﻿of 
  Matter 
  and 
  Mass. 
  25 
  

  

  In 
  each 
  the 
  kinetic 
  energy 
  of 
  the 
  body 
  in 
  motion 
  is 
  increased, 
  

   in 
  the 
  one 
  case 
  by 
  hydrodynamic 
  and 
  in 
  the 
  other 
  by 
  thermo- 
  

   dynamic 
  relations. 
  And 
  yet 
  no 
  one 
  claims 
  that 
  to 
  speak 
  of 
  

   this 
  increase 
  in 
  mass 
  is 
  anything 
  more 
  than 
  a 
  figurative 
  way 
  

   of 
  saying 
  that 
  the 
  fluid 
  pressure 
  acts 
  as 
  if 
  it 
  had 
  increased 
  

   the 
  true 
  inertia 
  of 
  the 
  moving 
  body. 
  Why 
  then 
  should 
  we 
  

   claim 
  otherwise 
  for 
  a 
  moving 
  body 
  radiating 
  light? 
  The 
  

   same 
  can 
  be 
  said 
  of 
  the 
  apparent 
  increase 
  of 
  inertia 
  of 
  an 
  

   electrified 
  body 
  moving 
  in 
  an 
  electromagnetic 
  field. 
  

  

  While 
  no 
  one 
  has 
  used 
  the 
  hydrodynamic 
  equations 
  in 
  the 
  

   above 
  form 
  to 
  explain 
  the 
  cause 
  of 
  inertia^ 
  yet 
  it 
  is 
  essentially 
  

   the 
  foundation 
  of 
  Lord 
  Kelvin's 
  theory 
  of 
  vortices 
  moving 
  

   in 
  a 
  primitive 
  fluid. 
  It 
  was 
  a 
  promising 
  and 
  ingenious 
  

   attempt 
  to 
  explain 
  the 
  nature 
  of 
  matter, 
  and 
  it 
  readily 
  and 
  

   suflicientW 
  accounted 
  for 
  such 
  fundamental 
  attributes 
  as 
  

   impenetrability, 
  diversity, 
  conservatism, 
  &c., 
  but 
  it 
  failed 
  

   because 
  the 
  efi'ective 
  inertia 
  of 
  the 
  vortex 
  ring 
  was 
  not 
  

   invariable 
  but 
  dependent 
  upon 
  the 
  position 
  and 
  influence 
  of 
  

   its 
  neighbours. 
  

  

  Maxwell* 
  certainly 
  felt 
  this 
  to 
  be 
  the 
  fatal 
  defect 
  in 
  the 
  

   theory 
  of 
  the 
  vortex 
  atom 
  as 
  in 
  other 
  similar 
  theories, 
  and 
  

   has 
  expressed 
  his 
  opinion 
  with 
  such 
  perspicuity 
  that 
  I 
  shall 
  

   quote 
  from 
  his 
  article 
  at 
  some 
  length 
  : 
  — 
  

  

  " 
  One 
  of 
  the 
  first, 
  if 
  not 
  the 
  very 
  first 
  desideratum 
  in 
  a 
  

   complete 
  theory 
  of 
  matter 
  is 
  to 
  explain 
  — 
  first 
  mass, 
  and 
  

   second 
  gravitation. 
  To 
  explain 
  mass 
  may 
  seem 
  an 
  absurd 
  

   achievement. 
  We 
  generally 
  suppose 
  that 
  it 
  is 
  of 
  the 
  essence 
  

   of 
  matter 
  to 
  be 
  the 
  receptacle 
  of 
  momentum 
  and 
  energy, 
  and 
  

   even 
  Thomson, 
  in 
  his 
  definition 
  of 
  his 
  primitive 
  fluid, 
  attri- 
  

   butes 
  to 
  it 
  the 
  possession 
  of 
  mass. 
  But 
  according 
  to 
  Thomson, 
  

   though 
  the 
  primitive 
  fluid 
  is 
  the 
  only 
  true 
  matter, 
  yet 
  that 
  

   which 
  we 
  call 
  matter 
  is 
  not 
  the 
  primitive 
  fluid 
  itself, 
  

   but 
  a 
  mode 
  of 
  motion 
  of 
  that 
  primitive 
  fluid. 
  It 
  is 
  the 
  

   mode 
  of 
  motion 
  which 
  constitutes 
  the 
  vortex 
  rings, 
  and 
  which 
  

   furnishes 
  us 
  with 
  examples 
  of 
  that 
  permanence 
  and 
  continuity 
  

   of 
  existence 
  which 
  we 
  are 
  accustomed 
  to 
  attribute 
  to 
  matter 
  

   itself. 
  The 
  primitive 
  fluid, 
  the 
  only 
  true 
  matter, 
  entirely 
  

   eludes 
  our 
  perceptions 
  when 
  it 
  is 
  not 
  endued 
  with 
  the 
  mode 
  

   of 
  motion 
  which 
  converts 
  certain 
  portions 
  of 
  it 
  into 
  vortex 
  

   rings, 
  and 
  thus 
  renders 
  it 
  molecular. 
  

  

  " 
  In 
  Thomson''s 
  theory, 
  therefore, 
  the 
  mass 
  of 
  bodies 
  re- 
  

   quires 
  explanation. 
  We 
  have 
  to 
  explain 
  the 
  inertia 
  of 
  what 
  

   is 
  only 
  a 
  mode 
  of 
  motion, 
  and 
  inertia 
  is 
  a 
  property 
  of 
  matter, 
  

   not 
  of 
  modes 
  of 
  motion. 
  It 
  is 
  true 
  that 
  a 
  vortex 
  ring 
  at 
  any 
  

   given 
  instant 
  has 
  a 
  definite 
  momentum 
  and 
  a 
  definite 
  energy, 
  

   * 
  Maxwell, 
  'The 
  Atom/ 
  Encyc. 
  Brit. 
  

  

  