HITMKORI) SI'KC'I'IMIlKIJOOliAIMr. 1 H^) 



llint (liosc iiiiiHilc llocciili lire coliiiuiis of ciilciiiin \;i])()i', risin<>: iil)()\'i' 

 the coliiiiiiis of coiKlcnscd \ ;i|)()rs of which (lie pholosphoric " liTiiins '' 

 lire the siminiits. 



On such an assumption it l)c('()nu's inlorostin<>; to inquiiv whether 

 tlie hir<>'(M' calciuni (locculi are made up of simihir columns of cah-ium 

 \ai)()i". As a i-uU', the seeing is hardly li'ood enougli (o permit a deci- 

 sion to he reached on this point. r>ut under the host conditions th<'re 

 appears to he distinct evidence of a lihimentarv structure, tlie fihi- 

 mentji seeming to spread out like the hi'anches of a tive (fig. 2, pi. v). 

 Tt is evident that much light could he tlr.'own on the question if it 

 were |)ossihle to i)hotograi)h sections of the flocculi at ditferent eleva- 

 tions al)ov(> the photosphere, since in this way the form and size of 

 distinct columns of calcium vapor, if such were present, could he 

 determined at different levels. 



FORM AND EXTENT ()!•' CAI-CIUM FLOCCULI AT VARIOUS ELEVATIONS ABOVE 



THE PHOTOSPHERE. 



Fortunately, it is possible to accomplish this very result, if the 

 ])resent mode of explaining the photographs may be regarded as 

 sound. We have alivady had occasion to consider some of the charac- 

 teristics of the II and K reversals of the chromospliere. In the solar 

 spectrum itself the appearance of the II and K lines clearly indicates 

 that calcium vapor occurs under widely different conditions of inten- 

 sity at various levels above the photosphere. It is a well-known fact 

 that if a considerable quantity of calcium vapor is introduced into an 

 electric arc, broad bands, bright in the center and fading toward 

 both edges, will appear at the position of the H and K lines (fig. "2, 

 pi. hi)." The width of the bands may be taken as an approximate 

 measure of the density of the calcium vapor, which decreases toward 

 the outer part of the arc, where the bands are reduced to narrow lines. 

 The narrow dark lines at the center of the bright bands are caused by 

 the absorption of the comparatively cool and rare calciuni vapor in 

 the outer part of the arc. 



A similar condition of things undoubtedly exists in the sun. In 

 the first place, Ave have broad diU'use dark bands in the solar spectrum 

 at II and K, produced by comparatively dense calcium vapor close 

 lo the photosphere. For convenience of reference these bands will 

 be called II, and Ki- As the bright reversals at the base of the 

 chromosphere, when photographed at the sun's limb with a tan- 

 gential slit, or at a total eclipse, are much narrower than these bands, 

 it may be concluded that the dense calcium vapor in the cliromo- 



a Photographed in the electric arc with the solar si)Oftrosraph of the Snow 

 horizontal telescoiK'. The Ki'atin.ir temporarily employ*'*! gives strong ghosts, 

 which are conspicuous in the photograph. 



