﻿MECHANICAL 
  ACTION 
  OF 
  HEAT. 
  149 
  

  

  emission 
  of 
  light 
  and 
  of 
  radiant 
  heat, 
  the 
  transference 
  of 
  motion 
  from 
  the 
  atmo- 
  

   spheres 
  to 
  their 
  nuclei. 
  

  

  Although 
  in 
  all 
  undulations 
  of 
  sensible 
  length 
  and 
  amplitude, 
  such 
  as 
  those 
  

   of 
  sound, 
  the 
  nuclei 
  must 
  carry 
  their 
  atmospheres 
  along 
  with 
  them, 
  and 
  vibrating 
  

   thus 
  loaded, 
  produce 
  a 
  comparatively 
  slow 
  velocity 
  of 
  propagation 
  ; 
  yet 
  in 
  all 
  

   probability 
  the 
  minute 
  vibrations 
  of 
  light 
  and 
  radiant 
  heat 
  may 
  be 
  performed 
  by 
  

   the 
  atomic 
  nuclei 
  in 
  transparent 
  and 
  diathermanous 
  bodies, 
  without 
  moving 
  the 
  

   atmospheres 
  more 
  than 
  by 
  that 
  amount 
  which 
  constitutes 
  absorption 
  ; 
  and 
  those 
  

   vibrations 
  will 
  therefore 
  be 
  transmitted 
  according 
  to 
  the 
  laws 
  of 
  the 
  elasticity 
  of 
  

   perfect 
  solids, 
  and 
  with 
  a 
  rapidity 
  corresponding 
  to 
  the 
  extreme 
  smallness 
  of 
  the 
  

   masses 
  set 
  in 
  motion, 
  as 
  compared 
  with 
  the 
  mutual 
  forces 
  exerted 
  by 
  them. 
  

  

  This 
  supposition 
  is 
  peculiar 
  to 
  my 
  own 
  view 
  of 
  the 
  hypothesis, 
  and 
  is, 
  in 
  fact, 
  the 
  

   converse 
  of 
  the 
  idea 
  hitherto 
  adopted, 
  of 
  an 
  ether 
  surrounding 
  ponderable 
  particles. 
  

  

  The 
  second 
  and 
  third 
  suppositions 
  involve 
  the 
  assumption, 
  that 
  motion 
  can 
  

   be 
  communicated 
  between 
  the 
  nuclei 
  and 
  their 
  atmospheres, 
  and 
  between 
  the 
  

   different 
  parts 
  of 
  the 
  atmospheres 
  ; 
  so 
  that 
  there 
  is 
  a 
  tendency 
  to 
  produce 
  some 
  

   permanent 
  condition 
  of 
  motion, 
  which 
  constitutes 
  equilibrium 
  of 
  heat. 
  It 
  is 
  now 
  

   to 
  be 
  considered 
  what 
  kind 
  of 
  motion 
  is 
  capable 
  of 
  producing 
  increase 
  of 
  elasticity, 
  

   and 
  what 
  are 
  the 
  conditions 
  of 
  permanency 
  of 
  that 
  motion.' 
  

  

  It 
  is 
  obvious, 
  that 
  the 
  parts 
  of 
  the 
  atomic 
  atmospheres 
  may 
  have 
  motions 
  of 
  

   alternate 
  expansion 
  and 
  contraction, 
  or 
  of 
  rectilinear 
  oscillation 
  about 
  a 
  position 
  

   of 
  equilibrium, 
  without 
  affecting 
  the 
  superficial 
  atomic 
  elasticity, 
  except 
  by 
  small 
  

   periodical 
  changes. 
  Should 
  they 
  have 
  motions, 
  however, 
  of 
  revolution 
  about 
  

   centres, 
  so 
  as 
  to 
  form 
  a 
  group 
  of 
  vortices, 
  the 
  centrifugal 
  force 
  will 
  have 
  the 
  effect 
  

   of 
  increasing 
  the 
  density 
  of 
  the 
  atmosphere 
  at 
  what 
  I 
  have 
  called 
  the 
  bounding 
  

   surfaces 
  of 
  the 
  atoms, 
  and 
  thus 
  of 
  augmenting 
  the 
  elasticity 
  of 
  the 
  body. 
  

  

  In 
  this 
  summary, 
  I 
  shall 
  not 
  enter 
  into 
  the 
  details 
  of 
  mathematical 
  analysis, 
  

   but 
  shall 
  state 
  results 
  only. 
  The 
  following, 
  then, 
  are 
  the 
  conditions 
  which 
  

   must 
  be 
  fulfilled, 
  in 
  order 
  that 
  a 
  group 
  of 
  vortices, 
  of 
  small 
  size 
  as 
  compared 
  with 
  

   the 
  bulk 
  of 
  an 
  atom, 
  and 
  of 
  various 
  diameters, 
  may 
  permanently 
  coexist, 
  whether 
  

   side 
  by 
  side, 
  or 
  end 
  to 
  end, 
  in 
  the 
  atomic 
  atmospheres 
  of 
  one 
  substance, 
  or 
  of 
  

   various 
  substances 
  mixed. 
  

  

  First, 
  The 
  mean 
  elasticity 
  must 
  vary 
  continuously 
  ; 
  which 
  involves 
  the 
  condi- 
  

   tion, 
  that 
  at 
  the 
  surface 
  of 
  contact 
  of 
  two 
  vortices 
  of 
  different 
  substances, 
  side 
  by 
  

   side, 
  or 
  end 
  to 
  end, 
  the 
  respective 
  densities 
  at 
  each 
  point 
  of 
  contact 
  must 
  be 
  

   inversely 
  proportional 
  to 
  the 
  coefficients 
  of 
  elasticity. 
  Hence 
  the 
  specific 
  gravities 
  

   of 
  the 
  atmospheric 
  parts 
  of 
  all 
  substances, 
  under 
  precisely 
  similar 
  circumstances 
  as 
  to 
  

   heat 
  and 
  molecular 
  forces 
  (a 
  condition 
  realised 
  in 
  perfect 
  gases 
  at 
  the 
  same 
  pres- 
  

   sure 
  and 
  temperature), 
  are 
  inversely 
  proportional 
  to 
  the 
  coefficients 
  of 
  atmospheric 
  

   elasticity. 
  Therefore 
  let 
  p. 
  represent 
  the 
  mass 
  of 
  the 
  atmosphere 
  of 
  one 
  atom 
  of 
  

  

  