Progi'GSS and Problems of Solar Physics. 131 



character of sunspot spectra demands much more 

 attention at the hands of solar observers, and many 

 problems connected with them are awaiting solution. 



No less interesting than the dark spots on the solar 

 surface are the irregular streaks and large masses of 

 greater brilliancy than the general surface of the disc, 

 which are at all times present in greater or less numbers, 

 except at a period of sunsjjot minimum, when they also 

 disappear, and leave the brilliant orb of day spotless, 

 tranquil and serene. 



Without question now these faculae are elevated 

 portions of the iDhotosphere. This can be clearly seen 

 by direct observation. The spectrum also is identical 

 with the continuous spectrum of the photosphere. 

 Formerly they were thought to be luminous masses of 

 calcium vapor floating in the solar atmosphere and 

 possibly identical with the prominences. This view 

 originated by the observation of double reversals of the 

 great H and K bands due to calcium in the solar spec- 

 trum and the spectroheliograph work of Hale and 

 Delandres; but in a very recent paper by Professors Hale 

 and Ellerman, of the Yerkes observator-y, on Calcium 

 and Hydrogen Flocculi ^^^ the authors give a brief 

 description of some of their latest investigations into the 

 nature of these phenomena. Their conclusion is that the 

 faculae are elevated regions of the photosphere charac- 

 terized by a continuous spectrum, but the flocculi are 

 clouds of gas or vapor lying at a higher level than the 

 faculae, and are only visible in photographs taken w^ith 

 the spectroheliograph. 



Two varieties of prominences differing visually, 

 chemically and in solar location are observed, — the 

 eruptive or metallic, and the quiescent or hydrogen 

 forms. The eruptive variety is by far the more interest- 

 ing, consisting of mainly compact forms resembling 

 banyan trees, spike-like jets and flames, etc., of an 

 intense scarlet color and appearing principally in the 

 sunspot zones; while the quiescent variety are more 

 cloud-like, often of great extent, with occasionally ex- 

 plosive outbursts, and found in all directions from the 

 poles to the solar equator. The eruptive class usually 

 attain heights of about 20,000 to 30,000 miles, although 



