﻿498 
  Dr. 
  N. 
  Bohr 
  on 
  the 
  Constitution 
  

  

  2, 
  4, 
  8, 
  16 
  may 
  be 
  due 
  to 
  a 
  gradual 
  interchange 
  of 
  electrons 
  

   between 
  the 
  rings, 
  such 
  as 
  is 
  indicated 
  on 
  p. 
  495. 
  Since 
  a 
  

   ring 
  of 
  18 
  electrons 
  will 
  not 
  be 
  stable 
  the 
  electrons 
  may 
  be 
  

   arranged 
  in 
  two 
  parallel 
  rings 
  (see 
  p. 
  486). 
  Such 
  a 
  con- 
  

   figuration 
  of 
  the 
  inner 
  electrons 
  will 
  act 
  upon 
  the 
  outer 
  

   electrons 
  in 
  very 
  nearly 
  the 
  same 
  way 
  as 
  a 
  nucleus 
  of 
  

   charge 
  (N 
  — 
  18)<?. 
  It 
  might 
  therefore 
  be 
  possible 
  that 
  

   with 
  increase 
  of 
  N 
  another 
  configuration 
  of 
  the 
  same 
  type 
  

   will 
  be 
  formed 
  outside 
  the 
  first, 
  such 
  as 
  is 
  suggested 
  by 
  the 
  

   presence 
  of 
  a 
  second 
  period 
  of 
  18 
  elements. 
  

  

  On 
  the 
  same 
  lines, 
  the 
  presence 
  of 
  the 
  group 
  of 
  the 
  rare 
  

   earths 
  indicates 
  that 
  for 
  still 
  greater 
  values 
  of 
  1ST 
  another 
  

   gradual 
  alteration 
  of 
  the 
  innermost 
  rings 
  will 
  take 
  place. 
  

   Since, 
  however, 
  for 
  elements 
  of 
  higher 
  atomic 
  weight 
  than 
  

   those 
  of 
  this 
  group, 
  the 
  laws 
  connecting 
  the 
  variation 
  of 
  the 
  

   chemical 
  properties 
  with 
  the 
  atomic 
  weight 
  are 
  similar 
  to 
  

   those 
  between 
  the 
  elements 
  of 
  low 
  atomic 
  weight, 
  we 
  may 
  

   conclude 
  that 
  the 
  configuration 
  of 
  the 
  innermost 
  electrons 
  

   will 
  be 
  again 
  repeated. 
  The 
  theory, 
  however, 
  is 
  not 
  

   sufficiently 
  complete 
  to 
  give 
  a 
  definite 
  answer 
  to 
  such 
  

   problems. 
  

  

  § 
  5. 
  Characteristic 
  Rontgen 
  Radiation. 
  

  

  According 
  to 
  the 
  theory 
  of 
  emission 
  of 
  radiation 
  given 
  in 
  

   Part 
  I., 
  the 
  ordinary 
  line-spectrum 
  of 
  an 
  element 
  is 
  emitted 
  

   during 
  the 
  reformation 
  of 
  an 
  atom 
  when 
  one 
  or 
  more 
  of 
  the 
  

   electrons 
  in 
  the 
  outer 
  rings 
  are 
  removed. 
  In 
  analogy 
  it 
  may 
  

   be 
  supposed 
  that 
  the 
  characteristic 
  Rontgen 
  radiation 
  is 
  sent 
  

   out 
  during 
  the 
  settling 
  down 
  of 
  the 
  system 
  if 
  electrons 
  in 
  

   inner 
  rings 
  are 
  removed 
  by 
  some 
  agency, 
  e.g. 
  by 
  impact 
  

   of 
  cathode 
  particles. 
  This 
  view 
  of 
  the 
  origin 
  of 
  the 
  

   characteristic 
  Rontgen 
  radiation 
  has 
  been 
  proposed 
  by 
  

   Sir 
  J. 
  J. 
  Thomson*. 
  

  

  Without 
  any 
  special 
  assumption 
  in 
  regard 
  to 
  the 
  constitu- 
  

   tion 
  of 
  the 
  radiation, 
  we 
  can 
  from 
  this 
  view 
  determine 
  the 
  

   minimum 
  velocity 
  of 
  the 
  cathode 
  rays 
  necessary 
  to 
  produce 
  

   the 
  characteristic 
  Rontgen 
  radiation 
  of 
  a 
  special 
  type 
  by 
  

   calculating 
  the 
  energy 
  necessary 
  to 
  remove 
  one 
  of 
  the 
  

   electrons 
  from 
  the 
  different 
  rings. 
  Even 
  if 
  we 
  knew 
  the 
  

   numbers 
  of 
  electrons 
  in 
  the 
  rings, 
  a 
  rigorous 
  calculation 
  of 
  

   this 
  minimum 
  energy 
  might 
  still 
  be 
  complicated, 
  and 
  the 
  

   result 
  largely 
  dependent 
  on 
  the 
  assumptions 
  used; 
  for, 
  as 
  

   mentioned 
  in 
  Part 
  I., 
  p. 
  19, 
  the 
  calculation 
  cannot 
  be 
  per- 
  

   formed 
  entirely 
  on 
  the 
  basis 
  of 
  the 
  ordinary 
  mechanics. 
  We 
  

   can, 
  however, 
  obtain 
  very 
  simply 
  an 
  approximate 
  comparison 
  

   * 
  Comp. 
  J. 
  J. 
  Thomson, 
  Phil. 
  Mag. 
  xxiii. 
  p. 
  456 
  (1912). 
  

  

  