THE FUEL OF THE SUN. 25 



phere that envelopes the photosphere, will radiate more 

 freely, its dissociated matter will combine more abundantly, 

 and will thicken the photosphere immediately below; this 

 thicker flame will be more luminous than the normal sur- 

 face, and thus produce the phenomena of t\\e faculcz. 



Besides these great ground-swells of the flaming ocean of 

 the photosphere, there must be lesser billows, and ripples 

 upon these, and mountain tongues of flame all over the 

 surface. The crests of these waves, and the summits of 

 these flame-alps, presenting to the terrestrial observer a 

 greater depth of flaming matter, must be brighter than the 

 hollows and valleys between; and their splendor must be 

 further increased by the fact, that such upper ridges and 

 summits are less deeply immersed in the outer ocean of 

 absorbing vapors, which limits the radiation of the light' 

 as well as the heat of the photosphere. The effect of look- 

 ing upon the surface of such a w'ild fury of troubled flame, 

 with its confused intermingling of gradations of luminosity, 

 must be very puzzling and difficult to describe; and hence 

 the "willow leaves," "rice grains,'' "mottling," "granules," 

 "things," "flocculi," "bits of white thread," "cumuli of 

 cotton wool," "excessively minute fragments of porcelain," 

 fc untidy circular masses," "ridges," "waves." "hill 

 knolls," etc., etc., to which the luminous irregularities have 

 been compared. 



At the time I wrote, the means of examination of the 

 edge of the sun by the spectroscope was but newly discov- 

 ered, and the results then published referred chiefly to the 

 prominences proper. Since that, a new term has been in- 

 troduced to solar technology, the " sierra," and the observa- 

 tions of the actual appearances of this sierra precisely cor- 

 respond to my theoretical description of the limiting surface 

 of the photosphere, which was written before I was ac- 

 quainted with these observed facts. This will be seen by 

 reference to Chapter x., the subject of which is, "The 

 Varying Splendor of Different Portions of the Photo- 

 sphere. * 



* Still more recently (1882) the magnificent photographs of Jannsen 

 have displayed further evidence of the flame-tongue character of 

 the mottling. 



