﻿t 
  Lord 
  Kelvin 
  on 
  the 
  Clustering 
  of 
  

  

  mutual 
  attraction 
  between 
  its 
  parts 
  its 
  equilibrium 
  would 
  be 
  

   unstable, 
  unless 
  it 
  were 
  infinitely 
  incompressible. 
  But 
  here, 
  

   again, 
  I 
  am 
  reminded 
  of 
  the 
  critical 
  character 
  of 
  the 
  ground 
  

   on 
  which 
  we 
  stand 
  in 
  speaking 
  of 
  properties 
  of 
  matter 
  

   beyond 
  what 
  we 
  see 
  or 
  feel 
  by 
  experiment. 
  I 
  am 
  afraid 
  I 
  

   must 
  here 
  express 
  a 
  view 
  different 
  from 
  that 
  which 
  Professor 
  

   Riicker 
  announced 
  in 
  his 
  Address, 
  when 
  he 
  said 
  that 
  con- 
  

   tinuity 
  of 
  matter 
  implied 
  absolute 
  resistance 
  to 
  condensation. 
  

   We 
  have 
  no 
  right 
  to 
  bar 
  condensation 
  as 
  a 
  property 
  of 
  ether. 
  

   While 
  admitting 
  ether 
  not 
  to 
  have 
  any 
  atomic 
  structure, 
  it 
  

   is 
  postulated 
  as 
  a 
  material 
  which 
  performs 
  functions 
  of 
  which 
  

   we 
  know 
  something, 
  and 
  which 
  may 
  have 
  properties 
  allow- 
  

   ing 
  it 
  to 
  perform 
  other 
  functions 
  of 
  which 
  we 
  are 
  not 
  

   yet 
  cognisant. 
  If 
  we 
  consider 
  ether 
  to 
  be 
  matter, 
  we 
  pos- 
  

   tulate 
  that 
  it 
  has 
  rigidity 
  enough 
  for 
  the 
  vibrations 
  of 
  

   light, 
  but 
  we 
  have 
  no 
  right 
  to 
  say 
  that 
  it 
  is 
  absolutely 
  

   incompressible. 
  We 
  must 
  admit 
  that 
  sufficiently 
  great 
  

   pressure 
  all 
  round 
  could 
  condense 
  the 
  ether 
  in 
  a 
  given 
  space, 
  

   allowing 
  the 
  ether 
  in 
  surrounding 
  space 
  to 
  come 
  in 
  towards 
  

   the 
  ideal 
  shrinking 
  surface. 
  When 
  I 
  say 
  that 
  ether 
  must 
  

   be 
  outside 
  the 
  law 
  of 
  gravitation, 
  I 
  assume 
  that 
  it 
  is 
  not 
  

   infinitely 
  incompressible. 
  I 
  admit 
  that 
  if 
  it 
  were 
  infinitely 
  

   incompressible, 
  it 
  might 
  be 
  subject 
  to 
  the 
  law 
  of 
  mutual 
  

   gravitation 
  between 
  its 
  parts 
  ; 
  but 
  to 
  my 
  mind 
  it 
  seems 
  

   infinitely 
  improbable 
  that 
  ether 
  is 
  infinitely 
  incompressible, 
  

   and 
  it 
  appears 
  more 
  consistent 
  with 
  the 
  analogies 
  of 
  the 
  

   known 
  properties 
  of 
  molar 
  matter, 
  which 
  should 
  be 
  oar 
  

   guides, 
  to 
  suppose 
  that 
  ether 
  has 
  not 
  the 
  quality 
  of 
  exerting 
  

   an 
  infinitely 
  great 
  force 
  against 
  compressing 
  action 
  of 
  gravi- 
  

   tation. 
  Hence, 
  if 
  we 
  assume 
  that 
  it 
  extends 
  through 
  all 
  

   space, 
  ether 
  must 
  be 
  outside 
  the 
  law 
  of 
  gravitation 
  — 
  that 
  is 
  

   to 
  say, 
  truly 
  imponderable. 
  I 
  remember 
  the 
  contempt 
  and 
  

   self-complacent 
  compassion 
  with 
  which 
  sixty 
  years 
  ago 
  — 
  I 
  

   myself, 
  I 
  am 
  afraid 
  — 
  and 
  most 
  of 
  the 
  teachers 
  of 
  that 
  time 
  

   looked 
  upon 
  the 
  ideas 
  of 
  the 
  elderly 
  people 
  who 
  went 
  before 
  

   us, 
  who 
  spoke 
  of 
  ' 
  the 
  imponderables/ 
  I 
  fear 
  that 
  in 
  this, 
  

   as 
  in 
  a 
  great 
  many 
  other 
  things 
  in 
  science, 
  we 
  have 
  to 
  hark 
  

   back 
  to 
  the 
  dark 
  ages 
  of 
  fifty, 
  sixty, 
  or 
  a 
  hundred 
  years 
  ago, 
  

   and 
  that 
  we 
  must 
  admit 
  there 
  is 
  something 
  which 
  we 
  cannot 
  

   refuse 
  to 
  call 
  matter, 
  but 
  which 
  is 
  not 
  subject 
  to 
  the 
  

   Newtonian 
  law 
  of 
  gravitation. 
  That 
  the 
  sun, 
  stars, 
  planets, 
  

   and 
  meteoric 
  stones 
  are 
  all 
  of 
  them 
  ponderable 
  matter 
  is 
  true, 
  

   but 
  the 
  title 
  of 
  my 
  paper 
  implies 
  that 
  there 
  is 
  something 
  else. 
  

   Ether 
  is 
  not 
  any 
  part 
  of 
  the 
  subject 
  of 
  this 
  paper 
  : 
  what 
  we 
  

   are 
  concerned 
  with 
  is 
  gravitational 
  matter, 
  ponderable 
  matter. 
  

  

  