﻿638 
  Prof. 
  S. 
  B. 
  McLaren 
  on 
  a 
  

  

  constitutions 
  of 
  matter. 
  In 
  §61 
  explain 
  that 
  which 
  seems 
  

   to 
  me 
  the 
  simplest. 
  According 
  to 
  this 
  there 
  is 
  but 
  one 
  

   ultimate 
  substance, 
  a 
  fluid 
  whose 
  density 
  and 
  motion 
  are 
  

   everywhere 
  continuous. 
  The 
  substance 
  has, 
  however, 
  two 
  

   forms, 
  "matter" 
  and 
  " 
  aether," 
  which 
  are 
  exclusive 
  one 
  of 
  

   the 
  other. 
  Matter 
  is 
  a 
  region 
  where 
  the 
  fluid 
  grows 
  or 
  

   decays. 
  In 
  this 
  process 
  the 
  momentum 
  of 
  the 
  aether 
  " 
  born" 
  

   or 
  "dying" 
  is 
  acquired 
  from 
  the 
  surrounding 
  aether, 
  and 
  

   all 
  momentum 
  is 
  that 
  of 
  the 
  one 
  fluid 
  substance. 
  " 
  Decay" 
  

   or 
  "growth" 
  of 
  aether 
  involves, 
  however, 
  an 
  extraneous 
  

   source 
  of 
  energy, 
  and 
  the 
  principle 
  of 
  conservation 
  of 
  energy 
  

   is 
  only 
  a 
  mathematical 
  fiction 
  preserved 
  by 
  attributing 
  to 
  

   matter 
  an 
  amount 
  of 
  energy 
  equal 
  per 
  unit 
  volume 
  to 
  

  

  — 
  mj. 
  

  

  The 
  equations 
  of 
  motion, 
  of 
  the 
  substance 
  thus 
  constituted 
  

   are 
  considered 
  in 
  § 
  6. 
  It 
  is 
  shown 
  that 
  permanent 
  irrota- 
  

   tional 
  motion 
  of 
  the 
  type 
  formulated 
  in 
  (40) 
  is 
  always 
  

   possible. 
  

  

  In 
  "aether" 
  there 
  is 
  no 
  growth 
  or 
  decay, 
  but 
  the 
  fluid 
  

   now 
  possesses 
  polar 
  properties. 
  These 
  are 
  defined 
  by 
  the 
  

   electromagnetic 
  vectors 
  E 
  and 
  H, 
  satisfying 
  Maxwell's 
  

   equations 
  

  

  ^=cCurlH, 
  ^ 
  = 
  - 
  C 
  CurlE~! 
  

  

  at 
  at 
  y 
  

  

  DivE 
  = 
  0, 
  DivH 
  = 
  0. 
  J 
  

  

  At 
  the 
  boundary 
  between 
  " 
  matter 
  " 
  and 
  " 
  aether 
  " 
  the 
  

   ultimate 
  substance 
  passes 
  freely 
  from 
  one 
  form 
  to 
  the 
  other, 
  

   moving 
  continuously 
  in 
  so 
  doing. 
  The 
  conditions 
  which 
  

   determine 
  the 
  surface 
  of 
  transition 
  are, 
  firstly, 
  that 
  E 
  and 
  H 
  

   behave 
  as 
  at 
  a 
  perfectly 
  reflecting 
  surface. 
  And 
  further 
  

  

  ^_(E2-H 
  2 
  )+mJo=a-F 
  a 
  . 
  . 
  . 
  . 
  (94) 
  

  

  a 
  is 
  here 
  a 
  constant 
  and 
  V 
  a 
  is 
  a 
  potential 
  function 
  which 
  

   vanishes 
  in 
  a 
  purely 
  mechanical 
  theory 
  (see 
  § 
  10). 
  The 
  

   condition 
  (94) 
  is 
  required 
  to 
  secure 
  conservation 
  of 
  the 
  

   energy 
  and 
  momentum 
  (§ 
  7). 
  J 
  Q 
  in 
  (94) 
  is 
  not 
  identical 
  

   with 
  J, 
  but 
  differs 
  from 
  it 
  by 
  a 
  term 
  proportional 
  to 
  t 
  the 
  

   time. 
  

  

  J=J 
  -p 
  Q 
  cH 
  (92) 
  

  

  p 
  is 
  the 
  density 
  of 
  the 
  aether 
  at 
  infinity, 
  J 
  is 
  the 
  Newtonian 
  

   potential 
  differing 
  thus 
  slightly 
  from 
  the 
  velocity 
  potential. 
  

  

  