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POPULAR SCIENCE MONTHLY 



ful telescope. The sun has a diameter of 860,000 miles and, as its dis- 

 tance from the earth is only 93,000,000 miles, an extremely small frac- 

 tion of the distance of the other stars, it is possible to observe and to 

 study in detail its extraordinary phenomena, which are incomparably 

 more violent than anything observed on the earth. When we speak of 

 the sun we speak collectively of a great number of phenomena, some of 

 which extend for millions of miles from the sun's visible disk. Chief of 

 these is the corona, a vast filmy atmosphere so rare that it offers little or 

 no resistance to the passage of a comet, as it sweeps around the sun 

 under the action of gravitation and returns into the space from which 

 it came. The polar streamers of the corona (Fig. 9) suggest the 



Fig. 9. The Solar Coeona. 



Photographed by Yerkes Observatory Eclipse Expedition, May 28, 1900 (Barnard and 



Kitchey). 



action of magnetic forces and offer material for long continued study 

 of this, the most mysterious of all the solar appendages. At the base of 

 the corona, rising out of a sea of flame which completely encircles the 

 sun, are the prominences, some of which occasionally attain a height 

 of nearly 400,000 miles. Like the corona, the prominences are hidden 

 by the brilliant illumination of our own atmosphere, and are visible to 

 the naked eye only when the direct light of the sun's disk is cut off by 



