S. P. Langley—Minute structure of the Solar Photosphere. 101 
its equator, while the evidence as to this point is not yet con- 
clusive. 
In the penumbre there are not only numerous small 
cyclones, and even right and left-handed whirls in the same 
spot, but probably currents ascending nearly vertically, while 
the action of superposed approximately horizontal currents is 
so general that they must be considered a prominent feature in 
our study of solar meteorology. 
_A-study of the outer penumbral edge leads to the conclu- 
sion that it is formed by rupture. 
. 
_ Speaking without reference to spectroscopic investigations, 
it seems to me that we have in the behavior o ti 
of otherwise isolated truths under a single law. 
Allegheny Observatory, Dec., 1873. 
