﻿120 
  MR 
  JAMES 
  CLERK 
  MAXWELL 
  ON 
  THE 
  EQUILIBRIUM 
  OF 
  SOLIDS. 
  

  

  4th, 
  In 
  Coulomb's 
  balance 
  of 
  torsion, 
  the 
  angles 
  of 
  torsion 
  are 
  proportional 
  to 
  the 
  twisting 
  

   forces. 
  

  

  It 
  would 
  appear 
  from 
  these 
  experiments, 
  that 
  compressions 
  are 
  always 
  proportional 
  to 
  pressures. 
  

  

  Professor 
  Stokes 
  has 
  expressed 
  this 
  by 
  making 
  one 
  of 
  his 
  coefficients 
  depend 
  on 
  the 
  cubical 
  

   elasticity, 
  while 
  the 
  other 
  is 
  deduced 
  from 
  the 
  displacement 
  of 
  shifting 
  produced 
  by 
  a 
  given 
  tangential 
  

   force. 
  

  

  M. 
  Cauchy 
  makes 
  one 
  coefficient 
  depend 
  on 
  the 
  linear 
  compression 
  produced 
  by 
  a 
  force 
  acting 
  

   in 
  one 
  direction, 
  and 
  the 
  other 
  on 
  the 
  change 
  of 
  volume 
  produced 
  by 
  the 
  same 
  force. 
  

  

  Both 
  of 
  these 
  methods 
  lead 
  to 
  a 
  correct 
  result 
  ; 
  but 
  the 
  coefficients 
  of 
  Stokes 
  seem 
  to 
  have 
  more 
  

   of 
  a 
  real 
  signification 
  than 
  those 
  of 
  Cauchy 
  ; 
  I 
  have 
  therefore 
  adopted 
  those 
  of 
  Stokes, 
  using 
  the 
  

   symbols 
  m 
  and 
  /J., 
  and 
  the 
  fundamental 
  equations 
  (4.) 
  and 
  (5.), 
  which 
  define 
  them. 
  

  

  Note 
  C. 
  

  

  As 
  the 
  coefficient 
  a), 
  which 
  determines 
  the 
  optical 
  effect 
  of 
  pressure 
  on 
  a 
  substance, 
  varies 
  from 
  

   one 
  substance 
  to 
  another, 
  and 
  is 
  probably 
  a 
  function 
  of 
  the 
  linear 
  elasticity, 
  a 
  determination 
  of 
  its 
  

   value 
  in 
  different 
  substances 
  might 
  lead 
  to 
  some 
  explanation 
  of 
  the 
  action 
  of 
  media 
  on 
  light. 
  

  

  