iv PURSUIT OF KNOWLEDGE 61 



After argon had been isolated from the atmosphere, 

 many sources of nitrogen were examined to see if they 

 also contained the gas mixed with argon or with argon 

 compounds. In the furtherance of this research, Sir 

 William Ramsay was led to experiment upon cleveite 

 a rare Norwegian mineral which had been found to 

 give off, when boiled with weak oil of vitriol, two per 

 cent, of a gas supposed to be nitrogen. The question 

 to be decided was " Did this gas contain any argon, 

 either free or combined ? " ; and the experiments 

 showed that there was only a mere trace of nitrogen in 

 it. To determine readily the character of the remainder, 

 some of it was sealed up in a glass tube, through which 

 an electric discharge was passed this being the usual 

 method of making a gas luminous, so that the quality 

 of its light can be observed by means of the spectroscope. 



The light from the luminous gas from cleveite passed 

 into this marvellous instrument of analysis, and was 

 sifted into its component parts by the glass prism. 

 When the bright lines into which it was resolved were 

 observed, they were found to comprise a number of 

 prominent rays of which the origin was not known ; in 

 other words, the gas which had been believed to be 

 nitrogen was something quite different. One of these 

 rays was especially brilliant ; and it was identified as 

 a line due to helium an element only observed pre- 

 viously in analyses of light from the sun. 



During the total eclipse of the sun in 1868, the spectro- 

 scope showed that the red flames or solar prominences 

 visible here and there around the sun's edge, when the 

 dark body of the moon had cut off the dazzling light of 

 the sun's visible surface, consisted of luminous gases, 

 chief among which was hydrogen. Shortly afterwards 

 Sir Norman Lockyer devised a method of observing 



