OF SPECTRA AT THE SOLAR ECLIPSE OF JANUARY 22, 1898. 
399 
values of tlie more refrangible lines in No. 3, although they were obtained by 
quite independent methods of reduction. The measures of this jdate, however, 
cannot be given the same weight as those of the other two, the definition being 
poor owing to imperfect focus. 
The lines in the visible spectrum Ha, y, and 8 are entered for the sake of com¬ 
pleteness, but they are not to be compared in accuracy with the ultra-violet lines. 
This is largely due to the difficulty in measuring the broad over-exposed lines /3, y, 
and 8 on No. 3 spectrum, and partly to the small dispersion in this region. 
The line 8 appears in all the measures to be largely displaced towards the red, but 
this is probably accidental. It is remarkalde, however, that in RowLxVNd’s table of 
the solar lines H8 is given at \ 4102’000, which is also less refrangible than the 
theoretical position, the diflPerence being TO tenth-metre. The almost perfect agree¬ 
ment of the other absorption lines in his table, and the very close agreement of the 
best defined ultra-violet lines in Nos. 3 and 4 spectra with the positions assigned by the 
formula, suggests that the wave-length of this line has been erroneously estimated. 
Mr. Jewell, however, who made the measures of Rowland’s plates, while admitting 
some uncertainty in estimating the centre of the line in the solar spectrum, finds 
on re-examining his measures, no justification for altering his original estimate 
(‘ Astro-Physical Journal,’ vol. 9, p. 211). 
It is very desirable that acciirate measures be made of H8 in the upper chromo¬ 
sphere where the line is narrow and free from interfering lines. 
The limit of the hydrogen series defined by the formula when s = oo is at X 3646. 
But in the chromosphere spectra the lines fade away to invisibility long before 
reaching this point. I would call particular attention, however, to tlie very 
remarkable band of continuous spectrum shown by the prominences and lower 
chromosphere, beginning near the end of the tabulated series and extending indefi¬ 
nitely towards the more refrangible end of the spectrum. The interspaces between 
the hydrogen lines are quite clear of this continuous spectrum, which begins abruptly 
at about 3668. (See Plate 12.) 
It seems probable that this faint spectrum may be itself due to hydrogen. In 
the ahsorption spectrum of white stars of Type I., Sir William Huggins has 
observed an analogous feature. This consists in the “ rather sudden fall of intensity 
of the continuous spectrum at about the place of tlie end of the series of dark hydrogen 
lines. The enfeebled spectrum continues to run on without further enfeeblement 
until it is stopped by the absorption of our atmosphere.”^ 
This seems clearly to be the absorption effect of the matter giving the faint con¬ 
tinuous spectrum in my plates, and the fact that the feature is characteristic of white 
stars in which the hydrogen absorption is very strong points to its being due to 
hydrogen itself 
* ‘ An Atlas of Representative Stellar Spectra ’ (Sir William and Lady Huggins), p. 85. 
