﻿Theory 
  of 
  Gravity. 
  673 
  

  

  relativity, 
  since 
  J 
  vanishes 
  at 
  infinity. 
  V 
  m 
  in 
  (93) 
  trans- 
  

   forms 
  by 
  any 
  Lorentz-Einstein 
  substitution 
  so 
  as 
  to 
  give 
  a 
  

   force 
  jnst 
  balancing 
  the 
  momentum 
  flowing 
  in 
  to 
  matter 
  

   from 
  infinity. 
  Thus 
  the 
  gravitational 
  attraction 
  is 
  due 
  only 
  

   to 
  the 
  potential 
  J 
  . 
  

  

  I 
  think 
  that 
  at 
  this 
  point 
  the 
  limits 
  of 
  mechanical 
  theory 
  

   are 
  reached. 
  I 
  should 
  hardly 
  expect 
  the 
  views 
  maintained 
  

   in 
  this 
  paper 
  to 
  be 
  seriously 
  regarded 
  but 
  for 
  one 
  circum- 
  

   stance. 
  There 
  is 
  a 
  widespread 
  feeling 
  that 
  something 
  is 
  amiss 
  

   with 
  the 
  classical 
  mechanical 
  theories 
  of 
  matter. 
  They 
  fail, 
  

   and 
  seem 
  to 
  fail 
  without 
  hope, 
  of 
  reaching 
  any 
  solution 
  of 
  

   the 
  problems 
  of 
  radiation. 
  Here 
  the 
  conflict 
  between 
  fact 
  

   and 
  theory 
  seems 
  insoluble. 
  Some 
  license 
  may 
  perhaps 
  be 
  

   allowed, 
  therefore, 
  to 
  speculations 
  which 
  retain 
  as 
  much 
  as 
  

   possible 
  of 
  the 
  mechanical 
  spirit 
  and 
  yet 
  allow 
  a 
  natural 
  

   way 
  of 
  escape 
  from 
  its 
  limitations. 
  

  

  The 
  function 
  V 
  a 
  of 
  (91) 
  represents 
  in 
  effect 
  a 
  tension 
  

   applied 
  to 
  the 
  surface 
  of 
  matter. 
  Suppose 
  we 
  resign 
  the 
  

   attempt 
  to 
  account 
  for 
  its 
  presence 
  mechanically. 
  It 
  is 
  

   derived 
  from 
  a 
  potential 
  function 
  V 
  a 
  existing 
  in 
  the 
  aether. 
  

   Any 
  further 
  knowledge 
  of 
  its 
  properties 
  remains 
  to 
  be 
  

   derived 
  from 
  observations 
  of 
  the 
  laws 
  of 
  nature. 
  What 
  is 
  

   important 
  is 
  that 
  this 
  externally 
  applied 
  force 
  does 
  not 
  

   disturb 
  the 
  electromagnetic 
  field 
  or 
  the 
  irrotational 
  motion 
  

   of 
  aether. 
  

  

  Conservation 
  of 
  energy 
  and 
  momentum 
  are 
  practically 
  

   secured 
  if 
  on 
  the 
  average 
  

  

  j3Jjv 
  W 
  ,=o, 
  mj£ 
  

  

  dv 
  a 
  dt 
  =■ 
  0. 
  

  

  These 
  conditions 
  are 
  consistent 
  with, 
  the 
  principle 
  of 
  rela- 
  

   tivity. 
  They 
  attribute 
  energy 
  of 
  amount 
  V 
  a 
  in 
  unit 
  volume 
  

   to 
  the 
  aether. 
  

  

  It 
  seems 
  to 
  me 
  that 
  Einstein's 
  quantum 
  is 
  an 
  idea 
  belonging 
  

   to 
  the 
  same 
  order 
  as 
  these. 
  It 
  too 
  involves 
  an 
  extra- 
  

   mechanical 
  constraint. 
  But 
  the 
  quantum 
  introduces 
  into 
  

   Physics 
  ideas 
  which 
  seem 
  incapable 
  of 
  coming 
  to 
  any 
  kind 
  

   of 
  terms 
  with 
  ordinary 
  mechanical 
  concepts. 
  I 
  suggest 
  that 
  

   we 
  ought 
  rather 
  to 
  seek 
  some 
  system 
  in 
  which 
  as 
  much 
  as 
  

   possible 
  of 
  the 
  old 
  may 
  be 
  retained. 
  That 
  is 
  the 
  end 
  sought 
  

   in 
  this 
  essay. 
  

  

  April 
  1913. 
  

  

  