﻿COSMICAL. 
  PHYSICS 
  JEANS 
  

  

  179 
  

  

  If 
  we 
  arrange 
  the 
  stars 
  in 
  order 
  of 
  radiation 
  per 
  unit 
  mass, 
  we 
  shall 
  

   find 
  that 
  we 
  have 
  arranged 
  them 
  neither 
  in 
  order 
  of 
  temperature 
  nor 
  

   of 
  density, 
  but 
  very 
  approximately 
  in 
  order 
  of 
  age; 
  the 
  youngest 
  

   stars 
  radiate 
  most 
  energetically, 
  regardless 
  of 
  their 
  interior 
  tempera- 
  

   tures 
  and 
  density 
  ; 
  the 
  older 
  stars 
  appear 
  to 
  be 
  tired 
  out. 
  

   The 
  general 
  tendency 
  is 
  shown 
  in 
  the 
  following 
  table 
  : 
  

  

  If 
  it 
  is 
  asked 
  whether 
  densities 
  so 
  high 
  as 
  these 
  can 
  really 
  exist 
  

   at 
  the 
  centers 
  of 
  the 
  stars, 
  the 
  answer 
  is 
  provided 
  by 
  the 
  companion 
  

   to 
  Sirius 
  (Sirius 
  B). 
  Direct 
  observation 
  has 
  shown 
  that 
  the 
  mean 
  

   density 
  of 
  this 
  star 
  is 
  about 
  53,000, 
  and 
  the 
  central 
  density 
  must 
  of 
  

   course 
  be 
  higher. 
  Incidentally, 
  as 
  Eddington 
  has 
  remarked, 
  this 
  

   provides 
  striking 
  confirmation 
  of 
  our 
  view 
  that 
  stellar 
  matter 
  con- 
  

   sists 
  of 
  atoms 
  broken 
  up 
  into 
  their 
  fundamenal 
  constituents. 
  It 
  is 
  

   impossible 
  to 
  compress 
  matter 
  formed 
  of 
  complete 
  atoms 
  of 
  radii 
  

   10"^ 
  cm. 
  or 
  more 
  to 
  anything 
  approaching 
  these 
  high 
  densities, 
  but 
  

   there 
  is 
  no 
  difficulty 
  as 
  regards 
  minute 
  nuclei 
  and 
  electrons 
  of 
  radii 
  

   of 
  the 
  order 
  of 
  10 
  ~^^ 
  cm. 
  

  

  It 
  has 
  to 
  be 
  admitted 
  that 
  many 
  of 
  the 
  entries 
  in 
  the 
  table 
  are 
  

   highly 
  conjectural, 
  and 
  few 
  can 
  claim 
  any 
  great 
  accuracy. 
  But 
  

   while 
  man}'^ 
  astronomers 
  may 
  prefer 
  different 
  values 
  for 
  individual 
  

   entries 
  in 
  the 
  table, 
  I 
  doubt 
  if 
  any 
  would 
  seriously 
  challenge 
  the 
  

   general 
  contention 
  that 
  a 
  star's 
  energy-generating 
  capacity 
  depends 
  

   primarily 
  on 
  its 
  age, 
  and 
  not, 
  at 
  any 
  rate 
  primarily, 
  on 
  its 
  central 
  

   temperature 
  or 
  density. 
  

  

  No 
  doubt 
  exceptions 
  to 
  the 
  general 
  rule 
  can 
  be 
  found. 
  An 
  extreme 
  

   example 
  is 
  provided 
  by 
  the 
  earth 
  and 
  sun 
  ; 
  the 
  matter 
  of 
  which 
  these 
  

   two 
  bodies 
  are 
  formed 
  must 
  be 
  of 
  the 
  same 
  ultimate 
  age, 
  yet 
  they 
  

   radiate 
  at 
  very 
  different 
  rates 
  per 
  unit 
  mass. 
  This 
  is 
  readily 
  ex- 
  

   plained 
  if 
  we 
  suppose 
  the 
  heavy 
  atoms 
  from 
  which 
  the 
  sun's 
  energy 
  

   originates 
  to 
  have 
  sunk 
  deep 
  into 
  its 
  interior, 
  and 
  so 
  not 
  to 
  have 
  

   entered 
  into 
  the 
  composition 
  of 
  the 
  earth 
  and 
  planets. 
  A 
  similar 
  

   explanation 
  will 
  account 
  for 
  the 
  different 
  radiating 
  capacities 
  of 
  the 
  

   components 
  of 
  binary 
  systems. 
  But 
  these 
  exce]>tioiis 
  result 
  from 
  

   special 
  conditions 
  prevailing 
  in 
  special 
  cases 
  ; 
  they 
  do 
  not 
  affect 
  the 
  

  

  