RTTMFORD SPECTROHELIOGRAPH. 137 



M. Doslaiulres's latest oxplanation of the calcium regions is un- 

 doubtedly more nearly correct than my earlier one, though at the time 

 I did not ai)preciate this. His solar investigations at the Paris Ob- 

 servatory were confined for some years to the photography (^f the 

 spectrum of various parts of the sun's disk, but in 181)4 he undertook 

 work with the spectroheliograph. The bright reversals of the IT and 

 K lines photograi)hed by M. Deslandres on the sun's disk were at 

 first considered by him to represent the prominences; later he 

 ascribed (hem to bright regions at the base of the prominences, and 

 finally he spoke of them as the brightei- regions at the base of the 

 chromosphere projected on the disk. This last designation now 

 appears to me to describe the facts much more accurately than the 

 term " facnhe " (meaning calcium vapor of the facula:-) at first em- 

 ployed by myself. In suggesting the term flocculi (flocculus, dim. of 

 floccus, " a bit of wool ") to distinguish the vaporous clouds photo- 

 graphed on the disk from the underlying facuhe, I have distinctly 

 avoided the use of a name which might in any sense be taken as indi- 

 cating the nature of the phenomena. A glance at plate iii will show 

 that the woi-d is more or less descriptive of the photographs, so far as 

 their ai)i)ea ranee is concerned." 



Tt is necessary to speak of calcium flocculi, hydrogen flocculi, etc., 

 as the photographs show that the forms of the various vapors in the 

 same part of the disk are not identical. Some of the phenomena com- 

 prised under this name are undoubtedly prominences seen in projec- 

 tion, l)ut most of them correspond to much lower levels, near the base 

 of the chromosphere, or within the reversing layer. 



MINUTE STRUCTl RE OF THE FLOCCULI. 



The extensive literature which embodies the long discussion regard- 

 ing the " willow leaf " and " rice grain " structure of the photosphere 

 has in large part become obsolete since the publication of Langley's 

 important ])aper •' On the minute structure of the solar photosphere," 

 and of Janssen's excellent photographs, noAV generally accessible in. 

 the first volume of the Annals of the Observatory of Meudon. After 

 speaking of the cloud-like character of the photosi)here, Langley goes 

 on to describe the more minute details in the following words: ^ 



Under high powers used in favorable monionts, the surface of any one of the 

 fleecy patclies is resolved into a congeries of small, intensely bright bodies, irreg- 

 ularly distributed, which seem to be suspendetl in a comparatively dark medium, 

 .md whose definitcnoss of size and outline, although not absolute, is yet striUing 

 by contrast with the vagueness of the cloud-forms seen before, and which Wf 

 now i)crc('ive to lie due to their aggregation. The "dots" seen before are con- 



o The name was suggested by my Iriond. Di-. L. F. Karker. after seeing the 

 photographs. 



''American Joui-nal of Science. \'ol. Vll ( Feln'uary, 1S74). 



