﻿260 
  Lord 
  Kelvin 
  : 
  

  

  § 
  8. 
  In 
  the 
  mathematical 
  theory 
  of 
  electricity 
  in 
  equilibrium, 
  

   it 
  is 
  a 
  matter 
  of 
  perfect 
  indifference 
  which 
  of 
  the 
  opposite 
  

   electric 
  manifestations 
  we 
  call 
  positive 
  and 
  which 
  negative. 
  

   But 
  the 
  great 
  differences 
  in 
  the 
  disruptive 
  and 
  luminous 
  

   effects, 
  when 
  the 
  forces 
  are 
  too 
  strong 
  for 
  electric 
  equilibrium, 
  

   presented 
  by 
  the 
  two 
  modes 
  of 
  electrification, 
  which 
  have 
  

   been 
  known 
  from 
  the 
  earliest 
  times 
  of 
  electric 
  science, 
  show 
  

   physical 
  properties 
  not 
  touched 
  by 
  the 
  mathematical 
  theory. 
  

   And 
  Varley's 
  comparatively 
  recent 
  discovery* 
  of 
  the 
  mole- 
  

   cular 
  torrent 
  of 
  resinously 
  electrified 
  particles 
  from 
  the 
  

   " 
  kathode 
  " 
  or 
  resinous 
  electrode 
  in 
  apparatus 
  for 
  the 
  trans- 
  

   mission 
  of 
  electricity 
  through 
  vacuum 
  or 
  highly 
  rarefied 
  air, 
  

   gives 
  strong 
  reason 
  for 
  believing 
  that 
  the 
  mobile 
  electricity 
  

   of 
  Aepinus'' 
  theory 
  is 
  resinous, 
  and 
  not 
  vitreous 
  as 
  he 
  acci- 
  

   dentally 
  made 
  it. 
  I 
  shall 
  therefore 
  assume 
  that 
  our 
  electrions 
  

   act 
  as 
  extremely 
  minute 
  particles 
  of 
  resinously 
  electrified 
  

   matter 
  ; 
  that 
  a 
  void 
  atom 
  acts 
  simply 
  as 
  a 
  little 
  globe 
  of 
  

   atomic 
  substance, 
  possessing 
  as 
  an 
  essential 
  quality 
  vitreous 
  

   electricity 
  uniformly 
  distributed 
  through 
  it 
  or 
  through 
  a 
  

   smaller 
  concentric 
  globe; 
  and 
  that 
  ordinary 
  ponderable 
  

   matter, 
  not 
  electrified, 
  consists 
  of 
  a 
  vast 
  assemblage 
  of 
  atoms, 
  

   not 
  void, 
  but 
  having 
  within 
  the 
  portions 
  of 
  space 
  which 
  they 
  

   occupy 
  just 
  enough 
  of 
  electrions 
  to 
  annul 
  electric 
  force 
  for 
  

   all 
  places 
  of 
  which 
  the 
  distance 
  from 
  the 
  nearest 
  atom 
  is 
  

   large 
  in 
  comparison 
  with 
  the 
  diameter 
  of 
  an 
  atom, 
  or 
  mole- 
  

   cular 
  cluster 
  of 
  atoms. 
  

  

  § 
  9. 
  This 
  condition 
  respecting 
  distance 
  would, 
  because 
  of 
  

   the 
  inverse 
  square 
  of 
  the 
  distance 
  law 
  for 
  the 
  forces, 
  be 
  

   unnecessary 
  and 
  the 
  electric 
  force 
  would 
  be 
  rigorously 
  null 
  

   throughout 
  all 
  space 
  outside 
  the 
  atoms, 
  if 
  every 
  atom 
  had 
  

   only 
  a 
  single 
  electrion 
  at 
  its 
  centre, 
  provided 
  that 
  the 
  electric 
  

   quantities 
  of 
  the 
  opposite 
  electricities 
  (reckoned 
  according 
  to 
  

   the 
  old 
  definition 
  of 
  mathematical 
  electrostatics) 
  are 
  equal 
  in 
  

   the 
  atom 
  and 
  in 
  the 
  electrion. 
  But 
  even 
  if 
  every 
  neutralized 
  

   separate 
  atom 
  contains 
  just 
  one 
  electrion 
  in 
  stable 
  equilibrium 
  

   at 
  its 
  centre, 
  it 
  is 
  obvious 
  that, 
  when 
  two 
  atoms 
  overlap 
  so 
  far 
  

   that 
  the 
  centre 
  of 
  one 
  of 
  them 
  is 
  within 
  the 
  spherical 
  boundary 
  

   of 
  the 
  other, 
  the 
  previous 
  equilibrium 
  of 
  the 
  two 
  electrions 
  is 
  

   upset, 
  and 
  they 
  must 
  find 
  positions 
  of 
  equilibrium 
  elsewhere 
  

   than 
  at 
  the 
  centres. 
  Thus 
  in 
  fig. 
  1 
  each 
  electrion 
  is 
  at 
  the 
  

   centre 
  of 
  its 
  atom, 
  and 
  is 
  attracted 
  and 
  repelled 
  with 
  equal 
  

   forces 
  by 
  the 
  neighbouring 
  atom 
  and 
  electrion 
  at 
  its 
  centre. 
  

   In 
  fig. 
  2, 
  if 
  E 
  and 
  E' 
  were 
  at 
  the 
  centres 
  0, 
  C, 
  of 
  the 
  two 
  

   atoms, 
  E 
  would 
  be 
  repelled 
  by 
  E' 
  more 
  than 
  it 
  would 
  be 
  

  

  * 
  Proc. 
  Roy. 
  Soc. 
  vol. 
  xix. 
  pp. 
  239, 
  240 
  (1871). 
  

  

  