ATMOSPHERE OF THE SUN DESLANDRES. 



349 



three one-hundredths Angstrom or greater either the K 2 line or one 

 of the components of K 3 , thus obtaining very pure images of each 

 corresponding stratum free from all extraneous light. The corre- 

 sponding slit widths are crosshatched in section in figure 1. 



The vapor of calcium, which beyond the limb rises higher than all 

 the other vapors, thus shows us three distinct strata, and if to these 

 we add the ordinary surface of the sun we have four layers which 

 are interesting to compare. 



August 10, 1908. 

 N 



September 18, 1908. 

 N 



Fig. 3. — Network of alignments noted in the upper layer of the solar atmosphere. The 

 full dark traces correspond to the continuous and very sharp dark lines called filaments ; 

 the discontinuous traces to the similar lines though less sharp and the dotted lines to 

 those still less visible and often broken. The hatched places are the larger regions of 

 bright faculae. 



As we rise above the surface of the sun the faculse, or bright 

 regions, grow progressively in extent and relative brightness. The 

 average-sized flocculi increase, although the small ones disappear 

 or become scarcely visible. There results a certain aspect of the 

 K 3 layer which at once distinguishes it from the K 2 layer photo- 

 graphed in 1892. (See the two spectroheliograms in K, and K 2 of 

 the 18th of September, 1908.) I would also add that the peculiar 

 network (reseau) of flocculi, called by me in 1894 the chromospheric 



