﻿798 
  Sir 
  J. 
  J. 
  Thomson 
  on 
  the 
  

  

  The 
  total 
  amount 
  of 
  energy 
  in 
  the 
  Rontgen 
  radiation 
  is 
  

   proportional 
  to 
  

  

  rt 
  oo 
  , 
  70 
  v 
  o 
  

  

  J 
  W) 
  dt 
  > 
  

  

  or 
  since 
  d 
  2 
  x 
  Ge 
  

  

  and 
  „ 
  Ge 
  

  

  X-— 
  V 
  2 
  r 
  + 
  

  

  the 
  energy 
  is 
  proportional 
  to 
  

  

  if 
  

  

  CVdt 
  

  

  ™.» 
  Ar,,, 
  . 
  Oe 
  V 
  

  

  >V 
  4 
  

  

  16 
  a/CW 
  

  

  Thus 
  the 
  energy 
  in 
  the 
  Rontgen 
  radiation 
  is 
  proportional 
  

   to 
  the 
  fourth 
  power 
  of 
  the 
  velocity 
  of 
  the 
  cathode 
  rays 
  which 
  

   excites 
  it 
  ; 
  this 
  result, 
  which 
  I 
  gave 
  in 
  a 
  paper 
  in 
  the 
  ' 
  Philo- 
  

   sophical 
  Magazine 
  ' 
  (August 
  1907), 
  has 
  been 
  confirmed 
  by 
  

   Mr. 
  Whiddington's 
  experiments. 
  

  

  We 
  can 
  get 
  some 
  idea 
  of 
  the 
  magnitude 
  of 
  the 
  attractive 
  

   forces 
  varying 
  inversely 
  as 
  the 
  square 
  of 
  the 
  distance 
  by 
  

   considering 
  the 
  energy 
  required 
  to 
  excite 
  radiation 
  in 
  the 
  

   atom. 
  We 
  assume 
  that 
  the 
  mechanism 
  of 
  radiation 
  is 
  some- 
  

   what 
  as 
  follows. 
  A 
  corpuscle 
  is 
  driven 
  out 
  from 
  a 
  position 
  

   of 
  equilibrium 
  in 
  the 
  atom, 
  leaving 
  such 
  a 
  position 
  vacant; 
  

   then 
  either 
  this 
  corpuscle 
  or 
  some 
  other 
  falls 
  into 
  the 
  vacant 
  

   place, 
  vibrates 
  about 
  the 
  position 
  of 
  equilibrium, 
  and 
  dis- 
  

   sipates 
  the 
  kinetic 
  energy 
  it 
  has 
  acquired 
  by 
  falling 
  into 
  it 
  

   as 
  radiant 
  energy. 
  Thus, 
  to 
  excite 
  the 
  vibration, 
  we 
  have 
  to 
  

   drive 
  a 
  corpuscle 
  out 
  of 
  its 
  position 
  of 
  equilibrium; 
  if 
  this 
  is 
  

   at 
  a 
  distance 
  a 
  from 
  the 
  centre 
  of 
  the 
  atom, 
  the 
  work 
  required 
  

   is 
  Ae/a, 
  and 
  since 
  a 
  = 
  G/A 
  this 
  is 
  equal 
  to 
  A 
  2 
  e/G. 
  

  

  Mr. 
  Whiddington's 
  experiments 
  (Proc. 
  Eoy. 
  Soc. 
  A. 
  

   vol 
  lxxxv. 
  p. 
  323) 
  show 
  that, 
  to 
  excite 
  the 
  hardest 
  charac- 
  

   teristic 
  Rontgen 
  radiation, 
  the 
  K 
  radiation, 
  in 
  an 
  atom 
  whose 
  

   atomic 
  weight 
  is 
  ot, 
  the 
  cathode 
  particle 
  must 
  have 
  a 
  velocity 
  

   not 
  less 
  than 
  lOV 
  cm./sec. 
  The 
  kinetic 
  energy 
  of 
  one 
  of 
  

   these 
  particles 
  is 
  thus 
  not 
  less 
  than 
  ±10 
  l6 
  >& 
  2 
  m; 
  equating 
  this 
  

   to 
  A 
  2 
  e/G, 
  we 
  get 
  

  

  G 
  

  

  