59 



them in its advance. Tn the eclipse of 1868, the spectro- 

 scope showed that the solar prominences are immense 

 masses of gaseous matter at a high temperature thrown 

 up from the sun, hydrogen being the leading component. 

 A few days after the eclipse, two different observers suc- 

 ceeded in obtaining their spectra in full sunlight, and now 

 not only can their spectra be obtained on a clear day, but 

 the prominences themselves are made visible. 



[A spectroscope was here exhibited and its construc- 

 tion explained.] 



Solid bodies, if sufficiently heated, give a continuous 

 spectrum, that is a band of light with colors varying from 

 red on one end to violet on the other. Gases give not 

 continuous spectra, but bright lines peculiar to each gas, 

 whose positions for many substances have been carefully 

 mapped for reference. The sun gives a continuous spec- 

 trum crossed by dark lines, several thousand of which 

 have been observed. It was discovered long ago that 

 some of the dark lines corresponded in position with the 

 bright lines of certain gases, which led to the conjecture 

 that there was some connection between them. But in 

 1859, the famous Kirchoff found that by passing the light 

 from incandescent lime, which gives a continuous spec- 

 trum, though the sodium flame, which gives a bright 

 yellow line, he obtained the continuous spectrum with a 

 dark line in place of the bright one. He also found that 

 by using the solar spectrum combined with that of the 

 sodium flame, a conspicuous dark line in the yellow of 

 the solar spectrum could be made bright or dark by vary- 

 ing the intensity of the sunlight. He thus established 

 the fact that the dark lines in the sun indicate the pres- 

 ence of gaseous substances surrounding a glowing body 

 probably solid ; at least it gives a continuous spectrum 

 like a heated solid. He soon found that the bright lines 



