﻿COSMICAL 
  PHYSICS 
  JEANS 
  177 
  

  

  is 
  still 
  probably 
  the 
  prevalent 
  belief, 
  it 
  now 
  looks 
  as 
  though 
  the 
  

   atoms 
  in 
  a 
  star 
  become 
  simpler 
  as 
  the 
  star 
  grows 
  older; 
  evolution 
  

   appears 
  to 
  be 
  from 
  complex 
  to 
  simple, 
  and 
  not, 
  as 
  in 
  biology, 
  from 
  

   simple 
  to 
  complex. 
  There 
  is 
  at 
  present 
  no 
  direct 
  experimental 
  

   evidence 
  bearing 
  on 
  this 
  question 
  except 
  that 
  provided 
  by 
  radio- 
  

   activity, 
  where 
  evolution 
  is 
  certainly 
  from 
  complex 
  to 
  simple, 
  atoms 
  

   of 
  lower 
  atomic 
  weight 
  being 
  continually 
  produced 
  by 
  the 
  disap- 
  

   pearance 
  of 
  atoms 
  of 
  higher 
  atomic 
  weight. 
  

  

  The 
  evidence 
  of 
  physical 
  astronomy, 
  pointing 
  to 
  an 
  evolution 
  of 
  

   matter 
  in 
  the 
  same 
  direction, 
  suggests 
  that 
  the 
  main 
  evolution 
  of 
  

   matter 
  in 
  the 
  universe 
  may 
  be 
  of 
  the 
  same 
  type 
  as, 
  but 
  a 
  generaliza- 
  

   tion 
  of, 
  the 
  radioactive 
  processes 
  as 
  they 
  occur 
  on 
  earth. 
  The 
  evi- 
  

   dence 
  so 
  far 
  given 
  has 
  been 
  based 
  entirely 
  on 
  Kramers' 
  theory 
  of 
  

   opacity 
  for 
  X 
  radiation. 
  This 
  theory 
  has 
  been 
  found 
  to 
  agree 
  

   very 
  well 
  with 
  the 
  observed 
  absorption 
  in 
  the 
  laboratory 
  of 
  radiation 
  

   of 
  about 
  the 
  wave-length 
  which 
  occurs 
  in 
  stellar 
  interiors, 
  while 
  its 
  

   theoretical 
  basis 
  has 
  been 
  discussed 
  fully 
  and 
  critically 
  by 
  Eddington, 
  

   Milne, 
  and 
  others, 
  who 
  have 
  been 
  unable 
  to 
  suggest 
  any 
  substantial 
  

   alteration. 
  Still, 
  if 
  the 
  evidence 
  from 
  Kramers' 
  formula 
  were 
  the 
  

   only 
  evidence 
  available, 
  our 
  conclusions 
  would 
  be 
  open 
  to 
  the 
  charge 
  

   of 
  resting, 
  if 
  not 
  on 
  a 
  slight, 
  at 
  least 
  oji 
  a 
  single, 
  foundation. 
  But 
  

   there 
  is 
  plenty 
  of 
  further 
  evidence, 
  as 
  Ave 
  shall 
  now 
  see. 
  

  

  DISTRIBUTION 
  OF 
  CHEMICAL 
  ELEMENTS 
  IN 
  A 
  STAR 
  

  

  A 
  star 
  necessarily 
  arranges 
  itself 
  so 
  that 
  there 
  is 
  a 
  great 
  concentra- 
  

   tion 
  of 
  matter 
  near 
  its 
  center. 
  This 
  is 
  primarily 
  a 
  consequence 
  of 
  

   the 
  inverse 
  square 
  law 
  of 
  gravitation, 
  although 
  the 
  opacity 
  law 
  is 
  

   involved 
  also 
  to 
  some 
  extent. 
  With 
  Kramers' 
  formula 
  for 
  the 
  opac- 
  

   ity 
  the 
  arrangement 
  is 
  such 
  that 
  the 
  central 
  density 
  is 
  one 
  hundred 
  or 
  

   more 
  times 
  the 
  mean 
  density, 
  while 
  at 
  least 
  some 
  90 
  or 
  95 
  per 
  cent 
  of 
  

   the 
  star's 
  total 
  mass 
  is 
  concentrated 
  in 
  a 
  sphere 
  of 
  half 
  the 
  radius, 
  

   and 
  so 
  of 
  only 
  one-eighth 
  the 
  volume, 
  of 
  the 
  star. 
  But 
  the 
  degree 
  of 
  

   central 
  condensation 
  is 
  rather 
  insensitive 
  to 
  changes 
  in 
  the 
  opacity 
  

   formula, 
  and 
  any 
  reasonable 
  formula 
  would 
  still 
  give 
  very 
  high 
  

   central 
  condensation. 
  A 
  strict 
  mathematical 
  argument 
  based 
  on 
  

   this 
  circumstance 
  (Mon. 
  Not. 
  E. 
  A. 
  S., 
  June, 
  1926, 
  p. 
  561) 
  enables 
  

   us 
  to 
  rule 
  out 
  the 
  possibility 
  of 
  convection 
  currents 
  stirring 
  up 
  a 
  

   star's 
  interior 
  in 
  the 
  way 
  in 
  which 
  boiling 
  water 
  is 
  stirred 
  up 
  in 
  a 
  

   kettle. 
  Convection 
  occurs 
  in 
  a 
  kettle 
  because 
  the 
  hot 
  water 
  at 
  the 
  

   bottom 
  is 
  of 
  lower 
  density 
  than 
  the 
  cool 
  water 
  at 
  the 
  top; 
  it 
  is 
  

   absent 
  in 
  a 
  star 
  because 
  the 
  hot 
  matter 
  near 
  the 
  center, 
  notwith- 
  

   standing 
  its 
  intense 
  heat, 
  is 
  still 
  far, 
  far 
  denser 
  than 
  the 
  cool 
  matter 
  

   near 
  the 
  surface. 
  Thus, 
  the 
  mixture 
  of 
  matter 
  in 
  a 
  star's 
  interior 
  

   is 
  not 
  analogous 
  to 
  that 
  in 
  the 
  earth's 
  lower 
  atmosphere, 
  where 
  the 
  

   constituent 
  gases 
  are 
  kept 
  thoroughly 
  mixed 
  by 
  v.'inds 
  and 
  storms. 
  

  

  