﻿278 
  Lord 
  Kelvin 
  : 
  

  

  horizontal 
  glass 
  plate 
  * 
  with 
  A 
  1 
  above 
  it. 
  Let 
  Bj 
  be 
  at 
  the 
  

   centre 
  of 
  A 
  x 
  , 
  A 
  2 
  , 
  A 
  3 
  , 
  A 
  4 
  , 
  and 
  let 
  B 
  1? 
  B 
  2 
  , 
  B 
  3 
  , 
  B 
  4 
  be 
  a 
  quartet 
  

   of 
  the 
  B's 
  similarly 
  oriented 
  to 
  A 
  ]? 
  A 
  2 
  , 
  A 
  3 
  , 
  A 
  4 
  . 
  We 
  see 
  that 
  

   B 
  2 
  , 
  B 
  3 
  , 
  B 
  4 
  lie 
  below 
  the 
  glass 
  plate, 
  and 
  that 
  the 
  quartet 
  

   Bj, 
  B 
  2 
  , 
  B 
  3 
  , 
  B 
  4 
  has 
  none 
  of 
  the 
  A's 
  at 
  its 
  centre. 
  But 
  the 
  

   vertically 
  opposite 
  quartet 
  B 
  1? 
  B' 
  2 
  , 
  B' 
  3 
  , 
  B' 
  4 
  contains 
  Aj 
  within 
  

   it 
  ; 
  and 
  it 
  is 
  oppositely 
  oriented 
  to 
  the 
  quartet 
  A 
  l} 
  A 
  2 
  , 
  A 
  3 
  , 
  A 
  4 
  . 
  

   Thus 
  we 
  see 
  that, 
  while 
  the 
  half 
  of 
  all 
  the 
  quartets 
  of 
  A's 
  

   which 
  are 
  oriented 
  oppositely 
  to 
  A 
  l5 
  A 
  2 
  , 
  A 
  8 
  , 
  A 
  4 
  are 
  void 
  of 
  

   B's, 
  the 
  half 
  of 
  the 
  quartets 
  of 
  B's 
  oppositely 
  oriented 
  to 
  

   A 
  1? 
  A 
  2 
  , 
  A 
  3 
  , 
  A 
  4 
  have 
  each 
  an 
  A 
  within 
  it, 
  while 
  the 
  other 
  half 
  

   of 
  the 
  quartets 
  of 
  the 
  B's 
  are 
  all 
  void 
  of 
  A's. 
  

  

  § 
  37. 
  Now 
  let 
  all 
  the 
  A's 
  and 
  all 
  the 
  B's 
  be 
  centres 
  of 
  

   equal 
  and 
  similar 
  spherical 
  atoms, 
  each 
  containing 
  a 
  quartet 
  

   of 
  electrions. 
  The 
  electrions 
  will 
  be 
  in 
  stable 
  equilibrium, 
  

   under 
  the 
  influence 
  of 
  their 
  own 
  mutual 
  repulsions 
  and 
  the 
  

   attractions 
  of 
  the 
  atoms, 
  if 
  they 
  are 
  placed 
  as 
  equilateral 
  

   quartets 
  of 
  proper 
  magnitude, 
  concentric 
  with 
  the 
  atoms, 
  and 
  

   oriented 
  all 
  as 
  any 
  one 
  quartet 
  of 
  the 
  A's 
  or 
  B's. 
  To 
  see 
  

   that 
  this 
  is 
  true, 
  confine 
  attention 
  first 
  to 
  the 
  five 
  atoms 
  

   A 
  1? 
  A 
  2 
  , 
  A 
  3 
  , 
  A 
  4 
  , 
  B 
  x 
  . 
  If 
  the 
  electrions 
  within 
  A 
  v 
  , 
  A 
  £ 
  ., 
  A 
  3 
  , 
  A 
  4 
  are 
  

   all 
  held 
  similarly 
  oriented 
  to 
  the 
  quartet 
  of 
  the 
  centres 
  of 
  these 
  

   atoms, 
  the 
  quartet 
  of 
  electrions 
  within 
  B 
  x 
  must 
  obviously 
  be 
  

   similarly 
  oriented 
  to 
  the 
  other 
  quartets 
  of 
  electrions. 
  If, 
  

   again, 
  these 
  be 
  held 
  oriented 
  oppositely 
  to 
  the 
  quartet 
  of 
  the 
  

   atoms, 
  the 
  stable 
  configuration 
  of 
  the 
  electrions 
  within 
  B 
  x 
  

   will 
  still 
  be 
  similar 
  to 
  the 
  orientation 
  of 
  the 
  quartets 
  within 
  

   A 
  1? 
  A 
  2 
  , 
  A 
  3 
  , 
  A 
  4 
  , 
  though 
  opposite 
  to 
  the 
  orientation 
  of 
  the 
  centres 
  

   of 
  these 
  atoms. 
  If, 
  when 
  the 
  quartets 
  of 
  electrions 
  are 
  all 
  

   thus 
  similarly 
  oriented 
  either 
  way, 
  the 
  quartet 
  within 
  B 
  : 
  is 
  

   turned 
  to 
  reverse 
  orientation, 
  this 
  will 
  canse 
  all 
  the 
  others 
  to 
  

   turn 
  and 
  settle 
  in 
  stable 
  equilibrium 
  according 
  to 
  this 
  reversed 
  

   orientation. 
  Applying 
  the 
  same 
  consideration 
  to 
  every 
  atom 
  

   of 
  the 
  assemblage 
  and 
  its 
  four 
  nearest 
  neighbours, 
  we 
  have 
  

   proof 
  of 
  the 
  proposition 
  asserted 
  at 
  the 
  commencement 
  of 
  the 
  

   present 
  section. 
  It 
  is 
  most 
  interesting 
  to 
  remark 
  that 
  if, 
  in 
  

   a 
  vast 
  homogeneous 
  assemblage 
  of 
  the 
  kind 
  with 
  which 
  we 
  

   are 
  dealing, 
  the 
  orientation 
  of 
  any 
  one 
  of 
  the 
  quartets 
  of 
  

   electrions 
  be 
  reversed 
  and 
  held 
  reversed, 
  all 
  the 
  others 
  will 
  

   follow 
  and 
  settle 
  in 
  stable 
  equilibrium 
  in 
  the 
  reversed 
  

   orientation. 
  

  

  § 
  38. 
  This 
  double 
  homogeneous 
  assemblage 
  of 
  tetra-elec- 
  

   trionic 
  atoms 
  seems 
  to 
  be 
  absolutely 
  the 
  simplest! 
  molecular 
  

   structure 
  in 
  which 
  Haiiy's 
  octo-polar 
  electric 
  quality 
  can 
  

  

  * 
  Parallel 
  glass 
  plates 
  are 
  useful 
  auxiliaries 
  for 
  graphic 
  construction 
  

   and 
  illustrative 
  models 
  in 
  the 
  molecular 
  theory 
  of 
  crystals. 
  

   t 
  Not 
  the 
  simplest. 
  See 
  § 
  40 
  below. 
  

  

  