706 
PROFESSOR J. R. LOCKYER OR THE PHOTOGRAPHIC 
ci Herculis. 
I S Virgiiiis. 
S Ophiuclii. 
fx Geminorum. 
(2.) Sub-division jS . 
Characteristics of the Spectra.. 
All the spectra of the stars of Sub-division /S of Table C are practically identical, 
and only that of a Tauri is therefore reproduced. 
This is shown in Plate 26, and on comparison with the spectrum of a Orionis the 
close similarity in the photographic region will be evident. 
In all the stars named the intensity of the spectrum beyond G is feeble, and long 
exposures are required in order to obtain photographs in that region. The falling off 
of intensity, however, is not so strongly marked as in the stars of Sub-division a. 
As in a Orionis, the origins of the chief lines have been traced to hydrogen, iron, 
calcium, manganese, chromium, magnesium, titanium, cobalt, and strontium. The 
lines of calcium, especially the low temperature line at X 4226, are particularly broad. 
The manganese lines near X 4029, and the iron line near X 4045, are remarkably con¬ 
spicuous. The latter is relatively much stronger than the other iron lines in the 
same region, as compared with stars like the Sun, and this suggests that it may be 
strengthened by a line of some unknowm substance which has very nearly the same 
wave-length. On reference to the photograph it will be seen also that the two iron 
lines X 4.383 and X 4405 are also considerably intensified in this group of stars. These 
two pairs of lines, with the strong line of calcium at X 4226 and the weakness of the 
spectrum beyond G, serve for the ready identification of all stars resembling a Tauri. 
Duner* describes the spectrum of a Hydrm as more resembling that of the Sun 
than that of a Tauri, but the photographic spectrum is practically identical with 
a Tauri. The calcium line X 4226 is very strong, as are also the other characteristic 
lines to which reference has been made. 
Possible Variation in the Spectrum of a. Tauri. 
An interesting point has followed from the comparison of the Kensington photo¬ 
graphs of a Tauri with one taken and kindly forwarded to me by Professor Pickering. 
The strong line, about X 4406, in the Kensington photographs is hardly visible in the 
photograph taken by Professor Pickering, and it would, therefore, appear that the 
spectrum must be variable. This particular line, it may be remarked, probably forms 
* ‘ Snr les Etoiles,’ <fcc., p. 88. 
