﻿156 
  

  

  MR 
  W. 
  J. 
  M. 
  RANKINE 
  ON 
  THE 
  

  

  The 
  following 
  are 
  some 
  additional 
  values 
  of 
  the 
  constant 
  a 
  for 
  steam, 
  corre- 
  

   sponding 
  to 
  various 
  units 
  of 
  pressure 
  used 
  in 
  practice. 
  

  

  Units 
  of 
  Pressure. 
  

  

  Atmospheres 
  of 
  760 
  millimetres 
  of 
  mercury, 
  

  

  = 
  29-922 
  inches 
  of 
  mercury, 
  

  

  = 
  14*7 
  lb. 
  on 
  the 
  square 
  inch, 
  

  

  = 
  1-0333 
  kilogrammes 
  on 
  the 
  square 
  centimetre. 
  

   Atmospheres 
  of 
  30 
  inches 
  of 
  mercury, 
  

  

  =761*99 
  millimetres, 
  

  

  = 
  1474 
  lb. 
  on 
  the 
  square 
  inch, 
  

  

  = 
  1-036 
  kilogrammes 
  on 
  the 
  square 
  centimetre, 
  

   Kilogrammes 
  on 
  the 
  square 
  centimetre, 
  . 
  

   Kilogrammes 
  on 
  the 
  circular 
  centimetre, 
  

   Pounds 
  avoirdupois 
  on 
  the 
  square 
  inch, 
  

   Pounds 
  avoirdupois 
  on 
  the 
  circular 
  inch, 
  

   Pounds 
  avoirdupois 
  on 
  the 
  square 
  foot, 
  

  

  Values 
  of 
  a. 
  

  

  4-950433 
  

  

  4-949300 
  

   4-964658 
  

   4-859748 
  

   6-117662 
  

   6-012752 
  

   8-276025 
  

  

  All 
  the 
  numerical 
  values 
  of 
  the 
  constants 
  are 
  for 
  common 
  logarithms. 
  

  

  Section 
  I. 
  — 
  Of 
  the 
  Mutual 
  Conversion 
  of 
  Heat 
  and 
  Expansive 
  Power. 
  

  

  (1.) 
  The 
  quantity 
  of 
  heat 
  in 
  a 
  given 
  mass 
  of 
  matter, 
  according 
  to 
  the 
  hypo- 
  

   thesis 
  of 
  molecular 
  vortices, 
  as 
  well 
  as 
  every 
  other 
  hypothesis 
  which 
  ascribes 
  the 
  

   phenomena 
  of 
  heat 
  to 
  motion, 
  is 
  measured 
  by 
  the 
  mechanical 
  power 
  to 
  which 
  that 
  

   motion 
  is 
  equivalent, 
  that 
  being 
  a 
  quantity 
  the 
  total 
  amount 
  of 
  which 
  in 
  a 
  given 
  

   system 
  of 
  bodies 
  cannot 
  be 
  altered 
  by 
  their 
  mutual 
  actions, 
  although 
  its 
  distribu- 
  

   tion 
  and 
  form 
  may 
  be 
  altered. 
  This 
  is 
  expressed 
  in 
  Equation 
  XII. 
  of 
  the 
  Intro- 
  

   duction, 
  where 
  the 
  quantity 
  of 
  heat 
  in 
  unity 
  of 
  weight, 
  Q, 
  is 
  represented 
  by 
  the 
  

  

  height 
  s- 
  , 
  from 
  which 
  a 
  body 
  must 
  fall 
  in 
  order 
  to 
  acquire 
  the 
  velocity 
  of 
  the 
  

  

  molecular 
  oscillations. 
  This 
  height, 
  being 
  multiplied 
  by 
  the 
  weight 
  of 
  a 
  body, 
  

   gives 
  the 
  mechanical 
  power 
  to 
  which 
  the 
  oscillations 
  constituting 
  its 
  heat 
  are 
  

   equivalent. 
  The 
  real 
  specific 
  heat 
  of 
  unity 
  of 
  weight, 
  as 
  given 
  in 
  Equation 
  XIII. 
  

   of 
  the 
  Introduction, 
  

  

  d 
  SL 
  3k 
  

  

  dr 
  ' 
  ' 
  2C«jU 
  

  

  represents 
  the 
  depth 
  of 
  fall, 
  which 
  is 
  equivalent 
  to 
  one 
  degree 
  of 
  rise 
  of 
  temperature 
  

   in 
  any 
  given 
  weight 
  of 
  the 
  substance 
  under 
  consideration. 
  

  

  We 
  know, 
  to 
  a 
  greater 
  or 
  less 
  degree 
  of 
  precision, 
  the 
  ratios 
  of 
  the 
  specific 
  

   heats 
  of 
  many 
  substances 
  to 
  each 
  other, 
  and 
  they 
  are 
  commonly 
  expressed 
  by 
  

   taking 
  that 
  of 
  water 
  at 
  the 
  temperature 
  of 
  melting 
  ice 
  as 
  unity 
  ; 
  but 
  their 
  actual 
  

   mechanical 
  values 
  have 
  as 
  yet 
  been 
  very 
  imperfectly 
  ascertained, 
  and, 
  in 
  fact, 
  the 
  

   data 
  necessary 
  for 
  their 
  determination 
  are 
  incomplete. 
  

  

  (2.) 
  Mr 
  Joule, 
  indeed, 
  has 
  made 
  several 
  very 
  interesting 
  series 
  of 
  experi- 
  

   ments, 
  in 
  order 
  to 
  ascertain 
  the 
  quantity 
  of 
  heat 
  developed 
  in 
  various 
  substances 
  

  

  

  