APRIL 9, 1914| 
prolonged quiescence. The following brief table is 
gathered from the report above mentioned, and brings 
out clearly the exceptional nature of the year 1913 :— 
Wear Days with- Mean daily spotted No. of separate 
out » pots area in millionths groups 
Ig! 183 Gea 47, 02 
1912 246 37 39 
1913 S100 RS 5 15 
It is stated that no year since 1810 has given such 
a barren record as that just elapsed. The new cycle 
was indicated last year by two groups in high latitude, 
the chief criterion for the beginning of a new cycle. 
RELATION BETWEEN STELLAR SPECTRA, COLOURS, 
AND ParattaxEs.—In  Astronomische Nachrichten, 
No. 4722, Herr P. Nashan describe the results he has 
obtained in comparing the colours, spectra, and 
parallaxes of a number of stars. Dealing first with 
1o1 stars, he divides them first into three classes, 
a, B, and y, according as the stars are white, yellow, 
or red; the parallaxes are also grouped with three 
divisions as follows :—o-000” to 0-050", 0-050” to. 0-100", 
and o-100” to 0-200”.. The comparison shows that the 
white stars decrease with increasing parallaxes; on 
the other hand, the red stars increase with increasing 
parallaxes. The fact that there is a close relationship 
between the colour and the spectrum of a star has 
led him to compare-the spectra of 246 stars with their 
parallaxes. The results are best shown as follows :— 
Parallax 
Spectrum | Bee | Bidca—a'0s0 0'050—0'100 0°100—-0'r50 | ors 
| n Ws n % n He nu i, 
B PE 2 | 63°6 | 3.) 2738 iempers |. 0 oO 
A 25) 8:| 28°5 | 8 | aesheeeie25-o), 5 | 18:9 
EB. 59 | 19 | 322 | 22 | 373.) 45) 255 | 3 | S7 
G G4.) 13, | 20 3 | 22 | aeaelezeieae-2 | 29) 371 
K Bahu 13 |.18°6 | 21 | aoremeese|oe-o | 13. | 18°5 
M 4) 3 | 214] 2) 14°35 1357 | 4 | 28°6 
Herr Nashan then couples up the B and A stars 
into a white group, the F and G into a yellow group, 
and the K and M stars into a red group, and con- 
cludes that the relative number of white stars decreases 
with increasing parallaxes, while the relative number 
of the red stars increases with increasing parallaxes, 
a result similar to that obtained with colour alone. 
The communication concludes with the list of the 
246 stars employed, giving their positions for 1900-0, 
parallax, type of spectrum, and colour. 
SERIES LINES IN SPARK SPECTRA.1! 
REVIOUS work on series lines in spectra has 
dealt chiefly with lines produced in the electric arc, 
or in vacuum tubes with discharges of moderate in- 
tensity. The lines discussed in the present communi- 
cation are some of those which are specially developed 
in the condensed spark, belonging to Lockyer’s class 
of ‘‘enhanced lines.’’ The investigation was under- 
taken in connection with the new lines (A 4686, etc.) 
produced in 1912 by passing strong condensed dis- 
charges through helium tubes, which always contained 
an impurity of hydrogen. These lines are of great 
interest in celestial spectroscopy, and, following Ryd- 
berg, they were assigned to hydrogen, to the lines of 
which they seemed to have a simple relation, while 
having no apparent connection with those of helium. 
1 Summary of Bakerian lecture delivered at the Royal Society on April 2’ 
by Prof. A. Fowler, F.R.S. 
NO. 2319, VOL. 93] 
NATURE 
pate: 
| might be reached. 
145 
The evidence for assigning the lines to hydrogen, 
however, was still numerical rather than experimental, 
and further inquiry was called for, especially in view 
of the presence of an intermediate set of lines asso- 
ciated with the Rydberg series. A search for other 
series of this character was therefore instituted in the 
hope that some generalisation with ‘regard to them 
The well-known spark line of 
magnesium, 4481, was subsequently found to be the 
leader of a series of this kind, but no relation to other 
magnesium series was then traced. 
The lines of the ‘*‘ 4686” series have since become 
of increased importance, in connection with theories 
of the constitution of the atom, through the theoretical 
work of Dr. Bohr, who explains them as being pro- 
duced during the first stage in the re-formation of 
helium atoms from which both electrons have been 
removed by the strong discharges employed. The 
‘4686’ and the intermediate series were thus united 
in a single series of a new type, in which the Rydberg 
series constant N(=109675) had four times the value 
associated with hydrogen. A similar modification of 
the usual formula was found to be applicable to the 
magnesium series, and also to some lines of calcium, 
strontium, and barium observed by Lyman in the 
Schumann region. At this stage a valuable contribu- 
tion to the investigation was made by the work of 
Lorenser, from which it results that the enhanced lines 
of the elements named form groups of series similar 
to those found in are spectra. Further calculations 
have shown that these series are best represented by 
the Hicks formula with 4N for numerator. 
A further experimental investigation of mag- 
nesium has resulted in the production of many new 
enhanced (spark) lines, from which it appears that the 
‘‘4481’’ series is the fundamental series of a system 
of narrow doublets, in which the separation of the 
pairs is identical with that calculated for the second 
member of the principal series of wider doublets pre- 
viously known. It has also been shown that the 
‘“4481’’ series consists of very close doublets with 
constant separation. Two well-defined combination 
series related to 4481 -have also been identified. 
From these investigations of enhanced metallic lines 
it follows that two kinds of series must now be recog- 
nised :—(1) Series of the arc type, having Rydberg’s 
“N” for the series constant; and (2) series of the 
spark, or enhanced line, type, having a series con- 
stant equal to 4N. No numerical relations between 
the two sets of series occurring in the same element 
have been traced. 
The ‘‘ 4686” series produced in helium tubes is of 
the spark (4N) type, and can no longer be considered 
to belong to the same group as the Balmer series of 
hydrogen, which is of the are (N) type. It is con- 
cluded that the lines in question are due to helium, 
as indicated by Bohr, and it is suggested that they 
should be designated ‘‘ proto-helium”’ lines in accord- 
ance with the convenient nomenclature of Lockyer. 
The ‘‘Pickering”’ lines associated with the ‘ 4686” 
series probably have a similar origin, in which case 
the series would include intermediate lines nearly 
coincident with the Balmer lines of hydrogen. Observa- 
tional evidence on this point is incomplete, but indirect 
evidence is furnished by the fact that one of the new 
combination series is related to the 4481 series exactly 
as the extended Pickering series would be related to 
the ‘‘ 4686” series of proto-helium. 
Dr. Bohr has shown that the slight differences in 
the observed positions of alternate lines of the 
‘4686’ series and those calculated for the principal 
series of hydrogen by Rydberg are accounted for when 
his theoretical formulz are corrected for the mass of 
the electron (NatTurRE, October 23, -1913). If the 
