﻿of 
  Atoms 
  and 
  Molecules. 
  501 
  

  

  will 
  involve 
  an 
  alteration 
  in 
  the 
  configuration 
  of 
  the 
  bound 
  

   electrons, 
  since 
  the 
  charge 
  remaining 
  on 
  the 
  nucleus 
  is 
  

   different 
  from 
  the 
  original. 
  In 
  order 
  to 
  consider 
  the 
  latter 
  

   effect 
  let 
  us 
  regard 
  a 
  single 
  ring 
  o£ 
  electrons 
  rotating 
  round 
  

   a 
  nucleus 
  o£ 
  charge 
  Ne, 
  and 
  let 
  us 
  assume 
  that 
  an 
  a-particle 
  

   is 
  expelled 
  from 
  the 
  nucleus 
  in 
  a 
  direction 
  perpendicular 
  

   to 
  the 
  plane 
  of 
  the 
  ring. 
  The 
  expulsion 
  of 
  the 
  particle 
  

   will 
  obviously 
  not 
  produce 
  any 
  alteration 
  in 
  the 
  angular 
  

   momentum 
  of 
  the 
  electrons; 
  and 
  if 
  the 
  velocity 
  of 
  the 
  

   a-particle 
  is 
  small 
  compared 
  with 
  the 
  velocity 
  of 
  the 
  elec- 
  

   trons 
  — 
  as 
  it 
  will 
  be 
  if 
  we 
  consider 
  inner 
  rings 
  of 
  an 
  atom 
  of 
  

   high 
  atomic 
  weight 
  — 
  the 
  ring 
  during 
  the 
  expulsion 
  will 
  

   expand 
  continuously, 
  and 
  after 
  the 
  expulsion 
  will 
  take 
  the 
  

   position 
  claimed 
  by 
  the 
  theory 
  for 
  a 
  stable 
  ring 
  rotating 
  

   round 
  a 
  nucleus 
  of 
  charge 
  (N— 
  T)e. 
  The 
  consideration 
  of 
  

   this 
  simple 
  case 
  strongly 
  indicates 
  that 
  the 
  expulsion 
  of 
  an 
  

   a-particle 
  will 
  not 
  have 
  a 
  lasting 
  effect 
  on 
  the 
  stability 
  of 
  the 
  

   internal 
  rings 
  of 
  electrons 
  in 
  the 
  residual 
  atom. 
  

  

  The 
  question 
  of 
  the 
  origin 
  of 
  /3-particles 
  may 
  also 
  be 
  con- 
  

   sidered 
  from 
  another 
  point 
  of 
  view, 
  based 
  on 
  a 
  consideration 
  

   of 
  the 
  chemical 
  and 
  physical 
  properties 
  of 
  the 
  radioactive 
  

   substances. 
  As 
  is 
  well 
  known, 
  several 
  of 
  these 
  substances- 
  

   have 
  very 
  similar 
  chemical 
  properties 
  and 
  have 
  hitherto 
  

   resisted 
  every 
  attempt 
  to 
  separate 
  them 
  by 
  chemical 
  means. 
  

   There 
  is 
  also 
  some 
  evidence 
  that 
  the 
  substances 
  in 
  question 
  

   show 
  the 
  same 
  line-spectrum*. 
  It 
  has 
  been 
  suggested 
  by 
  

   several 
  writers 
  that 
  the 
  substances 
  are 
  different 
  only 
  in 
  

   radio-active 
  properties 
  and 
  atomic 
  weight 
  but 
  identical 
  in 
  all 
  

   other 
  physical 
  and 
  chemical 
  respects. 
  According 
  to 
  the 
  

   theory, 
  this 
  would 
  mean 
  that 
  the 
  charge 
  on 
  the 
  nucleus, 
  as 
  

   well 
  as 
  the 
  configuration 
  of 
  the 
  surrounding 
  electrons, 
  was 
  

   identical 
  in 
  some 
  of 
  the 
  elements, 
  the 
  only 
  difference 
  being 
  

   the 
  mass 
  and 
  the 
  internal 
  constitution 
  of 
  the 
  nucleus. 
  From 
  

   the 
  considerations 
  of 
  § 
  4 
  this 
  assumption 
  is 
  already 
  strongly 
  

   suggested 
  by 
  the 
  fact 
  that 
  the 
  number 
  of 
  radioactive 
  sub- 
  

   stances 
  is 
  greater 
  than 
  the 
  number 
  of 
  places 
  at 
  our 
  disposal 
  

   in 
  the 
  periodic 
  system. 
  If, 
  however, 
  the 
  assumption 
  is 
  

   right, 
  the 
  fact 
  that 
  two 
  apparently 
  identical 
  elements 
  emit 
  

   /3-particles 
  of 
  different 
  velocities, 
  shows 
  that 
  the 
  /3-rays 
  as 
  

   well 
  as 
  the 
  a-rays 
  have 
  their 
  origin 
  in 
  the 
  nucleus. 
  

  

  This 
  view 
  of 
  the 
  origin 
  of 
  a- 
  and 
  /3-particles 
  explains 
  very 
  

   simply 
  the 
  way 
  in 
  which 
  the 
  change 
  in 
  the 
  chemical 
  pro- 
  

   perties 
  of 
  the 
  radioactive 
  substances 
  is 
  connected 
  with 
  the 
  

  

  * 
  See 
  A. 
  S. 
  Eussell 
  and 
  R. 
  Rossi, 
  Proc. 
  Roy. 
  Soc. 
  A. 
  lxxxvii. 
  p. 
  47& 
  

   (1912). 
  

  

  