﻿180 
  ANNUAL 
  KEPORT 
  SMITHSONIAN 
  INSTITUTION, 
  1927 
  

  

  general 
  law 
  that 
  a 
  star's 
  generation 
  of 
  energy 
  is 
  not 
  determined 
  by 
  

   either 
  its 
  density 
  or 
  its 
  temperature. 
  

  

  The 
  accompanying 
  table 
  shows 
  that 
  the 
  law 
  is 
  well 
  supported 
  by 
  

   observational 
  astronomy; 
  it 
  can 
  also 
  be 
  reached 
  from 
  a 
  theoretical 
  

   study 
  of 
  the 
  actual 
  process 
  of 
  generation 
  of 
  energy 
  in 
  a 
  star. 
  A 
  

   mass 
  of 
  evidence, 
  mostly 
  dynamical, 
  indicates 
  that 
  the 
  stars 
  must 
  

   have 
  existed 
  for 
  millions 
  of 
  millions 
  of 
  years. 
  To 
  take 
  one 
  example, 
  

   newly 
  formed 
  binary 
  stars 
  have 
  circular, 
  or 
  nearly 
  circular, 
  orbits; 
  

   this 
  is 
  a 
  consequence 
  of 
  the 
  manner 
  of 
  their 
  formation. 
  Every 
  

   gravitational 
  pull 
  on 
  a 
  circular 
  orbit 
  tends 
  to 
  make 
  the 
  orbit 
  more 
  

   elliptical, 
  so 
  that 
  the 
  older 
  a 
  binary 
  star 
  is, 
  the 
  more 
  elliptical 
  its 
  

   orbit 
  ought 
  to 
  be. 
  This 
  is 
  actually 
  found 
  to 
  be 
  the 
  case. 
  But 
  from 
  

   our 
  general 
  knowledge 
  of 
  the 
  number 
  and 
  masses 
  of 
  the 
  stars 
  

   wandering 
  about 
  in 
  space, 
  we 
  can 
  estimate 
  the 
  rates 
  at 
  which 
  the 
  

   ellipticities 
  of 
  the 
  orbits 
  of 
  binary 
  stars 
  ought 
  to 
  increase, 
  and 
  this 
  

   in 
  turn 
  makes 
  it 
  possible 
  to 
  estimate 
  the 
  ages 
  of 
  actual 
  stars. 
  It 
  is 
  

   a 
  mere 
  problem 
  of 
  dynamics, 
  and 
  the 
  answer 
  comes 
  out 
  in 
  millions 
  

   of 
  millions 
  of 
  years. 
  

  

  We 
  can 
  now 
  estimate 
  the 
  total 
  amount 
  of 
  radiation 
  which 
  must 
  

   have 
  been 
  emitted 
  by 
  particular 
  stars 
  in 
  the 
  millions 
  of 
  millions 
  of 
  

   years 
  they 
  have 
  existed 
  ; 
  and, 
  except 
  in 
  the 
  case 
  of 
  the 
  youngest 
  stars 
  

   of 
  all, 
  the 
  total 
  mass 
  of 
  this 
  radiation 
  is 
  found 
  to 
  be 
  far 
  greater 
  than 
  

   the 
  present 
  mass 
  of 
  the 
  star. 
  We 
  obtain 
  the 
  mass 
  of 
  the 
  star 
  at 
  its 
  

   birth 
  by 
  adding 
  the 
  mass 
  of 
  all 
  this 
  radiation 
  to 
  that 
  of 
  the 
  matter 
  

   now 
  remaining 
  in 
  the 
  star. 
  Thus 
  its 
  mass 
  at 
  birth 
  must 
  have 
  been 
  far 
  

   greater 
  than 
  now. 
  But, 
  as 
  a 
  star's 
  mass 
  at 
  any 
  instant 
  consists 
  almost 
  

   wholly 
  of 
  the 
  mass 
  of 
  the 
  matter 
  of 
  which 
  it 
  is 
  composed, 
  we 
  see 
  that 
  

   the 
  greater 
  part 
  of 
  the 
  matter 
  contained 
  in 
  the 
  original 
  star 
  has 
  

   ceased 
  to 
  exist 
  as 
  matter; 
  it 
  has 
  been 
  annihilated 
  and 
  transformed 
  

   into 
  radiation 
  which 
  the 
  star 
  has 
  radiated 
  awaj'^ 
  into 
  space. 
  So 
  far 
  

   back 
  as 
  1904 
  (Nature, 
  70, 
  p. 
  101) 
  I 
  put 
  out 
  the 
  suggestion 
  that 
  energy 
  

   might 
  be 
  created 
  by 
  the 
  annihilation 
  of 
  matter 
  ; 
  it 
  now 
  appears 
  that 
  

   this 
  process 
  must 
  in 
  actual 
  truth 
  be 
  the 
  source 
  of 
  the 
  energy 
  emitted 
  

   by 
  the 
  sun 
  and 
  stars. 
  Throughout 
  a 
  star's 
  interior 
  electrons 
  and 
  

   protons 
  must 
  at 
  intervals 
  fall 
  into 
  one 
  another 
  and 
  mutually 
  destroy 
  

   one 
  another, 
  the 
  energy 
  of 
  their 
  fall 
  being 
  set 
  free 
  as 
  radiation. 
  

  

  The 
  energy 
  of 
  tliis 
  fall 
  is 
  enormous, 
  being 
  sufficient 
  to 
  set 
  both 
  

   the 
  masses 
  involved 
  into 
  motion 
  with 
  a 
  velocity 
  of 
  0.866 
  times 
  that 
  

   of 
  light. 
  In 
  no 
  other 
  way 
  can 
  a 
  given 
  mass 
  of 
  matter 
  be 
  made 
  te 
  

   yield 
  energy 
  of 
  amount 
  comparable 
  with 
  this 
  ; 
  for 
  example, 
  whereas 
  

   the 
  ordinary 
  combustion 
  of 
  a 
  ton 
  of 
  coal 
  provides 
  energy 
  enough 
  to 
  

   drive 
  an 
  express 
  locomotive 
  for 
  an 
  hour, 
  the 
  annihilation 
  of 
  a 
  ton 
  

   of 
  coal 
  would 
  provide 
  enough 
  energy 
  for 
  all 
  the 
  heating, 
  lighting, 
  

   power, 
  and 
  transport 
  in 
  Great 
  Britain 
  for 
  a 
  century. 
  

  

  