RTTMFOilD SPECTROflELIOGRAPH. 137 



M. Deslandres's Jatest explanation of the calcium regions is un- 

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

 I did not appreciate this. His solar investigations at the Paris Ob- 

 servatory were confined for some years to the photography of the 

 spectrum of various parts of the sun's disk, but in ISO-t he undertook 

 work with the spectroheliogra})h. The bright reversals of the H and 

 K lines photograj^hed by M. Deslandres on the sun's disk were at 

 first considered by him to represent the prominences; later he 

 ascribed them to l)right regions at the base of the prominences, and 

 finally he spoke of them as the brighter 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 " facula^ " (meaning calcium vapor of the facul») 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 faculoe, 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 word is more or less descri[)tive of the photographs, so far as 

 their appearance is concerned." 



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

 as the })liotographs 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. 



jMinute structure 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 jjaper " On the minute structure of the solar photosphere.*' 

 and of Janssen's excellent })hotographs, now generally accessible in 

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

 speaking of the cloud-like character of the photosphere, Langley g<^es 

 on to describe the more minute details in the following Avords: '' 



Under high powers used in favonilile moments, the surface of any one of the 

 fleecy patches is resolved into a conjjjeries of small, intensely hright l)odies, irrejr- 

 iilarly distributed, which seem to be suspended in a comparatively dark niedumi, 

 and whose definiteness of size and outline, although not absolute, is yet striking 

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

 now perceive to be (Uu> to their aggregation. The "dots" seen before are con- 



" The name was suggested by my friend. Dr. L. F. Barker, after seeing the 

 photographs. 



6Americau .Journal of Science. \'oI. XW (February, 1S74). 



