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  792 
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  LXVII. 
  On 
  tlie 
  Structure 
  of 
  tlie 
  Atom. 
  

   By 
  Sir 
  J. 
  J. 
  Thomson, 
  O.M., 
  F.R.S.*. 
  

  

  A 
  LARGE 
  and 
  important 
  class 
  of 
  atomic 
  properties 
  

   involves 
  the 
  relation 
  iv 
  = 
  lin 
  between 
  the 
  energy 
  w 
  

   communicated 
  to 
  some 
  of 
  the 
  corpuscles 
  in 
  the 
  atom 
  and 
  the 
  

   frequency 
  n 
  of 
  the 
  light 
  from 
  which 
  this 
  energy 
  is 
  derived 
  ; 
  

   h 
  is 
  Planck's 
  constant, 
  which 
  is 
  the 
  same 
  for 
  every 
  kind 
  of 
  

   atom 
  and 
  on 
  the 
  C.Gr.S. 
  system 
  of 
  units 
  =6*5 
  x 
  10~ 
  27 
  , 
  its 
  

   dimensions 
  are 
  those 
  of 
  a 
  moment 
  of 
  momentum. 
  

  

  Examples 
  of 
  this 
  type 
  of 
  properties 
  are 
  : 
  (1) 
  photo-electric 
  

   effects, 
  where 
  the 
  corpuscles 
  ejected 
  under 
  the 
  influence 
  of 
  

   this 
  light 
  start 
  with 
  an 
  amount 
  of 
  energy 
  equal 
  to 
  hn; 
  (2) 
  the 
  

   relation 
  between 
  the 
  " 
  hardness 
  " 
  of 
  Rontgen 
  rays 
  and 
  the 
  

   kinetic 
  energy 
  of 
  the 
  cathode 
  rays 
  which 
  produce 
  them 
  ; 
  

   (3) 
  the 
  nature 
  of 
  the 
  " 
  characteristic 
  " 
  Rontgen 
  radiation 
  

   emitted 
  by 
  the 
  atom 
  and 
  probably 
  also 
  that 
  of 
  its 
  visible 
  

   spectrum. 
  In 
  fact, 
  all 
  the 
  effects 
  produced 
  by 
  radiation, 
  

   whether 
  this 
  be 
  ordinary 
  light 
  or 
  Rontgen 
  rays, 
  seem 
  to 
  be 
  

   manifestations 
  of 
  this 
  principle. 
  

  

  It 
  is 
  usual 
  to 
  regard 
  Planck's 
  equation 
  as 
  an 
  indication 
  

   that 
  radiant 
  energy 
  is 
  molecular 
  in 
  structure. 
  I 
  have 
  sug- 
  

   gested, 
  in 
  papers 
  in 
  the 
  ' 
  Proceedings 
  of 
  the 
  Cambridge 
  

   Philosophical 
  Society 
  ' 
  (vol. 
  xvi. 
  p. 
  643) 
  and 
  the 
  f 
  Philo- 
  

   sophicnl 
  Magazine' 
  (May, 
  1912), 
  that 
  the 
  same 
  result 
  would 
  

   follow 
  without 
  any 
  such 
  assumption 
  as 
  to 
  the 
  character 
  of 
  

   radiant 
  energy, 
  if 
  the 
  mechanism 
  in 
  the 
  atom 
  by 
  which 
  the 
  

   radiant 
  energy 
  is 
  transformed 
  to 
  kinetic 
  energy 
  is 
  such 
  as 
  to 
  

   require 
  the 
  transference 
  to 
  the 
  mechanism 
  of 
  a 
  definite 
  amount 
  

   of 
  energy, 
  sufficient, 
  for 
  example 
  to 
  rupture 
  some 
  system, 
  

   before 
  the 
  transference 
  can 
  take 
  place 
  ; 
  that, 
  in 
  fact, 
  Planck's 
  

   relation 
  depends 
  on 
  the 
  properties 
  of 
  the 
  atom, 
  the 
  agent 
  

   b}^ 
  which 
  the 
  energy 
  is 
  transformed, 
  rather 
  than 
  upon 
  the 
  

   existence 
  of 
  a 
  structure 
  in 
  the 
  energy 
  itself. 
  

  

  In 
  the 
  following 
  paper 
  I 
  have 
  attempted 
  to 
  describe 
  an 
  

   atom 
  of 
  such 
  a 
  kind 
  that 
  the 
  transformation 
  of 
  radiant 
  into 
  

   kinetic 
  energy 
  would 
  take 
  place 
  in 
  accordance 
  with 
  Planck's 
  

   law. 
  

  

  Phenomena 
  wdiich 
  involve 
  this 
  law 
  seem 
  especially 
  suitable 
  

   for 
  consideration 
  in 
  connexion 
  with 
  theories 
  of 
  the 
  structure 
  

   of 
  the 
  atom, 
  for 
  their 
  general 
  character 
  is 
  the 
  same 
  for 
  all 
  

   atoms, 
  and 
  thus 
  the 
  mechanism 
  to 
  which 
  they 
  are 
  due 
  must 
  

   exist 
  in 
  every 
  kind 
  of 
  atom, 
  and 
  must, 
  therefore, 
  be 
  of 
  funda- 
  

   mental 
  importance 
  in 
  any 
  theory 
  of 
  atomic 
  structure. 
  

  

  * 
  Communicated 
  bv 
  the 
  Author. 
  Head 
  at 
  the 
  British 
  Association, 
  

   Sept. 
  11, 
  1913. 
  

  

  