﻿10 
  Dr. 
  N. 
  Bohr 
  on 
  the 
  Constitution 
  

  

  intensity 
  sufficient 
  for 
  observation 
  the 
  space 
  tilled 
  with 
  the 
  

   gas 
  must 
  be 
  very 
  great. 
  If 
  the 
  theory 
  is 
  right, 
  we 
  may 
  

   therefore 
  never 
  expect 
  to 
  be 
  able 
  in 
  experiments 
  with 
  vacuum 
  

   tubes 
  to 
  observe 
  the 
  lines 
  corresponding 
  to 
  high 
  numbers 
  of 
  

   the 
  Balmer 
  series 
  of 
  the 
  emission 
  spectrum 
  of 
  hydrogen 
  ; 
  it 
  

   might, 
  however, 
  be 
  possible 
  to 
  observe 
  the 
  lines 
  by 
  investi- 
  

   gation 
  of 
  the 
  absorption 
  spectrum 
  of 
  this 
  gas 
  (see 
  § 
  4). 
  

  

  It 
  will 
  be 
  observed 
  that 
  we 
  in 
  the 
  above 
  way 
  do 
  not 
  

   obtain 
  other 
  series 
  of 
  lines, 
  generally 
  ascribed 
  to 
  hydrogen 
  ; 
  

   for 
  instance, 
  the 
  series 
  first 
  observed 
  by 
  Pickering* 
  in 
  the 
  

   spectrum 
  of 
  the 
  star 
  £ 
  Puppis, 
  and 
  the 
  set 
  of 
  series 
  recently 
  

   found 
  by 
  Fowler 
  f 
  by 
  experiments 
  with 
  vacuum 
  tubes 
  

   containing 
  a 
  mixture 
  of 
  hydrogen 
  and 
  helium. 
  We 
  shall, 
  

   however, 
  see 
  that, 
  by 
  help 
  of 
  the 
  above 
  theory, 
  we 
  can 
  

   account 
  naturally 
  for 
  these 
  series 
  of 
  lines 
  if 
  we 
  ascribe 
  them 
  

   to 
  helium. 
  

  

  A 
  neutral 
  atom 
  of 
  the 
  latter 
  element 
  consists, 
  according 
  to 
  

   Rutherford's 
  theory, 
  of 
  a 
  positive 
  nucleus 
  of 
  charge 
  2e 
  and 
  

   two 
  electrons. 
  Now 
  considering 
  the 
  binding 
  of 
  a 
  single 
  

   electron 
  by 
  a 
  helium 
  nucleus, 
  we 
  get, 
  putting 
  E 
  = 
  2e 
  in 
  the 
  

   expressions 
  (3) 
  on 
  page 
  5, 
  and 
  proceeding 
  in 
  exactly 
  the 
  same 
  

   way 
  as 
  above, 
  

  

  Sir 
  2 
  me 
  

   ""A 
  

  

  *fL 
  1 
  \ 
  27r 
  2 
  me 
  A 
  1 
  _ 
  1 
  

  

  If 
  we 
  in 
  this 
  formula 
  put 
  t 
  2 
  =1 
  or 
  t 
  2 
  = 
  2, 
  we 
  get 
  series 
  of 
  

   lines 
  in 
  the 
  extreme 
  ultra-violet. 
  If 
  we 
  put 
  t 
  2 
  = 
  3, 
  and 
  let 
  

   t 
  2 
  vary, 
  we 
  get 
  a 
  series 
  which 
  includes 
  2 
  of 
  the 
  series 
  

   observed 
  by 
  Fowler, 
  and 
  denoted 
  by 
  him 
  as 
  the 
  first 
  and 
  

   second 
  principal 
  series 
  of 
  the 
  hydrogen 
  spectrum. 
  If 
  we 
  put 
  

   T 
  2 
  = 
  4, 
  we 
  get 
  the 
  series 
  observed 
  by 
  Pickering 
  in 
  the 
  

   spectrum 
  of 
  f 
  Puppis. 
  Every 
  second 
  of 
  the 
  lines 
  in 
  this 
  

   series 
  is 
  identical 
  with 
  a 
  line 
  in 
  the 
  Balmer 
  series 
  of 
  

   the 
  hydrogen 
  spectrum; 
  the 
  presence 
  of 
  hydrogen 
  in 
  the 
  

   star 
  in 
  question 
  may 
  therefore 
  account 
  for 
  the 
  fact 
  that 
  

   these 
  lines 
  are 
  of 
  a 
  greater 
  intensity 
  than 
  the 
  rest 
  of 
  the 
  

   lines 
  in 
  the 
  series. 
  The 
  series 
  is 
  also 
  observed 
  in 
  the 
  expe- 
  

   riments 
  of 
  Fowler, 
  and 
  denoted 
  in 
  his 
  paper 
  as 
  the 
  Sharp 
  

   series 
  of 
  the 
  hydrogen 
  spectrum. 
  If 
  we 
  finally 
  in 
  the 
  above 
  

   formula 
  put 
  t 
  2 
  = 
  5, 
  6,.. 
  , 
  we 
  get 
  series, 
  the 
  strong 
  lines 
  of 
  

   which 
  are 
  to 
  be 
  expected 
  in 
  the 
  ultra-red. 
  

  

  The 
  reason 
  why 
  the 
  spectrum 
  considered 
  is 
  not 
  observed 
  in 
  

  

  * 
  E. 
  C. 
  Pickering, 
  Astrophys. 
  J. 
  iv. 
  p. 
  369 
  (1896); 
  v. 
  p. 
  92 
  (1897). 
  

   t 
  A. 
  Fowler, 
  Month. 
  ISot, 
  Koy. 
  Abtr. 
  Soc. 
  Ixxiii. 
  Dec. 
  1912. 
  

  

  