  (p 
  

  

  