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POPULAR SCIENCE MONTHLY 



above the photosphere is as great as 4,000 miles. The bright lines are 

 identified as belonging to iron, titanium, chromium, hydrogen and other 

 elements. Tlie origin of some of the lines is unknown. 



Although no other time may be so favorable for the study of the 

 reversing layer as at total eclipses, the chromosphere and prominences 

 may nevertheless be well studied on any clear day. 



In connection with the eclipse of 1868 Janssen and Lockyer each in- 

 dependently discovered that by spectroscopic means the light of the 

 chromosphere and prominences may be so separated from that of the 

 sky as to become visible without an eclipse. The light from the region 

 just outside the sun's limb is composed of skylight and the light of 

 the solar atmosphere. Each is about equally bright. When this com- 

 bined light is passed through a prism, that due to the sky is spread 

 out into a continuous surface, thus becoming much fainter, while that 

 due to the chromosphere or prominence, from its gaseous nature, is 

 collected into bright bands, which thus surpass the skylight in in- 

 tensity and may be seen or photographed. This line of work has been 



Fig. 3. Gkkat Kkii'tivk I'imim i nence. 

 With Hale Spectkoheliookapii. Made 

 March 25, 1895, lOh. 34 m. A.M. 



V\i. 1, i.ki.n Va[\ iti\ i; 1'i:(imim:m I.. W ri u 

 Hale Spectkoheliouraph. Made March 

 25, 1895, lOh. 58n3., A. M. 



greatly extended by different scientists, notably by Hale, of this 

 country, who, by a device knowDi as the spectro-heliograph, has suc- 

 ceeded in maki]ig, ^A'ithout an eclipse, photographs showing all the 

 pro;minences surrounding the sun and the details of the solar surface 

 at the same time. These photographs are made in monochromatic 

 light. They represent what would be seen if the eye were sensitive to 

 light of the wave-length of the K line only. Figures 3 and 4 show a 

 great eruptive prominence photographed by Professor Hale, March 25, 

 1895. The interval between the two photographs was 24 minutes, dur- 

 ing wliich time the prominence was thrown upward from a height of 



