CHEMICAL  ANALYSES  BY  SPECTRUM  OBSERVATIONS.  225 
which  gives  a  flame  of  very  high  temperature  and  very  slight 
luminosity,  is  well  adapted  for  experiments  on  the  bright  lines  of 
the  flame-spectra  produced  as  above  described. 
The  apparatus  employed  by  Messrs.  Kirchoff"  and  Bunsen  in 
their  spectrum  observations  is  thus  represented  and  described  in 
Poggendorff's  Annalen^  (Bd.  ex.  §  161): — 
A  is  a  box  blackened  on  the  inside,  having  its  horizontal  sec- 
tion in  the  form  of  a  trapezium,  and  resting  on  three  feet ;  the 
two  inclined  sides  of  the  box,  which  are  placed  at  an  angle  of 
about  58^  from  each  other,  carry  the  two  small  telescopes  B  and 
C.  The  eye-piece  of  the  first  telescope  is  removed,  and  in  its 
place  is  inserted  a  plate,  in  which  a  slic  made  by  two  brass  knife- 
edges  is  so  arranged  that  it  coincides  with  the  focus  of  the 
object-glass.  The  gas-lamp  D  stands  before  the  slit  in  such  a 
position  that  the  mouth  of  the  flame  is  in  a  straight  line  with  the 
axis  of  the  telescope  B.  Somewhat  lower  than  the  point  at 
which  the  axis  of  the  tube  produced  meets  the  mouth,  the  end 
of  a  fine  platinum  wire  bent  round  to  a  hook  is  placed  in  the 
flame.  The  platinum  wire  is  supported  in  this  position  by  a 
small  holder  E,  and  on  to  the  hook  is  melted  a  globule  of  the  dried 
chloride  which  it  is  required  to  examine.  Between  the  object- 
glasses  of  the  telescopes  B  and  C  is  placed  a  hollow  prism  F, 
filled  with  bisulphide  of  carbon,  and  having  a  refracting  angle 
of  60° ;  the  prism  rests  upon  a  brass  plate,  moveable  about  a 
vertical  axis.  The  axis  carries  on  its  lower  part  the  mirror  G, 
and  above  that  the  arm  H,  which  serves  as  a  handle  for  turning 
15 
