200 
The  Chemical  Elements. 
{Am.  Jour.  Pharnu 
April,  1879. 
In  the  first  place,  the  temperature  of  the  sun  is  beyond  all  definition  ;  secondly, 
the  vapors  are  not  confined  ;  and,  thirdly,  there  is  an  enormous  number  of  them  all 
mixed  together,  and  tree,  as  it  were,  to  find  their  own  level.  Nor  is  this  all.  Astron- 
omers have  not  only  determined  that  the  sun  is  a  star,  and  have  approximately  fixed 
his  place  in  nature  as  regaids  size  and  brilliancy,  but  they  have  compared  the  spec- 
trum of  this  star,  this  sun  of  ours,  with  those  of  the  other  bodies  which  people  space, 
and  have  thus  begun  to  lay  the  foundations  of  a  science  which  we  may  christen 
Comparative  Stellar  Chemistry.  Dealing  with  the  knowledge  already  acquired  along 
this  line,  we  may  say  roughly  that  there  are  four  kinds  of  stars  recognizable  by  their 
spectra. 
We  have  first  the  brightest  and  presumably  hottest  stars,  and  of  these  the  spectrum 
is  marvelously  simple — so  simple,  in  fact,  that  we  say  their  atmospheres  consist  in  the 
main  of  only  two  substances — a  statement  founded  on  the  observation  that  the  lines 
in  the  spectra  are  matched  by  lines  which  we  see  in  the  spectra  of  hydrogen  and  cal- 
cium ;  theie  are  traces  of  magnesium,  and  perhaps  of  sodium  too,  but  the  faintness 
of  the  indication  of  these  two  latter  substances  only  intensifies  the  unmistakable 
development  of  the  phenomena  by  which  the  existence  of  the  former  is  indicated. 
So  much,  then,  for  the  first  class  ;  now  for  the  second.  In  this  we  find  our  sun. 
In  the  spectra  of  stars  of  this  class,  the  indications  of  hydrogen  are  enfeebled,  the 
the  evidences  by  which  the  existence  of  calcium  has  been  traced  in  stars  of  the  first 
class  are  increased  in  intensity,  and,  accompanying  these  changes  we  find  all  sim- 
plicity vanished  from  the  spectrum.  The  sodium  and  magnesium  indications  have 
increased,  and  a  spectrum  in  which  the  lines  obviously  visible  may  be  counted  on 
the  fingers  is  replaced  by  one  of  terrific  complexity. 
The  complexity  which  we  meet  with  in  passing  from  the  first  class  to  the  second 
is  one  brought  about  by  the  addition  of  the  lines  produced  by  bodies  of  chemical 
substances  of  moderate  atomic  weight.  The  additional  complexity  observed  when 
we  pass  from  the  second  stage  to  the  third  is  brought  about  by  the  addition  of  lines  due 
in  the  main  to  bodies  of  higher  atomic  weight.  And — this  is  a  point  of  the  highest 
importance — at  the  third  stage  the  hydrogen,  which  existed  in  such  abundance  in 
stars  of  the  first  class,  has  now  entirely  disappeared. 
In  the  last  class  of  stars  to  which  I  have  referred,  the  fourth,  the  lines  have  given 
place  to  fluted  bands,  at  the  same  time  that  the  light  and  color  of  the  star  indicate 
that  we  have  almost  reached  the  stage  of  extinction.  These  facts  have  long  been 
familiar  to  students  of  solar  and  stellar  physics.  Indeed,  in  a  letter  written  to  M. 
Dumas,  December  3,  1873,  ana"  printed  in  the  "  Comptes  Rendus,"  I  thus  summa- 
rized a  memoir  which  has  since  appeared  in  the  "Philosophical  Transactions": 
II  semble  que  plus  une  etoile  est  chaude,  plus  son  spectre  est  simple,  et  que  les 
elements  metalliques  se  font  voir  dans  l'ordre  de  leurs  poids  atomiques.1 
Ainsi  nous  avons  : 
1.  Des  etoiles  tres-brillantes  ou  nous  ne  voyons  que  Thydrogene  en  qantite  enormey 
et  le  magnesium  ,• 
2.  Des  etoiles  plus  froides,  comme  notre  soleil,  oil  nous  trouvons  : 
IHydrogene  -f-  Magnesium  -j-  Sodium 
Hydrcgene  -j-  Magnesium  -\-  Sodium  -j-  Calcium  -j-  Fer,  .  .  .  ; 
dans  ces  etoiles,  pas  de  metalfoides  ; 
1  The  old  system  of  atomic  weights  was  the  one  referred  to. 
