﻿148 
  MR 
  W. 
  J. 
  M. 
  RANKLNE 
  ON 
  THE 
  

  

  centres 
  of 
  the 
  body 
  balance 
  each 
  other 
  ; 
  and 
  the 
  elasticity 
  of 
  the 
  body 
  is 
  made 
  up 
  

   of 
  two 
  parts 
  : 
  First, 
  the 
  elasticity 
  of 
  the 
  atomic 
  atmospheres 
  at 
  the 
  imaginary 
  

   boundaries 
  of 
  the 
  atoms, 
  which 
  I 
  shall 
  call 
  the 
  superficial-atomic 
  elasticity 
  ; 
  and, 
  

   secondly, 
  the 
  force 
  resulting 
  from 
  the 
  mutual 
  actions 
  of 
  distinct 
  atoms. 
  If 
  the 
  

   atmospheres 
  are 
  so 
  much 
  condensed 
  round 
  their 
  nuclei 
  or 
  centres, 
  that 
  the 
  super- 
  

   ficial-atomic 
  elasticity 
  is 
  insensible, 
  and 
  that 
  the 
  resultants 
  of 
  the 
  mutual 
  actions 
  

   of 
  all 
  parts 
  of 
  the 
  distinct 
  atoms 
  are 
  forces 
  acting 
  along 
  the 
  lines 
  joining 
  the 
  

   nuclei 
  or 
  centres, 
  then 
  the 
  body 
  is 
  a 
  perfect 
  solid, 
  having 
  a 
  tendency 
  to 
  preserve 
  

   not 
  only 
  a 
  certain 
  bulk, 
  but 
  a 
  certain 
  figure 
  ; 
  and 
  the 
  elasticity 
  of 
  figure, 
  or 
  rigid- 
  

   ity, 
  bears 
  certain 
  definite 
  relations 
  to 
  the 
  elasticity 
  of 
  volume. 
  

  

  If 
  the 
  atmospheres 
  are 
  less 
  condensed 
  about 
  their 
  centres, 
  so 
  that 
  the 
  mutual 
  

   actions 
  of 
  distinct 
  atoms 
  are 
  not 
  reducible 
  to 
  a 
  system 
  of 
  forces 
  acting 
  along 
  the 
  

   lines 
  joining 
  the 
  atomic 
  centres, 
  but 
  produce 
  merely 
  a 
  cohesive 
  force 
  sufficient 
  to 
  

   balance 
  the 
  superficial-atomic 
  elasticity, 
  then 
  the 
  condition 
  is 
  that 
  of 
  a 
  perfect 
  

   liquid 
  ; 
  and 
  the 
  intermediate 
  conditions 
  between 
  this 
  and 
  perfect 
  solidity 
  consti- 
  

   tute 
  the 
  gelatinous, 
  plastic, 
  and 
  viscous 
  states. 
  

  

  When 
  the 
  mutual 
  actions 
  of 
  distinct 
  atoms 
  are 
  very 
  small 
  as 
  compared 
  with 
  

   the 
  superficial-atomic 
  elasticity, 
  the 
  condition 
  is 
  that 
  of 
  gas 
  or 
  vapour 
  ; 
  and 
  when 
  

   the 
  substance 
  is 
  so 
  far 
  rarefied 
  that 
  the 
  influence 
  of 
  the 
  atomic 
  nuclei 
  or 
  centres 
  

   in 
  modifying 
  the 
  superficial 
  elasticity 
  of 
  their 
  atmospheres 
  is 
  insensible, 
  it 
  is 
  then 
  

   in 
  the 
  state 
  of 
  perfect 
  gas. 
  

  

  So 
  far 
  as 
  our 
  experimental 
  knowledge 
  goes, 
  the 
  elasticity 
  of 
  a 
  perfect 
  gas 
  at 
  

   a 
  given 
  temperature 
  varies 
  simply 
  in 
  proportion 
  to 
  its 
  density. 
  I 
  have 
  therefore 
  

   assumed 
  this 
  to 
  be 
  the 
  law 
  of 
  the 
  elasticity 
  of 
  the 
  atomic 
  atmospheres, 
  ascribing 
  

   a 
  specific 
  coefficient 
  of 
  elasticity 
  to 
  each 
  substance. 
  

  

  The 
  second 
  supposition, 
  being 
  that 
  from 
  which 
  the 
  hypothesis 
  of 
  molecular 
  

  

  vortices 
  derives 
  its 
  name, 
  is 
  the 
  following 
  : 
  — 
  That 
  the 
  elasticity 
  due 
  to 
  heat 
  arises 
  

  

  from 
  the 
  centrifugal 
  force 
  of 
  revolutions 
  or 
  oscillations 
  among 
  the 
  particles 
  of 
  the 
  

  

  atomic 
  atmospheres 
  ; 
  so 
  that 
  quantity 
  of 
  heat 
  is 
  the 
  vis 
  viva 
  of 
  those 
  revolutions 
  or 
  

  

  oscillations. 
  

  

  This 
  supposition 
  appears 
  to 
  have 
  been 
  first 
  definitely 
  stated 
  by 
  Sir 
  Humphry 
  

   Davy. 
  It 
  has 
  since 
  been 
  supported 
  by 
  Mr 
  Joule, 
  whose 
  valuable 
  experiments 
  to 
  

   establish 
  the 
  convertibility 
  of 
  heat 
  and 
  mechanical 
  power 
  are 
  well 
  known. 
  So 
  

   far 
  as 
  I 
  am 
  aware, 
  however, 
  its 
  consequences 
  have 
  not 
  hitherto 
  been 
  mathema- 
  

   tically 
  developed. 
  

  

  To 
  connect 
  this 
  hypothesis 
  with 
  the 
  undulatory 
  theory 
  of 
  radiation, 
  I 
  have 
  

   introduced 
  a 
  third 
  supposition: 
  — 
  That 
  the 
  medium 
  which 
  transmits 
  light 
  and 
  

   radiant 
  heat 
  consists 
  of 
  the 
  nuclei 
  of 
  the 
  atoms, 
  vibrating 
  independently, 
  or 
  almost 
  

   independently, 
  of 
  their 
  atmospheres 
  ; 
  — 
  so 
  that 
  the 
  absorption 
  of 
  light 
  and 
  of 
  radiant 
  

   heat, 
  is 
  the 
  transference 
  of 
  motion 
  from 
  the 
  nuclei 
  to 
  their 
  atmospheres, 
  and 
  the 
  

  

  