Am.  Jour.  Pharm. ) 
April,  1879.  ) 
The  Chemical  Elements. 
207 
eliminated,  or  in  which  the  freedom  from  mutual  impurity  has  been  demonstrated  by 
the  absence  of  the  longest  lines. 
The  explanation  of  this  result  on  the  hypothesis  that  the  elements  are  elementary 
does  not  lie  on  the  surface,  but  it  does  on  the  assumption  that  they  are  compounds 
and  behave  like  them. 
This  is  the  first  point.  We  now  pass  from  the  results  brought  about  at  the  same 
temperature  with  different  substances  to  those  observed  at  different  temperatures  with 
the  same  substance. 
I  find  that  when  the  temperature  is  greatly  varied,  the  elements  behave  spectroscop- 
ically  exictly  as-compound  bodies  do,  as  we  have  already  seen.  New  lines  are  devel- 
oped with  increasing  temperatures,  and  others  fade  in  precisely  the  same  way  as  the 
metallic  lines  made  their  appearance  in  the  salts  at  the  expense  of  the  latter,  which 
faded  too. 
In  short,  the  observations  and  reasoning  which  I  formerly  employed  to  show  how 
acknowledged  compounds  behave  in  the  spectroscope  are  now  seen  to  indicate  the 
compound  nature  of  the  chemical  elements  themselves.. 
In  a  paper  communicated  to  the  Royal  Society  in  1874,  referring,  among  other 
.matters,  to  the  reversal  of  some  lines  in  the  solar  spectrum,  I  remarked  : 
**  It  is  obvious  that  greater  attention  will  have  to  be  given  to  the  precise  character 
as  well  as  to  the  position  of  each  of  the  Fraunhofer  lines,  in  the  thickness  of  which  I 
have  already  observed  several  anomalies.  I  may  refer  more  particularly  at  present  to 
the  two  H  lines  3933  and  3968  belonging  to  calcium,  which  are  much  thicker  in  all 
photographs  of  the  solar  spectrum  (I  might  have  added  that  they  were  by  far  the 
thickest  lines  in  the  solar  spectrum)  than  the  largest  calcium  line  of  this  region 
(4226*3),  this  latter  being  invariably  thicker  than  the  H  lines  in  all  photographs  of 
the  calcium  spectrum,  and  remaining,  moreover,  visible  in  the  spectrum  of  substances 
containing  calcium  in  such  small  quantities  as  not  to  show  any  traces  of  the  H  lines. 
**  How  far  this  and  similar  variations  between  photographic  records  and  the  solar 
spectrum  are  due  to  causes  incident  to  the  photographic  record  itself,  or  to  variations 
in  the  intensities  of  the  various  molecular  vibrations  under  solar  and  terrestrial  con- 
ditions, are  questions  which  up  to  the  present  time  I  have  been  unable  to  discuss." 
The  progress  of  the  work  has  shown  that  the  differences  here  indicated  are  not 
exceptions,  but  are  truly  typical  when  the  minute  anatomy  of  the  solar  spectrum  is 
studied. 
Kirchhoff,  indeed,  as  early'as  1869  seems^to  have  got  a  glimpse  of  the  same  thing, 
for  in  his  memorable  paper,  which  may  justly  be  regarded  as  the  basis  of  all  subse- 
quent work,  he  is  careful  to  state  that  the  sixty  iron  lines  in  the  sun,  to  which  he 
referred,  only  agree  "  as  a  rule  "  in  intensity  with  those  observed  in  the  electric  spark. 
Those  who  have  given  an  account  of  his  work  have  not  always  been  so  cautious. 
Indeed,  I  find  Professor  Roscoe  1  running  far  beyond  the  record  in  the  following 
sentence : 
"In  order  to  map  and  determine  the  positions  of  the  bright  lines  found  in  the  elec- 
tric spectra  of  the  various  metals,  Kirchhoff,  as  I  have  already  stated,  employed  the 
dark  lines  in  the  solar  spectrum  as  his  guides.    Judge  of  his  astonishment  when  he 
1  "Spectrum  Analysis,"  third  edition,  p.  240. 
