﻿of 
  Atoms 
  and 
  Molecules. 
  19 
  

  

  Experiments 
  on 
  the 
  phenomena 
  of 
  X-rays 
  suggest 
  that 
  not 
  

   only 
  the 
  emission 
  and 
  absorption 
  of 
  radiation 
  cannot 
  be 
  

   treated 
  by 
  the 
  help 
  of 
  the 
  ordinary 
  electrodynamics, 
  but 
  not 
  

   even 
  the 
  result 
  of 
  a 
  collision 
  between 
  two 
  electrons 
  of 
  which 
  

   the 
  one 
  is 
  bound 
  in 
  an 
  atom. 
  This 
  is 
  perhaps 
  most 
  clearly 
  

   shown 
  by 
  some 
  very 
  instructive 
  calculations 
  on 
  the 
  energy 
  

   of 
  /3-part.icles 
  emitted 
  from 
  radioactive 
  substances 
  recently 
  

   published 
  by 
  Rutherford 
  *. 
  These 
  calculations 
  strongly 
  

   suggest 
  that 
  an 
  electron 
  of 
  great 
  velocity 
  in 
  passing 
  through 
  

   an 
  atom 
  and 
  colliding 
  with 
  the 
  electrons 
  bound 
  will 
  loose 
  

   energy 
  in 
  distinct 
  finite 
  quanta. 
  As 
  is 
  immediately 
  seen, 
  

   this 
  is 
  very 
  different 
  from 
  what 
  we 
  might 
  expect 
  if 
  the 
  result 
  

   of 
  the 
  collisions 
  was 
  governed 
  by 
  the 
  usual 
  mechanical 
  laws. 
  

   The 
  failure 
  of 
  the 
  classical 
  mechanics 
  in 
  such 
  a 
  problem 
  

   might 
  also 
  be 
  expected 
  beforehand 
  from 
  the 
  absence 
  of 
  any- 
  

   thing 
  like 
  equipartition 
  of 
  kinetic 
  energy 
  between 
  free 
  

   electrons 
  and 
  electrons 
  bound 
  in 
  atoms. 
  From 
  the 
  point 
  of 
  

   view 
  of 
  the 
  " 
  mechanical 
  " 
  states 
  we 
  see, 
  however, 
  that 
  the 
  

   following 
  assumption 
  — 
  which 
  is 
  in 
  accord 
  with 
  the 
  above 
  

   analogy 
  — 
  might 
  be 
  able 
  to 
  account 
  for 
  the 
  result 
  of 
  Ruther- 
  

   ford's 
  calculation 
  and 
  for 
  the 
  absence 
  of 
  equipartition 
  of 
  

   kinetic 
  energy 
  : 
  two 
  colliding 
  electrons, 
  bound 
  or 
  free, 
  will, 
  

   after 
  the 
  collision 
  as 
  well 
  as 
  before, 
  be 
  in 
  mechanical 
  states. 
  

   Obviously, 
  the 
  introduction 
  of 
  such 
  an 
  assumption 
  would 
  not 
  

   make 
  any 
  alteration 
  necessary 
  in 
  the 
  classical 
  treatment 
  of 
  a 
  

   collision 
  between 
  two 
  free 
  particles. 
  But, 
  considering 
  a 
  col- 
  

   lision 
  between 
  a 
  free 
  and 
  a 
  bound 
  electron, 
  it 
  would 
  follow 
  

   that 
  the 
  bound 
  electron 
  by 
  the 
  collision 
  could 
  not 
  acquire 
  a 
  

   less 
  amount 
  of 
  energy 
  than 
  the 
  difference 
  in 
  energy 
  corre- 
  

   sponding 
  to 
  successive 
  stationary 
  slates, 
  and 
  consequently 
  

   that 
  the 
  free 
  electron 
  which 
  collides 
  with 
  it 
  could 
  not 
  lose 
  a 
  

   less 
  amount. 
  

  

  The 
  preliminary 
  and 
  hypothetical 
  character 
  of 
  the 
  above 
  

   considerations 
  needs 
  not 
  to 
  be 
  emphasized. 
  The 
  intention, 
  

   however, 
  has 
  been 
  to 
  show 
  that 
  the 
  sketched 
  generalization 
  

   of 
  the 
  theory 
  of 
  the 
  stationary 
  states 
  possibly 
  may 
  afford 
  a 
  

   simple 
  basis 
  of 
  representing 
  a 
  number 
  of 
  experimental 
  facts 
  

   which 
  cannot 
  be 
  explained 
  by 
  help 
  of 
  the 
  ordinary 
  electro- 
  

   dynamics, 
  and 
  that 
  the 
  assumptions 
  used 
  do 
  not 
  seem 
  to 
  be 
  

   inconsistent 
  with 
  experiments 
  on 
  phenomena 
  for 
  which 
  a 
  

   satisfactory 
  explanation 
  has 
  been 
  given 
  by 
  the 
  classical 
  

   dynamics 
  and 
  the 
  wave 
  theory 
  of 
  light, 
  

  

  * 
  E. 
  Rutherford, 
  Phil. 
  Mag. 
  xxiv. 
  pp. 
  453 
  & 
  893(1912). 
  

  

  C2 
  

  

  