350 ANNUAL, REPORT SMITHSONIAN INSTITUTION, 1910. 



reseau, and often formed over a considerable area, composed of 

 polygons touching each other at their sides and corners, is in general 

 more distinct in the upper layer. 



On the other hand, the black spots which are the principal char- 

 acteristic of the surface diminish progressively as we go above the 

 surface and often disappear. 



Yet, further, there appear dark lines not seen in the lower layers, 

 lines often very long and called by me filaments. Generally the fila- 

 ments have extensions from each side reaching to the limb neither 

 so dark nor so sharp, which I call "alignments." The ensemble of 

 filaments and alignments form a definite network over the solar disk. 

 They are a new phenomenon characteristic of the upper layer. Here 

 the filaments have the same importance as the spot at the surface. 

 They persist, like them, during several rotations, and like them also 

 are the seats of special disturbances which are accompanied by 

 prominences. 



G. THE DISCLOSURE OF THE UPPER H a LAYER OF HYDROGEN. 



In my first studies I likened the spots to depressions (" lows ") 

 or cyclones in our atmosphere and the filaments to anticyclones. 

 I will come back later to this comparison, which I will develop. 



During the following year we (d'Azambuja and I) used this 

 same apparatus in the study of the hydrogen lines, and especially the 

 the red Ha. Hale and Ellermann had already isolated these lines 

 with the spectroheliograph, obtaining very curious results. In 1893 

 they noted that in the H/3, Hy, and HS spectroheliograms the faculse 

 were no longer bright with reference to the background, as in the 

 calcium images, but, on the contrary, are often dark. With H , iso- 

 lated in 1908, they found all about the spots a series of fine demarca- 

 tions, giving the impression of whirls, and which Hale has described 

 here at a special meeting. Indeed, these Ha images are beautiful 

 and abounding in fine details. 



However, these American Ha images were obtained by the isola- 

 tion and use of the whole dark line. I stated in 1908 that they must 

 be composed of the mixture of the two or three images belonging to 

 different strata. For, according to Rowland, the Ha line is doubly 

 reversed like the K line, due to calcium although more feebly. Its 

 width, including the shading edges, is 1.24 Angstroms ; without them, 

 0.90. We would, therefore, expect somewhat different results as 

 different portions of the line are isolated. 



This we have already clearly shown to be true, and indeed, con- 

 trary to all our expectations, the differences existing between the 

 various hydrogen images are greater than for calcium. 



The exact results are as follows : 



When the shaded portion close to the edge of the line is used, 

 corresponding to K a of calcium, at a distance from the center of the 



