﻿2 
  Dr. 
  N. 
  Bohr 
  on 
  the 
  Constitution 
  

  

  instability 
  of 
  the 
  system 
  of 
  electrons 
  : 
  difficulties 
  purposely 
  

   avoided 
  in 
  atom-models 
  previously 
  considered, 
  for 
  instance, 
  

   in 
  the 
  one 
  proposed 
  by 
  Sir 
  J. 
  J. 
  Thomson*. 
  According 
  to 
  

   the 
  theory 
  of 
  the 
  latter 
  the 
  atom 
  consists 
  of 
  a 
  sphere 
  of 
  

   uniform 
  positive 
  electrification, 
  inside 
  which 
  the 
  electrons 
  

   move 
  in 
  circular 
  orbits. 
  

  

  The 
  principal 
  difference 
  between 
  the 
  atom-models 
  proposed 
  

   by 
  Thomson 
  and 
  Rutherford 
  consists 
  in 
  the 
  circumstance 
  

   that 
  the 
  forces 
  acting 
  on 
  the 
  electrons 
  in 
  the 
  atom-model 
  of 
  

   Thomson 
  allow 
  of 
  certain 
  configurations 
  and 
  motions 
  of 
  the 
  

   electrons 
  for 
  which 
  the 
  system 
  is 
  in 
  a 
  stable 
  equilibrium 
  ; 
  

   sach 
  configurations, 
  however, 
  apparently 
  do 
  not 
  exist 
  for 
  

   the 
  second 
  atom-model. 
  The 
  nature 
  of 
  the 
  difference 
  in 
  

   question 
  will 
  perhaps 
  be 
  most 
  clearly 
  seen 
  by 
  noticing 
  that 
  

   among 
  the 
  quantities 
  characterizing 
  the 
  first 
  atom 
  a 
  quantity 
  

   appears 
  — 
  the 
  radius 
  of 
  the 
  positive 
  sphere 
  — 
  of 
  dimensions 
  

   of 
  a 
  length 
  and 
  of 
  the 
  same 
  order 
  of 
  magnitude 
  as 
  the 
  linear 
  

   extension 
  of 
  the 
  atom, 
  while 
  such 
  a 
  length 
  does 
  not 
  appear 
  

   among 
  the 
  quantities 
  characterizing 
  the 
  second 
  atom, 
  viz. 
  

   the 
  charges 
  and 
  masses 
  of 
  the 
  electrons 
  and 
  the 
  positive 
  

   nucleus 
  ; 
  nor 
  can 
  it 
  be 
  determined 
  solely 
  by 
  help 
  of 
  the 
  

   latter 
  quantities. 
  

  

  The 
  way 
  of 
  considering 
  a 
  problem 
  of 
  this 
  kind 
  has, 
  how- 
  

   ever, 
  undergone 
  essential 
  alterations 
  in 
  recent 
  years 
  owing 
  

   to 
  the 
  development 
  of 
  the 
  theory 
  of 
  the 
  energy 
  radiation, 
  

   and 
  the 
  direct 
  affirmation 
  of 
  the 
  new 
  assumptions 
  introduced 
  

   in 
  this 
  theory, 
  found 
  by 
  experiments 
  on 
  very 
  different 
  phe- 
  

   nomena 
  such 
  as 
  specific 
  heats, 
  photoelectric 
  effect, 
  Rontgen- 
  

   rays, 
  &c. 
  The 
  result 
  of 
  the 
  discussion 
  of 
  these 
  questions 
  

   seems 
  to 
  be 
  a 
  general 
  acknowledgment 
  of 
  the 
  inadequacy 
  of 
  

   the 
  classical 
  electrodynamics 
  in 
  describing 
  the 
  behaviour 
  of 
  

   systems 
  of 
  atomic 
  sizef. 
  Whatever 
  the 
  alteration 
  in 
  the 
  

   laws 
  of 
  motion 
  of 
  the 
  electrons 
  may 
  be, 
  it 
  seems 
  necessary 
  

   to 
  introduce 
  in 
  the 
  laws 
  in 
  question 
  a 
  quantity 
  foreign 
  to 
  

   the 
  classical 
  electrodynamics, 
  i. 
  e. 
  Planck's 
  constant, 
  or 
  as 
  it 
  

   often 
  is 
  called 
  the 
  elementary 
  quantum 
  of 
  action. 
  By 
  the 
  

   introduction 
  of 
  this 
  quantity 
  the 
  question 
  of 
  the 
  stable 
  con- 
  

   figuration 
  of 
  the 
  electrons 
  in 
  the 
  atoms 
  is 
  essentially 
  changed, 
  

   as 
  this 
  constant 
  is 
  of 
  such 
  dimensions 
  and 
  magnitude 
  that 
  it, 
  

   together 
  with 
  the 
  mass 
  and 
  charge 
  of 
  the 
  particles, 
  can 
  

   determine 
  a 
  length 
  of 
  the 
  order 
  of 
  magnitude 
  required. 
  

  

  This 
  paper 
  is 
  an 
  attempt 
  to 
  show 
  that 
  the 
  application 
  of 
  

   the 
  above 
  ideas 
  to 
  Rutherford's 
  atom-model 
  affords 
  a 
  basis 
  

  

  * 
  J. 
  J. 
  Thomson, 
  Phil. 
  Mag. 
  vii. 
  p. 
  237 
  (1904). 
  

  

  t 
  See 
  f. 
  inst., 
  ' 
  Theorie 
  du 
  ravonnement 
  et 
  les 
  quanta.' 
  Rapports 
  de 
  

   la 
  reunion 
  a 
  Bruxelles, 
  Nov. 
  lull. 
  

  

  