G88 
PROFESSOE J. N. LOCKYER ON THE PHOTOGRAPHIC 
(5.) Spectra taken with Instrument E. 
1 
1 
Name of star. 
Number of 
photographs. 
Name of star. 
Number of 
photographs. 
Orion Nebula. 
5 
a quilrn. 
1 
a. Orionis. 
2 
a Bootis. 
1 
a Coronse. 
1 
a Aurigse. 
1 
IV.—TABULATION OF SIMILAR SPECTRA. 
As in the case of stellar spectra observed in the usual way, the photographic 
spectra vary very considerably in jrassing from star to star, and well-marked gTOups 
may be recognised. 
In the classification of stars which has been adopted from a consideration of the 
v^isual observations, only the broader differences iir the spectra have been taken into 
account. Professor Picrering, however, has suggested a provisiorral classification in 
connection with the Henry Draper Memorial photographs of stellar spectra, but this 
chiefly relates to photographs taken with small dispersion. Now that it has become 
possible to obtain large dispersion photographs of the spectra, much more detail is 
revealed, and it becomes necessary to deal with the presence or absence of individual 
lines to a greater extent than by Professor Pickering. 
Hence, in the first instance, I have arranged the various stars of ’which the spectra 
have been photographed at Kensington in tables, without reference to any of the 
existing classifications, and taking into account the finer details. 
The basis upon which tlie first grouping is founded is the extent of the continuous 
spectrum. Such a distinction was not possible in the case of eye observations, and it 
is only by a consideration of the photographs that the classification from this point of 
view can be made. 
Some spectra show a remarkable continuous absorption either in the ultra-violet or 
violet, in others this absorption extends to about K, -whilst in a third class it reaches 
as far as G. This practically amounts to the same thing as classifying the spectra 
according to the thickness of the hydrogen lines, for it is found that where the 
continuous absorption is least the hydrogen lines are broadest. But it must not be 
forgotten that the bj'oadness of these lines depends, to an as yet undetermined extent, 
upon the time of exposure, and it may further be that other causes besides temperature 
may be effective in producing the broadening;. 
