﻿PHYSICS 
  OF 
  THE 
  UNIVERSE 
  JEANS 
  171 
  

  

  the 
  shorter 
  the 
  wave 
  length 
  of 
  the 
  corresponding 
  radiation. 
  It 
  follows 
  

   that 
  a 
  very 
  compact 
  structure 
  can 
  only 
  be 
  disturbed 
  by 
  radiation 
  of 
  

   very 
  short 
  wave 
  length. 
  

  

  As 
  a 
  rough 
  working 
  guide 
  we 
  may 
  say 
  that 
  any 
  structure 
  will 
  only 
  

   be 
  disturbed 
  by 
  radiation 
  whose 
  wave 
  length 
  is 
  less 
  than 
  860 
  times 
  the 
  

   dimensions 
  of 
  the 
  structure. 
  The 
  energy 
  needed 
  to 
  separate 
  two 
  

   electric 
  charges 
  + 
  e 
  and 
  — 
  e, 
  at 
  a 
  distance 
  r 
  apart, 
  is 
  e^/'r, 
  and, 
  in 
  general, 
  

   the 
  energy 
  needed 
  to 
  rearrange 
  or 
  break 
  up 
  a 
  structure 
  of 
  electrons 
  

   and 
  protons 
  of 
  hnear 
  dimensions 
  r 
  will 
  be 
  comparable 
  with 
  this. 
  

   If 
  X 
  is 
  the 
  wave 
  length 
  of 
  the 
  requisite 
  radiation, 
  the 
  energy 
  made 
  

   available 
  by 
  the 
  absorption 
  of 
  this 
  radiation 
  is 
  the 
  quantum 
  AC/X. 
  

   Combining 
  this 
  vdth 
  the 
  ch'cumstance 
  that 
  the 
  value 
  of 
  h 
  is 
  very 
  

   approximately 
  860 
  e^jC, 
  we 
  find 
  that 
  the 
  requisite 
  wave 
  length 
  of 
  

   radiation 
  is 
  about 
  860 
  times 
  the 
  dimensions 
  of 
  the 
  structure 
  to 
  be 
  

   broken 
  up. 
  In 
  brief, 
  the 
  reason 
  why 
  blue 
  light 
  affects 
  photographic 
  

   plates, 
  while 
  red 
  light 
  does 
  not, 
  is 
  that 
  the 
  wave 
  length 
  of 
  blue 
  light 
  is 
  

   loss, 
  and 
  that 
  of 
  red 
  light 
  is 
  greater, 
  than 
  860 
  times 
  the 
  diameter 
  of 
  

   the 
  molecule 
  of 
  silver 
  nitrate; 
  we 
  must 
  get 
  below 
  the 
  860-limit 
  before 
  

   anything 
  begins 
  to 
  happen. 
  

  

  The 
  wave 
  length 
  of 
  the 
  light 
  emitted 
  by 
  an 
  atom 
  when 
  it 
  dis- 
  

   charges 
  its 
  reservoir 
  of 
  energy 
  is 
  precisely 
  the 
  same 
  as 
  that 
  of 
  the 
  

   light 
  absorbed 
  when 
  it 
  originally 
  stored 
  up 
  this 
  energy, 
  for 
  as 
  the 
  

   two 
  quanta 
  of 
  energy 
  are 
  the 
  same, 
  the 
  corresponding 
  wave 
  lengths 
  

   are 
  the 
  same. 
  It 
  follows 
  that 
  the 
  light 
  emitted 
  by 
  any 
  electrical 
  

   structure 
  will 
  have 
  a 
  wave 
  length 
  of 
  about 
  860 
  times 
  the 
  dimensions 
  

   of 
  the 
  structure. 
  For 
  example, 
  ordinary 
  visible 
  light 
  has 
  a 
  wave 
  

   length 
  equal 
  to 
  about 
  860 
  atomic 
  diameters. 
  

  

  Atomic 
  nuclei, 
  like 
  the 
  atoms 
  themselves, 
  are 
  structures 
  of 
  positive 
  

   and 
  negative 
  electrical 
  charges, 
  and 
  so 
  ought 
  to 
  behave 
  similarly 
  

   with 
  respect 
  to 
  the 
  radiation 
  falling 
  upon 
  them. 
  The 
  radiation 
  which 
  

   the 
  atomic 
  nuclei 
  emit, 
  and 
  consequently 
  also 
  that 
  which 
  they 
  are 
  

   prepared 
  to 
  absorb, 
  is, 
  however, 
  of 
  far 
  shorter 
  wave 
  length 
  than 
  

   that 
  emitted 
  or 
  absorbed 
  by 
  complete 
  atoms. 
  Ellis 
  and 
  others 
  have 
  

   found, 
  for 
  example, 
  that 
  the 
  radiation 
  which 
  is 
  emitted 
  during 
  the 
  

   disintegration 
  of 
  radium-5 
  has 
  wave 
  lengths 
  of 
  3.52, 
  4.20, 
  4.80, 
  

   5.13, 
  and 
  23 
  X 
  10-^" 
  cm. 
  These 
  wave 
  lengths 
  are 
  only 
  about 
  a 
  hun- 
  

   dred-thousandth 
  part 
  of 
  those 
  of 
  visible 
  light. 
  The 
  reason 
  is, 
  of 
  

   course, 
  that 
  the 
  nucleus 
  has 
  only 
  about 
  a 
  hundred-thousandth 
  part 
  

   the 
  dimensions 
  of 
  the 
  atom. 
  

  

  Since 
  the 
  wave 
  length 
  of 
  the 
  radiation 
  absorbed 
  or 
  emitted 
  by 
  an 
  

   atom 
  is 
  inversely 
  proportional 
  to 
  the 
  quantum 
  of 
  energy, 
  it 
  follows 
  

   that 
  the 
  quantum 
  of 
  energy 
  needed 
  to 
  work 
  the 
  atomic 
  nucleus 
  is 
  

   about 
  100,000 
  times 
  as 
  great 
  as 
  that 
  needed 
  to 
  work 
  the 
  atom. 
  If 
  

  

  