138 RITMFORT) SPEOTROHELIOGRAPH. 



sidor.ililo fi])onin2:s onused by the iibsenee of the white nodules at certain point?, 

 and liie coiisiMjiient e.\iM)siu'e of tlie gray medium whicli forms tlie general back- 

 ground. These openings have been called pores; their variety of size makes 

 any measurements nearly valueless, though we may estimate in a very rough 

 way the diameter of llie more conspicnons at from 2" to i". The bright 

 nodules are themselves not uniforndy bright (some being notably more brilliant 

 than their fellows and even unequally bright in portions of the same nodule), 

 neither are they uniform in shajie. They have just been spoken of as relatively 

 definite in outline, but this outline is commonly found to be irregular on nnnute 

 study, while it yet affects, as a whole, an elongated or oval contour. Mr. Stone 

 has called them "rice grains." a term only descriptive of their appearance with 

 an aperture of 3 to 4 inches, but which I will use provisionally. It depicts their 

 whiteness, their relative individuality, and their api)roximate form, but not their 

 irregular outline, nor a certain tendency to foliate structure which is character- 

 istic of them, and which has not been sufficiently remarked upon. This iri'egu- 

 larity and diversity of outline have been already observed by Mr. Iluggins. 

 Estimates of the main size of these bodies vary very widely. Probably Mr. 

 Huggins has taken a .judicious mean in averaging their longer diameter at l".r> 

 and their shorter at 1", while remarking that they are occasionally l)etween 2" 

 and .">", and sometimes less than 1", in l<>ngth. 



* * * In moments of rarest delinitiou I have resolved these " rice grains" 

 into minuter components, sensibly round, which are seen singly as ])oints of light, 

 and whose aggregation produces the "rice-grain" structure. Tliese minutest 

 bodies, which I will call graiuiles, it will appear subsequently, can hardly ecjual 

 {).'",) in diameter, and are probably less. 



* * * It seems to me that there is no room for doul)t tliat " filaments " and 

 "granules" are names for different aspects of the same thing; that filaments in 

 reality are floating vertically all over the sun, their upper extremities ajjpearing 

 at the surface as gratmles, and that in spots we only see the general structure 

 of the i)hotos]ihere, as if in section, owing to the filaments being here inclined. 



* * * Speaking without reference to spectroscopic investigations, it seems 

 to me tliat we have in the behavior of our filaments a presumption as to the 

 existence of ascending currents in the outer jienumbra, and of both ascending 

 and descending currents at the umbral edge ; ascending ones being the more 

 usual. 



An examination of the minute calcium flocculi photographed vUh 

 the Eumford spectroheliograph will show that they closely reseml>le 

 the photospheric " grains '' described by Langley and illustrated in 

 Janssen's photographs. Plate vi is reproduced from one of our nega- 

 tives on the scale chosen for the majority of the photographs in Vol- 

 ume I of the INIeudon Annals. This photograph was made with tlie 

 slit set at the center of the H line on a day when the seeing was par- 

 ticularly good. In fig. 3, pi. Ill, squares 10 seconds of arc on si 

 side are shown. These permit of an accurate determination of the 

 size of the individual elements of the structure. Measurements made 

 on our best negatives show that the minute calcium flocculi range in 

 diameter from less than 1 second to several seconds of arc, thus cor- 

 resi)onding closely with the " grains '' of the photosphere. 



On the woiking hypothesis at present employed to interpret llie 

 results obtained with the Rumford spectroheliograph, it is considered 



