﻿270 
  Lord 
  Kelvin: 
  

  

  centre 
  than 
  are 
  the 
  three 
  in 
  the 
  equatorial 
  plane. 
  In 
  this 
  

   case 
  the 
  equilibrium 
  is 
  clearly 
  stable. 
  Another 
  obvious 
  con- 
  

   figuration, 
  also 
  stable, 
  of 
  five 
  electrions 
  within 
  an 
  atom 
  is 
  one 
  

   at 
  the 
  centre, 
  and 
  four 
  on 
  a 
  concentric 
  spherical 
  surface 
  at 
  

   the 
  corners, 
  of 
  a 
  tetrahedron. 
  From 
  any 
  case 
  of 
  any 
  number 
  

   of 
  electrions 
  all 
  on 
  one 
  spherical 
  surface, 
  we 
  may 
  pass 
  to 
  

   another 
  configuration 
  with 
  one 
  more 
  electrion 
  placed 
  at 
  the 
  

   centre 
  and 
  the 
  proper 
  proportionate 
  increase 
  in 
  the 
  electric 
  

   strength 
  of 
  the 
  atom. 
  Thus 
  from 
  the 
  cases 
  described 
  in 
  

   § 
  19, 
  we 
  may 
  pass 
  to 
  configurations 
  of 
  equilibrium 
  for 
  seven, 
  

   nine, 
  eleven, 
  thirteen, 
  and 
  twenty-one 
  electrions. 
  All 
  these 
  

   cases, 
  with 
  questions 
  of 
  stability 
  or 
  instability 
  and 
  of 
  the 
  

   different 
  amounts 
  of 
  work 
  required 
  to 
  pluck 
  all 
  the 
  electrions 
  

   out 
  of 
  the 
  atom 
  and 
  remove 
  them 
  to 
  infinite 
  distances, 
  present 
  

   most 
  interesting 
  subjects 
  for 
  not 
  difficult 
  mathematical 
  work; 
  

   and 
  I 
  regret 
  not 
  being 
  able 
  to 
  pursue 
  them 
  at 
  present. 
  

  

  § 
  23. 
  Consider 
  now 
  the 
  electric 
  properties 
  of 
  a 
  real 
  body, 
  

   gaseous, 
  liquid, 
  or 
  solid, 
  constituted 
  by 
  an 
  assemblage 
  of 
  

   atoms 
  with 
  their 
  electrions. 
  It 
  follows 
  immediately 
  from 
  our 
  

   hypothesis, 
  that 
  in 
  a 
  monatomic 
  gas 
  or 
  in 
  any 
  sufficiently 
  

   sparse 
  assemblage 
  of 
  single 
  atoms, 
  fixed 
  or 
  moving, 
  Faraday's 
  

   u 
  conducting 
  power 
  for 
  lines 
  of 
  electric 
  force" 
  or 
  ivhat 
  is 
  now 
  

   commonly 
  called 
  the 
  specific 
  electro-inductive 
  capacity, 
  or 
  the 
  

   electro-inductive 
  permeability, 
  exceeds 
  unity 
  by 
  three 
  times 
  the 
  

   ratio 
  of 
  the 
  sum 
  of 
  the 
  volumes 
  of 
  the 
  atoms 
  to 
  the 
  whole 
  volume 
  

   of 
  space 
  occupied 
  by 
  the 
  assemblage, 
  whether 
  the 
  atoms 
  be 
  

   monelectrionic 
  or 
  polyelectrionic, 
  and 
  however 
  much 
  the 
  

   electrion, 
  or 
  group 
  of 
  electrions, 
  within 
  each 
  atom 
  is 
  set 
  to 
  

   vibrate 
  or 
  rotate 
  with 
  each 
  collision, 
  according 
  to 
  the 
  kinetic 
  

   theory 
  of 
  gases. 
  To 
  prove 
  this, 
  consider, 
  in 
  a 
  uniform 
  field 
  

   of 
  electrostatic 
  force 
  of 
  intensity 
  F, 
  a 
  single 
  atom 
  of 
  radius 
  

   a, 
  and, 
  at 
  rest 
  within 
  it, 
  a 
  group 
  of 
  i 
  electrions 
  in 
  stable 
  

   equilibrium. 
  The 
  action 
  of 
  F 
  produces 
  simply 
  displacements 
  

   of 
  the 
  electrions 
  relatively 
  to 
  the 
  atom, 
  equal 
  and 
  in 
  parallel 
  

   lines, 
  with 
  therefore 
  no 
  change 
  of 
  shape 
  and 
  no 
  rotation 
  ; 
  

   and, 
  oo 
  denoting 
  the 
  amount 
  of 
  this 
  displacement, 
  the 
  equation 
  

  

  for 
  the 
  equilibrium 
  of 
  each 
  electrion 
  is 
  -^ 
  =F. 
  This 
  gives 
  

  

  iex 
  = 
  d 
  d 
  ¥ 
  for 
  the 
  electric 
  moment 
  of 
  the 
  electrostatic 
  polariza- 
  

   tion 
  induced 
  in 
  the 
  atom 
  by 
  F. 
  In 
  passing, 
  remark 
  that 
  a 
  3 
  F 
  

   is 
  also 
  equal 
  to 
  the 
  electric 
  moment 
  of 
  the 
  polarization 
  pro- 
  

   duced 
  in 
  an 
  insulated 
  unelectrified 
  metal 
  globe 
  of 
  radius 
  a,. 
  

   when 
  brought 
  into 
  an 
  electrostatic 
  field 
  of 
  intensity 
  F 
  : 
  and 
  

   conclude 
  that 
  the 
  electric 
  inductive 
  capacity 
  of 
  a 
  uniformly 
  

   dense 
  assemblage 
  of 
  fixed 
  metallic 
  globules, 
  so 
  sparse 
  that 
  

  

  