458 REPORT—1904. 
The following Papers were read :— 
1. The Spectra of Sun-spots. 
By the Rev. A. L. Cortiz, S.., F.R.A.S. 
The paper contains a reduction of all the observations of sun-spot spectra taken 
at Stonyhurst during the years 1883-1901 with a 12-prism spectroscope attached 
to either the 8-inch or 15-inch equatorial. A discussion of the observations of 
the spectra of ninety sun-spots, observed during the period 1883-1889, appeared in 
the ‘Memoirs R.A.S.’ vol. 1, and of twenty-four other spots observed in the 
period 1890-1901 in the ‘Monthly Notices R.A.S.’ vol. Ixiii. No. 8. All the 
observations have been taken by the same observer, and are not restricted to a few 
lines, but on each occasion some particular region of the spectrum between B and 
D has been selected for detailed study, after a general view of this part of the 
spectrum had been secured for determining the most widened lines. The 
earlier observations of the widened lines were catalogued according to Angstrém’s 
wave-length numbers, as corrected in the British Association ‘Catalogue of the 
Oscillation-frequencies of the Solar Rays’ (1878) ; the later observations according 
to Rowland’s numbers. The present catalogue of 346 widened lines between 
wave-lengths 5884'03 and 6867°46, which combines all former lists, is based on 
Rowland’s numbers, and contains 5486 individual observations. 
The chief phenomena in the spectra of sun-spots are, as regards the general 
absorption, a want of uniformity of blackness in various regions of the 
spectrum sometimes observed, and, as regards the selective line absorption, 
the widening of lines, darkening of lines without widening, displacement 
of lines, obliteration of lines, extension of the widening through the penum- 
bra, reversal of lines, hazy fringes to lines, and spot-bands. The following 
tables contain, the one, the mean relative widening of the lines of the chief 
elements identified, and the other, a list of the most widened lines. The numbers 
for relative widening are estimated in terms of the normal width of the line multi- 
plied by the factor 10, and for intensities are taken from Rowland’s Catalogue, 
where 1 is a line just clearly visible, and successive zeros indicate increasing 
degrees of faintness. 
The tables show the importance of faint lines of vanadium and titanium in 
the sun-spot spectra (‘ Monthly Notices R.A.S.’ vol. lviii. No. 7). These faint 
lines have been always, and at all times of the sun-spot period, among the most 
widened lines (loc. cit. vol. xlix. No. 8; vol. lxii. No. 7). The observations 
give no evidence of a crossing of the most widened lines at an epoch between sun- 
spot maximum and minimum. They show, however, that the iron lines are more 
affected in minimum than in maximum spots; no conclusion can be drawn as to 
a difference of character and temperature between maximum and minimum spots 
from the behaviour of such faint widened lines. The iron lines brightened in the 
chromosphere, which are mostly arc lines, are not differently affected in sun-spots 
from lines not brightened. The widening of some oxygen lines in sun-spots in 
the a band seems to be a real phenomenon, the single hydrogen line (C) is 
generally thinned, and almost reversed over spots, and frequently reversed and 
distorted in their immediate neighbourhood. If oxygen and hydrogen are present 
in sun-spots, water-vapour might be formed over them. Spot-bands sometimes 
seen (loc. cit. vol. xlvii. No. 1) are a probable witness to a reduction of tempera- 
ture sufficient for the formation of compounds, But the widened lines accredited 
to water-vapour occur generally in crowded parts of the spectrum, so that the 
widening may be really due to faint solar lines in juxtaposition with them. The 
predominance of vanadium and titanium in sun-spots is important in view of 
Mr. Fowler’s recent identification of the flutings in Secchi’s third-type stars as 
due to titanium or a titanium compound, and Sir Norman Lockyer’s matching of 
the lines intensified in the spectrum of Arcturus with lines of the same element. 
Professor Hale has also shown that many of the lines in the fourth-type stars 
are coincident with lines observed as widened in sun-spots by Mr. Maunder and 
myself, 
