PROF. A. FOWLER ON SERIES LINES IN SPARK SPECTRA. 
261 
series (helium group) than for the single line series (“ parhelium ” group), and he 
infers that the atoms which act as carriers in the former case have a single positive 
charge, while in the second case there is a double positive charge .* Both sets of series, 
however, are of the “ arc ” type, with N for the series constant, whereas on Bohr’s 
theory, one should be of the N, and the other of the 4N type if Stark’s deduction is 
correct. 
In the case of aluminium, Stark has similarly found evidence of atoms with one, 
two, and three positive charges.! The first is associated with the doublets of the arc 
spectrum, the second with a spark line at 4663'5, and the third with three spark lines 
at 45297, 4513'0, and 4480'0. Attention is drawn to the fact that the higher charges 
are connected with the enhanced lines, and differences in the behaviour of the two 
sets of spark lines when the spark is passed in hydrogen are indicated. The series to 
which the spark lines of aluminium belong have not yet been recognised, but Stark’s 
results for this element are in general agreement with the conclusion indicated by 
Bohr’s theory that enhanced lines are associated with atoms of greater positive charges 
than those giving rise to arc lines. In the case of helium it does not seem possible to 
reconcile Stark’s conclusions with those of Bohr, since the doubly-charged atoms, on 
Bohr’s theory, can only give rise to the system of series of which 4686 is the leading 
member. 
Stark’s conclusions are equally at variance with those of Lenard,| who found 
reason to believe that while principal series are produced by neutral atoms, the 
subordinate series originate in atoms which have become positively charged through 
the loss of one or more electrons. Bohr’s theory differs from both in leading to the 
conclusion that all series having the same series constant should be produced by atoms 
having the same charge. 
A knowledge of the charges of the atoms giving the arc and enhanced lines 
respectively would possibly aid in the interpretation of the peculiarities of the spectrum 
of the solar chromosphere, and further investigations bearing on this subject are very 
desirable. 
Whatever may be its significance in connection with the atom, the change in the 
character of the series in passing from arc to spark lines suggests the spectra of 
“ early-type ” stars as a possible source of series requiring still greater multiples of the 
ordinary series constant in the formulae representing them. In passing from the later 
to the earlier type stars, as shown by the work of Lockyer and others, the arc lines 
of various metallic elements are gradually replaced by enhanced lines, while lines of 
hydrogen, helium, and other gases become more prominent. For such metallic 
elements as are known to belong to series, the change is definitely from series of the 
arc (N) type to series of the spark (4N) type. A considerable number of lines remain 
* ‘Ann. cler Physik,’ vol. 40, p. 540 (1913). 
f ‘ Ann. der Physik,’ vol. 42, p. 254 (1913). 
I ‘ Ann. der Physik,’ vol. 17, p. 197 (1905). 
