1130 
Physics. — “The red lithium line’. By Prof. P. Zewman. 
Only those spectrum lines, which belong to pair series or to 
threefold series, are resolved by magnetic fields into complicated 
types, i.e. not into triplets. The cause of the complicated resolution 
is intimately connected with the presence in the spectrum of natural 
groups of two or three lines (series-doublet or series-triplet). It has 
nothing to do with the distribution of lines in series, for there exist 
connected series of lines, which are resolved into triplets by mag- 
netic fields *). 
Recently *) Pascnen and Back discovered that lines belonging toa 
very close series-triplet or series-doublet, influence each other in a 
very peculiar manner. Under the action of a sufficiently strong mag- 
netie field we might expect to observe a superposition of the types 
of separation of the compounds, but contrary to expectation a normal 
triplet is seen. 
Among the lines investigated by PascuEn and Back are also the 
lithium lines. Many physicists by analogy with ihe other alkali metals 
and their series expect that the lithium lines are very close pairs. 
Sometimes the opinion has been expressed that the laws for the 
other alkali metals do not apply to lithium. This then might explain 
the result obtained by Voter*) that the red lithium line (6708) 
contrary to Preston’s rule is resolved by a magnetic field into a 
triplet, which is at least nearly normal. The measurements of BACK *) 
for four lithium lines prove that within the limits of the errors of 
observation the separation has the normal value. 
It is therefore very interesting to know whether the lithium lines 
are really very narrow pairs or not. In the first case Pascnen and 
Back are right placing the lithium lines in parallel with the other 
doublets they investigate, but they also indicate 6708 Li as a ‘“‘theo- 
retische Doppellinie”, because it has never been resolved. 
I have been able to do this, using the method given in the 
foregoing communication. 
As glass is strongly attacked by heated lithium it is necessary to 
place a small iron or copper vessel inside the giass tube; the life 
of the tube is then at least increased. 
1) LOHMANN, Physik. Zeitschr. 9 p. 145, 1908; PASCHEN, Ann. d. Phys. 30, 
746, 1909, 35, 860, 1911, Royps 30, 1024, 1909. 
2) PASCHEN u. Back, Normale u. anomale ZEEMAN-effekte, Ann. d. Phys 39, 
897, 1912. 
3) Vorer, Physik. Zeitschr. 6, 217, 1912. 
kt, Anhang Back. |. c. z 
