THE DISCOVERY OF HELIUM AND WHAT 

 CAME OF IT. 



By C. G. Abbot, 

 Assistant Secretory, Smithsonian Institution. 



This story is about a chemical element that was discovered in the 

 sun, confirmed in the stars, recognized long after upon the earth, 

 Avas instrumental in realizing the dreams of the alchemists, and 

 finally found a useful place in the great war. It came upon our 

 stage at the time of one of those wonderful natural phenomena called 

 total solar eclipses. 



About once every year the moon comes exactly between the sun 

 and the earth, and as its apparent size is generally slightly greater 

 than that of the sun, although in reality far smaller, it covers over 

 the brilliant disk of the sun and allows us to see those objects which 

 are so close to the sun in their apparent position as ordinarily to 

 be obscured by the brilliant glare of the sky in the solar neighbor- 

 hood. 



On August 18, 1868, a very notable total solar eclipse was visible 

 in India. Many astronomers journeyed there to observe it, among 

 them the French astronomer, Janssen. It was only a few years before 

 this that the spectroscope began to reveal the inmost nature of 

 substances when these are heated sufficiently to give off light. Many 

 astronomers employed the spectroscope at the Indian eclipse and all 

 made substantially the same report. They found that the bright 

 prominences which shot out to different heights about the sun's disk, 

 and which had been seen in many previous eclipses, revealed spectra 

 consisting of bright lines. Conspicuous among these lines were the 

 lines of hydrogen, but other bright lines were seen in the prominence 

 spectrum, among them one of yellow, which they mistook for the 

 characteristic bright line of sodium. Their observations completely 

 demonstrated the fact that the prominences are enormous masses 

 of highly heated gaseous matter shot up to immense distances above 

 the surface of the sun, and that of these gases hydrogen is among 

 the most prominent. So far all were agreed, but Janssen went beyond 

 this. The lines were so brilliant during the eclipse, as seen in his 

 spectroscope, that he believed he could see them also in full sun- 



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