﻿DYNAMICAL 
  THEORY 
  OF 
  HEAT. 
  267 
  

  

  in 
  form, 
  either 
  is 
  a 
  consequence 
  of 
  the 
  other. 
  The 
  reasoning 
  in 
  each 
  demonstra- 
  

   tion 
  is 
  strictly 
  analogous 
  to 
  that 
  which 
  Caenot 
  originally 
  gave. 
  

  

  15. 
  A 
  complete 
  theory 
  of 
  the 
  motive 
  power 
  of 
  heat 
  would 
  consist 
  of 
  the 
  ap- 
  

   plication 
  of 
  the 
  two 
  propositions 
  demonstrated 
  above, 
  to 
  every 
  possible 
  method 
  of 
  

   producing 
  mechanical 
  effect 
  from 
  thermal 
  agency.* 
  As 
  yet 
  this 
  has 
  not 
  been 
  

   done 
  for 
  the 
  electrical 
  method, 
  as 
  far 
  as 
  regards 
  the 
  criterion 
  of 
  a 
  perfect 
  engine, 
  

   implied 
  in 
  the 
  second 
  proposition, 
  and 
  probably 
  cannot 
  be 
  done 
  without 
  certain 
  

   limitations 
  ; 
  but 
  the 
  application 
  of 
  the 
  first 
  proposition 
  has 
  been 
  very 
  thoroughly 
  

   investigated, 
  and 
  verified 
  experimentally, 
  by 
  Mr 
  Joule, 
  in 
  his 
  researches 
  " 
  On 
  

   the 
  Calorific 
  Effects 
  of 
  Magneto-Electricity 
  ;" 
  and 
  on 
  it 
  is 
  founded 
  one 
  of 
  his 
  ways 
  

   of 
  determining 
  experimentally 
  the 
  mechanical 
  equivalent 
  of 
  heat. 
  Thus, 
  from 
  

   his 
  discovery 
  of 
  the 
  laws 
  of 
  generation 
  of 
  heat 
  in 
  the 
  galvanic 
  circuit,! 
  it 
  follows 
  

   that, 
  when 
  mechanical 
  work 
  by 
  means 
  of 
  a 
  magneto-electric 
  machine 
  is 
  the 
  source 
  

   of 
  the 
  galvanism, 
  the 
  heat 
  generated 
  in 
  any 
  given 
  portion 
  of 
  the 
  fixed 
  part 
  of 
  the 
  

   circuit 
  is 
  proportional 
  to 
  the 
  whole 
  work 
  spent; 
  and 
  from 
  his 
  experimental 
  

   demonstration 
  that 
  heat 
  is 
  developed 
  in 
  any 
  moving 
  part 
  of 
  the 
  circuit 
  at 
  exactly 
  

   the 
  same 
  rate 
  as 
  if 
  it 
  were 
  at 
  rest, 
  and 
  traversed 
  by 
  a 
  current 
  of 
  the 
  same 
  strength, 
  

   he 
  is 
  enabled 
  to 
  conclude 
  — 
  

  

  (1.) 
  That 
  heat 
  may 
  be 
  created 
  by 
  working 
  a 
  magneto-electric 
  machine. 
  

  

  (2.) 
  That 
  if 
  the 
  current 
  excited 
  be 
  not 
  allowed 
  to 
  ^produce 
  any 
  other 
  than 
  

   thermal 
  effects, 
  the 
  total 
  quantity 
  of 
  heat 
  produced 
  is, 
  in 
  all 
  circumstances, 
  

   exactly 
  proportional 
  to 
  the 
  quantity 
  of 
  work 
  spent. 
  

  

  16. 
  Again, 
  the 
  admirable 
  discovery 
  of 
  Peltier, 
  that 
  cold 
  is 
  produced 
  by 
  an 
  

   electrical 
  current 
  passing 
  from 
  bismuth 
  to 
  antimony, 
  is 
  referred 
  to 
  by 
  Joule, 
  as 
  

   shewing 
  how 
  it 
  may 
  be 
  proved 
  that, 
  when 
  an 
  electrical 
  current 
  is 
  continuously 
  

   produced 
  from 
  a 
  purely 
  thermal 
  source, 
  the 
  quantities 
  of 
  heat 
  evolved 
  electrically 
  

   in 
  the 
  different 
  homogeneous 
  parts 
  of 
  the 
  circuit 
  are 
  only 
  compensations 
  for 
  a 
  loss 
  

   from 
  the 
  junctions 
  of 
  the 
  different 
  metals, 
  or 
  that, 
  when 
  the 
  effect 
  of 
  the 
  current 
  

   is 
  entirely 
  thermal, 
  there 
  must 
  be 
  just 
  as 
  much 
  heat 
  emitted 
  from 
  the 
  parts 
  not 
  

   affected 
  by 
  the 
  source 
  as 
  is 
  taken 
  in 
  from 
  the 
  source. 
  

  

  17. 
  Lastly, 
  t 
  when 
  a 
  current 
  produced 
  by 
  thermal 
  agency 
  is 
  made 
  to 
  work 
  an 
  

  

  * 
  " 
  There 
  are 
  [at 
  present 
  known] 
  two, 
  and 
  only 
  two, 
  distinct 
  ways 
  in 
  which 
  mechanical 
  effect 
  

   can 
  be 
  obtained 
  from 
  heat. 
  One 
  of 
  these 
  is 
  by 
  the 
  alterations 
  of 
  volume 
  which 
  bodies 
  experience 
  

   through 
  the 
  action 
  of 
  heat, 
  the 
  other 
  is 
  through 
  the 
  medium 
  of 
  electric 
  agency." 
  — 
  Account 
  of 
  Car- 
  

  

  not's 
  Theory, 
  § 
  4. 
  (Transactions, 
  Vol. 
  XVL, 
  Part 
  V.) 
  A 
  paper 
  by 
  Mr 
  Jouxe, 
  

  

  containing 
  demonstrations 
  of 
  these 
  laws, 
  and 
  of 
  others 
  on 
  the 
  relations 
  of 
  the 
  chemical 
  and 
  thermal 
  

   agencies 
  concerned, 
  was 
  communicated 
  to 
  the 
  Royal 
  Society 
  on 
  the 
  17th 
  December 
  1840, 
  but 
  was 
  not 
  

   published 
  in 
  the 
  Transactions. 
  (See 
  abstract 
  containing 
  a 
  statement 
  of 
  the 
  laws 
  quoted 
  above, 
  in 
  the 
  

   Philosophical 
  Magazine, 
  vol. 
  xviii., 
  p. 
  308). 
  It 
  was 
  published 
  in 
  the 
  Philosophical 
  Magazine 
  in 
  

   October 
  1841 
  (vol. 
  xix., 
  p. 
  260). 
  

  

  f 
  That, 
  in 
  a 
  given 
  fixed 
  part 
  of 
  the 
  circuit, 
  the 
  heat 
  evolved 
  in 
  a 
  given 
  time 
  is 
  proportional 
  to 
  

   the 
  square 
  of 
  the 
  strength 
  of 
  the 
  current, 
  and 
  for 
  different 
  fixed 
  parts, 
  with 
  the 
  same 
  strength 
  of 
  

   current, 
  the 
  quantities 
  of 
  heat 
  evolved 
  in 
  equal 
  times 
  are 
  as 
  the 
  resistances. 
  

  

  J 
  This 
  reasoning 
  was 
  suggested 
  to 
  me 
  by 
  the 
  following 
  passage 
  contained 
  in 
  a 
  letter 
  which 
  I 
  

  

  