398 
MR. J. EVERSHED OX WAVE-LENGTH DETERMINATIONS, ETC. 
identified. In the region between XX 3340 and 4000 there are 29 such lines in a total 
of 225, and all of them are weak lines. The strongest (intensity 2) correspond in 
position with dark lines in Rowland’s table which have not been identified with any 
element, and these are given in 
the folioAvin 
g list:— 
Wave4ength in flash. 
Intensity. 
WaA'e4ength in ©. 
Intensity 
3567-77 
3567-835 
4 
3589-72 
•> 
3589-773 
5 
3645-35 
O 
[3645-429 
3 
13645-475 
3 
3655-78 
1 
3655-801 
3 
These are tlie only unknown lines in the flash sj^ectrum with an intensity greater 
than I, and it is just possible that they belong to the same element. 
The Hydrogen Speetrum. 
The wave-lengths of the hydrogen lines taken from Tables I. and II. are entered 
separately in Table III., together with the values computed from Balmee’s formula. 
The latter were computed for a vacuum and corrected foi' air in accordance with a 
table of Runge (‘ Astronomy and Astro-jjhysics,’ vol. 12, No. 5). 
In the formula ._ 8° 
^ “ a(S2 - 4) ’ 
S is the series numlDer of the liiie, and a is a constant derived from Rowland’s 
measures of the lines Ha, Hyd, and Hy in the solar spectrum reduced to a vacuum, the 
mean value adopted being a = 27418'75. 
In obtaining the mean values gi’ven in column 4, ecjual weights are given to No. 3 
and No. 4 spectra, both of which are in good focus Ijeyond K, and give equally 
consistent measures in this region. No. 4 spectrum is, however, much the better of 
the two in the visible region, where the images are comparatively small, well-defined 
spots. This spectrum, as already mentioned, consists of a series of images of a very 
small bright jE’ominence, and very consistent measures were obtained throughout. 
The good agreement of the wave-lengths of the metallic lines with Rowland’s values 
will be seen on referring to Table II. 
The very close agreement of the hydrogen lines with tlie computed values is shown 
in column 6 of Table III. (observation — calculation). It will be noticed, however, 
that the wave-leiigths of the more refrangible members of the series are appreciably 
smaller than the theoretical values, the differences increasing tov'ards the limit of the 
series. This may be due to the greater uncertainty of measurement of the fainter 
lines, which are apt to be confused Avith other lines closely contiguous, or it may 
possibly be due to a slight progressive error in the scale value for this region. 
The results obtained for No. 7 spectrum given in column 7 appear to confirm the 
