260 SCIENCE PROGRESS. 



chemical origins of them, may be made with a considerable 

 amount of certainty as depending upon very accurate work. 



The various classes in which the stars have been 

 classified by different observers according to their spectra 

 are discussed elsewhere, but some of the more salient differ- 

 ences must be pointed out here ; thus we have stars with 

 many lines in their spectra, others with comparatively few. 

 I will take the many-lined stars first. 



The diagram (Fig. 8) represents the spectrum of 

 Arcturus, a star the spectrum of which closely resembles 

 that of the sun. In a Cygni we have another star with 

 many lines, but here we note, when we leave the hydrogen 

 on one side and deal with the other stronger lines, that 

 there is little relation between the solar spectrum and these 

 lines. 



I next come to the stars with few lines : these are well 

 represented by many of the chief stars in the Constellation 

 of Orion. Bellatrix is given as an example (Fig. 9). 



Then, I have next to say that in the photographs of the 

 spectra of many stars, chiefly of those more or less like 

 Bellatrix, we found the same lines which we have so far 

 classified as unknown for the reason that in our laboratories 

 we have not been able to get any lines which correspond 

 with them. I again mention D 3 , 4471 and 4026, previously 

 noted as appearing both in the chromosphere and in the 

 nebula of Orion. 



But the thing is much more interesting even than this ; 

 not only these, but all the chief unknown lines appearing in 

 the nebula of Orion are also found in these stars. And this 

 is so absolutely true that there is no necessity to give a list 

 of the unknown lines seen in Bellatrix ; every one of them 

 given in the nebula has found its place, and (so far) practically 

 no others. 



This of course marked a great development of the 

 inquiry, and makes the question of the unknown lines 

 more important than ever. 



