﻿COSMICAL 
  PHYSICS 
  JEANS 
  171 
  

  

  needed 
  to 
  dissociate 
  these 
  into 
  their 
  constituent 
  electrical 
  charges, 
  

   but 
  the 
  electrons 
  must 
  of 
  necessity 
  nearly 
  all 
  be 
  torn 
  off 
  atoms 
  of 
  

   moderate 
  atomic 
  weight 
  and 
  the 
  nuclei 
  left 
  almost 
  or 
  entirely 
  bare. 
  

   To 
  a 
  first 
  rough 
  approximation 
  we 
  may 
  regard 
  stellar 
  matter, 
  

   at 
  any 
  rate 
  in 
  the 
  star's 
  hot 
  central 
  regions, 
  as 
  consisting 
  of 
  a 
  mixture 
  

   of 
  bare 
  nuclei 
  and 
  free 
  electrons. 
  Passing 
  outward 
  toward 
  the 
  

   star's 
  surface, 
  the 
  temperature 
  falls, 
  and 
  we 
  come 
  to 
  atoms 
  wdiich 
  

   are 
  more 
  and 
  more 
  fully 
  formed, 
  until 
  finally, 
  close 
  to 
  the 
  surface, 
  

   we 
  meet 
  atoms 
  which 
  are 
  completely 
  formed 
  except 
  perhaps 
  for 
  one 
  

   or 
  two 
  of 
  their 
  outermost 
  electrons. 
  In 
  the 
  surfaces 
  of 
  the 
  coolest 
  

   istars 
  of 
  all, 
  we 
  even 
  find 
  complete 
  molecules, 
  as, 
  for 
  example, 
  the 
  

   molecules 
  of 
  titanium 
  oxide 
  and 
  magnesium 
  hj^dride, 
  which 
  appear 
  

   in 
  the 
  spectra 
  of 
  certain 
  classes 
  of 
  stars. 
  

  

  THE 
  MECHANISM 
  OF 
  STELLAR 
  INTERIORS 
  

  

  The 
  mixture 
  of 
  free 
  electrons 
  and 
  bare 
  nuclei 
  or 
  imperfectly 
  

   formed 
  atoms 
  will 
  behave 
  like 
  a 
  mixture 
  of 
  monatomic 
  gases. 
  In 
  

   completely 
  broken-up 
  hydrogen, 
  each 
  hydrogen 
  molecule 
  gives 
  rise 
  

   to 
  four 
  flying 
  units 
  — 
  two 
  protons 
  and 
  two 
  free 
  electrons 
  — 
  so 
  that 
  

   the 
  effective 
  molecular 
  weight 
  of 
  the 
  mixture 
  will 
  be 
  0.5. 
  The 
  

   corresponding 
  figure 
  for 
  helium 
  is 
  1.33, 
  for 
  calcium 
  1.90, 
  for 
  

   iron 
  2.07, 
  and 
  for 
  lead 
  2.50, 
  but 
  since 
  atoms 
  of 
  lead 
  would 
  

   not 
  be 
  completely 
  broken 
  up 
  at 
  stellar 
  temperatures, 
  the 
  actual 
  value 
  

   for 
  stellar 
  lead 
  would 
  be 
  somewhat 
  higher. 
  If 
  we 
  momentarily 
  

   adopt 
  2 
  as 
  a 
  mean 
  molecular 
  weight 
  of 
  stellar 
  matter, 
  we 
  find 
  that 
  

   Emden's 
  calculations 
  give 
  31,500,000° 
  for 
  the 
  central 
  temperature 
  

   of 
  the 
  sun 
  if 
  formed 
  of 
  hydrogen 
  molecules 
  (mol. 
  wt. 
  2). 
  Various 
  

   adjustments 
  must 
  be 
  made 
  in 
  this 
  figure, 
  but 
  they 
  are 
  of 
  compara- 
  

   tively 
  minor 
  importance, 
  and 
  Emden's 
  original 
  figure 
  of 
  31,500,000° 
  

   is 
  probably 
  not 
  very 
  far 
  from 
  the 
  actual 
  temperature 
  of 
  the 
  sun's 
  

   center. 
  Indeed, 
  Russell 
  has 
  recently 
  suggested 
  that 
  the 
  great 
  ma- 
  

   jority 
  of 
  stars 
  have 
  central 
  temperatures 
  fairly 
  close 
  to 
  32,000,000°. 
  

   (Nature, 
  August 
  8, 
  1925.) 
  

  

  One 
  of 
  the 
  necessary 
  adjustments 
  arises 
  from 
  Emden's 
  calcula- 
  

   tions 
  having 
  neglected 
  the 
  pressure 
  of 
  radiation 
  in 
  stellar 
  interiors.- 
  

   At 
  31,500,000° 
  the 
  pressure 
  of 
  radiation 
  is 
  about 
  2,500,000,000 
  atmos- 
  

   pheres. 
  Huge 
  though 
  this 
  is 
  in 
  comparison 
  with 
  terrestrial 
  pres- 
  

   sure, 
  it 
  is 
  only 
  some 
  5 
  per 
  cent 
  of 
  the 
  ordinary 
  gas 
  pressure 
  of 
  the 
  

  

  ' 
  I 
  first 
  directed 
  attention 
  to 
  this 
  in 
  reviewing 
  Emden's 
  book 
  (Astrophys. 
  Jour., 
  30 
  

   (1909), 
  p. 
  72), 
  and 
  gave 
  a 
  reasonably 
  accurate 
  estimate 
  of 
  the 
  ratio 
  of 
  this 
  pressure 
  

   to 
  ordinary 
  gas 
  pressure 
  in 
  stellar 
  interiors 
  in 
  1917 
  (Bakerian 
  Lecture, 
  May 
  17, 
  1917, 
  

   p. 
  209). 
  Some 
  months 
  previously 
  Eddington 
  bad 
  given 
  an 
  estimate 
  which 
  made 
  this 
  

   ratio 
  some 
  hundreds 
  of 
  times 
  too 
  large. 
  He 
  corrected 
  this 
  at 
  the 
  earliest 
  opportunity 
  

   (Mon. 
  Not. 
  R. 
  A. 
  S., 
  Juno, 
  1917), 
  but 
  not 
  in 
  time 
  to 
  overtake 
  sensational 
  statements, 
  still 
  

   occasionally 
  encountered, 
  that 
  pressure 
  of 
  radiation 
  is 
  of 
  predominant 
  importance 
  in 
  

   the 
  dynamics 
  of 
  stellar 
  interiors. 
  

  

  