EVOLUTION IN THE SUNS 59 



Now, on looking at a stellar spectrum such, 

 for example, as that of our own sun, the stellar 

 chemist is soon able to pick out many familiar 

 series of lines as those belonging to well-known 

 terrestrial elements, but in addition to these 

 there are many which are not known terres- 

 trially although the number of these latter 

 is diminishing as research proceeds. Another 

 interesting point is that spectra of different 

 suns differ from one another. Some are quite 

 like that of our own sun, such as the spectrum 

 of the star Arcturus, while others show a 

 considerable difference. If the spectra of a 

 large number of suns are frequently compared 

 until the trained observer begins to grow 

 familiar with them, certain series of lines 

 become associated as being always absent 

 from or present in a spectrum together, and 

 so are proven to be related to a common cause, 

 and probably to belong to the same element 

 present in some suns and absent in others. 

 In this way, some years ago, Lockyer had 

 connoted a series of lines containing three 

 prominent lines and had ascribed these to an 

 element unknown terrestrially, which he 

 provisionally named helium, from its presence 

 in our own sun's spectrum. 



For some years this element was entirely 

 unknown upon earth, but after Ramsay had 



