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  ANNUAL 
  RErORT 
  SMITHSONIAN 
  INSTITUTION, 
  192*7 
  

  

  but 
  rather 
  to 
  a 
  serene 
  upper 
  atmosphere 
  in 
  which 
  the 
  lightest 
  ele- 
  

   ments 
  float 
  to 
  the 
  top 
  while 
  the 
  heaviest 
  sink 
  downward 
  under 
  

   gravity. 
  

  

  Such 
  considerations 
  as 
  these 
  suggest 
  at 
  once 
  that 
  the 
  elements 
  

   which 
  indicate 
  their 
  presence 
  in 
  the 
  spectra 
  of 
  the 
  outermost 
  layers 
  

   of 
  the 
  sun 
  and 
  stars 
  are 
  only 
  the 
  very 
  lightest 
  of 
  the 
  series 
  of 
  

   elements 
  existing 
  in 
  the 
  star. 
  It 
  is 
  natural 
  that 
  the 
  earth, 
  formed 
  

   originally 
  out 
  of 
  the 
  sun's 
  outer 
  layers, 
  should 
  contain 
  precisely 
  

   the 
  same 
  chemical 
  elements 
  as 
  these 
  outer 
  layers, 
  but 
  it 
  now 
  appears 
  

   that 
  there 
  ought 
  to 
  be 
  heavier 
  elements 
  inside. 
  The 
  calculation 
  

   which 
  assigns 
  to 
  stellar 
  matter 
  atomic 
  numbers 
  higher 
  than 
  that 
  of 
  

   uranium 
  no 
  longer 
  looks 
  suspicious 
  or 
  paradoxical 
  ; 
  it 
  begins 
  to 
  look 
  

   natural, 
  and 
  indeed 
  almost 
  inevitable. 
  

  

  THE 
  GENERATION 
  OF 
  ENERGY 
  IN 
  A 
  STAR 
  

  

  Further 
  evidence 
  that 
  the 
  atomic 
  weights 
  of 
  stellar 
  atoms 
  are 
  

   higher 
  than 
  those 
  of 
  any 
  known 
  terrestrial 
  atoms 
  may 
  be 
  obtained 
  

   by 
  considering 
  the 
  rate 
  of 
  generation 
  of 
  energy 
  inside 
  a 
  star. 
  The 
  

   sun 
  radiates 
  energy 
  at 
  about 
  2 
  ergs 
  per 
  second 
  for 
  each 
  gram 
  of 
  

   its 
  mass, 
  and 
  so 
  must 
  generate 
  energy 
  at 
  this 
  rate 
  in 
  its 
  interior. 
  

   To 
  the 
  best 
  of 
  our 
  knowledge 
  it 
  has 
  generated 
  and 
  radiated 
  at 
  this, 
  

   or 
  a 
  greater, 
  rate 
  for 
  some 
  millions 
  of 
  millions 
  of 
  years. 
  Could 
  the 
  

   sun 
  have 
  any 
  such 
  radiating 
  capacity 
  if 
  its 
  interior 
  were 
  formed 
  of 
  

   the 
  common 
  terrestrial 
  elements, 
  calcium, 
  iron, 
  silicon, 
  etc.? 
  

  

  One's 
  first 
  im.pulse 
  is 
  to 
  say, 
  " 
  No." 
  Even 
  if 
  the 
  sun 
  were 
  built 
  of 
  

   pure 
  uranium, 
  its 
  radiating 
  power 
  would 
  be 
  only 
  about 
  one-half 
  

   of 
  that 
  observed, 
  and 
  would 
  only 
  last 
  for 
  a 
  minute 
  fraction 
  of 
  what 
  

   is 
  believed 
  to 
  have 
  been 
  the 
  sun's 
  life. 
  A 
  sun 
  of 
  pure 
  radium 
  would 
  

   radiate 
  more 
  than 
  enough 
  for 
  the 
  moment, 
  but 
  its 
  life 
  would 
  be 
  

   limited 
  to 
  a 
  few 
  thousand 
  years. 
  No 
  possible 
  combination 
  of 
  ter- 
  

   restrial 
  elements 
  can 
  give 
  the 
  combination 
  of 
  high 
  radiation 
  and 
  of 
  

   staying 
  power 
  which 
  is 
  observed 
  in 
  the 
  sun 
  and 
  stars. 
  

  

  We 
  must, 
  however, 
  remember 
  that 
  stellar 
  interiors 
  are 
  at 
  pres- 
  

   sures 
  and 
  temperatures 
  which 
  are 
  quite 
  unattainable 
  in 
  our 
  labora- 
  

   tories. 
  We 
  are 
  led 
  to 
  wonder 
  whether 
  our 
  terrestrial 
  elements 
  would 
  

   behave 
  quite 
  differently 
  if 
  they 
  were 
  exposed 
  to 
  stellar 
  conditions. 
  

   Is 
  it 
  possible, 
  for 
  example, 
  that 
  the 
  sun's 
  interior 
  is 
  formed 
  of 
  

   ordinary 
  terrestrial 
  elements, 
  which 
  owe 
  their 
  high 
  generation 
  of 
  

   energy 
  merely 
  to 
  their 
  high 
  temperatures 
  and 
  pressures? 
  

  

  A 
  general 
  survey 
  of 
  astronomy 
  throws 
  a 
  good 
  deal 
  of 
  light 
  on 
  

   this 
  question. 
  We 
  find 
  immediately 
  that 
  the 
  stars 
  v/hich 
  radiate 
  

   most 
  energetically 
  (per 
  unit 
  mass) 
  are 
  not, 
  broadly 
  speaking, 
  the 
  

   hottest 
  stars, 
  and 
  neither 
  are 
  they 
  the 
  densest. 
  Some 
  of 
  the 
  hottest 
  

   and 
  densest 
  stars 
  are 
  entirely 
  put 
  to 
  shame 
  in 
  the 
  matter 
  of 
  radia- 
  

   tion 
  by 
  very 
  cool 
  stars 
  of 
  low 
  density 
  such 
  as 
  Antares 
  and 
  Betelgeuse. 
  

  

  