﻿490 
  Dr. 
  N. 
  Bohr 
  on 
  the 
  Constitution 
  

  

  given 
  by 
  v 
  = 
  Z"21 
  w 
  . 
  The 
  fact 
  that 
  the 
  latter 
  frequency 
  

   is 
  great 
  compared 
  with 
  that 
  observed 
  might 
  explain 
  that 
  

   the 
  number 
  of 
  electrons 
  in 
  a 
  helium 
  atom, 
  calculated 
  by 
  help 
  

   of 
  Drude's 
  theory 
  from 
  the 
  experiments 
  on 
  dispersion, 
  is 
  

   only 
  about 
  two-thirds 
  of 
  the 
  number 
  to 
  be 
  expected. 
  (Using 
  

  

  = 
  5*31 
  . 
  10 
  17 
  the 
  value 
  calculated 
  is 
  1*2.) 
  

   m 
  

  

  For 
  a 
  configuration 
  of 
  a 
  helium 
  nucleus 
  and 
  three 
  electrons, 
  

   we 
  get 
  

  

  2(3) 
  a 
  = 
  0'703rt 
  , 
  &) 
  = 
  2-02^0, 
  W 
  = 
  6*07W 
  . 
  

  

  Since 
  W 
  for 
  this 
  configuration 
  is 
  smaller 
  than 
  for 
  the 
  con- 
  

   figuration 
  2(2), 
  the 
  theory 
  indicates 
  that 
  a 
  helium 
  atom 
  

   cannot 
  acquire 
  a 
  negative 
  charge. 
  This 
  is 
  in 
  agreement 
  

   with 
  experimental 
  evidence, 
  which 
  shows 
  that 
  helium 
  atoms 
  

   have 
  no 
  "affinity 
  " 
  for 
  free 
  electrons 
  *. 
  

  

  In 
  a 
  later 
  paper 
  it 
  will 
  be 
  shown 
  that 
  the 
  theory 
  offers 
  a 
  

   simple 
  explanation 
  of 
  the 
  marked 
  difference 
  in 
  the 
  tendency 
  

   of 
  hydrogen 
  and 
  helium 
  atoms 
  to 
  combine 
  into 
  molecules. 
  

  

  N=3. 
  Lithium. 
  

  

  In 
  analogy 
  with 
  the 
  cases 
  of 
  hydrogen 
  and 
  helium 
  we 
  

   must 
  expect 
  that 
  during 
  the 
  binding 
  of 
  an 
  electron 
  by 
  a 
  

   nucleus 
  of 
  charge 
  3e, 
  a 
  spectrum 
  is 
  emitted, 
  given 
  by 
  

  

  2TT 
  2 
  me 
  4 
  / 
  1 
  1 
  \ 
  

  

  On 
  account 
  of 
  the 
  great 
  energy 
  to 
  be 
  spent 
  in 
  removing 
  all 
  

   the 
  electrons 
  bound 
  in 
  a 
  lithium 
  atom 
  (see 
  below) 
  the 
  

   spectrum 
  considered 
  can 
  only 
  be 
  expected 
  to 
  be 
  observed 
  in 
  

   extraordinary 
  cases. 
  

  

  In 
  a 
  recent 
  note 
  Nicholson 
  f 
  has 
  drawn 
  attention 
  to 
  the 
  

   fact 
  that 
  in 
  the 
  spectra 
  of 
  certain 
  stars, 
  which 
  show 
  the 
  

   Pickering 
  spectrum 
  with 
  special 
  brightness, 
  some 
  lines 
  occur 
  

   the 
  frequencies 
  of 
  which 
  to 
  a 
  close 
  approximation 
  can 
  be 
  

   expressed 
  by 
  the 
  formula 
  

  

  "= 
  K 
  (3-(^b> 
  

  

  where 
  K 
  is 
  the 
  same 
  constant 
  as 
  in 
  the 
  Balmer 
  spectrum 
  of 
  

   hydrogen. 
  From 
  analogy 
  with 
  the 
  Balmer- 
  and 
  Pickering- 
  

   spectra, 
  Nicholson 
  has 
  suggested 
  chat 
  the 
  lines 
  in 
  question 
  

   are 
  due 
  to 
  hydrogen. 
  

  

  * 
  See 
  J. 
  Franck, 
  Verh. 
  d. 
  Deutsch. 
  Phi/s. 
  Ges. 
  xii. 
  p. 
  613 
  (1910). 
  

  

  t 
  J. 
  W. 
  Nicholson, 
  Month. 
  Not. 
  Roy. 
  Astr. 
  Soc. 
  lxxiii. 
  p. 
  382 
  (1913). 
  

  

  