﻿820 
  Prof. 
  J. 
  Clerk 
  Maxwell 
  on 
  the 
  

  

  We 
  can 
  already 
  distinguish 
  two 
  lines 
  along 
  which 
  dyna- 
  

   mical 
  science 
  is 
  working 
  its 
  way 
  to 
  undermine 
  at 
  least 
  the 
  

   outworks 
  of 
  Chemistry, 
  and 
  the 
  chemists 
  of 
  the 
  present 
  day, 
  

   instead 
  of 
  upholding 
  the 
  mystery 
  of 
  their 
  craft, 
  are 
  doing 
  all 
  

   they 
  can 
  to 
  open 
  their 
  gates 
  to 
  the 
  enemy. 
  

  

  Of 
  these 
  two 
  lines 
  of 
  advance 
  one 
  is 
  conducted 
  by 
  the 
  help 
  

   of 
  the 
  hypothesis 
  that 
  bodies 
  consist 
  of 
  molecules 
  in 
  motion, 
  

   and 
  it 
  seeks 
  to 
  determine 
  the 
  structure 
  of 
  the 
  molecules 
  and 
  

   the 
  nature 
  of 
  their 
  motion 
  from 
  the 
  phenomena 
  of 
  portions 
  

   of 
  matter 
  of 
  sensible 
  size. 
  

  

  The 
  other 
  line 
  of 
  advance, 
  that 
  of 
  Thermodynamics, 
  makes 
  

   no 
  hypothesis 
  about 
  the 
  ultimate 
  structure 
  of 
  bodies, 
  but 
  

   deduces 
  relations 
  among 
  observed 
  phenomena 
  by 
  means 
  of 
  

   two 
  general 
  principles 
  — 
  the 
  conservation 
  of 
  energy 
  and 
  its 
  

   tendency 
  towards 
  diffusion. 
  The 
  thermodynamical 
  problem 
  

   of 
  the 
  equilibrium 
  of 
  heterogeneous 
  substances 
  was 
  attacked 
  

   by 
  Kirchhoff 
  in 
  1855, 
  when 
  the 
  science 
  was 
  yet 
  in 
  its 
  

   infancy, 
  and 
  his 
  method 
  has 
  been 
  lately 
  followed 
  by 
  0. 
  Neu- 
  

   mann. 
  But 
  the 
  methods 
  introduced 
  by 
  Professor 
  J. 
  Willard 
  

   Gibbs, 
  of 
  Yale 
  College, 
  Connecticut 
  *, 
  seem 
  to 
  me 
  to 
  be 
  more 
  

   likely 
  than 
  any 
  others 
  to 
  enable 
  us, 
  without 
  any 
  lengthy 
  

   calculations, 
  to 
  comprehend 
  the 
  relations 
  between 
  the 
  different 
  

   physical 
  and 
  chemical 
  states 
  of 
  bodies, 
  and 
  it 
  is 
  to 
  these 
  that 
  

   I 
  now 
  w 
  T 
  ish 
  to 
  direct 
  your 
  attention. 
  

  

  In 
  studying 
  the 
  properties 
  of 
  a 
  homogeneous 
  mass 
  of 
  fluid, 
  

   consisting 
  of 
  n 
  component 
  substances, 
  Professor 
  Gibbs 
  takes- 
  

   as 
  his 
  principal 
  function 
  the 
  energy 
  of 
  the 
  fluid, 
  as 
  depending 
  

   on 
  its 
  volume 
  and 
  entropy 
  together 
  with 
  the 
  masses, 
  m 
  lf 
  

   m 
  2 
  , 
  . 
  . 
  . 
  . 
  m 
  n 
  of 
  its 
  n 
  components, 
  these 
  n 
  + 
  2 
  variables 
  being 
  

   regarded 
  as 
  independent. 
  Each 
  of 
  these 
  variables 
  is 
  such 
  

   that 
  its 
  value 
  for 
  any 
  material 
  system 
  is 
  the 
  sum 
  of 
  its 
  values 
  

   fur 
  the 
  different 
  parts 
  of 
  the 
  system. 
  

  

  By 
  differentiating 
  the 
  energy 
  with 
  respect 
  to 
  each 
  of 
  these 
  

   variables 
  we 
  obtain 
  n 
  + 
  2 
  other 
  quantities, 
  each 
  of 
  which 
  has 
  

   a 
  physical 
  significance 
  which 
  is 
  related 
  to 
  that 
  of 
  the 
  variable 
  

   to 
  which 
  it 
  corresponds. 
  

  

  Thus, 
  by 
  differentiating 
  with 
  respect 
  to 
  the 
  volume, 
  we 
  

   obtain 
  the 
  pressure 
  of 
  the 
  fluid 
  with 
  its 
  sign 
  reversed 
  ; 
  by 
  

   differentiating 
  with 
  respect 
  to 
  the 
  entropy, 
  we 
  obtain 
  the 
  

   temperature 
  on 
  the 
  thermodynamic 
  scale 
  ; 
  and 
  by 
  differ- 
  

   entiating 
  with 
  respect 
  to 
  the 
  mass 
  of 
  any 
  one 
  of 
  the 
  com- 
  

   ponent 
  substances, 
  we 
  obtain 
  what 
  Professor 
  Gibbs 
  calls 
  the. 
  

   potential 
  of 
  that 
  substance 
  in 
  the 
  mass 
  considered. 
  

  

  As 
  this 
  conception 
  of 
  the 
  potential 
  of 
  a 
  substance 
  in 
  a 
  

  

  * 
  Transactions 
  of 
  the 
  Academy 
  of 
  Sciences 
  of 
  Connecticut, 
  vol. 
  iii. 
  

  

  