﻿o24 
  Dr. 
  IT. 
  Wilde 
  on 
  the 
  Moving 
  Force 
  of 
  Terrestrial 
  and 
  

  

  2. 
  The 
  proposition 
  was 
  enunciated 
  by 
  Descartes 
  in 
  his 
  

   ' 
  Principia 
  '*, 
  " 
  That 
  when 
  a 
  part 
  of 
  matter 
  is 
  moved 
  with 
  

   double 
  the 
  quickness 
  of 
  another, 
  and 
  that 
  other 
  is 
  twice 
  the 
  

   ■size 
  of 
  the 
  former, 
  there 
  is 
  just 
  precisely 
  as 
  much 
  motion, 
  

   but 
  no 
  more, 
  in 
  the 
  less 
  body 
  as 
  in 
  the 
  greater." 
  Forty 
  

   years 
  later 
  Newton 
  adopted 
  in 
  his 
  'Principia^ 
  Descartes' 
  

   definition 
  of 
  the 
  quantity 
  of 
  motion 
  in 
  a 
  moving 
  body 
  in 
  

   substantially 
  the 
  same 
  terms 
  as 
  follows 
  : 
  — 
  " 
  The 
  quantity 
  of 
  

   motion 
  is 
  the 
  measure 
  of 
  the 
  same 
  arising 
  from 
  the 
  velocity 
  

   and 
  quantity 
  of 
  matter 
  conjointly. 
  The 
  motion 
  of 
  the 
  whole 
  

   is 
  the 
  sum 
  of 
  the 
  motion 
  of 
  all 
  of 
  its 
  parts 
  ; 
  and 
  therefore 
  in 
  

   a 
  body 
  double 
  in 
  quantity 
  with 
  equal 
  velocity 
  the 
  motion 
  is 
  

   double 
  ; 
  with 
  twice 
  the 
  velocity 
  it 
  is 
  quadruple.^"' 
  To 
  make 
  

   this 
  definition 
  more 
  explicit, 
  Newton 
  states 
  under 
  his 
  second 
  

   law, 
  " 
  if 
  any 
  force 
  generates 
  a 
  motion, 
  a 
  double 
  force 
  will 
  

   generate 
  double 
  the 
  motion, 
  a 
  triple 
  force 
  triple 
  the 
  motion, 
  

   whether 
  that 
  force 
  be 
  impressed 
  altogether 
  and 
  at 
  once, 
  or 
  

   gradually 
  and 
  successively 
  T 
  

  

  3. 
  Although 
  Galilei 
  had 
  long 
  before 
  demonstrated 
  that 
  

   the 
  spaces 
  described 
  by 
  heavy 
  bodies 
  from 
  the 
  beginning 
  of 
  

   their 
  descent 
  are 
  as 
  the 
  squares 
  of 
  the 
  times 
  and 
  also 
  of 
  the 
  

   velocities 
  acquired 
  in 
  falling 
  through 
  those 
  spaces, 
  yet 
  the 
  

   significance 
  of 
  this 
  law 
  in 
  relation 
  to 
  the 
  moving 
  force 
  of 
  

   bodies 
  was 
  entirely 
  overlooked 
  until 
  Leibnitz 
  made 
  the 
  

   announcement 
  that 
  the 
  force 
  of 
  a 
  body 
  in 
  motion, 
  by 
  the 
  

   free 
  action 
  of 
  gravity, 
  is 
  as 
  the 
  square 
  of 
  the 
  velocity. 
  To 
  

   this 
  measure 
  of 
  moving 
  force 
  Leibnitz 
  applied 
  the 
  term, 
  vis 
  

   viva, 
  or 
  living 
  force. 
  

  

  4. 
  The 
  controversy 
  which 
  has 
  since 
  gathered 
  round 
  the 
  

   question 
  of 
  the 
  measure 
  of 
  moving 
  force, 
  and 
  still 
  remains 
  

   unsettled, 
  forms 
  a 
  remarkable 
  chapter 
  in 
  the 
  history 
  of 
  the 
  

   physical 
  sciences. 
  As 
  might 
  have 
  been 
  anticipated 
  a 
  priori^ 
  

   philosophers, 
  mathematicians, 
  metaphysicians, 
  and 
  men 
  of 
  

   letters, 
  unskilled 
  in 
  experimental 
  methods 
  of 
  interrogating 
  

   nature, 
  adopted 
  the 
  Cartesian 
  measure 
  of 
  moving 
  force. 
  Of 
  

   these 
  may 
  be 
  mentioned, 
  Maclaurin, 
  Hutton, 
  and 
  Young 
  ; 
  

   Locke, 
  Kant, 
  Schopenhauer, 
  Voltaire, 
  and 
  other 
  writers 
  of 
  

   more 
  or 
  less 
  note 
  up 
  to 
  the 
  present 
  epoch. 
  Happily 
  for 
  the 
  

   progress 
  of 
  science 
  a 
  number 
  of 
  natural 
  philosophers, 
  among 
  

   whom 
  Smeaton, 
  Wollaston, 
  Ewart, 
  Dalton, 
  Joule, 
  and 
  Pair- 
  

   bairn 
  stand 
  pre-eminent, 
  have 
  proved 
  conclusively 
  by 
  various 
  

   methods, 
  that 
  the 
  true 
  measure 
  of 
  the 
  moving 
  force 
  of 
  a 
  body 
  

   under 
  the 
  free 
  action 
  of 
  gravity 
  is 
  as 
  the 
  square 
  of 
  the 
  

  

  * 
  Principia 
  Philosophies, 
  Pars. 
  2, 
  § 
  XXXV., 
  ]643. 
  

  

  