Lithium. — In  the  case  of  lithium  both  Hagenbach  and
Konen  and  Saunders  have  discovered  a  system  of  new  lines
which  together  form  a  series.  '  By  analogy  with  the  other
alkali  metals  it  is  to  be  expected  that  the  lithium  lines  consist
of  narrow  pairs.  Hagenbach  finds,  however,  that  the  red
lithium  line  is  single,  while  he  and  Saunders  agree  that  the
line  X  =  4602  of  the  first  subordinate  series  is  double,  but
the  distance  between  the  pair  is  twice  as  great  as  was  to  be
expected.  Although  Saunders  finds  that  the  line  X  =  6103
is  single,  Konen  and  Hagenbach  conclude  that  the  line  is
double,  owing  to  the  fact  that  they  observed  a  double  reversal


S£Ii/ES   OF  LINES   IN  SPECTRA  603

in  it.  It  must  be  remembered  that  the  components  of  this
line  should  be  still  further  separated  than  those  of  the  line
X  =  4602.  Now,  it  may  be  concluded  from  the  relation
between  the  squares  of  the  atomic  weights  mentioned  below
(p.  625)  that  p\  —  p'i  should  be  equal  to  o'oooos.  From
analogy  with  the  other  alkali  metals  it  can  only  be  said  that
TTi  —  TTg  is  of  the  same  order,  and  not  that  it  is  zero.  Now,
Ritz  has  shown  that  p  =  —  o"o48i5,  and  tt  =  o'o257,  and  if
we  put/i  =  p,-K^  =  TTj/a  =  p  -V  o'oooos,  and  ttj  =  tt  +  o'oooz,
it  can  be  seen  that  the  fundamental  line  w  =  2  of  the  principal
series,  just  as  that  of  the  secondary  series,  is  not  a  pair.  For
higher  values  of  m  the  lines  are  still  only  a  few  hundredths  of
an  Angstrom  unit  apart  and  so  cannot  be  separated.
