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  XV. 
  — 
  On 
  the 
  Dynamical 
  Theory 
  of 
  Heat, 
  with 
  numerical 
  results 
  deduced 
  from 
  Mr 
  

   Joule's 
  equivalent 
  of 
  a 
  Thermal 
  Unit, 
  and 
  M. 
  Regnault's 
  Observations 
  on 
  

   Steam. 
  By 
  William 
  Thomson, 
  M.A., 
  Fellow 
  of 
  St 
  Peter's 
  College, 
  Cam- 
  

   bridge, 
  and 
  Professor 
  of 
  Natural 
  Philosophy 
  in 
  the 
  University 
  of 
  Glasgow. 
  

  

  (Read 
  17th 
  March 
  1851.) 
  

   INTRODUCTORY 
  NOTICE. 
  

  

  1. 
  Sir 
  Humphrey 
  Davy, 
  by 
  his 
  experiment 
  of 
  melting 
  two 
  pieces 
  of 
  ice 
  by 
  

   rubbing 
  them 
  together, 
  established 
  the 
  following 
  proposition 
  : 
  — 
  " 
  The 
  phenomena 
  

   of 
  repulsion 
  are 
  not 
  dependent 
  on 
  a 
  peculiar 
  elastic 
  fluid 
  for 
  their 
  existence, 
  or 
  

   caloric 
  does 
  not 
  exist." 
  And 
  he 
  concludes 
  that 
  heat 
  consists 
  of 
  a 
  motion 
  excited 
  

   among 
  the 
  particles 
  of 
  bodies. 
  " 
  To 
  distinguish 
  this 
  motion 
  from 
  others, 
  and 
  to 
  

   signify 
  the 
  cause 
  of 
  our 
  sensation 
  of 
  heat," 
  and 
  of 
  the 
  expansion 
  or 
  expansive 
  

   pressure 
  produced 
  in 
  matter 
  by 
  heat, 
  " 
  the 
  name 
  repulsive 
  motion 
  has 
  been 
  

   adopted."* 
  

  

  2. 
  The 
  Dynamical 
  Theory 
  of 
  Heat, 
  thus 
  established 
  by 
  Sir 
  Humphrey 
  Davy, 
  

   is 
  extended 
  to 
  radiant 
  heat 
  by 
  the 
  discovery 
  of 
  phenomena, 
  especially 
  those 
  of 
  

   the 
  polarization 
  of 
  radiant 
  heat, 
  which 
  render 
  it 
  excessively 
  probable 
  that 
  heat 
  

   propagated 
  through 
  vacant 
  space, 
  or 
  through 
  diathermane 
  substances, 
  consists 
  of 
  

   waves 
  of 
  transverse 
  vibrations 
  in 
  an 
  all-pervading 
  medium. 
  

  

  3. 
  The 
  recent 
  discoveries 
  made 
  by 
  Mayer 
  and 
  JouLE,f 
  of 
  the 
  generation 
  of 
  

   heat 
  through 
  the 
  friction 
  of 
  fluids 
  in 
  motion, 
  and 
  by 
  the 
  magneto-electric 
  excita- 
  

   tion 
  of 
  galvanic 
  currents, 
  would, 
  either 
  of 
  them 
  be 
  sufficient 
  to 
  demonstrate 
  the 
  

   immateriality 
  of 
  heat 
  ; 
  and 
  would 
  so 
  afford, 
  if 
  required, 
  a 
  perfect 
  confirmation 
  of 
  

   Sir 
  Humphrey 
  Davy's 
  views. 
  

  

  * 
  From 
  Davy's 
  first 
  work, 
  entitled 
  " 
  An 
  Essay 
  on 
  Heat, 
  Light, 
  and 
  the 
  Combinations 
  of 
  

   Light," 
  published 
  in 
  1799, 
  in 
  " 
  Contributions 
  to 
  Physical 
  and 
  Medical 
  Knowledge, 
  principally 
  from 
  

   the 
  West 
  of 
  England, 
  collected 
  by 
  Thomas 
  Beddoes, 
  M.D.," 
  and 
  republished 
  in 
  Dr 
  Davy's 
  edition 
  of 
  

   his 
  brother's 
  collected 
  worlds, 
  vol. 
  ii. 
  Lond. 
  1836. 
  

  

  f 
  In 
  May 
  1842, 
  Mayer 
  announced 
  in 
  the 
  " 
  Annalen" 
  of 
  Wohler 
  and 
  Liebig, 
  that 
  he 
  had 
  

   raised 
  the 
  temperature 
  of 
  water 
  from 
  12° 
  to 
  13° 
  cent, 
  by 
  agitating 
  it. 
  In 
  August 
  1843, 
  Joule 
  

   announced 
  to 
  the 
  British 
  Association, 
  " 
  That 
  heat 
  is 
  evolved 
  by 
  the 
  passage 
  of 
  water 
  through 
  

   narrow 
  tubes 
  ;" 
  and 
  that 
  he 
  had 
  " 
  obtained 
  one 
  degree 
  of 
  heat 
  per 
  lb. 
  of 
  water 
  from 
  a 
  mechanical 
  

   force 
  capable 
  of 
  raising 
  770 
  lbs. 
  to 
  the 
  height 
  of 
  one 
  foot;" 
  and 
  that 
  heat 
  is 
  generated 
  when 
  

   work 
  is 
  spent 
  in 
  turning 
  a 
  magneto- 
  electric 
  machine, 
  or 
  an 
  electro-magnetic 
  engine. 
  (See 
  his 
  

   paper 
  " 
  On 
  the 
  Calorific 
  Effects 
  of 
  Magneto-Electricity, 
  and 
  on 
  the 
  Mechanical 
  Value 
  of 
  Heat." 
  

   Phil. 
  Mag. 
  vol. 
  xxiii. 
  1843.) 
  

  

  VOL. 
  XX. 
  PART 
  II. 
  4 
  B 
  

  

  