108 
ASTRONOMY: HALE AND ELLERMAN 
hypothesis that they result from the absorptive effect of the cooler 
hydrogen. 
It may be added that many spectroheliograms previously and subse- 
quently obtained, especially when this region was carried to the west 
limb by the sun's rotation, fully bear out the above interpretation of 
the stereoscopic effect, which is in harmony with the conclusions already 
stated. Thus they confirm the usefulness of the stereoscopic method, 
and further substantiate the view as to the nature of these long dark 
lioccuh (called 'filaments' by Deslandres) which we expressed when we 
hrst detected them with the line at the Yerkes Observatory in 1903^ 
and again when we photographed them with Ha on Mount Wilson in 
1908.^ 
We have shown in th's paper that the minute structure of the 
quiescent solar atmosphere resembles that of the photosphere. In 
disturbed regions, the small granular elements (minute fiocculi) are re- 
placed by numerous slender filaments, lying side by side, and recalling 
the structure of the penumbra in sun-spots. While these results ap- 
pear to support the hypothesis that the solar atmosphere consists of 
parallel columns of ascending and expanding gases, which are drawn 
out horizontally in spot penumbrae and in disturbed regions of the 
chromosphere, such questions as the dimensions of the columns and 
the direction of motion and velocity of the vapor in sun-spots and in 
the atmosphere about them are reserved for subsequent discussion. 
A full account of this work, with additional observations and photo- 
graphs, will be published in the Astro physical Journal. 
^ Amer. J. Sci., Ser. 3, 7, 87 (1874). Figure 2, Plate I, is taken from this article. 
This remark applies to visual observations. The valuable photographic results of 
Janssen, Hansky, Chevalier and others will be discussed in another paper. 
^ Chevalier, from a series of measures of the bright grains on his excellent photographs 
of the photosphere, concludes that they cover approximately one-third of the solar sur- 
face; Ann. Obs. Zo-Se, 8, C 20 (1912). 
* We have shown in a previous paper {Ptib. Yerkes Obs., 3, Part I, p. 14) that the aver- 
age cross-section of the calcium fiocculi at the lower (Hi) level is apparently smaller than at 
the H2 level. Thus the calcium vapor probably expands as it rises. 
^ Figure 3, which is taken from our paper cited above, does not give a correct impression 
of the area occupied by the minute calcium fiocculi, as several larger aggregations are present. 
In determining the size of the minute fiocculi, the instrumental conditions, as well as the 
seeing, must also be taken into account. 
The bright eruptive fiocculi of hydrogen are not in question here. 
^ The direction of rotation of sun-spot vortices will be discussed in another paper. 
8 Pub. Yerkes Obs., 3, part I, p. 21. 
' Solar \^ortices. Contrib. Ml. Wilson Solar Obs., No. 26, Astrophys. J., 28, 100 (1908). 
