THE 



POPULAR SCIENCE 

 MONTHLY. 



FEBRUARY, 1874. 



THE CHROMOSPHERE AND SOLAR PROMINENCES. 



By C. A. YOUNG, 



PROFESSOR OF ASTRONOMY IN DARTMOUTH COLLEGE. 



WHAT we see of the sun under ordinary circumstances is but a 

 fraction of his total bulk. While by far the greater portion 

 of the solar mass is included within the photosphere, the blazing cloud- 

 layer which seems to form the sun's true surface, and is the principal 

 source of his light and heat, yet the larger portion of his volume lies 

 without, and constitutes an atmosphere whose diameter is at least 

 double, and its bulk therefore sevenfold that of the central globe. 



Atmosphere, however, is hardly the proper term ; for this outer 

 envelope, though gaseous in the main, is not spherical, but has an out- 

 line exceedingly irregular and variable. It seems to be made up not 

 of overlying strata of different density, but rather of flames, beams, 

 and streamers, as transient and unstable as those of our own aurora 

 borealis. It is divided into two portions, separated by a boundary as 

 definite, though not so regular, as that which parts them both from the 

 photosphere. The outer and far more extensive portion, which in 

 texture and rarity seems to resemble the tails of comets, and may al- 

 most, without exaggeration, be likened to " the stuff that dreams are 

 made of," is known as the " coronal atmosphere," since to it is chiefly 

 due the " corona " or glory which surrounds the darkened sun during 

 an eclipse, and constitutes the most impressive feature of the occasion. 



At its base, and in contact with the photosphere, is what resembles 

 a sheet of scarlet fire. The appearance, which probably indicates a 

 fact, is as if countless jets of heated gas were issuing through vents 

 and spiracles over the whole surface, thus clothing it with flame 

 which heaves and tosses like the blaze of a conflagration. 



This is the " chromosphere " (or chromatosphere, if one is fastidi- 

 ous as to the proper formation of a Greek derivative), a name first 

 proposed by Frankland and Lockyer in 1869, and intended to signify 

 vol. iv — 25 



