﻿lb" 
  Dr. 
  N. 
  Bohr 
  on 
  the 
  Constitution 
  

  

  the 
  passing 
  of 
  the 
  system 
  between 
  different 
  stationary 
  states.. 
  

   Let 
  ns 
  consider 
  the 
  radiation 
  emitted 
  during 
  the 
  passing 
  of 
  

   the 
  system 
  between 
  two 
  stationary 
  states 
  A 
  1 
  and 
  A 
  2 
  corre- 
  

   sponding 
  to 
  values 
  for 
  r 
  equal 
  to 
  r 
  1 
  and 
  t 
  2 
  , 
  t 
  1 
  > 
  t 
  2 
  . 
  As 
  the 
  

   necessary 
  condition 
  for 
  an 
  emission 
  of 
  the 
  radiation 
  in 
  question 
  

   was 
  the 
  presence 
  of 
  systems 
  in 
  the 
  state 
  A 
  l5 
  we 
  must 
  assume 
  

   that 
  the 
  necessary 
  condition 
  for 
  an 
  absorption 
  of 
  the 
  radiation 
  

   is 
  the 
  presence 
  of 
  systems 
  in 
  the 
  state 
  A 
  2 
  . 
  

  

  These 
  considerations 
  seem 
  to 
  be 
  in 
  conformity 
  with 
  expe- 
  

   riments 
  on 
  absorption 
  in 
  gases. 
  In 
  hydrogen 
  gas 
  at 
  ordinary 
  

   conditions 
  for 
  instance 
  there 
  is 
  no 
  absorption 
  of 
  a 
  radiation 
  of 
  

   a 
  frequency 
  corresponding 
  to 
  the 
  line-spectrum 
  of 
  this 
  gas 
  ; 
  

   such 
  an 
  absorption 
  is 
  only 
  observed 
  in 
  hydrogen 
  gas 
  in 
  

   a 
  luminous 
  state. 
  This 
  is 
  what 
  'we 
  should 
  expect 
  according 
  

   to 
  the 
  above. 
  We 
  have 
  on 
  p. 
  9 
  assumed 
  that 
  the 
  radiation 
  

   in 
  question 
  was 
  emitted 
  during 
  the 
  passing 
  of 
  the 
  systems 
  

   between 
  stationary 
  states 
  corresponding 
  to 
  r^_2. 
  The 
  state 
  

  

  of 
  the 
  atoms 
  in 
  hydrogen 
  gas 
  at 
  ordinary 
  conditions 
  should, 
  

   however, 
  correspond 
  to 
  f=.l; 
  furthermore, 
  hydrogen 
  atoms 
  

   at 
  ordinary 
  conditions 
  combine 
  into 
  molecules, 
  i. 
  e. 
  into 
  

   systems 
  in 
  which 
  the 
  electrons 
  have 
  frequencies 
  different 
  

   from 
  those 
  in 
  the 
  atoms 
  (see 
  Part 
  III.). 
  From 
  the 
  circum- 
  

   stance 
  that 
  certain 
  substances 
  in 
  a 
  non-luminous 
  state, 
  as, 
  

   for 
  instance, 
  sodium 
  vapour, 
  absorb 
  radiation 
  corresponding 
  

   to 
  lines 
  in 
  the 
  line-spectra 
  of 
  the 
  substances, 
  we 
  may, 
  on 
  the 
  

   other 
  hand, 
  conclude 
  that 
  the 
  lines 
  in 
  question 
  are 
  emitted 
  

   during 
  the 
  passing 
  of 
  the 
  system 
  between 
  two 
  states, 
  one 
  of 
  

   which 
  is 
  the 
  permanent 
  state. 
  

  

  How 
  much 
  the 
  above 
  considerations 
  differ 
  from 
  an 
  inter- 
  

   pretation 
  based 
  on 
  the 
  ordinary 
  electrodynamics 
  is 
  perhaps 
  

   most 
  clearly 
  shown 
  by 
  the 
  fact 
  that 
  we 
  have 
  been 
  forced 
  to 
  

   assume 
  that 
  a 
  system 
  of 
  electrons 
  will 
  absorb 
  a 
  radiation 
  of 
  a 
  

   frequency 
  different 
  from 
  the 
  frequency 
  of 
  vibration 
  of 
  the 
  

   electrons 
  calculated 
  in 
  the 
  ordinary 
  way. 
  It 
  may 
  in 
  this 
  

   connexion 
  be 
  of 
  interest 
  to 
  mention 
  a 
  generalization 
  of 
  the 
  

   considerations 
  to 
  which 
  we 
  are 
  led 
  by 
  experiments 
  on 
  the 
  

   photo-electric 
  effect, 
  and 
  which 
  may 
  be 
  able 
  to 
  throw 
  some 
  

   light 
  on 
  the 
  problem 
  in 
  question. 
  Let 
  us 
  consider 
  a 
  state 
  of 
  

   the 
  system 
  in 
  which 
  the 
  electron 
  is 
  free, 
  i. 
  e. 
  in 
  which 
  the 
  

   electron 
  possesses 
  kinetic 
  energy 
  sufficient 
  to 
  remove 
  to 
  infinite 
  

   distances 
  from 
  the 
  nucleus. 
  If 
  we 
  assume 
  that 
  the 
  motion 
  of 
  

   the 
  electron 
  is 
  governed 
  by 
  the 
  ordinary 
  mechanics 
  and 
  that 
  

   there 
  is 
  no 
  (sensible) 
  energy 
  radiation, 
  the 
  total 
  energy 
  of 
  

   the 
  system 
  — 
  as 
  in 
  the 
  above 
  considered 
  stationary 
  states- 
  

   will 
  be 
  constant. 
  Further, 
  there 
  will 
  be 
  perfect 
  continuity 
  

   between 
  the 
  two 
  kinds 
  of 
  states 
  ; 
  as 
  the 
  difference 
  between 
  

  

  