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  PROFESSOR 
  WILLIAM 
  THOMSON 
  ON 
  THE 
  

  

  engine 
  and 
  produce 
  mechanical 
  effect, 
  there 
  will 
  be 
  less 
  heat 
  emitted 
  from 
  the 
  

   parts 
  of 
  the 
  circuit 
  not 
  affected 
  by 
  the 
  source 
  than 
  is 
  taken 
  in 
  from 
  the 
  source, 
  by 
  

   an 
  amount 
  precisely 
  equivalent 
  to 
  the 
  mechanical 
  effect 
  produced 
  ; 
  since 
  Joule 
  

   demonstrates 
  experimentally 
  that 
  a 
  current 
  from 
  any 
  kind 
  of 
  source, 
  driving 
  an 
  

   engine, 
  produces 
  in 
  the 
  engine 
  just 
  as 
  much 
  less 
  heat 
  than 
  it 
  would 
  produce 
  in 
  a 
  

   fixed 
  wire 
  exercising 
  the 
  same 
  resistance 
  as 
  is 
  equivalent 
  to 
  the 
  mechanical 
  effect 
  

   produced 
  by 
  the 
  engine. 
  

  

  18. 
  The 
  equality 
  of 
  thermal 
  effects, 
  resulting 
  from 
  equal 
  causes 
  through 
  very 
  

   different 
  means, 
  is 
  beautifully 
  illustrated 
  by 
  the 
  following 
  statement, 
  drawn 
  from 
  

   Mr 
  Joule's 
  paper 
  on 
  magneto-electricity. 
  

  

  Let 
  there 
  be 
  three 
  equal 
  and 
  similar 
  galvanic 
  batteries, 
  furnished 
  with 
  equal 
  

   and 
  similar 
  electrodes 
  : 
  let 
  A 
  1 
  and 
  B 
  1 
  be 
  the 
  terminations 
  of 
  the 
  electrodes 
  (or 
  wires 
  

   connected 
  with 
  the 
  two 
  poles) 
  of 
  the 
  first 
  battery 
  ; 
  A 
  2 
  and 
  B 
  2 
  the 
  terminations 
  

   of 
  the 
  corresponding 
  electrodes 
  of 
  the 
  second 
  ; 
  and 
  A 
  3 
  and 
  B 
  3 
  of 
  the 
  third 
  battery. 
  

   Let 
  A 
  l 
  and 
  B 
  t 
  be 
  connected 
  with 
  the 
  extremities 
  of 
  a 
  long 
  fixed 
  wire 
  ; 
  let 
  A 
  2 
  and 
  

   B 
  2 
  be 
  connected 
  with 
  the 
  " 
  poles 
  " 
  of 
  an 
  electrolytic 
  apparatus 
  for 
  the 
  decompo- 
  

   sition 
  of 
  water 
  ; 
  and 
  let 
  A 
  3 
  and 
  B 
  3 
  be 
  connected 
  with 
  the 
  poles 
  (or 
  ports 
  as 
  they 
  

   might 
  be 
  called) 
  of 
  an 
  electro-magnetic 
  engine. 
  Then 
  if 
  the 
  length 
  of 
  the 
  wire 
  

   between 
  A, 
  and 
  B 
  : 
  , 
  and 
  the 
  speed 
  of 
  the 
  engine 
  between 
  A 
  3 
  and 
  B 
  :J 
  , 
  be 
  so 
  adjusted 
  

   that 
  the 
  strength 
  of 
  the 
  current 
  (which, 
  for 
  simplicity, 
  we 
  may 
  suppose 
  to 
  be 
  con- 
  

   tinuous 
  and 
  perfectly 
  uniform 
  in 
  each 
  case) 
  may 
  be 
  the 
  same 
  in 
  the 
  three 
  circuits, 
  

   there 
  will 
  be 
  more 
  heat 
  given 
  out 
  in 
  any 
  time 
  in 
  the 
  wire 
  between 
  A 
  1 
  and 
  B 
  l 
  than 
  

   in 
  the 
  electrolytic 
  apparatus 
  between 
  A 
  2 
  and 
  B,, 
  or 
  the 
  working 
  engine 
  between 
  

   A 
  3 
  and 
  B.,. 
  But 
  if 
  the 
  hydrogen 
  were 
  allowed 
  to 
  burn 
  in 
  the 
  oxygen, 
  within 
  the 
  

   electrolytic 
  vessel, 
  and 
  the 
  engine 
  to 
  waste 
  all 
  its 
  work 
  without 
  producing 
  any 
  

   other 
  than 
  thermal 
  effects 
  (as 
  it 
  would 
  do, 
  for 
  instance, 
  if 
  all 
  its 
  work 
  were 
  spent 
  

   in 
  continuously 
  agitating 
  a 
  limited 
  fluid 
  mass), 
  the 
  total 
  heat 
  emitted 
  would 
  be 
  

   precisely 
  the 
  same 
  in 
  each 
  of 
  these 
  two 
  pieces 
  of 
  apparatus 
  as 
  in 
  the 
  wire 
  between 
  

  

  received 
  from 
  Mr 
  Joule 
  on 
  the 
  8th 
  of 
  July 
  1847. 
  " 
  In 
  Peltier's 
  experiment 
  on 
  cold 
  produced 
  at 
  

   the 
  bismuth 
  and 
  antimony 
  solder, 
  we 
  have 
  an 
  instance 
  of 
  the 
  conversion 
  of 
  heat 
  into 
  the 
  mechanical 
  

   force 
  of 
  the 
  current," 
  which 
  must 
  have 
  been 
  meant 
  as 
  an 
  answer 
  to 
  a 
  remark 
  I 
  had 
  made, 
  that 
  no 
  

   evidence 
  could 
  be 
  adduced 
  to 
  shew 
  that 
  heat 
  is 
  ever 
  put 
  out 
  of 
  existence. 
  I 
  now 
  fully 
  admit 
  the 
  

   force 
  of 
  that 
  answer, 
  but 
  it 
  would 
  require 
  a 
  proof 
  that 
  there 
  is 
  more 
  heat 
  put 
  out 
  of 
  existence 
  at 
  the 
  

   heated 
  soldei'ing 
  than 
  is 
  created 
  at 
  the 
  cold 
  soldering, 
  to 
  make 
  the 
  "evidence" 
  be 
  experimental. 
  

   That 
  this 
  is 
  the 
  case 
  I 
  think 
  is 
  certain, 
  because 
  the 
  statements 
  of 
  § 
  16 
  in 
  the 
  text 
  are 
  demonstrated 
  

   consequences 
  of 
  the 
  first 
  fundamental 
  proposition 
  ; 
  but 
  it 
  is 
  still 
  to 
  be 
  remarked, 
  that 
  neither 
  in 
  this 
  

   nor 
  in 
  any 
  other 
  case 
  of 
  the 
  production 
  of 
  mechanical 
  effect 
  from 
  purely 
  thermal 
  agency, 
  has 
  the 
  

   ceasing 
  to 
  exist 
  of 
  an 
  equivalent 
  quantity 
  of 
  heat 
  been 
  demonstrated 
  otherwise 
  than 
  theoretically. 
  

   It 
  would 
  be 
  a 
  very 
  great 
  step 
  in 
  the 
  experimental 
  illustration 
  (or 
  verification, 
  for 
  those 
  who 
  consider 
  

   such 
  to 
  be 
  necessary) 
  of 
  the 
  dynamical 
  theory 
  of 
  heat, 
  to 
  actually 
  shew, 
  in 
  any 
  one 
  case, 
  a 
  loss 
  of 
  

   heat 
  ; 
  and 
  it 
  might 
  be 
  done 
  by 
  operating 
  through 
  a 
  very 
  considerable 
  range 
  of 
  temperatures 
  with 
  a 
  

   good 
  air-engine 
  or 
  steam-engine, 
  not 
  allowed 
  to 
  waste 
  its 
  work 
  in 
  friction. 
  As 
  will 
  be 
  seen 
  in 
  

   Part 
  II. 
  of 
  this 
  paper, 
  no 
  experiment 
  of 
  any 
  kind 
  could 
  shew 
  a 
  considerable 
  loss 
  of 
  heat 
  without 
  

   employing 
  bodies 
  differing 
  considerably 
  in 
  temperature 
  ; 
  for 
  instance, 
  a 
  loss 
  of 
  as 
  much 
  as 
  -098, 
  or 
  

   about 
  one-tenth 
  of 
  the 
  whole 
  heat 
  used, 
  if 
  the 
  temperature 
  of 
  all 
  the 
  bodies 
  used 
  be 
  between 
  0° 
  and 
  

   30° 
  cent. 
  

  

  