PLATE IX. 



Fig. 1.— As romarked in the text, the contrast is too great in this photograph, 

 and tlie appearance of tlie hrigliter regions is deceptive. In reality tlie darlv 

 regions in general represent the hydrogen tloccnli, though tliere may he a few- 

 places near the spot where l)right tloccnli are present. 



Fig. 2. — This cnt i-epresents more nearly the appearance of the d:irk hydrogen 

 lloccnli on the neg.atives. As the slit did not coinci<te with the // line throngh- 

 ont its length, the tloccnli are not shown to the west of the spot. A small hright 

 tloccidns may he .seen at the extreme edge of the tignre on the left adjoining 

 the small spot. 



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