﻿796 
  Sir 
  J. 
  J. 
  Thomson 
  on 
  the 
  

  

  An 
  atom 
  of 
  this 
  kind 
  will 
  only 
  absorb 
  radiant 
  energy 
  of 
  

   frequency 
  n 
  by 
  multiples 
  of 
  hi. 
  For 
  unless 
  the 
  corpuscle 
  is 
  

   displaced 
  from 
  the 
  tube 
  in 
  which 
  it 
  is 
  situated 
  there 
  can 
  be 
  

   no 
  real 
  absorption 
  of 
  energy 
  ; 
  if 
  a 
  wave 
  of 
  light 
  passed 
  over 
  

   it 
  without 
  displacing 
  it 
  from 
  the 
  tube 
  it 
  would 
  leave 
  the 
  

   corpuscle 
  vibrating 
  with 
  the 
  same 
  frequency 
  as 
  the 
  light. 
  

   The 
  energy 
  of 
  this 
  vibratory 
  motion 
  would 
  be 
  dissipated 
  as 
  

   electrical 
  waves, 
  i. 
  e. 
  as 
  light, 
  so 
  that 
  the 
  only 
  result 
  would 
  

   be 
  a 
  scattering 
  of 
  the 
  light 
  without 
  absorption. 
  When, 
  

   however, 
  the 
  energy 
  given 
  to 
  the 
  corpuscle 
  is 
  sufficient 
  to 
  

   liberate 
  it 
  from 
  the 
  tube 
  there 
  is 
  a 
  real 
  absorption 
  of 
  energy 
  

   as 
  the 
  particle 
  ceases 
  to 
  vibrate, 
  and 
  its 
  energy 
  is 
  now 
  given 
  

   out 
  in 
  the 
  kinetic 
  form. 
  Thus 
  the 
  energy 
  is 
  absorbed 
  by 
  

   units, 
  the 
  unit 
  being 
  the 
  amount 
  of 
  energy 
  required 
  to 
  

   liberate 
  a 
  corpuscle 
  from 
  its 
  tube 
  — 
  this, 
  as 
  we 
  have 
  seen, 
  is 
  

   equal 
  to 
  27m. 
  

  

  Next 
  consider 
  the 
  conversion 
  of 
  potential 
  into 
  radiant 
  

   energy 
  by 
  an 
  atom 
  of 
  this 
  kind. 
  We 
  regard 
  the 
  light 
  as 
  

   produced 
  by 
  a 
  corpuscle 
  falling 
  from 
  outside 
  the 
  atom 
  into 
  

   its 
  position 
  of 
  equilibrium. 
  It 
  will 
  arrive 
  at 
  this 
  position 
  

   with 
  a 
  certain 
  amount 
  of 
  energy, 
  which 
  will 
  be 
  dissipated 
  as 
  

   light 
  as 
  the 
  corpuscle 
  vibrates 
  about 
  its 
  position 
  of 
  equilibrium 
  

   with 
  the 
  frequency 
  n. 
  

  

  The 
  kinetic 
  energy 
  possessed 
  by 
  the 
  corpuscle 
  when 
  it 
  falls 
  

   to 
  its 
  position 
  of 
  equilibrium 
  is 
  

  

  A 
  e 
  __ 
  1 
  Ce 
  _ 
  1 
  Ge 
  

  

  a 
  2 
  a 
  2- 
  2 
  a 
  2 
  ' 
  

  

  since 
  A 
  C 
  

  

  If 
  we 
  call 
  this 
  energy 
  iv 
  and 
  n 
  the 
  frequency 
  of 
  the 
  

   vibration 
  we 
  have 
  (see 
  p. 
  795) 
  

  

  w 
  = 
  hn. 
  

  

  Hence 
  the 
  potential 
  energy 
  of 
  the 
  corpuscle 
  outside 
  the 
  

   atom 
  is 
  converted 
  into 
  that 
  of 
  light 
  of 
  frequency 
  n 
  by 
  

   multiples 
  of 
  the 
  unit 
  Tin. 
  Hence 
  we 
  see 
  that 
  an 
  atom 
  of 
  the 
  

   kind 
  we 
  are 
  considering 
  will 
  possess 
  the 
  properties 
  of 
  the 
  

   real 
  atom 
  with 
  respect 
  to 
  the 
  phenomena 
  which 
  involve 
  

   transferences 
  to 
  and 
  fro 
  between 
  radiant 
  and 
  kinetic 
  or 
  

   potential 
  energy. 
  

  

  The 
  case 
  for 
  the 
  existence 
  of 
  a 
  repulsive 
  force 
  varying 
  

   inversely 
  as 
  the 
  cube 
  of 
  the 
  distance 
  is 
  strengthened, 
  I 
  think, 
  

   by 
  the 
  consideration 
  of 
  the 
  theory 
  of 
  the 
  production 
  of 
  

   Ilontgen 
  rays 
  by 
  cathode 
  rays. 
  

  

  