Relation bt-hvccn the Spectra of Sunspots and Stars. 



In comparing, for this purpose, the spectra taken with the 6-inch 

 Henry prismatic camera it was noticed that certain lines were 

 relatively intensified in passing from the spectrum of Capella to that 



of Arcturus. 



Similar comparisons of the Fraunhoferic spectrum with the spectra 

 of Capella and Arcturus respectively were next made. This work led 

 to the following conclusions : (1) That the line absorptions of Capella 

 and the sun are practically identical ; (2) that although, speaking 

 generally, the same lines occur in the spectra of the sun and Arcturus, 

 yet in the latter many lines are relatively more intense than in the 

 former. Moreover, in the great majority of such cases the lines so 

 intensified are probably due to Vanadium and Titanium. 



Thus we see that whilst the temperature classification mentioned 

 above certainly places Arcturus on a lower temperature level than 

 Capella and, therefore, the sun, the evidence obtained from a study of 

 the line absorptions of Arcturus and of sunspots indicates very clearly 

 that the temperature of the Arcturian absorbing atmosphere is about 

 the same as that of the sun spot nuclei during the above-mentioned 

 period. 



This conclusion justifies the ideas formulated by De la Rue, Stewart, 

 and Loewy that the spots are produced by the downrush of cooler 

 material. 



In a recent publication,* which has been received here since the 

 above-mentioned comparisons were completed, Professor Hale suggests 

 that because the lines which are widened in sunspots appear as strong 

 dark lines in Piscian stars, the effect may be produced because sun- 

 spots are more numerous in such stars. From the evidence adduced 

 above it seems a far more probable explanation to suppose that these 

 lines are intensified in sunspots, and strengthened in those stars which 

 have been placed on lower temperature levels than the sun, because 

 the general temperature conditions are similar. That is to say, the 

 fall of temperature experienced by the metallic vapours in passing 

 from the photosphere to the spot nucleus is of the same order as that 

 to which an absorbing atmosphere is subjected in passing from the 

 temperature conditions of Capella or the sun to that of Arcturus or 

 the lower temperature stars. 



