﻿DYNAMICAL 
  THEORY 
  OF 
  HEAT. 
  263 
  

  

  power 
  of 
  heat, 
  must 
  be 
  made 
  when 
  the 
  hypothesis 
  of 
  the 
  Dynamical 
  Theory, 
  

   contrary 
  as 
  it 
  is 
  to 
  Carnot's 
  fundamental 
  hypothesis, 
  is 
  adopted. 
  

  

  (2.) 
  To 
  point 
  out 
  the 
  significance 
  in 
  the 
  Dynamical 
  Theory 
  of 
  the 
  numerical 
  

   results 
  deduced 
  from 
  Regnault's 
  Observations 
  on 
  Steam, 
  and 
  communicated 
  

   about 
  two 
  years 
  ago 
  to 
  the 
  Society, 
  with 
  an 
  account 
  of 
  Carnot's 
  Theory, 
  by 
  

   the 
  author 
  of 
  the 
  present 
  paper 
  ; 
  and 
  to 
  shew 
  that 
  by 
  taking 
  these 
  numbers 
  

   (subject 
  to 
  correction 
  when 
  accurate 
  experimental 
  data 
  regarding 
  the 
  density 
  of 
  

   saturated 
  steam 
  shall 
  have 
  been 
  afforded), 
  in 
  connection 
  with 
  Joule's 
  mechanical 
  

   equivalent 
  of 
  a 
  thermal 
  unit, 
  a 
  complete 
  theory 
  of 
  the 
  motive 
  power 
  of 
  heat, 
  

   within 
  the 
  temperature 
  limits 
  of 
  the 
  experimental 
  data, 
  is 
  obtained. 
  

  

  (3.) 
  To 
  point 
  out 
  some 
  remarkable 
  relations 
  connecting 
  the 
  physical 
  properties 
  

   of 
  all 
  substances, 
  established 
  by 
  reasoning 
  analogous 
  to 
  that 
  of 
  Carnot, 
  but 
  

   founded 
  in 
  part 
  on 
  the 
  contrary 
  principle 
  of 
  the 
  Dynamical 
  Theory. 
  

  

  Part 
  I. 
  — 
  Fundamental 
  Principles 
  in 
  the 
  Theory 
  of 
  the 
  Motive 
  

  

  Power 
  of 
  Heat. 
  

  

  7. 
  According 
  to 
  an 
  obvious 
  principle, 
  first 
  introduced, 
  however, 
  into 
  the 
  

   theory 
  of 
  the 
  motive 
  power 
  of 
  heat 
  by 
  Carnot, 
  mechanical 
  effect 
  produced 
  in 
  any 
  

   process 
  cannot 
  be 
  said 
  to 
  have 
  been 
  derived 
  from 
  a 
  purely 
  thermal 
  source, 
  unless 
  

   at 
  the 
  end 
  of 
  the 
  process 
  all 
  the 
  materials 
  used 
  are 
  in 
  precisely 
  the 
  same 
  physical 
  

   and 
  mechanical 
  circumstances 
  as 
  they 
  were 
  at 
  the 
  beginning. 
  In 
  some 
  conceiv- 
  

   able 
  " 
  thermo-dynamic 
  engines," 
  as 
  for 
  instance 
  Faraday's 
  floating 
  magnet, 
  or 
  

   Barlow's 
  " 
  wheel 
  and 
  axle," 
  made 
  to 
  rotate 
  and 
  perform 
  work 
  uniformly 
  by 
  

   means 
  of 
  a 
  current 
  continuously 
  excited 
  by 
  heat 
  communicated 
  to 
  two 
  metals 
  in 
  

   contact, 
  or 
  the 
  thermo-electric 
  rotatory 
  apparatus 
  devised 
  by 
  Marsh, 
  which 
  has 
  

   been 
  actually 
  constructed 
  ; 
  this 
  condition 
  is 
  fulfilled 
  at 
  every 
  instant. 
  On 
  the 
  

   other 
  hand, 
  in 
  all 
  thermo-dynamic 
  engines, 
  founded 
  on 
  electrical 
  agency, 
  in 
  which 
  

   discontinuous 
  galvanic 
  currents, 
  or 
  pieces 
  of 
  soft 
  iron 
  in 
  a 
  variable 
  state 
  of 
  

   magnetization, 
  are 
  used 
  ; 
  and 
  in 
  all 
  engines 
  founded 
  on 
  the 
  alternate 
  expansions 
  

   and 
  contractions 
  of 
  media 
  ; 
  there 
  are 
  really 
  alterations 
  in 
  the 
  condition 
  of 
  mate- 
  

   rials 
  ; 
  but, 
  in 
  accordance 
  with 
  the 
  principle 
  stated 
  above, 
  these 
  alterations 
  must 
  

   be 
  strictly 
  periodical. 
  In 
  any 
  such 
  engine, 
  the 
  series 
  of 
  motions 
  performed 
  during 
  

   a 
  period, 
  at 
  the 
  end 
  of 
  which 
  the 
  materials 
  are 
  restored 
  to 
  precisely 
  the 
  same 
  

   condition 
  as 
  that 
  in 
  which 
  they 
  existed 
  at 
  the 
  beginning, 
  constitutes 
  what 
  will 
  be 
  

   called 
  a 
  complete 
  cycle 
  of 
  its 
  operations. 
  Whenever 
  in 
  what 
  follows, 
  the 
  work 
  

   done, 
  or 
  the 
  mechanical 
  effect 
  produced, 
  by 
  a 
  thermo-dynamic 
  engine 
  is 
  mentioned 
  

   without 
  qualification, 
  it 
  must 
  be 
  understood 
  that 
  the 
  mechanical 
  effect 
  produced, 
  

   either 
  in 
  a 
  non- 
  varying 
  engine, 
  or 
  in 
  a 
  complete 
  cycle 
  or 
  any 
  number 
  of 
  complete 
  

   cycles 
  of 
  a 
  periodical 
  engine 
  is 
  meant. 
  

  

  