182 ESSAYS BIOGRAPHICAL AND CHEMICAL 



sun's spectrum, discovered by Fraunhofer, is identical 

 with that of the two yellow lines visible in the spectrum 

 of glowing sodium vapour ; and Kirchoff concluded that 

 this coincidence furnished a proof of the presence of 

 sodium in the sun. Fraunhofer had named these lines 

 D : and D 2 . Similar conclusions were drawn from obser- 

 vations of the coincidence of other black solar lines with 

 those of elements found on the earth ; and the presence 

 of iron, lead, copper, and a host of elements in the sun 

 was proved. 



In 1868 a total eclipse of the sun took place; an 

 expedition was sent to India, from which a good view was 

 to be obtained. Monsieur Janssen, the distinguished 

 French astronomer, observed a yellow line, not a dark, but 

 a bright one, in the light which reached the earth from 

 the edge or ' limb ' of the sun, and which proceeded from 

 its coloured atmosphere or chromosphere. It was for 

 some time suspected that this line, which was almost 

 identical in position with the yellow lines of sodium, D l 

 and D 2 , and which Janssen named D 3 , was due to 

 hydrogen. But ordinary hydrogen had never been found 

 to show such a line ; and after Sir Edward Frankland and 

 Sir Norman Lockyer had convinced themselves by 

 numerous experiments that D 3 had nothing to do with 

 hydrogen, they ascribed it to a new element, the exist- 

 ence of which on the sun they regarded as probable ; 

 and for convenience, they named this undiscovered 

 element 'helium/ from the Greek word for the sun, 



It was not until the year 1895 that helium was found 

 on the earth. After the discovery of argon in 1894, 

 Ramsay repeated some experiments which had previously 

 been made by Dr. Hillebrand, of the United States Geo- 

 logical Survey. Hillebrand had found that certain 

 minerals, especially those containing the somewhat rare 



