﻿216 
  ANNUAL 
  EEPOET 
  SMITHSONIAN 
  INSTITUTION, 
  1927 
  

  

  The 
  problem 
  of 
  the 
  arrangement 
  of 
  the 
  protons 
  and 
  electrons 
  

   within 
  the 
  atomic 
  nuclei 
  is 
  still 
  unsolved, 
  but 
  evidence 
  is 
  rapidly/ 
  

   accumulating 
  which 
  should 
  ultimately 
  provide 
  a 
  solution 
  when 
  we 
  

   have 
  discovered 
  how 
  to 
  deal 
  with 
  it. 
  Some 
  information 
  is 
  provided 
  

   by 
  experiments 
  on 
  the 
  disintegration 
  of 
  the 
  nucleus. 
  It 
  is 
  interesting 
  

   to 
  notice, 
  for 
  example, 
  that 
  in 
  radioactive 
  disintegrations 
  the 
  parti- 
  

   cles 
  ejected 
  are 
  invariably 
  either 
  helium 
  nuclei, 
  forming 
  the 
  a 
  rays, 
  

   or 
  electrons 
  forming 
  the 
  fi 
  rays. 
  On 
  the 
  other 
  hand, 
  the 
  particles 
  

   ejected 
  during 
  the 
  artificial 
  disintegrations 
  studied 
  by 
  Rutherford 
  

   seem 
  to 
  be 
  invariably 
  protons. 
  The 
  most 
  probable 
  suggestion 
  at 
  the 
  

   moment 
  is 
  that 
  the 
  protons 
  and 
  electrons 
  in 
  the 
  nucleus 
  tend 
  to 
  

   combine 
  to 
  form 
  very 
  stable 
  helium 
  nuclei. 
  Some, 
  however, 
  either 
  

   because 
  they 
  are 
  present 
  in 
  insufficient 
  number 
  to 
  build 
  up 
  the 
  helium 
  

   structure, 
  or 
  for 
  other 
  reasons 
  at 
  present 
  unknown, 
  are 
  in 
  a 
  compara- 
  

   tivel}' 
  free 
  state, 
  and 
  are 
  thus 
  more 
  readily 
  dislodged 
  by 
  shocks 
  from 
  

   without. 
  This 
  view 
  is 
  supported 
  by 
  the 
  fact 
  that 
  all 
  efforts 
  to 
  dis- 
  

   integrate 
  the 
  atoms 
  of 
  carbon 
  and 
  oxygen, 
  whose 
  atomic 
  masses 
  are 
  

   exact 
  integral 
  multiples 
  of 
  that 
  of 
  helium, 
  have 
  so 
  far 
  failed, 
  though 
  

   other 
  elements 
  of 
  neighboring 
  atomic 
  mass 
  are 
  disintegrated 
  with 
  

   ease. 
  

  

  It 
  is 
  also 
  possible 
  to 
  conceive 
  of 
  the 
  nucleus 
  of 
  an 
  element 
  of 
  high 
  

   atomic 
  number 
  as 
  possessing 
  a 
  solid 
  core 
  of 
  protons 
  and 
  electrons, 
  

   arranged 
  in 
  some 
  kind 
  of 
  space 
  lattice 
  much 
  as 
  the 
  atoms 
  of 
  sodium 
  

   and 
  chlorine 
  are 
  arranged 
  in 
  a 
  crystal 
  of 
  rock 
  salt, 
  while 
  other 
  elec- 
  

   trons 
  and 
  protons, 
  not 
  yet 
  combinable 
  into 
  the 
  structure 
  of 
  this 
  

   central 
  core, 
  circulate 
  around 
  it 
  in 
  a 
  series 
  of 
  nuclear 
  orbits. 
  Exact 
  

   and 
  delicate 
  measurements 
  recently 
  made 
  by 
  Ellis, 
  and 
  by 
  Meit- 
  

   ner, 
  on 
  the 
  y 
  ray 
  sj^ectra 
  of 
  the 
  radioactive 
  elements 
  have 
  shown 
  

   fairly 
  conclusively 
  that 
  Bohr's 
  theory 
  of 
  X-ray 
  spectra 
  which 
  has 
  

   been 
  applied 
  with 
  so 
  much 
  success 
  to 
  elucidating 
  the 
  arrangement 
  

   of 
  the 
  planetary 
  electrons 
  in 
  the 
  atom, 
  can 
  be 
  extended 
  to 
  the 
  char- 
  

   acteristic 
  y 
  ray 
  spectra 
  of 
  these 
  radioactive 
  elements. 
  The 
  emission 
  

   of 
  y 
  radiation 
  is, 
  however, 
  a 
  function 
  of 
  the 
  nucleus. 
  Even 
  within 
  

   the 
  nucleus, 
  then, 
  it 
  appears 
  that 
  we 
  have 
  " 
  quantum 
  " 
  orbits, 
  asso- 
  

   ciated 
  with 
  definite 
  energy 
  levels, 
  corresponding, 
  though 
  governed 
  

   perhaps 
  by 
  other 
  laws, 
  to 
  the 
  electron 
  orbits 
  and 
  levels 
  in 
  the 
  outer 
  

   part 
  of 
  the 
  atom. 
  Experiments, 
  to 
  the 
  degree 
  of 
  accuracy 
  required, 
  

   are 
  difficult 
  and 
  the 
  results 
  are 
  not 
  always 
  easy 
  to 
  interpret 
  without 
  

   ambiguity. 
  We 
  may 
  reasonably 
  hope, 
  however, 
  that 
  before 
  long 
  

   the 
  nucleus, 
  inconceivably 
  minute 
  as 
  is 
  its 
  size, 
  will 
  yield 
  up 
  its 
  

   secrets 
  under 
  the 
  mass 
  attack 
  which 
  is 
  now 
  being 
  launched 
  against 
  

   it, 
  with 
  results 
  as 
  fascinating 
  and 
  as 
  important 
  as 
  those 
  obtained 
  in 
  

   the 
  investigation 
  of 
  the 
  structure 
  of 
  the 
  outer 
  parts 
  of 
  the 
  atom. 
  

  

  