The Evolution of the Sciences 



manner, with numerous metallic vapours of 

 magnesium, sodium, calcium, iron, chromium, 

 etc. It contains also another element. Among 

 the bright lines of the chromosphere a yellow 

 line defied for a long time identification with those 

 of the known terrestrial elements. Astronomers, 

 abandoning the research, and having exhausted 

 all alternative hypotheses, attributed it to an 

 unknown body, doubtless similar to hydrogen, 

 which they called helium. It has, however, since 

 been discovered that helium exists also on our 

 planet. Its presence has been recognised in a 

 Greenland mineral called cleveite, in some 

 mineral waters, and even in our atmosphere; 

 the sum of its properties connect it with 

 hydrogen. This is a truly remarkable instance 

 of the certainty of spectroscopic methods. 



The chromosphere does not form a uniform 

 layer. It is interesting to determine its dis- 

 tribution. The most elegant solution of the 

 problem has been supplied by the spectroscope, 

 which was certainly not intended for such a pur- 

 pose. This solution was first pointed out by 

 Huggins, and has since been employed by all 



astronomers. When the slit of the spectroscope, 



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