88 PROFESSOR J. N. LOCKYER ON THE PHOTOGRAPHIC 
calcium, and the lines at \ 4388 and \ 4471, appear as dark lines at an early stage in 
Group II. 
Other lines, however, do not appear dark until a later stage; \ 4025, \ 4069, and 
) 4269, for example, do not make their appearance as dark lines until Group IIIy., 
and others, such as 4205, do not appear until Group IV. is reached. 
Some of the dark lines, as 14025 and 4471, have their maximum intensity in 
Group IITy., whilst others are much less regular in their intensities in passing through 
the different groups, 

CRIV, & ANonoUcoe 
javincitis 
% ORIONIE 
GR. tly yo 
B 

OR, Ms 76 

GR. ill &TAURE 


O ORIONIS 

.l_ SRTLLINE STARS 

GR.i, ORION NEBULA 

CR.1, PLAN. NEBULA 

Fig. 4. Diagram showing the gradual change of bright to dark lines in condensing swarms of meteorites. 
In general, it may be taken that the absence of some of the lines from Group II. 
and the earlier stages of Group III. is due to the approximate equality of the 
radiating and absorbing areas of the vapours producing such lines. 
With the aid of a series of photographs taken with special exposures, it is possible 
to extend the comparison of the stars of Groups III. and IIIy. with the nebula into 
the ultra-violet region of the spectrum. These photographs have been reduced by 
Mr. SHackieton. The coincidences are shown in Table V. In this table Groups IT. 
