136 RUMFORD SPECTROHELIOGHAPH. 



spectrohelioo:raph is not vet sufficient for extended generalizations, 

 the variety of phenomena recorded is such as to call for some comment 

 here. A more complete discussion of the results must be reserved 

 for a future occasion. 



ON THE NATURE OF THE CALCIUM FLOCCULI. 



In my first published note on the bright calcium regions recorded 

 for the first time with tlie Kenwood spectroheliograph I ])riefly 

 described the results in tlie following words : 



The reversed regions are of great extent and in appearance closely resemble 

 facuhe. Several explanations may he suggested to account for them. They 

 may he : 



1. Ordinary prominences i)rojected on the disk. 



2. Prominences in which H and K are bright, while the hydrogen lines are 

 absent. 



3. Faculpe. 



4. Phenomena of a new class, similar to faciUiv, but showing H and K bright, 

 and not obtained in eye observations or ordinary photographs because of the 

 brilliant background upon which they are projected." 



It was subsequently shown that the bright calcium regions in gen- 

 eral coincide closely with the facuhe, and it was concluded that they 

 represent the hot calcium vapor in the upper part of the faculoe and 

 in the lower part of the adjoining chromosphere. Fig. 1, plate iii, 

 which is reproduced fi-om a photogra]3h of the K line taken at Ken- 

 w^ood Observatory, sho^^s that the bright reversals of the K line fre- 

 quently occur in regions of the disk where the continuous spectrum is 

 considerably strengthened. These regions are the facuhe proper. 

 The facula>, though apparently but little brighter than the photo- 

 sphere, are conspicuously vi-sible near the sun's limb. This is prob- 

 ably due to the fact that they reach a higher level, and thus escape 

 much of the general absorption exercised by a comparatively thin 

 stratum of a smoke-like nature which lies in close contact with the 

 ])hotosphei-e. The facuhe are, in general, the regions above which 

 the calcium vapor is hottest and most brilliant. 



But it appeared later that the calcium vaj^or is not confined to the 

 facuhe, but extends beyond their boundaries and frequently occurs in 

 regions of the solar disk where they are absent. The generally close 

 coincidence of the calcium clouds with the faculse, and a natural hesi- 

 tation to propose a new name l^efore the results obtained with the 

 spectroheliograph had been sufficiently studied, led me to apply this 

 term to the bright calcium regions photographed with the spectro- 

 heliograph. From my present point of view" I think it would have 

 tended to clearness, as M. Deslandres has pointed out, if some other 

 name had been adopted. 



oAstronomy and Astrophysics, Vol. TI (1892), p. 159. 



