MEETING  OF  THE  BRITISH  ASSOCIATION. 
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or  dark  colored  lines,  parallel  in  position,  but  of  various  dimen- 
sions, and  irregularly  distributed.  Another  fact  known  for 
some  time  is,  that  bodies,  rendered  intensely  luminous  by  a 
great  heat,  also  form  spectra,  each  of  which  is  peculiar,  so  as  to 
characterize  the  body.  One  substance  yields  one  color  of  spe- 
cial brightness;  another,  another;  and  the  shape,  size  and  rela- 
tive position  of  these  strips  of  color  are  also  characteristic.  A 
third  fact  in  the  series  is  that  a  substance  which,  when  intensely 
heated,  gives  a  peculiar  color  of  special  brightness,  absorbs  that 
same  color  at  a  lower  temperature;  in  other  words,  a  body  gives 
out,  at  a  high  heat,  the  peculiar  light  it  absorbs  when  at  a  lower 
one.  Hence,  if  a  substance,  in  the  form  of  vapor,  be  made  to 
intervene  between  the  source  of  light  and  the  solar  spectrum,  it 
produces  a  dark  line  in  the  same  position,  and  exactly  of  the 
same  shape  and  size  as  the  luminous  line  which  characterizes  it 
in  its  own  spectrum.  Still  another  fact  is,  that  any  of  the 
metals,  if  put  between  the  poles  of  a  suitable  galvanic  battery, 
or  other  suflficiently  powerful  electric  arrangement,  may  be 
brought  to  such  a  luminous  condition  as  to  yield  characteristic 
spectra;  and  thus,  an  exceedingly  easy  method  of  experiment- 
ing, for  the  detection  of  metals,  is  afforded.  Each  of  the  metals 
yields  a  peculiar  color,  and  all  the  salts  of  the  same  metal  the 
same  color,  probably  because  all  of  them  are  reduced  to  the 
metallic  state  by  the  intense  heat. 
Now,  what  may  be  considered  as  an  almost  sublime  result  of 
these  premises  is,  that  we  are  enabled  to  analyze  the  atmosphere 
of  the  sun  itself.  The  dark  lines  of  the  solar  spectrum  may  be, 
in  some  degree,  owing  to  the  absorbing  influence  of  substances 
in  the  outer  layer  of  the  sun's  atmosphere,  intervening  between 
the  central  source  of  light  and  the  eye.  Some  of  these  dark 
lines  correspond  exactly  with  the  luminous  lines  of  certain  known 
bodies,  as  sodium,  iron,  &c.,  and  may,  therefore,  in  accordance 
with  the  above  data,  be  ascribed  to  the  vapors  of  these  bodies 
in  the  outer  solar  atmosphere.  It  is  said  that,  in  relation  to 
sodium,  the  correspondence  is  so  entirely  precise,  that  the  in- 
ference is  irresistible.  But  (says  our  correspondent)  why 
should  not  the  presence  of  sodium  in  space,  or  in  our  own  at- 
mosphere, have  the  same  effect  ?  and  so  in  relation  to  all  other 
metals ;  for  the  quantity  requisite  to  produce  the  effect  is 
