PLATE XII. 



In this photograph the calcium vapor is much hotter shown than in Plate XI, 

 and the hesinniugs of eruittive ])henomena have hecome more distinctly evident. 



It is to he understood that although the changes going on in the eru])tive phe- 

 nomena of the spot group prevent a i)erfect comjiarison of all the details of the 

 successive i)hotographs in this and the sul)se(iuent series, the large masses of 

 floccnli change so slowly in form that they may he compared without danger of 

 serious erroi-. In general, the differences hetween the successive pictures are 

 therefore due to differences in the extent and hrightness of the vapor at different 

 levels rather than to changes in form which have taken jdace hetween exposures. 

 In order to render possihle a satisfactory comparison of the high and low level 

 tiocculi surrounding this si»ot, the matched pair of photographs, reproduced in 

 Plates XV, X\ I, is given for examinatiou with the stereoscope. 



157 



