196 S. P. Langley—Comparison of certain Theories of 
of the solar dise. If I do not misinterpret the indications given 
by the brightening ends, they can hardly be spread upon the 
surface of a liquid, or upon any single surface whatever,—they 
bend down and up. All through the umbra are to be not 
similar appearances; we seem to look down through increasing 
depths, but as far as vision extends, without coming to an 
liquid or solid floor,—always down through volumes of whirl- 
ing vapor, (whirling, if we judge from their forms, which are dis- 
posed as if by vortical action,) and growing fainter till lost to 
sight at an unknown depth below the surface. Speaking, then, 
without reference to any hypothesis, it seems to me that the re- 
semblance to crystalline structure (though I agree that it is strik- 
ing) does not appear to be more than superficial. We have at 
certain rare intervals remarkable cirrous clouds in our own at- 
mosphere, whose resemblance to these forms is equally close, 
and in which, I think, we may see not only a resemblance but 
an analogy. Some of these rarer cirrous types of our own sky, 
which I have studied in connection with solar forms, might, s0 
far as external appearance went, certainly be fancied to display 
crystalline action as clearly as any frost-figure on a window, 
yet we have no difficulty in seeing that in this case the eddies 
of our own atmosphere have been in some way a principal 
cause. While recognizing the danger of pushing too far, cou- 
clusions drawn from terrestrial analogy, I should then (pending 
amore complete study of these appearances), regard them 4S 
~~ nearly typified by certain cloud-forms of our own atmos 
ere 
