STAR OR STAR-MIST. 



149 



During its time of greatest observed brilliancy the new star in the 

 Swan was very carefully watched by spectroscopists. The results 

 were in many respects interesting. The star in the Crown had shown 

 the bright lines of hydrogen, superposed upon a faint rainbow-tinted 

 spectrum, which was understood to signify that around a real, though 

 probably a small, sun, some outburst of glowing hydrogen had taken 

 place, the chief part of the star's new light being due to this outburst. 

 The same bright hydrogen lines were seen also in the case of the star 

 in Cygnus. But in addition to them other bright lines were seen, 

 which seemed to be identical with those belonging to the solar sierra 

 (or, as many astronomers unclassically call it, the chromosphere) and 

 corona. This, at least, was the opinion of M. Cornu, of the Paris Ob- 

 servatory. Herr Vogel, who began his observations on December 5th, 

 when the star was between the fourth and fifth magnitude, and con- 

 tinued them to March 10th, when the star had sunk below the eighth 

 magnitude, does not agree on this point with M. Cornu, since aline not 

 agreeing with any known line in the spectrum of the sun's sierra was 

 clearly visible from the beginning in the spectrum of the new star. 

 But the most interesting point in connection with Vogel's observa- 

 tions, confirmed also by Mr. Copeland, at the Dunecht Observatory, 

 and by Mr. Backhouse, of Sunderland, was this : that, as the new star 

 died out, not only did the rainbow-tinted background of the spectrum 

 fade gradually out of view, but the relative lightness of the bright 

 lines steadily changed. At last, on March 10th, very little was left of 

 the spectrum which Cornu and Vogel had seen in December. The 

 blue and violet portion of the spectrum had faded entirely from view, 

 a dark gap had appeared in the green, and a very broad, dark band 

 in the blue. Of the bright lines two only remained. One, the F line 

 of hydrogen, in the green-blue, which had been singularly conspicuous 

 last December, was now faint. The other, in the green, which had 

 been faint in December, was now very bright in fact, nearly the 

 whole lio-ht of the star seemed at this time to come from this bright 



line. 



Now, the changes which had thus far taken place were altogether 

 unlike those which had been noticed in the case of the new star in the 

 Northern Crown. As that star faded from view the bright lines in- 

 dicative of glowing hvdrogen died out, and only the ordinary stellar 

 spectrum remained. In the case of the star in Cygnus the part of the 

 spectrum corresponding to stellar light that is to say, the rainbow- 

 tinted streak crossed by dark lines faded gradually from view, and 

 bright lines only were left, at least as conspicuous parts of the star's 

 spectrum. This body, then, did not seem to be returning to the stel- 

 lar condition at all, but actually fading out into a nebula. Not only 

 so, but the lines which still remained conspicuous last March were 

 lines known to belong to the so-called gaseous nebulae. One of them, 

 that which had been the faintest, but was now the brightest, corre- 



